SRNL-STI-2009-00636 Revision 0 Keywords: Iodine, Neptunium, Plutonium, Technetium I, Np, Pu, Tc Saltstone, Redox, Distribution Coefficients, Kd, Apparent Solubility Values, Glovebox, Retention: Permanent Iodine, Neptunium, Plutonium and Technetium Sorption to Saltstone and Cement Formulations Under Oxidizing and Reducing Conditions Michael S. Lilley (a) , Brian A. Powell (a) , and Daniel I. Kaplan December 16, 2009 (a) Department of Environmental Engineering and Earth Sciences Clemson University, Clemson, SC Savannah River National Laboratory Savannah River Nuclear Solutions Aiken, SC 29808 Prepared for the U.S. Department of Energy under contract number DE-AC09-08SR22470.
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SRNL-STI-2009-00636, Rev. 0, 'Iodine, Neptunium, Plutonium ...SRNL-STI-2009-00636 Revision 0 iv EXECUTIVE SUMMARY Sorption of 99 Tc, 127 I, 237 Np, and 242 Pu to two saltstone and
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SRNL-STI-2009-00636 Revision 0
Keywords Iodine Neptunium Plutonium Technetium I Np Pu Tc Saltstone Redox Distribution Coefficients Kd Apparent Solubility Values Glovebox Retention Permanent
Iodine Neptunium Plutonium and Technetium Sorption to Saltstone and Cement Formulations
Under Oxidizing and Reducing Conditions
Michael S Lilley(a) Brian A Powell(a) and Daniel I Kaplan
December 16 2009
(a) Department of Environmental Engineering and Earth Sciences Clemson University Clemson SC
Savannah River National Laboratory Savannah River Nuclear Solutions Aiken SC 29808 Prepared for the US Department of Energy under contract number DE-AC09-08SR22470
L B Romanowski Customer Savannah River Remediation Waste DeterminationsDate
EXECUTIVE SUMMARY
Sorption of 99Tc 127I 237Np and 242Pu to two saltstone and two cementitious materials was examined Np and Pu sorbed very strongly to all four cementitious formulations and appeared to reach steady state within 24 h Based on the sorption behavior there were some indications that partial reduction of Pu(IV) to Pu(III) and Np(V) to Np(IV) occurs in these systems However the Kd values for both Pu and Np remain gt105 mLg throughout the experiments This value compares favorably with previously reported Kd values for Pu but is significantly higher than the previously reported value of 3000-4000 mLg for Np (Kaplan et al 2008)
In all experiments regardless of the total concentration of Np and Pu in the system a relatively constant aqueous phase concentration of both Np and Pu was observed Therefore it appears that the aqueous concentrations of Np and Pu are solubility controlled rather than sorption controlled The measured concentrations for Np and Pu ranged from 10-11 molL to 10-13 molL These values are consistent with precipitation of actinide hydrous oxide solid phases consequently these tests strongly suggest that solubility (as described by solubility constants) and not sorption (as described by Kd values) will controlling Np and Pu aqueous concentration near the Saltstone Disposal Facility
Sorption of both Tc and I do not appear to have reached steady state during the four day equilibration times used in these experiments Similar to Np and Pu surface mediated redox processes were affecting Tc and I sorption However this observation was based on changes in sorption behavior not direct determination of Tc or I oxidation states Calculated I Kd values of 766 and 725 mLg for simulated Vault 2 concrete under oxidizing and reducing conditions respectively in the present work compare favorably with values of 894 and 715 mLg under similar conditions reported by Kaplan et al (2008) Although it appears steady state was not reached in Tc systems conditional Kd values were calculated and were found to be a factor of ~5 higher than values previously reported by Kaplan et al (2008) The fraction of reducing slag within each saltstone formulation appears to have an effect on Tc sorption Tc Kd values under oxidizing conditions ranged from 275 to 508 mLg Saltstone formulations under reducing conditions had Kd values between 32 (0 dry wt- slag) and 4370 mLg (45 dry wt- slag) but the system had not achieved steady state conditions at the time of measurement thus greater sorption may likely occur under natural conditions Cementitious formulation did not influence Pu Np or I sorption These data support the following changes in the SRS ldquobest Kdrdquo geochemical data package used as input to SRS performance assessment calculations
TABLE OF CONTENTS
10 Introduction15
20 Objectives15
30 Materials and Methods15
31 Preparation of ICP-MS Standards Stock Solutions and Working Solutions15
311 242Pu15
312 237Np16
313 99Tc17
314 127I18
315 Cementitious Materials Selected for Experiments19
32 ICP-MS Detection Limits20
33 Experimental Methods20
34 Experimental Protocol for Sorption Experiments under Aerobic Conditions21
35 Experimental Protocol for Sorption Experiments under Anerobic Conditions22
36 Examination of Sorption to Vial Walls for Solids and No Solids Controls23
37 Data Analysis23
40 Results and Discussion24
41 Radionuclide Sorption to Cementitious Formulations under Oxidizing Conditions24
42 Radionuclide Sorption to Vial Walls Under Oxidizing Conditions28
43 Radionuclide Sorption to Cementitious Formulations under Reducing Conditions32
44 Radionuclide Sorption to Vial Walls under Reducing Conditions38
50 Comparison of Radionuclide Sorption under Oxidizing and Reducing Conditions40
60 Comparison of Radionuclide Sorption and Solubility under Oxidizing and Reducing Conditions46
70 Summary and Recommendations for Future Work48
71 Comparison with Previous Data48
72 Suggested Future Work48
80 References49
90 Appendix A Data Tables of Radionuclide Sorption to Saltstone under Oxidizing Conditions51
91 Data Tables for No Solid Controls51
92 Data Tables for Vault 254
93 Data tables for saltstone TR54557
94 Data Tables for Saltstone TR54759
95 Data Tables for Aged Cement62
96 Data Tables for Sorption to Vial Walls65
100 Appendix B Data Tables of Radionuclide Sorption to Saltstone Under Reducing Conditions66
101 Data Tables for No-Solid Controls66
102 Data Tables for Vault 269
103 Data Tables for TR54572
104 Data Tables for TR54775
105 Data Tables for Aged Cement78
106 Data Tables for Sorption to Vial Walls80
110 Appendix C Dixon et al (2009) FY09 PACA Maintenance Program Additional Saltstone Property Testing SRNL L3100-2009-00019 Rev 082
Performance Assessments (PA) are risk calculations designed to determine (1) the maximum amount of radioactivity that can be safely buried in a subsurface facility and (2) the potential human risk associated with disposing of radioactive waste in a subsurface facility Special Analyses (SAs) are similar to PAs except that they are designed to address specific issues related to PAs such as a new discovery since the PA was issued Commonly parameters describing the extent that a radionuclide interacts with solids at the source vadose zone and aquifer influence the extent of calculated human risk The two parameters that the SRS use to represent radionuclidesolid interactions are Kd and apparent solubility values together these parameters are referred to as sorption values Sorption values vary with radionuclides groundwater chemistry and the type of solid phase (and for cementitious materials by the age of the material during the calculation) In this work Kd and apparent solubility values are reported for 99Tc 127I 237Np and 242Pu sorption to various cementitious formulations
20 Objectives
The objectives of this work were to
1 Determine the influence of cementitious formulation on technetium (Tc) iodine (I) neptunium (Np) and plutonium (Pu) sorption under oxidizing conditions The specific formulations that were evaluated included 1) an aged cement recovered from a 30-year old outdoor concrete pad on the SRS 2) Vault 2 concrete 3) TR545 saltstone and 4) TR547 saltstone (additional details are presented in Section 30 Materials and Methods)
2 Measure Tc I Np and Pu sorption to the cementitious formulations under reducing conditions
30 Materials and Methods
31 Preparation of ICP-MS Standards Stock Solutions and Working Solutions
311 242Pu
A National Institute of Standards and Technology Standard Reference Material (NIST SRM 434H) was used to prepare a stock 242Pu solution by dilution in 2 Aristar Optima HNO3 All volume additions were monitored gravimetrically This working solution was then used to make a set of 001 005 1 2 5 10 parts per billion (ppb) standards by dilution using 2 HNO3 Again all volume additions were monitored gravimetrically These standards were used to calibrate the Thermo Scientific X Series 2 inductively coupled plasma ndash mass spectrometer (ICP-MS) for quantification of 242Pu A representative calibration curve for 242Pu is shown in Figure 31 The instrument performance was monitored using 209Bi 232Th and 238U as internal standards The recovery of each sample during analysis was corrected based on the internal standard recovery The internal standard recoveries remained within standard quality assurancequality control QAQC protocols for the instrument (between 80 and 120)
A 242Pu stock solution was prepared by dissolving 1mg of Pu(NO3)4 obtained as a Certified Reference Material from New Brunswick Laboratory (CRM 130) This CRM is gt999 242Pu by atom percent The CRM was dissolved in 20mL of 8M HNO3 (Aristar Optima Grade) Because no chemicals or heat have been introduced to manipulate the Pu oxidation state it can be assumed that Pu(IV) is the predominant oxidation state in this stock solution A working solution to be used in spiking 242Pu experiments was prepared by diluting 25 mL of the CRM stock solution with 100 mL 10 M Aristar Optima HNO3 The concentration of 242Pu in this stock solution was determined using ICP-MS calibrated using the NIST SRM standards The concentration of Pu in this stock solution was 1065 ppb The total Pu concentration was also determined using liquid scintillation counting using the isotopic ratios reported for CRM 130 These compared favorably with the ICP-MS results but are reported here as a rigorous standardization because the isotopic ratios of CRM 130 have not yet been certified
Figure 31 Screen capture of a typical 242Pu calibration curve using Thermo PlasmaLab software to control the data collection and analysis R2=0999872 Intercept Conc (Detection Limit) = 0000044 ppb
312 237Np
A National Institute of Standards and Technology Standard Reference Material (NIST SRM 4341) was used to prepare a stock 237Np solution by dilution in 2 Aristar Optima HNO3 All volume additions were monitored gravimetrically This working solution was then used to make a set of 001 005 1 2 5 10 ppb standards by dilution using 2 HNO3 Again all volume additions were monitored gravimetrically These standards were used to calibrate the Thermo Scientific X Series 2 ICP-MS for quantification of 237Np A representative calibration curve for 237Np is shown in Figure 32 The instrument performance was monitored using 209Bi 232Th and 238U as internal standards The recovery of each sample during analysis was corrected based on the internal standard recovery The internal standard recoveries remained within standard QAQC protocols for the instrument (between 80 and 120)
A compiled 237Np stock solution from the Environmental Engineering and Earth Science (EEampES) inventory (primarily purchased from Isotope Products Valencia CA) was evaporated to dryness then the residue was brought up in approximately 5mL 80 M HNO3 Then 10 M hydroxylamine hydrochloride (NH2OHHCl EMD Chemicals ACS grade) and water were added to achieve a 3M HNO303M NH2OHHCl solution This solution was purified by extraction chromatography using Eichrom TEVA resin packed in a Bio-Rad poly-prep column The 3M HNO303 M NH2OHHCl neptunium solution was loaded on a 2 mL column and washed with 3 column volumes of 3 M HNO3 The Np(IV) was eluted with 002 M HCl + 02 M HF The effluent was evaporated to dryness then redissolved in 10 M HNO3 Additional 10 M HNO3 was added to maintain a approximately 10 mL then the solution was evaporated to incipient dryness and redissolved in a 50 mL of 10 M HNO3 An aliquot of the stock solution was evaporated to dryness on a stainless steel planchet and counted on the EGampG Ortec Alpha Spectrometer (Octete PC Detectors) No other alpha energies besides 237Np were observed The approximate concentration was determined using liquid scintillation counting and little 233Pa was observed The fuming in HNO3 as performed at the end of the purification procedure will drive Np to the soluble pentavalent state This is the stable oxidation state of Np under the experimental conditions Therefore experiments performed here can be assumed to be initially Np(V) The exact Np concentration in this solution was determined using ICP-MS calibrated with a NIST standard as discussed in section 312 below
A 237Np working solution (Working Solution 1) was created by pipetting an aliquot of the 237Np stock solution into a 100 mL Nalgene Teflon bottle and diluting with 2 BDH Aristar Ultra HNO3 to give a working solution concentration of 820 ppb All volumes were monitored gravimetrically Analysis on the ICP-MS calibrated against NIST Standards as described below gave a concentration of 820 ppb in Working Solution 1
Figure 32 Screen capture of a typical 237Np calibration curve using Thermo PlasmaLab software to control the data collection and analysis R2=0999981 Intercept Conc (Detection Limit) = 0000026 ppb
313 99Tc
A 99Tc working solution was prepared by diluting a stock solution of 99Tc (from the EEampES inventory purchased from Isotope Products Valencia CA) in distilled-deionized water (DDI Resistivity gt18 M(cm) The oxidation state of Tc was not measured However based on the aqueous concentration in the DDI water solution Tc(VII) is the expected oxidation state The reduced Tc(IV) oxidation state would not be soluble under these conditions The expected concentration of 950 ppb based on the dilution was verified using liquid scintillation counting The 99Tc working solution was used to make 001 005 1 2 5 and 10 ppb standards by dilution using 2 HNO3 These standards were used to calibrate the Thermo Scientific X Series 2 ICP-MS for quantification of 99Tc A screen shot of a representative calibration curve is shown in Figure 33 The instrument performance was monitored by interpolating between 89Y and 115In internal standards The recovery of each sample during analysis was corrected based on the internal standard recovery The internal standard recoveries remained within standard QAQC protocols for the instrument (between 80 and 120)
Figure 33 Screen capture of a typical 99Tc calibration curve using Thermo PlasmaLab software to control the data collection and analysis R2=0999984 Intercept Conc (Detection Limit) = 0000013 ppb
314 127I
A 100 microgmL iodate (IO3-) stock solution from High Purity Standards (Charleston SC) was used to make 1 5 10 50 and 100 ppb standards by dilution using the ldquotraprdquo solution (discussed in Section 32 below) These standards were used to calibrate the Thermo Scientific X Series 2 ICP-MS for quantification of 127I A screen shot of a representative calibration curve is shown in Figure 34 The use of a reducing basic trap solution for iodine analysis limits the number of available internal standards that can be used to monitor ICP-MS instrument performance during iodine analysis Experiments are underway to identify acceptable internal standards However the data presented in this work did not use any internal standards prior to rigorous testing and analysis of representative standards As with the analyses for all isotopes (Tc I Np and Pu) spiked QAQC samples were frequently analyzed throughout the analysis as a check on instrument performance While these values cannot be used to correct individual samples in the same manner that the internal standards can they can be used to ensure accurate measurements of each isotope In almost all cases QAQC standards were within 10 of the expected value Because the average internal standard recovery ranges between 80 and 120 for the ICP-MS the iodine QAQC standard appears to be acceptable However a significant amount of ongoing work is testing various internal standards to improve the accuracy of iodine analysis using ICP-MS In one experiment (discussed in detail below) the QAQC standards deviated by an average value of 195 This will be specifically discussed below
Because experiments were performed with 127I concentrations up to 1000 ppb the 100 microgmL (ppm) stock iodate solution from High Purity Standards was used as the working solution
Figure 34 Screen capture of a typical 127I calibration curve using Thermo PlasmaLab software to control the data collection and analysis R2=0999991 Intercept Conc (Detection Limit) = 024 ppb
315 Cementitious Materials Selected for Experiments
There were four cementitious materials selected for this sorption study The first referred to as Aged Cement is a 30 year old sample that does not contain any reducing slag The aggregate from the Vault 2 cement had its aggregate removed prior to conducted tests in an effort to make subsamples more uniform This was necessary because some of the aggregate were larger than the 05 g subsamples used in individual sorption tests The Vault 2 cementitious material contained 17 dry wt- reducing slag on a dry weight basis before the water was added to the mix (Table 31) The TR547 and TR545 saltstone formulations contain 45 dry wt- and 90 dry wt- reducing slag respectively
Table 31 Characteristics of saltstone formulations used in this work Kaplan et al (2008)
TR547 is referred to as the Baseline by Dixon et al (2008) and is described in more detail in Appendix C (Mix 2) by Dixon et al (2008) (Control-BFSPC) and 1 (Baseline)
TR545 saltstone contains 90 reducing slag and it is Mix 1 in Dixon et al (2008) and is described as
ldquoA control mix will be based on the baseline mix modified by exclusion of the Class F fly ash Consequently the cementitious materials premix will be a mixture of 90 blast furnace slag and 10 Portland cement The degree of reaction will be much greater than with the normal premix and therefore should result in a lower porosity and a lower permeability This bounding test at 060 wcm ratio is expected to yield a hydraulic conductivity at or below the detection limit for the Mactec permeameter measurement system Therefore this test should demonstrate the lowest level of detection of the Mactec system as well as show a resolvable difference between measurements of the control mix and the control mix with the normal premix compositionrdquo
32 ICP-MS Detection Limits
The PlasmaLab software platform determines a detection limit for each isotope based upon the intercept concentration A new calibration curve was generated for each experimental run and curves were very similar Using representative calibrations curves the detection limits for each isotope were as listed in Table 32 Note the higher detection limit for 127I is primarily due to the higher background count rate observed on the instrument This is believed to be due to the minimum purity levels of chemicals required for the iodine ldquotraprdquo solution as discussed in Section 33 below Therefore experiments were run with initial iodate concentrations higher than Tc Np and Pu to maintain analytical sensitivity
Table 32 Detection limits for each isotope based on representative calibration curves generated in PlasmaLab software associated with the ICP-MS
33 Experimental Methods
The experimental methods used in this work followed closely those previously described for experiments examining radionuclide sorption to saltstone (Kaplan et al 2007 Kaplan et al 2008) Brief descriptions of each method are provided below
Preparation of Calcite Solution Using a hotstirring plate 10 L of distilled-deionized (DDI) water was heated to 3-100C above room temperature Then 001 g CaCO3 (EM Science ACS grade) was added to the solution and the resulting suspension was mixed for 24 hours at the elevated temperature The solution was then vacuum filtered through a 045-m filter to ensure no solid CaCO3 remained in solution
Preparation of 2 HNO3 Analysis of Tc Np and Pu on the ICP-MS required dilution in 2 HNO3 This was prepared by adding 28 mL of Aristar Optima HNO3 from a clean graduated cylinder (designated to 2 HNO3) into a 1 L volumetric flask (designated to 2 HNO3) partially filled with DDI water and then further diluted to volume
Preparation of Trap Solution for Iodine Analysis Analysis of I required the use of a reducing basic solution that was capable of reducing iodate to iodine and holding the iodine in solution This minimized the loss of I during sample analysis A 1 L trap solution was prepared by weighing out 00500 g NaHSO3 (Fisher Scientific ACS Grade) on a calibrated Sartorous LA 230S scale and adding it to a 1L volumetric flask Then 40 mL of 25 ww tetramethylammonium hydroxide (Alfa Aesar electronic grade) and 10 mL CFA-C solution (Spectrasol Inc) were added to the volumetric flask via a calibrated 1000-5000 L Eppendorf Research pipette The solution was then diluted to volume with DDI water
34 Experimental Protocol for Sorption Experiments under Aerobic Conditions
Falcon BlueMax 15mL polypropylene vials were labeled and weighed to within 0001 g on a calibrated Sartorious LA 230S scale The scale was then zeroed and 025 +- 001 g of a given solid were added to each tube and the weight was recorded to within 0001g
For each of the four solids three sets of triplicate samples were prepared The three sets of samples were used to allow for experiments to be run with varying concentrations of each isotope Target initial concentrations for 99Tc 237Np and 242Pu samples were 1 ppb 5 ppb and 10 ppb Target initial concentrations for the 127I samples were 100 ppb 500 ppb and 1000 ppb A set of no solids controls at initial concentrations of 1 ppb and 10 ppb for 99Tc 237Np and 242Pu and initial concentrations of 100 ppb and 1000 ppb 127I were also prepared by adding the calcite solution to pre-weighed pre-labeled centrifuge tubes as discussed above
The solids were equilibrated with the calcite solution before spiking with the radionuclides This was done by adding 10 plusmn 01 mL of calcite solution to each tube and recording the mass The samples were then placed on a Thermo Scientific shaker overnight After 24 hours the solutions were allowed to settle for 1 hour The pH was then measured and the samples were then centrifuged for 15 minutes at 8000 rpm to further separate the solids The aqueous phase was then decanted and 10 plusmn 01 mL of calcite solution was added to each tube The weight of the tube (labeled tube + solid + calcite solution) was measured to within 0001g During this washing process the pH was monitored and held steady throughout the process The pH ranged from 11-12 depending on the particular saltstone used During the experiments the exact pH for all samples at all equilibration times was measured and is reported in Appendix A and B
The resulting suspensions were then spiked with 127I 237Np 242Pu and 99Tc It is important to note that all four isotopes were added to the same vial Use of the ICP-MS to determine the concentration of each isotope allows for a single solution to contain all analytes of concern This allowed for a greater variability in the sample set and increased replicates as opposed to running individual sorption tests for each isotope For the systems with initial 99Tc 237Np and 242Pu concentrations of 10 ppb and initial 127I concentration of 100 ppb a 100 L aliquot of each radionuclide working solution was added to the first three tubes for each solid The addition was made with the tube resting on a tared analytical balance so that the exact mass of each radionuclide solution added was recorded and the solution was gently swirled before the next radionuclide was added The 5 ppb 237Np 242Pu and 99Tc and 500 ppb 127I samples were prepared in the same manner but adding 50 L of the respective spike solutions The final three tubes with initial 237Np 242Pu and 99Tc concentrations of 1 ppb and 100 ppb 127I were prepared by using 10 L of the spike solutions for all four solids as well as a set of solid-free controls (No-Solids Controls) For clarity this experimental matrix is shown in Table 33 below
Table 33 Experimental Matrix of Sorption Experiments under Aerobic Conditions
After spiking the radionuclides a precalculated amount of 10M NaOH was added to each sample to counter the acidic radionuclide spike solutions and the pH of one of the triplicate samples was measured to ensure the proper pH range was reached The samples were then placed on and end-over-end shaker to mix at approximately 8 rpm After 24 hours the samples were removed from the shaker and the pH of each sample was measured using an Orion Ross semi-micro glass electrode calibrated against pH 4 7 and 10 buffers (Thermo) The samples were then shaken and a transfer pipette was used to transfer 35 mL of a homogenous suspension to a 5mL syringe The solution was then passed through a 100 nm nylon syringe filter The first 025-050 mL of filtrate was discarded and the remaining filtrate was collected in a clean polyethylene vial Then 10 mL of the filtrate was removed and diluted in 90 mL 2 HNO3 The mass of each phase was determined and recorded gravimetrically Then 10 mL of the remaining filtrate was transferred to a clean Falcon BlueMax 15mL vial and diluted with 90 mL of trap solution for 127I analysis Again the volume of each phase was monitored gravimetrically After the 24 hour sampling event the samples were put back on the shaker to mix for three additional days On day four the above sampling procedure was repeated
The 237Np 242Pu and 99Tc samples can be run on the Thermo Scientific ICP-MS using the standard setup and procedure which included a standard flow glass nebulizer and bulb spray chamber However for the 127I analysis the ICP-MS must be reconfigured to accommodate the basic reducing trap solution This is to alleviate problems with iodine signal stability over time frequently observed in ICP-MS analysis The reconfigured instrument uses an Elemental Science Microflow PFA-100 Teflon nebulizer with a flow rate of 100microLmin along with a sapphire torch and a Teflon spray chamber This configuration must be run with a low pump speed to prevent back pressure on the system Two 30 minute stability tests were performed using a 50 ppb iodate solution Each experiment consisted of 40 separate measurements After each experiment was completed the uncorrected mass counts were examined and found to stay steady over the sampling period The relative standard deviation ( RSD) over all samples for each experiment was 1866 and 1460 respectively This shows that there was no significant ldquomemoryrdquo or loss of the iodine signal over time and that the reconfigured instrument has a stable iodine signal over time However as will be discussed below some difficulty has been encountered in finding an adequate internal standard for iodine analysis
35 Experimental Protocol for Sorption Experiments under Anerobic Conditions
In order to examine the effects of reducing conditions of sorption of each isotope to the various cementitious samples a series of sorption experiments were performed in an anaerobic glovebox under a 2 H2(g) 98 N2(g) atmosphere Based on the measured pH and EH of these systems as discussed below these systems were at the point of reducing water Therefore they are expected to represent a lower end of the possible range for reducing conditions expected in the porewater available within cementitious materials
Preparation of Calcite for Reducing Conditions Approximately 35 L of DDI water was boiled for 45 minutes Argon was slowly bubbled through the water as it cooled Once it cooled to below 500C approximately 3 g of calcite was added This solution mixed overnight under a continuous Ar flow After 12 hours the solution was moved into an oxygen free glove bag for filtration as described in 3231 After filtration the calcite solution was moved into the glove box
Preparation of Working Solutions under Reducing Conditions The calcite and solid solutions were prepared in the glove box using the previously mentioned procedure used under aerobic conditions The radionuclide working solutions were transferred to the glovebox and stirred open to the reducing atmosphere for at least three days The concentration of each isotope in the working solutions was measured to determine any change in the concentration due to evaporation while the solutions were equilibrating
The preparation and spiking of samples for sorption experiments was performed exactly as described for the oxidizing conditions except all sample handling was performed in the glovebox After the 1 day and 4 day equilibration the samples were filtered within the glovebox then transferred outside for dilution and ICP-MS analysis similar to the description provided about for the oxidizing conditions For these experiments only 4 mL of either 2 HNO3 or trap solution were used to dilute the filtrate instead of the 90 mL used above for experiments performed under oxidizing conditions
36 Examination of Sorption to Vial Walls for Solids and No Solids Controls
As will be discussed below the solid-free controls samples indicated significant loss of Np and Pu Once the one and four days samples were collected and run on the ICP-MS it was necessary to determine the degree each radionuclide was sorbing to the vial walls The remaining suspensions and controls were emptied into a waste container Then 5 mL of the calcite solution was added to each vial using a calibrated pipette The vials were sonicated for approximately one minute and then emptied into the waste container Another 5 mL of calcite solution was added for the second wash and then discarded into the waste container This procedure was expected to remove any soluble Pu from the system or Pu associated with colloidal particles After each vial was washed 10 mL of 2 HNO3 was added using a calibrated pipette The acid solution is expected to remove any Tc Np or Pu associated with the vial walls This procedure has been shown to complete mass balances of Pu in similar sorption experiments using Pu (Powell et al 2002) This process was performed for both the solid suspension and the no solids controls The samples were then run on the ICP-MS to determine the concentration of 99Tc 237Np and 242Pu sorbed to the vial walls
37 Data Analysis
The solubilities of 242Pu and 237Np were calculated by using the formula
CICP-MS = aqueous concentration of nuclide from ICP-MS measurement (ppb gnuclidekgsolution)
Mnuclide = molecular mass of nuclide (gnuclidemolnuclide)
In order to determine the Kd values one first needs to determine the concentration on the solid by using
solid
calcite
spike
aq
spike
calcite
spike
stock
solid
m
m
m
C
m
m
m
C
C
)
(
)
(
)
(
+
uacute
uacute
ucirc
ugrave
ecirc
ecirc
euml
eacute
-
+
=
(Equation 32)
Csolid = calculated solid phase concentration of the nuclide (ppb)
Cstock = concentration of the nuclide stock solution (ppb)
mspike = mass of nuclide spiked into the saltstone suspension (g)
mcalcite = total mass of calcite solution used in the saltstone suspension (g)
Caq = aqueous concentration of nuclide from ICP-MS measurement (ppb)
msolid = mass of the saltstone used in the suspension (g)
The Kd can be calculated using the equation
aq
solid
d
C
C
K
=
(Equation 33)
Kd = solid-water partitioning coefficient (gsolutiongsolid assuming density of 10 gmL traditional unit of mLsolutiongsolid can be obtained)
This Kd Equation (33) is numerically equivalent to the traditional Kd equation proposed in ASTM D-4646 which has been used in previous saltstone experiments (Kaplan et al 2007 Kaplan et al 2008)
40 Results and Discussion
41 Radionuclide Sorption to Cementitious Formulations under Oxidizing Conditions
Figure 41 shows Pu Kd values ranging from 104 to gt105 mLg Generally for each solid the Kd increases with increasing initial Pu concentrations typical behavior of systems where the aqueous concentrations of the radionuclides are solubility controlled This is not expected because the Kd expression indicates that the Kd value should remain constant with increasing total Pu concentrations It was noted that aqueous phase concentration of Pu remained relatively constant in all samples (see discussion below regarding Pu solubility) Therefore the sorption capacity of each solid phase for Pu has not been overcome For each of these solid phases it appears the solutions had reached equilibrium before the first samples were taken at 24 hours In each case the Kd values for the one day and four day are similar A trend between the solid phases is not discernible The aged cement with no reducing slag was expected to have the lowest Kd values but in actuality it has the highest Kd Also there is no correlation with the concentration of reducing slag The Vault 2 samples with 17 dry wt- reducing slag has a Kd similar to that of the TR547 (45 dry wt- slag) while the saltstone with the most slag TR545 (90 dry wt- slag) has the lowest Kd value Others have observed that Pu Kd values of cementitious materials are similar in the absence and presence of slag (Allard et al 1984 Hoaglund et al 1985)
It was observed that similar aqueous concentrations of Pu were observed regardless of the solid phase present Figure 42 shows the average aqueous phase concentrations measured after one day and four days for all solids As stated above triplicate samples were prepared for each solid phase and each initial concentration Therefore each of the reported solubility values in Figure 42 is an average of nine measurements Using the highest reported value with the expected maximum error (0018 ppb for solid TR545) the maximum expected aqueous concentration of Pu in the pore water associated with the saltstone formulations will be approximately 7 x 10-11 molL as calculated using Equation 31 This is on the same order as the solubility of Pu hydrous oxide solid phases (Neck and Kim 2001)
Figure 41 Plutonium Kd Values under Oxidizing Conditions Plutonium Kd values for various saltstone formulations measured after one-day equilibration (1d) and four-day equilibration (4d under oxidizing conditions Total plutonium concentrations in each system were 1 ppb 5 ppb and 10 ppb Sample prepared in triplicate and error bars represent standard deviation of samples except as follows value for dataset TR547-4d 10 ppb is reported based on duplicate samples
Figure 42 Plutonium solubility for various saltstone formulations measured after one-day equilibration (1d) and four-day equilibration (4d) under oxidizing conditions Total plutonium concentrations in each system were 1 ppb 5 ppb and 10 ppb as noted Samples prepared in triplicate and an average of all samples (9) was used to determine average solubility The error bars represent standard deviation of samples
Overall the Kd values for Np range from 105 to gt106 with only a few outliers The most significant outlier is the 1 ppb solution in the TR545 sample after the four-day equilibration It drops two orders of magnitude while the 5 and 10 ppb solutions remain constant However this result is most likely an analytical artifact from working at the detection limits of the ICP-MS In the one-day equilibration samples only one of the triplicates S-2-E had detectable Np while in the four-day equilibration samples only S-2-F had detectable amounts present The graph also shows that with the exception of the 5 ppb sample in the aged cement Np sorption to TR545 (90 dry-wt- slag) and TR547 (45 dry wt- slag) have Kd values approximately one order of magnitude over the aged cement (no slag) and Vault 2 (17 dry wt- slag) samples
It was observed that similar aqueous concentrations of Np were observed regardless of the solid phase present Figure 44 shows the average aqueous phase concentrations measured after one day and four-day equilibrations for all solids As stated above triplicate samples were prepared for each solid phase and each initial concentration Therefore each of the reported solubility values in Figure 44 is an average of nine measurements of Np concentration unless stated otherwise Using the highest reported value with the expected maximum error (00026 ppb for solid TR545) the maximum expected aqueous concentration of Pu in the pore water associated with the saltstone formulations will be approximately 2 x 10-11 molL
Figure 43 Neptunium Kd values under oxidizing conditions Neptunium Kd values for various saltstone formulations measured after one-day equilibration (1d) and four-day equilibration (4d) under oxidizing conditions Total plutonium concentrations in each system were 1 ppb 5 ppb and 10 ppb as noted Samples prepared in triplicate and error bars represent standard deviation of samples except as follows value for datasets TR545-1d 1ppb TR545-4d 1 ppb TR547 4d 1 ppb TR545-4d 10 ppb TR547-1d 1ppb TR547-4d 10 ppb are reported based on a single sample and for dataset TR545-1d 5ppb is reported based on duplicate samples Kd values limited to gt106 were at instrumental background
The Kd values for Tc are significantly lower than that of Pu or Np As a whole the values are comparable The values for the one-day and four-day equilibrations solutions in the Vault 2 (17 dry wt- slag) and TR545 (90 dry wt- slag) remained constant within reasonable error with just a slight increase from the one-day to four-day equilibration However the Aged Cement (no slag) and TR547 (45 dry wt- slag) showed a noticeable decrease from day one to day four (Figure 45)
Figure 44 Average solubility of Np under oxidizing conditions Neptunium solubility for various saltstone formulations measured after one-day equilibration (1d) and four-day equilibration (4d) under oxidizing conditions Total Np concentrations in each system were 1 ppb 5 ppb and 10 ppb Samples prepared in triplicate and an average of all samples (9) was used to determine average solubility except as follows TR545-1d is based on 6 samples TR545- 4d on 5 samples TR547-1d on 7 samples and TR547- 4d on 5 samples The error bars represent standard deviation
Figure 45 Technetium Kd values under oxidizing conditions Tc Kd values for various saltstone formulations measured after one-day equilibration (1d) and four-day equilibration (4d) under oxidizing conditions Total Tc concentrations in each system were 1 ppb 5 ppb and 10 ppb as noted above Samples were prepared in triplicate and the error bars represent standard deviation of samples except as follows data sets for Vault 2-1d 1ppb were duplicates and TR547- 4d 10 ppb is based on a single dataset
Similar to the Tc Kd values the 127I Kd values are much lower than those of Pu and Np The amount of reducing slag present in each of the solids does not appear to have a drastic effect on the 127I Kd values In fact the initial (one day) Aged Cement (0 slag) samples had a Kd almost two orders of magnitude above those with reducing slag The cause of this behavior is not known but it has been shown that iodate IO3- the oxidized form of iodine sorbs more strongly than iodide I- to charged surfaces (Schwehr et al 2009 Yoshida et al 1992 Fukui et al 1996) It is possible that the slag is reducing the iodine to the I- form converting it to a species that is less likely to sorb to saltstone Additional work would be required to confirm the oxidation state of iodine when associated with saltstone
Figure 46 Iodine Kd Values under Oxidizing Conditions Iodine Kd values for various cementitious formulations measured after one-day equilibration (1d) and four-day equilibration (4d) under oxidizing conditions Total iodine concentrations in the systems were 100ppb 500 ppb and 1000 ppb as noted above Samples were prepared in triplicate and the error bars represent standard deviation of samples except as follows duplicates were used for dataset TR545- 1d 100ppb
42 Radionuclide Sorption to Vial Walls Under Oxidizing Conditions
Figure 47 shows the aqueous fractions found in the no-solids controls It provides a measure of the solubility of each radionuclide as well as examines the fraction of each radionuclide sorbed to the vial walls After one day only 25 of the Pu remained in solution and the concentration decreased even more after four days The loss of Pu from the aqueous phase may be due to sorption of Pu to the vial walls or precipitation of a Pu hydrous oxide solid (discussed with respect to Figure 49 below) Additional experiments would be required to examine the solubility of the Pu in high pH calcite saturated solutions
After one day about 80 of the Np remained in solution However the aqueous concentration in the initially 1-ppb solution was significantly reduced after four days Approximately 60 of the Np remained soluble in the initially 10-ppb solution Once again this drop could be due to sorption to the vial wall The Tc present after one day ranged from about 88 to about 95 and was virtually 100 after four days These values are consistent with internal standards used to monitor Tc detection performance on the ICP-MS Greater than 50 of the I remained in solution after the one-day and four-day equilibrations As shown in Figure 48 the standard deviation between the triplicate I control samples was quite large Additional control samples are required to understand the mechanism by which I is being lost from the aqueous phase in these samples
Figure 47 Plutonium Neptunium and Technetium Aqueous Fractions Fraction of Pu Np and Tc remaining in the aqueous phase for the No Solids controls after a one-day equilibration (1d) and four-day equilibration (4d) under oxidizing conditions The total concentration for each radionuclide 10 ppb as noted above Samples were prepared in triplicate and the error bars represent the standard deviation of the samples
Figure 48 Iodine Aqueous Fraction Iodine aqueous fraction for the no-solids controls after a one-day equilibration (1d) and four-day equilibration (4d) under oxidizing conditions The total concentration of iodine was 1000 ppb as noted above Samples were prepared in triplicate and the error bars represent the standard deviation of the samples
As discussed above the loss of Np and Pu from the no-solids control (Figure 47) could be due to precipitation of Np and Pu hydrous oxides or sorption to the vial walls To quantify the differences between these possible sinks the vials were washed as described in Section 36 The data in Figure 49 indicate that significant sorption of Np and Pu to the vial walls may occur When combining the mass of Np represented in Figure 47 and Figure 49 there is almost 100 mass recovery of the Np sorbed to the vial wall and the aqueous fraction measured Therefore no precipitation of Np is expected However because 100 recovery was not achieved for Pu a Pu hydrous oxide phase could be precipitating which was washed out of the vial during the cleaning procedure The data in Figure 47 represent the no-solids control samples where there was no solid phase present for Np or Pu to sorb to besides the vial walls However when a cementitious solid phase is present in the sample there will be competition between the vial walls and the cement for sorption of Np and Pu Based on the affinity of metals for metal oxide surfaces as opposed to the polypropylene surface and the much higher surface site density expected for the cementitious samples it is assumed that the cementitious samples will out-compete the vial walls for sorption sites This thesis was tested by taking one of the triplicate samples from each sorption experiment with a solid phase present removing the solid phase from the tubes and leaching any sorbed Np and Pu from the tubes with acid as described in Section 36 Figure 410 and Figure 411 show that although some of the Pu and Np sorbed to the vial walls of the samples this amount accounted for less than 2 in all samples Therefore sorption of Np and Pu to the vial walls does not appear to be a significant factor in experiments where the solid phase is present Note these results do not discount the possibility that Pu hydrous oxide precipitates were forming in both the no-solid control experiments and experiments with cement formulations present Based on the observation of a constant aqueous phase concentration of Pu regardless of the initial Pu concentration the presence of a solubility limiting Pu phase cannot be discounted based on these data Further experiments examining the solubility of Pu in high pH calcite saturated solutions are required
Like Pu Np shows little affinity for the vial walls in the presence of a solid phase In each case tested there was significantly less than 1 of the total Np sorbed to the vial walls This behavior is consistent with the ~100 mass balance on Np achieve in the solid-free controls The majority of Np remained soluble in the solid-free control experiments Therefore it is expected that sorption of Np to the vial walls was the primary reason for the loss of Np from the aqueous phase in the no-solids systems rather than precipitation of a Np solid phase similar to the process discussed for Pu above This assumption is based on the relative solubility of Np(V) as compared with Pu(IV)
Figure 49 Percent Pu and Np sorbed to vial walls of the no solids controls after the aqueous phases were discarded and the vials were washed Both the 10 ppb and 1 ppb datasets were prepared in triplicate and the error bars show the standard deviation
Figure 410 Percent Pu sorbed to vial walls after the solids and aqueous phases were removed and the vials were washed The graph illustrates one sample from each of the 1 ppb 5 ppb and 10 ppb systems Therefore no error bars are present
Figure 411 Percent Np sorbed to vial walls after the solids and aqueous phases were removed and the vials were washed The graph illustrates one sample from each of the 1 ppb 5 ppb and 10 ppb systems Therefore no error bars are present
43 Radionuclide Sorption to Cementitious Formulations under Reducing Conditions
Similar to the Pu Kd values under oxidizing conditions Pu Kd values ranged from 104 to gt105 under reducing conditions (Figure 412) Also similar to the results under oxidizing conditions the Kd increases with increasing initial Pu concentration Again this behavior is indicative of the aqueous phase concentration of Pu being controlled by solubility of Pu rather than by sorption In each case the samples appeared to reach steady state within 24 hours This equilibration is evident because the Kd values after one day and four days are very similar Also it appears that the amount of reducing slag does not make a significant difference in the Kd value In fact the TR547 solid consists of 45 reducing grout but produces approximately the same Kd values of the aged cement which does not have any reducing grout Each of these Kd values are higher than the TR545 which is 90 reducing grout These findings are in agreement with those conducted by Allard et al (1984) and Hoglund et al (1985) who reported that concrete containing reducing agents (slag similar to that used in our study) did not have greater Pu Kd values than those that did not contain slag
Similar aqueous concentrations of Pu were observed regardless of the solid phase present Figure 36 shows the average aqueous phase concentrations measured after one day and four days for all solids As stated above triplicate samples were prepared for each solid phase and each initial concentration Therefore each of the reported solubility values in Figure 412 is an average of up to nine measurements of the Pu aqueous concentrations Using the highest reported value with the expected maximum error (00045 ppb for solid Vault 2) the maximum expected aqueous concentration of Pu in the pore water associated with the cementitious formulations will be approximately 2 x 10-11 molL (calculated from Equation 31) This value is on the same order as the solubility of Pu hydrous oxide solid phases (Neck and Kim 2001) A best value would be 10-12 molL
Figure 412 Pu Kd Values under Reducing Conditions Plutonium Kd values for various cementitious formulations measured after one-day equilibration (1d) and four-day equilibration (4d) under reducing conditions Total plutonium concentrations in each system were 1ppb 5 ppb and 10 ppb Samples prepared in triplicate and error bars represent standard deviation
Figure 413 Average Solubility of Plutonium under Reducing Conditions Plutonium solubility for various cementitious formulations measured after one-day equilibration (1d) and four-day equilibration (4d) under reducing conditions Total plutonium concentrations in each system were 1ppb 5 ppb and 10 ppb as noted Samples prepared in triplicate and an average of all samples (9) was used to determine average solubility The error bars represent standard deviation of samples
The Np Kd values reported in Figure 414 obtained under reducing conditions are very similar to those obtained under oxidizing conditions In each case the samples appeared to reach steady state within 24 hours This equilibration is evident because the Kd values between the one-day and fourndashday equilibrations are similar As was the case with Pu the amount of slag present in each solid does not seem to have a significant effect on the Kd values Again the aged cement with no slag has as high a Kd as the TR545 with 90 reducing slag
Similar aqueous concentrations of Np were observed regardless of the solid phase present Figure 314 shows the average aqueous phase concentrations measured after one day and four days for all solids All Kd values were gt 105 mLg which is considerably larger than those reported by Kaplan and Coates (2007) who reported Np Kd values to 1300 to 1600 mLg This difference can be attributed to two important experimental differences 1) the experiment was designed to permit larger Kd values to be measured ( eg solid to liquid ratios and spike concentrations) and more importantly 2) a more sensitive analytical method ICP-MS was used instead of conventional low-energy gamma spectroscopy or liquid scintillation counting (LSC) analysis As stated above triplicate samples were prepared for each solid phase and each initial concentration Therefore each of the reported solubility values in Figure 415 is an average of up to nine measurements Using the highest reported value (to provide the most conservative most soluble values) with the expected maximum error (00045 ppb for solid TR545) the maximum expected aqueous concentration of Np in the pore water associated with the cementitious formulations will be approximately 2 x 10-11 molL A best value taking into consideration the less-than values which are depicted in Figure 414 as running off the top of the plot would be 10-12 molL
Figure 414 Np Kd Values under Reducing Conditions Neptunium Kd values for various cementitious formulations measured after one-day equilibration (1d) and four-day equilibration (4d) under reducing conditions Total Np concentrations in each system were 1 ppb 5 ppb and 10 ppb Samples were prepared in triplicate and the error bars represent standard deviation Kd values limited to gt106 were at instrumental background
Figure 415 Average Solubility of Neptunium under Reducing Conditions Neptunium solubility for various cementitious formulations measured after one day equilibration (1d) and four day equilibration (4d) under reducing conditions Total plutonium concentrations in each system were 1ppb 5 ppb and 10 ppb Samples prepared in triplicate and an average of all samples (9) was used to determine average solubility The error bars represent standard deviation
A plot of the Tc Kd values for each cementitious formulations under reducing conditions is shown in Figure 416 (log y-axis) and Figure 417 (reduced scale linear y-axis) The Kd values for each of the initial Tc concentrations are relatively similar This behavior is consistent with the Kd expression However the increasing Kd values from the one-day to four-day day equilibrations for each solid indicate that steady state was not reached within one day and it is unclear whether steady state was reached after four days A possible explanation for this behavior is that Tc(VII) was being reduced to Tc(IV) in these systems due to the reducing conditions As Tc(VII) was reduced the Kd would increase based on the high affinity of Tc(IV) for solid phases This proposed mechanism was observed by Lukens et al (2005) using an SRS saltstone material similar but not identical to TR547 Using synchrotron X-ray absorption fine structure spectroscopy they observed over a 453 month period that Tc(VII) incorporated into SRS saltstone slowly converted to Tc(IV) and that the nearest neighbor was initially predominantly oxygen and eventually became predominantly sulfur (described as a Tc(IV) phase TcSx) Lacking in Lukens et al (2005) is quantification of the solubility of Tc This analysis still needs to be completed along with re-oxidation studies ( ie what is the rate that reduced Tc reoxidizes under ambient natural saltstone conditions)
Unlike Np and Pu Tc Kd values changed with the amount of slag included in the formulation Tc Kd values noticeable increase as the amount of slag in the formulation increased TR547 (45 dry-wt- slag) Kd value is visibly higher than the Aged Cement and Vault 2 Kd values while the most reducing TR545 (90 dry wt- slag) Kd value is significantly higher than the others Following a similar trend the reduction capacity that is the total quantity of reductant in the saltstone on a mass basis (units of milli-equivalents of charge per g) of TR547 had slightly greater or equal reduction capacity to that of TR545 (Roberts and Kaplan 2009)
Figure 416 Tc Kd Values under Reducing Conditions Tc Kd values for various cementitious formulations measured after one-day equilibration (1d) and four-day equilibration (4d) under reducing conditions Total Tc concentrations in each system were 1 ppb 5 ppb and 10 ppb Sample prepared in triplicate and error bars represent standard deviation except as follows TR547-1d 1 ppb is based on a single dataset and datasets Vault 2-1d 5 ppb Vault 2- 4d 1 ppb Aged Cement-1d 5 ppb and Aged Cement-4d 1 ppb are duplicates
Figure 417 Data from Figure 416 replotted on a reduced linear scale for easier viewing Each sample was prepared in triplicate except as follows TR547-1d 1 ppb is based on a single dataset Vault 2-1d 5 ppb Vault 2- 4d 1 ppb Aged Cement-1d 5 ppb and Aged Cement-4d 1 ppb are duplicate datasets
The calculated Kd values for I sorption to cementitious samples under reducing conditions are shown in Figure 418 Before discussing the data it should be noted that spiked QAQC samples which were analyzed on the ICP-MS along with the samples used to generate the data in Figure 418 were off by an average of 195 with one outlier of approximately 40 This dataset did not include the use of internal standards as discussed in Section 31 above Due to a lack of an internal standard the iodine results presented in this report should be considered with a minimum error estimate of 20
The iodine Kd values under reducing conditions are different from those observed under oxidizing conditions Under oxidizing conditions it appears they are at a steady state by day one However under reducing conditions there is a noticeable difference between days one and four indicating steady state was not reached by day one and possibly not by day four Another interesting observation is that the Kd values are decreasing from day one to four A possible reason for this behavior may be due to redox chemistry of iodine in this system If iodine partially or entirely exists in the form as iodate (IO3-) it is possible it could be reduced to iodide I- within the reducing cementitious system These two iodine species sorb differently iodate sorbing to minerals more strongly than iodide (Denham et al 2009 Schwehr et al 2009 Fukui et al 1996 Yoshida et al 1992) It is hypothesized that the reducing environment of the saltstone is sufficient to reduce iodate ions to the more weakly binding form of iodine iodide
This is one of the few datasets (along with Tc) in this study where there may be a difference between the various solids The degree of iodate reduction would be expected to increase as the slag content increases As mentioned above reduction of iodate to iodide should result in a decrease in sorption Therefore higher Kd values should be observed for solids with less slag such as the Aged Cement (0 dry wt- slag) and Vault 2 (17 dry wt- slag) This is generally the case in Figure 418 where the highest Kd values are reported for the Aged Cement and the lowest values are for solid TR547 However this trend does not hold completely where the saltstone sample containing 90 slag (TR545) has generally equal or higher Kd values than the saltstone containing 45 dry wt- slag (TR547)
Figure 418 Iodine Kd Values under Reducing Conditions I Kd Values for various cementitious formulations measured after one day equilibration (1d) and four day equilibration (4d) under reducing conditions Total iodine concentrations in each system were 100 ppb 500 ppb and 1000 ppb as noted Sample prepared in triplicate and error bars represent standard deviation of samples except as follows Vault 2-4 d 100 ppb is a single dataset while the datasets for Vault 2-1 d 100 ppb 4 d 1000 ppb TR545-4 d 1000 ppb 100 ppb TR547-4 d 1000 ppb 500 ppb 100 ppb and Aged Cement- 4 d 1000 ppb and 100 ppb are all based on duplicates
44 Radionuclide Sorption to Vial Walls under Reducing Conditions
The aqueous concentrations for Pu Np and Tc in the no solids controls are shown in Figure 419 The results are similar to those presented for experiments performed under oxidizing conditions above The 1 ppb Pu aqueous fraction is approximately three times greater than the 10 ppb fraction at day one This fraction decreases over time and by day four they are approximately equal when taking error into account This behavior is similar to the aqueous fraction under oxidizing conditions The 1 ppb Np aqueous fraction is significantly higher on both day one and day four than the aqueous fraction of the 10 ppb samples However each remained constant from day one to day four The 10 ppb aqueous fraction is twice as low as under oxidizing conditions which suggests either higher sorption to the vial walls or more precipitating out under the reducing conditions Like Pu and Np Tc shows a decrease from day one to day four especially for the 1 ppb samples The decrease in the 10 ppb sample is minimal and the aqueous fraction remains around 09 This value is slightly lower than that under oxidizing conditions
To examine the degree of sorption to the vial walls the tubes were washed again as performed for the experiments under oxidizing conditions above and similar results were found Ninety percent of the 1 ppb Pu sample was sorbed to the vial wall upon completion of the experiment which gives a 100 mass recovery when comparing this value to that found in Figure 419 However this result is not the case with the 10 ppb samples where approximately 75 of the mass remains unaccounted It is noteworthy that approximately 25 of the Pu from the 10 ppb solution sorbed to the vial walls under both oxidizing and reducing conditions Np follows the same trend as Pu while less than 005 of the Tc sorbed to the wall
Figure 419 Plutonium Neptunium and Technetium No-Solids Aqueous Fractions under Reducing Conditions Pu Np and Tc aqueous fractions of No Solids controls after a one-day equilibration (1d) and four-day equilibration (4 d) under reducing conditions Total concentration for each radionuclide was 1 ppb and 10 ppb Samples were prepared in triplicate and the error bars represent the standard deviation
Figure 420 Percent of Pu Np and Tc sorbed to the vial walls of the No Solids control samples under reducing conditions Each the 1 ppb and 10 ppb samples were prepared in triplicate and the error bars represent the standard deviations of triplicate samples
Under reducing conditions the fraction of I remaining in the aqueous phase was around 90 with almost 100 mass recovery of the 100 ppb I after the four-day equilibration These graphs show that under reducing conditions there will only be a small fraction of I sorbing to the vial wall or coming out of solution This result is a much better mass recovery than under oxidizing conditions (Figure 48) which had a mass recovery of approximately 65 after four days This result is also consistent with the interpretation that there may be a iodine speciation change between the two redox treatments
Figure 421 Iodine No-Solids Aqueous Fractions under Reducing Conditions I aqueous fractions of No-Solids controls after a one-day equilibration (1d) and four-day equilibration (4d) under reducing conditions The total concentration for each system was 100 ppb and 1000 ppb Samples were prepared in triplicate and the error bars represent the standard deviation
50 Comparison of Radionuclide Sorption under Oxidizing and Reducing Conditions
In the following figures (Figure 51 through Figure 54) the data shown above has been replotted to allow comparison between the oxidizing and reducing conditions for each cementitious formulation General observations based on these data follow
Vault 2 Observations (Figure 51)
middot Pu Kds are greater than 104 under both oxidizing and reducing conditions and Pu Kds are slightly lower under reducing conditions This could possibly be due to reduction of Pu(IV) to Pu(III) However no oxidation state analysis was performed in this work
middot Np Kds are generally greater than 104 under both oxidizing and reducing conditions Interestingly Np Kds are higher under reducing conditions by almost an order of magnitude This could possibly be due to reduction of Np(V) to Np(IV) However no oxidation state analysis was performed in this work
middot Regardless of the initial Np or Pu concentration similar aqueous phase concentrations of Np or Pu were observed in all samples This trend indicates that ldquosorptionrdquo of Np and Pu in these systems may be a combination of adsorption absorption and (co)precipitation processes
middot Tc appears to reach a steady state within four days under oxidizing conditions This behavior does not appear to be the case under reducing conditions After four days similar Kd values are reached under both oxidizing and reducing conditions It is unclear whether the Kd value of Tc will continue to increase under reducing conditions consistent with reduction of Tc(VII) to Tc(IV) The similarity in Kd values under both oxidizing and reducing conditions is an interesting observation and certainly warrants additional studies
middot I Kd values are similar under both oxidizing and reducing conditions However reducing condition systems may not be at steady state after four days while systems under oxidizing conditions appeared to reach a steady state The difference in rates may be due to reduction of iodate to iodine
middot For all isotopes examined the sorption behavior to each of the solid phases is very similar
TR545 and TR547 Observations (Figure 52 and Figure 53)
middot Similar to the discussion above with respect to Vault 2 Pu Np and Tc all appear to reach a steady state under oxidizing conditions and approach steady state slower under reducing conditions
middot Np and Pu Kd values are greater than 104 for all systems and time steps The aqueous phase concentrations of Np and Pu appear to be better described as a solubility in terms of the aqueous phase concentration of Np and Pu Similar aqueous phase concentrations of both Np and Pu were reached The data indicate that the initial Np and Pu concentration generally does not affect the aqueous phase concentration at an apparent steady state The presence of each solid phase appears to limit the aqueous phase concentration of both Np and Pu on the order of 10-11 molL
middot Tc shows significantly higher Kd values under reducing conditions versus oxidizing conditions
middot For all isotopes examined the sorption behavior to each of the solid phases is very similar
Aged Cement Observations (Figure 54)
middot Pu appears to be close to steady state for each solid by day one with similar Kd values reached on between day one and day four
middot Np has a higher Kd under reducing conditions than oxidizing (105 under oxidizing conditions and gt105 under reducing conditions)
middot Neither set of Tc data was at steady state by day one and rates of sorptiondesorption reactions appear to be different Tc Kds decrease from day one to four under oxidizing conditions but increase under reducing conditions
middot The Kd values for I under oxidizing conditions were considerably higher than those measured for I with any other solid Similar Kd values obtained for the same solids under reducing conditions indicate that the reported Kd values under oxidizing conditions appear to be suspect However analysis of the raw data gives no indication of an experimental artifact As discussed above these observations may be explained based upon the amount of slag contained within the solids which will affect the reducing capacity (ie No reducing slag is in the aged cement which could be reason the reduction of iodate to iodide (speculated in other samples) is not evident)
middot The difference in sorption behavior of iodine to the aged cement between oxidizing and reducing conditions also indicates that the reducing conditions of the solution may affect I redox behavior in addition to any reactivity expected in the solid phases
Figure 51 Comparison of Tc I Np and Pu sorption to Vault 2 solid under oxidizing and reducing conditions
Figure 52 Comparison of Tc I Np and Pu sorption to TR 545 solid under oxidizing and reducing conditions
Figure 53 Comparison of Tc I Np and Pu sorption to TR547 solid under oxidizing and reducing conditions
Figure 54 Comparison of Tc I Np and Pu sorption to Aged Cement under oxidizing and reducing conditions
60 Comparison of Radionuclide Sorption and Solubility under Oxidizing and Reducing Conditions
To further summarize the data the following tables provide either the average solubility (for Np and Pu) or average Kd (for Tc and I) determined under both oxidizing and reducing conditions for each cementitious formulation Each table lists the average value standard deviation and the number of replicate samples used to calculate the reported values
The solubility of Pu in the presence of each solid under oxidizing and reducing conditions is shown in Table 61 (this is taken from experiments equilibrated for four days not one day) Under oxidizing conditions the apparent solubility values associated with the Aged Cement (0 dry wt- slag) Vault 2 (17 dry wt- slag) and TR547 (45 dry wt- slag) are all similar with only a slight increase in solubility as the amount of reducing slag increases There is a significant increase of almost an order of magnitude for the most reducing saltstone TR545 (90 dry wt- slag) However these samples also have a standard deviation on the same order of magnitude as the solubility itself which when taken into account brings the solubility back into the range of the others Under reducing conditions the apparent solubility values are slightly lower than under oxidizing conditions In this set of samples the Vault 2 saltstone with 10 dry wt- reducing slag had the highest apparent solubility but once again when considering the standard deviation the values are similar
Table 61 Comparison of plutonium apparent solubility values under oxidizing and reducing conditions
Table 62 lists the apparent solubility values of Np in the presence of each cementitious formulation under both oxidizing and reducing conditions Under oxidizing conditions the cementitious formulation does not appear to have a dramatic effect on the solubility The apparent solubility values are similar to those of Pu under similar conditions except the Np standard deviations are much higher The high standard deviations are an analytical artifact since the measured concentrations were close to or at the detection limit of the ICP-MS There does appear to be a slight decrease in Np solubility under reducing conditions However the statistical significance of this decrease was not calculated
Table 62 Comparison of neptunium apparent solubility values under oxidizing and reducing conditions
Unlike the apparent solubility values of Pu and Np the aqueousatmospheric conditions and cementitious formulation seem to have an effect on the Tc Kd values (Table 63) Under oxidizing conditions there is not a discernible difference among the different cementitious formulations especially when taking the respective standard deviations into account However when experiments were run under reducing conditions the specific formulation had a noticeable effect The two saltstone samples with the least amount of reducing slag Aged Cement (0 dry-wt- slag) and Vault 2 (17 dry wt- slag) had Kd values which were similar to those observed under oxidizing conditions However the TR547 (45 dry-wt- slag) increased by almost an order of magnitude while the TR545 (90 dry wt- slag) increased by about three orders of magnitude Although the respective standard deviations are large the higher Kd values do appear to be significant
Table 63 Comparison of technetium Kd values under oxidizing and reducing conditions
Unlike Tc I does not seem to be as affected by cementitious formulation and redox status (Table 64) The only treatment (possible outlier) that does not follow this trend is the Aged Cement under oxidizing conditions This Kd value is higher than the others but also has a much higher standard deviation which when accounted for gives a value similar to the others All other treatments had near identical Kd values irrespective of solid phase or redox condition But again the Aged Cement data cannot be discounted at this time given the possibility of the influence that redox may have on iodine speciation and the strong influence I speciation has on sorption to cementitious materials
Table 64 Comparison of iodine Kd values under oxidizing and reducing conditions
70 Summary and Recommendations for Future Work
71 Comparison with Previous Data
The increased sensitivity of the ICP-MS over conventional low-energy gamma spectroscopy or liquid scintillation counting (LSC) analysis allowed for much more accurate Kd values and apparent solubility values in this work than were previously obtainable Generally radioanalytical detection methods start with activities on the order of 103 to 104 counts per minute (cpm) and approach background levels of 1 to 5 cpm for strongly sorbing radionuclides Therefore the accuracy of the Kd value will be the difference in analytical sensitivity when the initial aqueous activity decreases by a factor of approximately 5000 ( ie the aqueous activity drops from approximately 5000 cpm to the instrument background of 1 cpm following almost complete sorption) As a result the reported Kd values can only be reliably reported up for a Kd of 103 to 104 This constraint is believed to be the difference between the observed Kd values for 237Np of gt 105 observed in this work when compared with the Kd values between 3000 and 4000 reported by Kaplan et al (2008) A similar observation was made for Pu because 242Pu was used for ICP-MS analysis and 238Pu was used in the work of Kaplan et al (2008) This constrint may account for the different Kd value of gt104 reported in Kaplan et al (2008) compared with the value of gt105 observed in this work
In the case of Tc Kaplan et al (2008) reported a Kd of 023 mLg for Vault 2 under oxidizing conditions and 093 mLg under reducing conditions while the above experiment determined the Vault 2 Kd to be 505 mLg under oxidizing conditions and 557 mLg under reducing conditions
Unlike the discrepancy in the Kd values for Np Pu and Tc between the above findings and those in Kaplan et al (2008) the reported Kd values for iodine are similar For Vault 2 Kaplan et al (2008) found 125I to have a Kd of 894 mLg under oxidizing conditions and 715 mLg under reducing conditions These values are similar to the Kd values of 766 mLg and 725 mLg observed under oxidizing and reducing conditions respectively in this work These findings appear to confirm the previously accepted Kd values of 0-10 mLg depending on the cementitious formulation
72 Suggested Future Work
The above data demonstrate several areas that require further examination The increasing Tc Kd values over time dataset suggest that steady state had not been achieved It would be beneficial to determine the amount of time required to reach steady state and allow determination of a more accurate Kd value (an assumption of the Kd construct is that it be measured at steady state) Also kinetic studies of both Tc and I are needed to better understand their respective interactions with the different cementitious formulations As for the I additional tests should be performed to test the hypothesis that iodine may in part exist as iodate which may initially sorb to the saltstone then undergo reduction to iodine or iodide and then desorbs causing a decrease in Kd
A final area of future work is to examine the possible causes for the similar behavior of each cementitious formulation despite the different slag content This discrepancy is not only observed in the above experiments but also in Kaplan et al (2008) which is illustrated in Table 31 and by recent work in measurements of saltstone reduction capacity (Roberts and Kaplan 2009) The reduction capacity (units in milli-equivalentsg solid) equivalents of the Aged Cement with no slag is 855 plusmn 101 and adding 10 slag gives a reducing equivalent of 2398 plusmn 311 However increasing the slag content to 23 causes the reducing capacity to increase to 8218 plusmn 81 which is almost equivalent to the 8324 plusmn 49 of the 100 slag Understanding the chemistry behind the reducing capacity of each cementitious formulation will help to define what reactions are important for controlling radionuclide release from the saltstone
80 References
Allard B L Eliasson S Hoglund and K Andersson 1984 ldquoSorption of Cs I and actinides in concrete systemsrdquo SKB Technical Report SKBKBS TR-84-15 DKB Stockholm Sweden
Denham M D I Kaplan and C Yeager2009 ldquoGroundwater radioiodine Prevalence biogeochemistry and potential remedial approachesrdquo SRNL-STI-2009-00463 Savannah River National Laboratory Aiken SC
Dixon K L M A Phifer and J R Harbour 2008 ldquoFY09 PACA Maintenance Program Additional Saltstone Property Testingrdquo SRNL-L3100-2009-00019 Rev0 Savannah River National Laboratory Aiken SC
Fukui M Fujikawa Y and Satta N 1996 ldquoFactors affecting interaction of radioiodide and iodate species with soilrdquo Journal of Environmental Radioactivity 31 199-216
Hoglund S L Eliasson B Allard K Andersson and B Torstenfelt 1985 ldquoSorption of some fission products and actinides in concrete systemsrdquo Mat Res Soc Symp Proc50 683-690
Kaplan D I 2007 Geochemical Data Package for Performance Assessment Calculations Related to the Savannah River Site WSRC-TR-2006-00004 Rev 1 Washington Savannah River Company Aiken SC
Kaplan D I and Coates J 2007 ldquoPartitioning of Dissolved Radionuclides to Concrete under Scenarios Appropriate for Tank Closure Performance Assessmentsrdquo WSRC-STI-2007-00640 Rev 0 Washington Savannah River Company Aiken SC 29808
Kaplan D I Roberts K Coates J Siegfried M Serkiz S 2008 ldquoSaltstone and concrete interactions with radionuclides Sorption (Kd) desorption and reduction capacity measurementsrdquo SRNS-STI-2008-00045 Savannah River National Laboratory Aiken SC 2008
Neck V and Kim J I 2001 ldquoSolubility and hydrolysis of tetravalent actinidesrdquo Radiochim Acta 89 1
Powell B A Fjeld R A Coates J T Kaplan D I Serkiz S M 2002 ldquoPlutonium Oxidation State Geochemistry in the SRS Subsurface Environmentrdquo WSRC-TR-2003-00035 Westinghouse Savannah River Company US DOE Savannah River Site Aiken SC
Roberts K A and D I Kaplan 2009 Reduction Capacity of Saltstone and Saltstone Componentsrdquo SRNL-STI-2009-00637 Rev0 Savannah River National Laboratory Aiken SC
Schwehr K A Santschi P H D I Kaplan C M Yeager and R Brinkmeyer 2009 ldquoOrgano-iodine formation in soils and aquifer sediments at ambient concentrationsrdquo Environ Sci Technol437258-7264
Yoshida S Muramatsu Y and Uchida S 1992 ldquoStudies on the sorption of I-(iodide) and IO3-(iodate) onto andosolsrdquo Water Air and Soil Pollution 63 321-329
90 Appendix A Data Tables of Radionuclide Sorption to Saltstone under Oxidizing Conditions
The following tables represent data collected for the no solids controls each saltstone and testing of radionuclide sorption to the vial walls The no solids controls tables include the concentration (ppb) of the radionuclide spiked into the sample along with the concentration of the radionuclide (ppb) measured in the aqueous phase after the given equilibration time The pH at the time the sample was taken is also recorded along with the fraction of the radionuclide which stayed in the aqueous phase The tables for the cementitious formulation data include the data above along with the addition of a Kd value The tables of the data for the radionuclides sorbed to the vial walls include the initial concentration (ppb) of the spike the concentration (ppb) of the radionuclide that had sorbed to the vial wall during the experiment and the percentage of the total concentration this represents
Important Notes
BDL- Below Detection Limit
lt01 denotes no notable sorption occurred
91 Data Tables for No Solid Controls
Table 91 Plutonium no solids control after one day
Table 92 Plutonium no solids control after four days
Table 93 Neptunium no solids control after one day
Table 94 Neptunium no solids control after four days
Table 95 Technetium no solids control after one day
Table 96 Technetium no solids control after four days
Table 97 Iodine no solids control after one day
Table 98 Iodine no solids control after four days
92 Data Tables for Vault 2
Table 99 Vault 2- plutonium after one day
Table 910 Vault 2- plutonium after four days
Table 911 Vault 2- neptunium after one day
Table 912 Vault 2- neptunium after four days
Table 913 Vault 2- technetium after one day
Table 914 Vault 2- technetium after four days
Table 915 Vault 2- iodine after one day
Table 916 Vault 2- iodine after four days
Table 917 TR545- plutonium after one day
93 Data tables for saltstone TR545
Table 918 TR545- plutonium after four days
Table 919 TR545- neptunium after one day
Table 920 TR545- neptunium after four days
Table 921 TR545- technetium after one day
Table 922 TR545- technetium after four days
Table 923 TR545- iodine after one day
Table 924 TR545- iodine after four days
94 Data Tables for Saltstone TR547
Table 925 TR547- plutonium after one day
Table 926 TR547- plutonium after four days
Table 927 TR547- neptunium after one day
Table 928 TR547- neptunium after four days
Table 929 TR547- technetium after one day
Table 930 TR547- technetium after four days
Table 931 TR547- iodine after one day
Table 932 TR547- iodine after four days
95 Data Tables for Aged Cement
Table 933 Aged cement- plutonium after one day
Table 934 Aged cement- plutonium after four days
Table 935 Aged cement- neptunium after one day
Table 936 Aged cement- neptunium after four days
Table 937 Aged cement- technetium after one day
Table 938 Aged cement- technetium after four days
Table 939 Aged cement- iodine after one day
Table 940 Aged cement- iodine after four days
96 Data Tables for Sorption to Vial Walls
Table 941 Plutonium sorbed to vial wall in no solids control
Table 942 Neptunium sorbed to vial wall in no solids control
100 Appendix B Data Tables of Radionuclide Sorption to Saltstone Under Reducing Conditions
The following tables represent data collected for the no solids controls each cementitious solid and testing of radionuclide sorption to the vial walls The no solids controls tables include the concentration (ppb) of the radionuclide spiked into the sample along with the concentration of the radionuclide (ppb) measured in the aqueous phase after the given equilibration time The pH at the time the sample was taken is also recorded along with the fraction of the radionuclide which stayed in the aqueous phase The tables for the cementitious solidsrsquo data include the data above along with the addition of a Kd value The tables of the data for the radionuclides sorbed to the vial walls include the initial concentration (ppb) of the spike the concentration (ppb) of the radionuclide that had sorbed to the vial wall during the experiment and the percentage of the total concentration this represents
Important Notes
BDL= Below Detection Limit
lt01 denotes no notable sorption occurred
101 Data Tables for No-Solid Controls
Table 101 Plutonium no solids control after one day
Table 102 Plutonium no solids control after four days
Table 103 Neptunium no solids control after one day
Table 104 Neptunium no solids control after four days
Table 105 Technetium no solids control after one day
Table 106 Technetium no solids control after four days
Table 107 Iodine no solids control after one day
Table 108 Iodine no solids control after four days
102 Data Tables for Vault 2
Table 109 Vault 2- plutonium after one day
Table 1010 Vault 2- plutonium after four days
Table 1011 Vault 2- neptunium after one day
Table 1012 Vault 2- neptunium after four days
Table 1013 Vault 2- technetium after one day
Table 1014 Vault 2- technetium after four days
Table 1015 Vault 2- iodine after one day
Table 1016 Vault 2- iodine after four days
103 Data Tables for TR545
Table 1017 TR545- plutonium after one day
Table 1018 TR545- plutonium after four days
Table 1019 TR545- neptunium after one day
Table 1020 TR545- neptunium after four days
Table 1021 TR545- technetium after one day
Table 1022 TR545- technetium after four days
Table 1023 TR545- iodine after one day
Table 1024 TR545- iodine after four days
104 Data Tables for TR547
Table 1025 TR547- plutonium after one day
Table 1026 TR547- plutonium after four days
Table 1027 TR547- neptunium after one day
Table 1028 TR547- neptunium after four days
Table 1029 TR547- technetium after one day
Table 1030 TR547- technetium after four days
Table 1031 TR547- iodine after one day
Table 1032 TR547- iodine after four days
105 Data Tables for Aged Cement
Table 1033 Aged cement- plutonium after one day
Table 1034 Aged cement- plutonium after four days
Table 1035 Aged cement- neptunium after one day
Table 1036 Aged cement- neptunium after four days
Table 1037 Aged cement- technetium after one day
Table 1038 Aged cement- technetium after four days
Table 1039 Aged cement- iodine after one day
Table 1040 Aged cement- iodine after four days
106 Data Tables for Sorption to Vial Walls
Table 1041 Plutonium sorbed to vial wall in no solids control
Table 1042 Neptunium sorbed to vial wall in no solids control
Table 1043 Technetium sorbed to vial wall in no solids control
From K L Dixon M A Phifer and J R Harbour
FY09 PACA Maintenance Program Additional Saltstone Property Testing
BACKGROUND
Additional tests have been identified for measurement of important hydraulic and physical properties of saltstone The initial phase of this work [1] was completed last year and the results were detailed in an internal report [2] The proposed testing for FY09 includes measurement of saturated hydraulic conductivity porosity bulk density particle density water retention and Youngrsquos modulus of simulated Saltstone grouts For completeness the bleed volumes and gel times for each mix will also be measured
The testing will be based on a projected salt solution composition for the ARPMCU stream that will be fed to the Saltstone Production Facility over the next few years The scope for FY09 will include testing to determine the impact of (1) admixtures (2) organics (3) wcm ratio (4) aluminate concentration and
(5) temperature of curing on the hydraulic properties of saltstone mixes Samples of selected batches prepared as part of this task will be provided to Dan Kaplan for measurement of Kd through leaching tests The eleven mixes that will be batched and tested are detailed in Table 1
Table 1 The Eleven Mixes That will be Batched and Tested
BFS is Blast Furnace Slag FA is Fly Ash and PC is Portland Cement
TEST DETAILS
Test 1 Control (Mix 1)
A control mix will be based on the baseline mix modified by exclusion of the Class F fly ash Consequently the cementitious materials premix will be a mixture of 90 blast furnace slag and 10 portland cement The degree of reaction will be much greater than with the normal premix and therefore should result in a lower porosity and a lower permeability This bounding test at 060 wcm ratio is expected to yield a hydraulic conductivity at or below the detection limit for the Mactec permeameter measurement system Therefore this test should demonstrate the lowest level of detection of the Mactec system as well as show a resolvable difference between measurements of the control mix and the control mix with the normal premix composition
Test 2 ndashImpact of Admixtures (Mixes 2 and 3)
Recent saltstone batches have required both a set retarder (Daratard 17) and an antifoam agent (Q2) for processing of the saltstone Therefore the baseline mix will be prepared with and without nominal levels of these two admixtures to determine whether these admixtures appreciably affect the hydraulic and physical properties of saltstone at these nominal concentrations
Test 3ndashImpact of Organics (Mixes 2 and 4)
The solvent extraction process is expected to result in some carryover of organics [3] Consequently a test will be performed on the impact of Caustic Side Solvent Extraction (CSSX) organics at 100 microliters per 1600 gram batch The CSSX solvent consists of 075 M 1-(2233-tetrafluoropropoxy)-3-(4-sec-butylphenoxy)-2-propanol (Cs-7SB) and 0003 M tri-n-octylamine (TOA) in an Isoparreg L diluent
Test 4ndashImpact of Combination of Admixtures and Organics (Mixes 2 5 10 and 11)
This test will determine the impact of a combination of admixtures (Test 2) and organics (Test 3) together in the mix vs the baseline case without admixtures and organics
Test 5ndash Impact of wcm Ratio (Mixes 2 6 and 7)
It is well known that decreasing the wcm ratio in a mix will improve permeability in normal portland cement water mixes This test will measure the variation in permeability for the case of the MCU salt solution at three different wcm ratios The initial selection of wcm ratios is 055 060 and 065 However if the mix at an as-batched 065 wcm ratio has significant bleed water and the resulting actual wcm ratio is close to 060 then the three ratios will be adjusted to provide a more evenly spaced set of values However the baseline mix at 060 will be included as one of the three mixes
Test 6 ndash Impact of Aluminate Concentration (Mixes 8 9 and 10)
The DWPF has modified its process flowsheet to include a caustic washing of HLW sludge to remove some of the aluminum from the HLW prior to vitrification The resulting aluminate stream will then be blended with tank 50 material and fed to the SPF This increased aluminate concentration in the salt solution has significant impact on heat of hydration and set times and consequently it is likely that it will also impact permeability Therefore a set of three samples will be made at wcm ratios of 055 060 and 065 (as in Test 3) with a higher level of aluminate (028 M) for testing
Test 7 ndash Impact of Increased Curing Temperature (Mix 11)
In an ongoing task there is evidence that Youngrsquos modulus (a performance indicator) [4] is reduced by increasing the curing temperature of the mix Since the vault temperature increases during curing as a result of the exothermic hydration reactions one of the baseline mixes with a combination of admixtures and organics will be cured at 60 oC rather than the normal 22 oC to determine the impact of curing temperature on the permeability
SCHEDULE
The schedule for the task of batching and testing of the samples is provided in Table 2 This schedule is based on the fact that the cementitious materials will be available for the testing as needed
Table 2 Additional Saltstone Hydraulic and Physical Property Tests
Distribution
Savannah River Site
A B Barnes999-W Rm 336
H H Burns999-W Rm 381
B T Butcher773-43A Rm 212
A D Cozzi999-W Rm 337
D A Crowley773-43A Rm 216
M E Denham773-42A Rm 218
J C Griffin773-A Rm A-231
J R Harbour999-W Rm 348
C A Langton773-43A Rm 219
M H Layton705-1C Rm 14
D I Kaplan (3 copies) 773-43A Rm 215
S L Marra773A Rm A-230
A M Murray773-A Rm 229
K A Roberts773-43A Rm 225
T C Robinson705-1C Rm 13
L B Romanowski705-1C Rm 19
K H Rosenberger705-1C Rm 16
F M Smith705-1C Rm 24
RPA File (2 copies)773-43A Rm 213
Clemson University Environmental Engineering and Earth Sciences 372 Computer Court LG Rich Environmental Laboratory Anderson SC 29625
M S Lilley (3 Copies)
B A Powell (3 Copies)
13
13
13
13
Clemson University is presently investigating appropriate internal standards for iodine analyses for ICP-MS Of those tested rhenium and molybdenum have shown some promise13
13
Item
Schedule
Start Work
12108
Test Plan Complete
1509
Preparation of 1st set of Samples Complete
11909
90-Day Cure Period for 1st set of Samples Complete
42009
Mix
Simulant
Descriptor
wcm
Aluminate
BFS
FA
PC
Type
ratio
molarity
wt
wt
wt
1
ARPMCU
Control - BFSPC
060
0054
90
0
10
2
ARPMCU
Baseline
060
0054
45
45
10
3
ARPMCU
Baseline with Admixtures
060
0054
45
45
10
4
ARPMCU
Baseline with Organics
060
0054
45
45
10
5
ARPMCU
Baseline Combo -Organics and Admixtures
060
0054
45
45
10
6
ARPMCU
wcm ratio impact
055
0054
45
45
10
7
ARPMCU
wcm ratio impact
065
0054
45
45
10
8
ARPMCU
Impact of Aluminate
055
0280
45
45
10
9
ARPMCU
Impact of Aluminate
065
0280
45
45
10
10
ARPMCU
Baseline Combo and Aluminate
060
0280
45
45
10
11
ARPMCU
Baseline Combo at 60 oC Cure Temp
060
0054
45
45
10
SRNL L3100-2009-00019 Rev 0
December 16 2008
Keywords
Performance
Permeability
Modulus
L B Romanowski
Waste Determinations
110 Appendix C Dixon et al (2009) FY09 PACA Maintenance Program Additional Saltstone Property Testing SRNL L3100-2009-00019 Rev 0
Sample ID
Initial Conc (ppb)
Conc In Wash of Vial
Sorbed to Walls
NS-A
1179928939
555806E-05
000047105
NS-B
12253209
774746E-05
000063228
NS-C
115498292
485721E-05
000042054
NS-E
1206356364
490926E-06
000040695
NS-F
1218363059
399779E-06
000032813
NS-G
1217636322
381518E-06
000031333
Sample ID
Initial Conc (ppb)
Conc In Wash of Vial
Sorbed to Walls
NS-A
1001822029
0056017
0559151
NS-B
1000816271
0036572
0365421
NS-C
9982091832
0029872
0299253
NS-E
1005570326
0000511
0050771
NS-F
1074652687
000057
0053056
NS-G
1030704749
0000249
0024193
Sample ID
Initial Conc (ppb)
Conc In Wash of Vial (ppb)
Sorbed to Walls
NS-A
8197769521
0082513388
100653462
NS-B
8221312733
00787687
095810368
NS-C
8126405694
0074648839
091859602
NS-E
0892430451
0003210839
035978593
NS-F
0851281521
0002677402
031451429
NS-G
0867134776
0002050021
023641316
Sample ID
Initial Aq Conc (ppb)
Equil Aq Conc (ppb)
pH
Fraction Aq
Kd
A
8418564
76877
1145
0913184256
423658
B
7971672
992224
1146
1244687434
lt01
C
8049572
7299231
1146
0906784993
4863719
D
4145684
3116002
1155
0751625609
1528223
E
411107
351634
1156
0855334565
7750838
F
4086431
3293867
1155
0806049742
1145648
G
7886779
7759404
1165
0983849604
0751874
H
8259334
88239
1162
1068354932
lt01
I
8399263
711941
1164
0847623085
7981093
Sample ID
Initial Aq Conc (ppb)
Equil Aq Conc (ppb)
pH
Fraction Aq
Kd
A
8418563537
737977259
1150
0876607103
6272787
B
7971671977
6853215035
1155
0859696066
7850152
C
8049572051
705537908
1153
0876491202
6667104
D
4145684267
2980931093
1156
0719044409
1807023
E
4111069758
310676185
1158
075570643
1481422
F
4086431184
3226673231
1158
0789606648
1268657
G
7886778865
6617517673
1160
0839064691
8785091
H
8259334117
6970070149
1160
084390219
8368448
I
839926338
664029369
1162
0790580482
1176026
Sample ID
Initial Aq Conc (ppb)
Equil Aq Conc (ppb)
pH
Fraction Aq
Kd
A
8426518
7387328
1145
0876676186
5966258
B
8638001
7419385
1146
0858923768
6960547
C
9323318
8036996
1146
0862031802
6818523
D
442651
3962629
1155
0895203859
4979995
E
4426849
4090424
1156
092400338
3395329
F
3929483
3698764
1155
0941285083
2958172
G
0817864
0742066
1165
0907321016
4428077
H
0878959
0720997
1162
0820285656
9047228
I
0772206
0788286
1164
1020823931
lt01
Sample ID
Initial Aq Conc (ppb)
Equil Aq Conc (ppb)
pH
Fraction Aq
Kd
A
8426518355
833290075
1150
098889012
0476492
B
8638001423
7823321167
1155
0905686487
4413063
C
9323317745
925927516
1153
0993130923
0294664
D
442651005
4300859603
1156
0971614106
1242837
E
4426849405
4336992073
1158
0979701742
0855315
F
3929483125
3938204338
1158
100221943
lt01
G
0817864386
081693181
1160
0998859743
0049487
H
0878958929
0792412508
1160
0901535306
4510199
I
0772205665
0871436364
1162
1128502941
lt01
Sample ID
Initial Aq Conc (ppb)
Equil Aq Conc (ppb)
pH
Fraction Aq
Kd
A
8849444
0000131
1145
148418E-05
3007445
B
8447823
0000111
1146
131529E-05
3662996
C
8590597
656E-05
1146
76328E-06
6209405
D
449125
BDL
1155
NA
NA
E
4391894
BDL
1156
NA
NA
F
4210704
BDL
1155
NA
NA
G
0863815
BDL
1165
NA
NA
H
0870502
BDL
1162
NA
NA
I
0861954
BDL
1164
NA
NA
Sample ID
Initial Aq Conc (ppb)
Equil Aq Conc (ppb)
pH
Fraction Aq
Kd
A
8849444124
0000306309
1150
346133E-05
1289533
B
8447823057
0000150131
1155
177715E-05
2711019
C
8590597085
0000199185
1153
231864E-05
2044057
D
4491250244
517162E-05
1156
115149E-05
4020064
E
4391894479
204591E-05
1158
465838E-06
9846089
F
4210703646
204376E-05
1158
485374E-06
9816203
G
086381524
522216E-06
1160
604546E-06
7577764
H
0870501884
BDL
1160
NA
NA
I
0861953838
BDL
1162
NA
NA
Sample ID
Initial Aq Conc (ppb)
Equil Aq Conc (ppb)
pH
Fraction Aq
Kd
A
9079225
0000712
1145
0000155192
5682151
B
8613005
0000626
1146
937652E-05
6617263
C
854192
0000454
1146
0000101047
8904598
D
4538279
0000394
1155
0000151561
5332446
E
4358906
0000314
1156
0000126728
6368014
F
4450335
0000237
1155
0000140068
8928327
G
0840654
000038
1165
0000614991
1014119
H
0897571
0000344
1162
0000501358
1179543
I
0921815
0000268
1164
0000644965
1527065
Sample ID
Initial Aq Conc (ppb)
Equil Aq Conc (ppb)
pH
Fraction Aq
Kd
A
9079224621
0001409021
1150
0000155192
2872173
B
8613004882
00008076
1155
937652E-05
5131447
C
8541919589
0000863136
1153
0000101047
468296
D
4538279014
0000687826
1156
0000151561
3051697
E
4358905759
0000552396
1158
0000126728
3616109
F
4450334725
0000623348
1158
0000140068
3399577
G
0840653709
0000516994
1160
0000614991
7443306
H
0897570902
0000450005
1160
0000501358
9019731
I
0921814908
0000594538
1162
0000644965
6879445
Sample ID
Initial Aq Conc (ppb)
Equil Aq Conc (ppb)
pH
Fraction Aq
Kd
A
8526222
7775594
1161
0911962405
3999451
B
8457478
9568055
1164
113131301
lt01
C
8454964
8191721
1168
0968865194
1299343
D
4263831
3716515
1171
087163741
5820501
E
4260938
6299986
1170
1478544594
lt01
F
4294941
3667886
1172
0854001563
6743887
G
855493
8268725
1173
0966545113
1400015
H
8819366
9558545
1170
1083813162
lt01
I
8300395
7943227
1173
0956969779
1828191
Sample ID
Initial Aq Conc (ppb)
Equil Aq Conc (ppb)
pH
Fraction Aq
Kd
A
8526222244
759657507
1155
089096611
5070018
B
8457478089
7831245583
116
0925955173
3298918
C
8454964361
7487755693
1162
0885604643
5222873
D
4263831311
3621172193
1165
0849276608
701438
E
4260937738
362895009
1166
0851678741
6966757
F
4294940694
3595565556
1163
0837163028
7672974
G
8554929637
7623627363
1164
0891138523
4941109
H
8819365709
7733611311
1164
0876889741
5728039
I
8300395228
7352643249
1162
0885818452
5240798
Sample ID
Initial Aq Conc (ppb)
Equil Aq Conc (ppb)
pH
Fraction Aq
Kd
A
9779963
8774052
1161
0897145797
108521
B
9835835
9081111
1164
0923267955
9140247
C
9507655
8622742
1168
0906926233
1008659
D
4824821
3174345
1171
0657919842
3008172
E
4872457
3023902
1170
0620611305
3477241
F
4913611
3011782
1172
0612946765
3513874
G
0962091
0511292
1173
0531438732
4885935
H
1005159
0493115
1170
0490584261
5607747
I
0887794
0473141
1173
0532939428
4965678
Sample ID
Initial Aq Conc (ppb)
Equil Aq Conc (ppb)
pH
Fraction Aq
Kd
A
9779962734
1060834347
1155
108470183
0910195
B
9835835051
1050945992
116
10684868
1638845
C
9507654819
1027484967
1162
1080692333
0941248
D
4824820947
507820462
1165
10525167
1843339
E
4872457168
5239952738
1166
1075423048
0880238
F
4913611454
5328321311
1163
1084400214
0509761
G
0962090763
10672488
1164
1109301577
lt01
H
100515912
1062338104
1164
1056885505
1452343
I
0887794331
0990729562
1162
1115944907
lt01
Sample ID
Initial Aq Conc (ppb)
Equil Aq Conc (ppb)
pH
Fraction Aq
Kd
A
8913321
0000242
1161
271084E-05
1769639
B
8957072
0000116
1164
128974E-05
3672542
C
8627854
0000116
1168
134188E-05
3582700
D
4445064
BDL
1171
NA
NA
E
4490502
605E-05
1170
13468E-05
3415784
F
4459269
806E-05
1172
180709E-05
2497898
G
090022
152E-05
1173
168369E-05
2777954
H
094654
605E-05
1170
639353E-05
7194887
I
0912956
BDL
1173
NA
NA
Sample ID
Initial Aq Conc (ppb)
Equil Aq Conc (ppb)
pH
Fraction Aq
Kd
A
8913321113
0000398128
1155
446666E-05
1073986
B
8957071854
000032779
116
365957E-05
1294283
C
8627854248
0000337955
1162
391703E-05
1227315
D
4445064053
0000242059
1165
544558E-05
8422798
E
4490502056
0000292509
1166
651396E-05
7061975
F
4459268715
0000676132
1163
0000151624
2976655
G
0900219568
454363E-05
1164
504725E-05
9266533
H
0946539946
0000171998
1164
0000181712
2531222
I
0912956209
606879E-05
1162
66474E-05
7212463
Sample ID
Initial Aq Conc (ppb)
Equil Aq Conc (ppb)
pH
Fraction Aq
Kd
A
7331081
0000518
1161
707249E-05
6782639
B
7328044
0000412
1164
562039E-05
8427222
C
7071427
0000332
1168
469813E-05
1023256
D
3635697
0000201
1171
553737E-05
8283164
E
3652535
0000192
1170
524331E-05
8773459
F
3684344
0000272
1172
738169E-05
6114676
G
0743961
96E-05
1173
0000129031
3624479
H
0777698
0000121
1170
0000155632
2955469
I
0723194
0000187
1173
0000258316
1855673
Sample ID
Initial Aq Conc (ppb)
Equil Aq Conc (ppb)
pH
Fraction Aq
Kd
A
7331081035
0001713462
1155
0000233726
2052086
B
7328043805
0000872426
116
0000119053
3978172
C
7071427186
0000766705
1162
0000108423
443366
D
3635696803
0000569848
1165
0000156737
2926072
E
3652534842
0000393375
1166
0000107699
4271111
F
3684343628
0000302746
1163
821708E-05
5492984
G
0743960581
0000514945
1164
0000692167
6752787
H
0777698097
0000252938
1164
0000325239
1413999
I
0723194348
0000177006
1162
0000244756
1958505
Sample ID
Initial Aq Conc (ppb)
Equil Aq Conc (ppb)
pH
Fraction Aq
Kd
A
8981132
8370881
118
0932051904
2953447
B
9131823
7195504
1182
7879592346
lt01
C
9347637
7543793
1183
0807026787
9912517
D
4575756
3638427
1185
0795153224
1075088
E
4700104
4030471
1186
0857527944
6725678
I
4964933
3830102
1183
0771430723
1202095
F
8821519
8163764
1187
0925437469
3309513
G
9104387
7374992
1185
0810048143
9375302
H
9116507
9183809
1184
1007382399
lt01
Sample ID
Initial Aq Conc (ppb)
Equil Aq Conc (ppb)
pH
Fraction Aq
Kd
A
898113225
8487458671
1178
0945032145
2356428
B
9131823285
7621244902
1181
0834580857
8159034
C
9347636536
7457911897
1184
0797839311
1050404
D
4575756317
3594537413
1187
0785561373
1139171
E
4700103984
3660617077
1184
0778837466
1149527
I
496493275
3718275456
1179
0748907517
534887
F
8821518816
7805147159
1188
0884784959
1292627
G
9104387158
688000471
1187
0755680156
9609413
H
9116507166
7366395982
1188
0808028321
1360264
Sample ID
Initial Aq Conc (ppb)
Equil Aq Conc (ppb)
pH
Fraction Aq
Kd
A
1106681
0688024
118
0062170019
6475252
B
10426
3454341
1182
0331319968
9420817
C
101667
4315917
1183
0424514804
6554265
D
5338797
0081828
1185
0015326992
3015309
E
5359438
004523
1186
0008439386
5351528
F
5582262
0050094
1183
0008973825
4920748
G
0935832
0006073
1187
0006489588
7228512
H
1063231
0006007
1185
0005649652
79025
I
1087754
0004734
1184
0004352288
1008486
Sample ID
Initial Aq Conc (ppb)
Equil Aq Conc (ppb)
pH
Fraction Aq
Kd
A
1106681063
7191335597
1178
0649811028
2313284
B
1042599825
7539402767
1181
0723134858
1787174
C
1016670487
8024108456
1184
0789253603
1291
D
533879659
2448368545
1187
0458599331
5540923
E
5359438061
2197371376
1184
041000033
6554461
F
5582261683
2335905009
1179
0418451363
6192481
G
0935831771
0069557071
1188
0074326469
5880414
H
1063230981
0071395625
1187
0067149685
623756
I
1087754
0052020649
1188
004782391
8777157
Sample ID
Initial Aq Conc (ppb)
Equil Aq Conc (ppb)
pH
Fraction Aq
Kd
A
9407194
0000126
118
133952E-05
3210587
B
8812043
0000303
1182
34346E-05
1361380
C
8601492
0000156
1183
181841E-05
2663305
D
4494913
0000347
1185
772991E-05
607659
E
4357754
906E-05
1186
207863E-05
2192696
F
4723672
0000207
1183
437691E-05
1018911
G
0915314
91E-05
1187
99443E-05
4749023
H
091253
BDL
1185
NA
NA
I
0908159
BDL
1184
NA
NA
Sample ID
Initial Aq Conc (ppb)
Equil Aq Conc (ppb)
pH
Fraction Aq
Kd
A
9407194102
0008139809
1178
0008139809
4966049
B
8812043306
0003090249
1181
0003090249
1332911
C
8601491692
0002857833
1184
0002857833
145718
D
4494913172
0002431822
1187
0002431822
8678061
E
4357753634
0001442135
1184
0001442135
1376821
F
4723671527
0000789191
1179
0000789191
2668996
G
091531421
0000557461
1188
0000557461
7750198
H
0912530034
0000387691
1187
0000387691
1056587
I
0908158622
0000165863
1188
0000165863
2413715
Sample ID
Initial Aq Conc (ppb)
Equil Aq Conc (ppb)
pH
Fraction Aq
Kd
A
7591216
0001366
118
000017994
2385788
B
7220545
0001296
1182
0000179541
2600341
C
6931443
0000913
1183
0000131752
3669937
D
3679791
0000811
1185
0000220318
213020
E
3700657
0001047
1186
0000282847
1610155
F
3870057
0000474
1183
0000122483
3638147
G
0733094
0000602
1187
0000820842
5748256
H
071454
0000498
1185
0000697618
6431762
I
0723484
0000479
1184
0000662029
665452
Sample ID
Initial Aq Conc (ppb)
Equil Aq Conc (ppb)
pH
Fraction Aq
Kd
A
7591216275
0003211762
1178
0000423089
1014432
B
7220544548
0002476226
1181
0000342942
1361143
C
6931442863
0002424369
1184
0000349764
1382125
D
3679791021
0002216217
1187
0000602267
7789595
E
3700656669
0001909447
1184
0000515975
8824483
F
3870057311
0001930251
1179
0000498765
8930885
G
0733093687
0001371053
1188
0001870229
2520255
H
0714539864
0001661534
1187
0002325321
1926446
I
072348416
0001140936
1188
0001577002
2791027
Sample ID
Initial Aq Conc (ppb)
Equil Aq Conc (ppb)
pH
Fraction Aq
Kd
A
8760849
787583
111
0898980219
4765962
B
8926622
5032039
1117
5637113657
lt01
C
8944823
7134714
1114
079763622
1079982
D
4667086
4589269
113
0983326499
072138
E
4500418
3745656
1131
0832290717
8317575
F
4044123
3214176
113
0794777097
1224497
G
1257756
1090023
1142
0866640978
6673619
H
9515164
3181754
1143
3343877675
lt01
I
8192283
9333398
1143
1139291501
lt01
Sample ID
Initial Aq Conc (ppb)
Equil Aq Conc (ppb)
pH
Fraction Aq
Kd
A
8760849289
7649889866
1105
0873190442
6159384
B
8926622427
7158886295
1110
0801970326
1046384
C
8944822597
719172491
1104
0804009787
1037675
D
4667085975
4379235651
1125
093832333
2796427
E
4500417953
3331662008
1128
0740300577
144803
F
404412292
3051584708
1120
0754572689
1542407
G
1257756141
1042917052
1129
0829188598
8933914
H
9515163608
6458872226
1132
0678797811
1954128
I
8192282988
8640513157
1133
1054713707
lt01
Sample ID
Initial Aq Conc (ppb)
Equil Aq Conc (ppb)
pH
Fraction Aq
Kd
A
8426518
7387328
111
0876676186
5966258
B
8638001
7419385
1117
0858923768
6960547
C
9323318
8036996
1114
0862031802
6818523
D
442651
3962629
113
0895203859
4979995
E
4426849
4090424
1131
092400338
3395329
F
3929483
3698764
113
0941285083
2958172
G
0817864
0742066
1142
0907321016
4428077
H
0878959
0720997
1143
0820285656
9047228
I
0772206
0788286
1143
1020823931
lt01
Sample ID
Initial Aq Conc (ppb)
Equil Aq Conc (ppb)
pH
Fraction Aq
Kd
A
8426518355
833290075
1105
098889012
0476492
B
8638001423
7823321167
1110
0905686487
4413063
C
9323317745
925927516
1104
0993130923
0294664
D
442651005
4300859603
1125
0971614106
1242837
E
4426849405
4336992073
1128
0979701742
0855315
F
3929483125
3938204338
1120
100221943
lt01
G
0817864386
081693181
1129
0998859743
0049487
H
0878958929
0792412508
1132
0901535306
4510199
I
0772205665
0871436364
1133
1128502941
lt01
Sample ID
Initial Aq Conc (ppb)
Equil Aq Conc (ppb)
pH
Fraction Aq
Kd
A
9425043
0001341
111
0000142314
2985674
B
9611386
0000792
1117
823889E-05
5153394
C
9579554
0000363
1114
379197E-05
1124764
D
4974
656E-05
113
131798E-05
3231076
E
4916732
0000212
1131
43111E-05
9584756
F
4373143
0000252
113
575681E-05
824464
G
0943366
355E-05
1142
375857E-05
1153591
H
1011746
353E-05
1143
349083E-05
1183195
I
0865253
202E-05
1143
233004E-05
2035123
Sample ID
Initial Aq Conc (ppb)
Equil Aq Conc (ppb)
pH
Fraction Aq
A
9425042625
0001709054
1105
0000181331
B
9611386476
0001184125
1110
00001232
C
9579553607
0001155517
1104
0000120623
D
4974000414
0000672325
1125
0000135168
E
4916731623
0000675371
1128
0000137362
F
4373142817
0000570681
1120
0000130497
G
0943366414
0000389738
1129
0000413136
H
1011745587
0000565648
1132
0000559081
I
0865252712
0000379545
1133
0000438653
Sample ID
Initial Aq Conc (ppb)
Equil Aq Conc (ppb)
pH
Fraction Aq
Kd
A
9405892
0007019
111
0000746258
5681206
B
9602498
0003294
1117
0000342992
123554
C
9630619
0002936
1114
0000304893
1396318
D
4945396
0001795
113
0000363011
1171688
E
4964945
0001373
1131
0000276484
1493015
F
4441601
0001516
113
0000341219
1389674
G
1079602
0001109
1142
0001027508
4215519
H
1031512
0000883
1143
0000855983
4820576
I
0939294
0000978
1143
0001040992
4550255
Sample ID
Initial Aq Conc (ppb)
Equil Aq Conc (ppb)
pH
Fraction Aq
Kd
A
94058918
0002841681
1105
0000302117
1403936
B
9602498
0002282224
1110
000023767
1783252
C
9630618675
0002608744
1104
000027088
1571697
D
4945396384
0002082692
1125
0000421137
1009911
E
4964945192
0001703548
1128
0000343115
1202999
F
4441601383
000165649
1120
0000372949
127140
G
1079602045
0001250199
1129
0001158019
3739933
H
1031512133
0003222175
1132
0003123739
1317961
I
0939293925
0001224667
1133
0001303816
3632054
Sample ID
Initial Aq Conc (ppb)
Equil Aq Conc (ppb)
pH
Fraction Aq
NS-A
959726097
8650033
1183
0901302
NS-B
959688424
9343247
1179
9735709
NS-C
9624703316
9025099
1180
0937702
NS-E
9624816906
9418273
1161
0978541
NS-F
9526296152
1160028
1171
1217711
NS-G
9616691794
927704
1165
0964681
Sample ID
Initial Aq Conc (ppb)
Equil Aq Conc (ppb)
pH
Fraction Aq
NS-A
959726097
8432881472
1178
0878675853
NS-B
959688424
8513714171
1176
0887133153
NS-C
9624703316
8757645753
1177
0909913321
NS-E
9624816906
8636792982
1166
0897346211
NS-F
9526296152
9198116117
1173
0965550091
NS-G
9616691794
8327792058
1171
0865972648
Sample ID
Initial Aq Conc (ppb)
Equil Aq Conc (ppb)
pH
Fraction Aq
NS-A
8794409081
8337459
1183
0948041
NS-B
9132734292
8065824
1179
0883177
NS-C
8608231557
8155761
1180
0947437
NS-E
0907236499
0877529
1161
0967255
NS-F
0916275429
0000146
1171
0000159
NS-G
0915720325
0000238
1165
000026
Sample ID
Initial Aq Conc (ppb)
Equil Aq Conc (ppb)
pH
Fraction Aq
NS-A
8794409081
8777467999
1178
0998073653
NS-B
9132734292
8531262277
1176
093414108
NS-C
8608231557
8553778159
1177
0993674264
NS-E
0907236499
0898199858
1166
0990039376
NS-F
0916275429
0000368379
1173
000040204
NS-G
0915720325
0925888607
1171
1011104135
Sample ID
Initial Aq Conc (ppb)
Equil Aq Conc (ppb)
pH
Fraction Aq
NS-A
9784205654
1843735
1183
018844
NS-B
9774386849
2360655
1179
0241514
NS-C
9748642055
440653
1180
0452015
NS-E
0990926695
0846694
1161
0854447
NS-F
1059013829
BDL
1171
NA
NS-G
1015695951
BDL
1165
NA
Sample ID
Initial Aq Conc (ppb)
Equil Aq Conc (ppb)
pH
Fraction Aq
NS-A
9784205654
2227968645
1178
0227710733
NS-B
9774386849
3506033589
1176
0358696013
NS-C
9748642055
4599509164
1177
0471810242
NS-E
0990926695
0923435978
1166
0931891312
NS-F
1059013829
BDL
1173
NA
NS-G
1015695951
0920736194
1171
0906507694
Sample ID
Initial Aq Conc (ppb)
Equil Aq Conc (ppb)
pH
Fraction Aq
NS-A
9865515956
0545394
1183
0055283
NS-B
9899624212
0468747
1179
004735
NS-C
9800690365
0439191
1180
0044812
NS-E
1082582721
0358897
1161
0331519
NS-F
1032892193
0000111
1171
0000107
NS-G
1052776412
455E-05
1165
432E-05
Sample ID
Initial Aq Conc (ppb)
Equil Aq Conc (ppb)
pH
Fraction Aq
NS-A
9865515956
0583283525
1178
0059123469
NS-B
9899624212
0663485207
1176
0067021252
NS-C
9800690365
0539915704
1177
0055089558
NS-E
1082582721
0431846663
1166
0398904079
NS-F
1032892193
0000301866
1173
0000292253
NS-G
1052776412
0488809417
1171
0464305061
Sample ID
Initial Conc
Conc In Wash of Vial (ppb)
Sorbed to Walls
NS-A
009717
00121
124524
NS-B
009881
000345
3491549
NS-C
009799
00208
2122666
NS-D
0011562
000333
2880125
NS-E
0010004
000316
3158737
NS-F
0009758
000382
3914737
NS-G
0097744
004938
5051972
NS-H
000984
000559
5680894
Sample ID
Initial Conc
Conc In Wash of Vial (ppb)
Sorbed to Walls
NS-A
0110121
003628
3294558
NS-B
0110228
00268
2431335
NS-C
0110121
002735
2483632
NS-D
0010863
000335
3083863
NS-E
001065
00035
3286385
NS-F
0010757
000386
3588528
NS-G
0111719
001536
1374878
NS-H
0010544
000313
2968513
Sample ID
Initial Aq Conc (ppb)
Equil Aq Conc (ppb)
pH
Fraction Aq
Kd
A
98750812
44961824
1167
04553059
5148943
B
95512808
6813704
1161
07133812
1911392
C
98368178
27708852
1161
02816851
1125817
D
99435208
71523103
1184
07192935
1616758
E
99201429
67909668
1187
06845634
1835712
F
10040161
65826354
1188
06556305
2115061
G
4856029
27420191
1177
05646628
3249713
H
4871988
18538966
1176
03805216
6937195
I
48770952
13893489
1176
02848722
1051135
Sample ID
Initial Aq Conc (ppb)
Equil Aq Conc (ppb)
pH
Fraction Aq
Kd
A
9875081178
4782787653
1167
0484328945
4601018
B
9551280827
1917864389
1154
0020079657
2112282
C
9836817804
2850427319
1163
0028977128
1457909
D
9943520802
5354401206
1181
053848142
3530201
E
992014285
3303880468
1182
0033304767
1145599
F
1004016064
4562722289
1184
0045444714
8391729
G
4856028999
2981077404
117
061389201
266613
H
4871988025
2455078723
1169
0050391723
7941965
I
4877095245
17301515
117
0354750402
7638668
Sample ID
Initial Aq Conc (ppb)
Equil Aq Conc (ppb)
pH
Fraction Aq
Kd
A
94166635
82267024
1167
08736324
7702806
B
94653193
85780661
1161
09062627
6210837
C
95691493
85417433
1161
08926335
6996406
D
10042956
09416563
1184
09376286
2898204
E
10316949
09196854
1187
08914316
4979791
F
09841346
0886981
1188
09012802
4545372
G
48951117
43441484
1177
08874462
602818
H
48622049
43653822
1176
08978195
5625012
I
4886869
43948285
1176
08993138
5472433
Sample ID
Initial Aq Conc (ppb)
Equil Aq Conc (ppb)
pH
Fraction Aq
Kd
A
9416663483
7667114947
1167
0814207172
1117916
B
9465319299
7556377889
1154
0798322555
1266251
C
9569149292
7922749629
1163
0827947123
107987
D
1004295601
0866599278
1181
0862892635
6684472
E
1031694856
0865518891
1182
0838929152
7750351
F
0984134558
0828238515
1184
0841590724
7688585
G
4895111728
4051996638
117
0827763872
9366864
H
4862204917
4190616825
1169
0861875815
758057
I
4886868983
4145489943
117
0848291607
8251034
Sample ID
Initial Aq Conc (ppb)
Equil Aq Conc (ppb)
pH
Fraction Aq
Kd
A
92800932
00038179
1167
00004114
1013042
B
93201398
00016426
1161
00001762
2458009
C
95085415
00009139
1161
9611E-05
452898
D
09702888
00002133
1184
00002198
1864504
E
10818908
00002982
1187
00002756
1431793
F
09944729
00003267
1188
00003285
121583
G
40620634
00001016
1177
2501E-05
1642830
H
4091296
00001998
1176
4884E-05
8621078
I
40793628
8206E-05
1176
2012E-05
2065348
Sample ID
Initial Aq Conc (ppb)
Equil Aq Conc (ppb)
pH
Fraction Aq
Kd
A
9280093212
0007108181
1167
000076596
5439288
B
9320139831
0004011335
1154
0000430394
1006297
C
9508541493
000166325
1163
0000174922
248828
D
097028876
0000726172
1181
0000748408
547375
E
1081890779
0000520905
1182
0000481476
8194895
F
0994472941
0000224317
1184
0000225563
1770803
G
4062063373
0000183026
117
450574E-05
9120486
H
4091295968
0000223825
1169
547076E-05
7696036
I
4079362752
0000254574
117
624054E-05
6657537
Sample ID
Initial Aq Conc (ppb)
Equil Aq Conc (ppb)
pH
Fraction Aq
Kd
A
10496619
00007248
1167
6905E-05
6028735
B
10446761
00005881
1161
5629E-05
7683924
C
10404944
00006194
1161
5953E-05
7298549
D
10695748
00005383
1184
00005033
8139848
E
11198849
00005656
1187
0000505
7810696
F
11327985
00003573
1188
00003154
1266063
G
549425
00003353
1177
6103E-05
6734657
H
54074665
00003576
1176
6612E-05
6367965
I
53502419
00004411
1176
8244E-05
5039541
Sample ID
Initial Aq Conc (ppb)
Equil Aq Conc (ppb)
pH
Fraction Aq
Kd
A
1049661917
000057716
1167
549853E-05
7570833
B
1044676116
0000712674
1154
682196E-05
634071
C
1040494422
0000659215
1163
633559E-05
6857795
D
1069574815
0000501161
1181
0000468561
8743806
E
1119884926
0000459622
1182
0000410419
9611808
F
1132798521
0000428241
1184
0000378038
1056264
G
5494249954
0000427061
117
777287E-05
5287854
H
5407466468
0000325564
1169
602064E-05
6993736
I
53502419
0000692442
117
0000129423
3210102
Sample ID
Initial Aq Conc (ppb)
Equil Aq Conc (ppb)
pH
Fraction Aq
Kd
A
99449204
84078927
116
0845446
9304586
B
99560061
84339692
1165
08471237
9547302
C
98221523
82821547
1164
08432118
9915886
D
10023918
89006508
1184
08879413
5357117
E
99182734
84480287
1189
0851764
703665
F
99181751
85844767
1191
08655299
6384908
G
51665706
41857945
1173
08101688
1046071
H
48478214
40068924
1175
08265347
9670412
I
48503814
43218665
1174
08910364
5894162
Sample ID
Initial Aq Conc (ppb)
Equil Aq Conc (ppb)
pH
Fraction Aq
Kd
A
9944920441
8813152965
1149
0886196427
738241
B
9956006121
8747156303
1157
0878580848
8007767
C
9822152291
8664470934
1153
0882135674
7988892
D
1002391846
9333490632
1172
0931121963
3368509
E
9918273427
6625075445
1177
0667966607
1551748
F
9918175056
8931364957
1181
0900504872
4773862
G
5166570628
4445386532
1169
0860413387
7961604
H
4847821413
410447427
1169
084666367
8664303
I
4850381381
4266693706
1164
0879661489
6413801
Sample ID
Initial Aq Conc (ppb)
Equil Aq Conc (ppb)
pH
Fraction Aq
Kd
A
94667993
NA
116
NA
NA
B
94395562
85812109
1165
09090693
5885474
C
93834931
84622373
1164
09018217
6279204
D
10619399
09580683
1184
09021869
4435663
E
09918273
08881507
1189
08954691
4835506
F
09719812
09036489
1191
0929698
3138862
G
48833371
4490415
1173
09195382
4312104
H
46914401
42054182
1175
08964024
5612948
I
48699394
43843193
1174
09002821
5536503
Sample ID
Initial Aq Conc (ppb)
Equil Aq Conc (ppb)
pH
Fraction Aq
Kd
A
9466799266
8233850788
1149
0869760788
8220086
B
9439556236
817653394
1157
0866198975
8165745
C
9383493063
8086024379
1153
0861728604
8430884
D
1061939876
0919992065
1172
0866331594
6241759
E
0991827343
0836511397
1177
0843404251
7590958
F
0971981155
0839862696
1181
0864073024
6354378
G
4883337077
414858839
1169
0849539633
7903986
H
4691440077
3996173112
1169
0851800949
8038249
I
486993937
4291285586
1164
0881178442
6558707
Sample ID
Initial Aq Conc (ppb)
Equil Aq Conc (ppb)
pH
Fraction Aq
Kd
A
9589772
NA
116
NA
NA
B
92932288
00002145
1165
2308E-05
1818463
C
10087255
00001628
1164
1614E-05
2591215
D
0952173
BDL
1184
NA
NA
E
09922241
BDL
NA
NA
F
09678155
5107E-05
1191
5277E-05
7460375
G
40684058
00001336
1173
3284E-05
1220544
H
40954317
8151E-05
1175
199E-05
2086795
I
40174066
00001322
1174
3292E-05
1289605
Sample ID
Initial Aq Conc (ppb)
Equil Aq Conc (ppb)
pH
Fraction Aq
Kd
A
9589772032
0000454463
1149
473903E-05
9116335
B
9293228768
0000260081
1157
27986E-05
1499475
C
1008725504
0000302018
1153
299405E-05
1397125
D
0952173007
000019177
1172
0000201403
1954603
E
0992224074
BDL
NA
NA
F
0967815522
402137E-05
1181
41551E-05
9474699
G
4068405786
0000222282
1169
546361E-05
7336986
H
409543171
0000531619
1169
0000129808
3199152
I
4017406611
0000410123
1164
0000102086
4157807
Sample ID
Initial Aq Conc (ppb)
Equil Aq Conc (ppb)
pH
Fraction Aq
Kd
A
104895
NA
116
NA
NA
B
10399436
0001828
1165
00001758
2383132
C
10846517
00010788
1164
9946E-05
4196159
D
10886869
00009131
1184
00008388
4689778
E
11196739
00010624
1189
00009488
4208928
F
10457228
00007967
1191
00007619
516258
G
53879811
00007915
1173
00001469
2728993
H
5412749
00008355
1175
00001544
2690641
I
53739488
00006103
1174
00001136
3737892
Sample ID
Initial Aq Conc (ppb)
Equil Aq Conc (ppb)
pH
Fraction Aq
Kd
A
1048950046
0002141023
1149
0000204111
2112281
B
1039943573
0001770549
1157
0000170254
2460487
C
1084651695
0001127533
1153
0000103953
4014918
D
1088686867
0001201087
1172
0001103244
3564524
E
1119673887
0000783288
1177
0000699568
5709897
F
1045722787
0000914861
1181
000087486
4495324
G
5387981131
0001444832
1169
0000268158
1494715
H
5412748988
0001143483
1169
0000211257
1965749
I
5373948758
00010003
1164
0000186139
2280472
Sample ID
Initial Aq Conc (ppb)
Equil Aq Conc (ppb)
pH
Fraction Aq
Kd
A
97124466
81545995
1188
08056055
9637661
B
99211859
79482276
1185
07686995
1245818
C
99557205
83867718
1185
08084252
9879
D
10224949
98946711
1197
09635008
154859
E
10030688
86788315
12
08615244
63087
F
89520172
75300141
1206
0837781
7697785
G
49403931
41351764
1196
08203095
8828858
H
48401764
39421041
1196
07984075
1042559
I
49912092
40122049
1194
07878369
1097334
Sample ID
Initial Aq Conc (ppb)
Equil Aq Conc (ppb)
pH
Fraction Aq
Kd
A
9712446639
8458491376
1181
0835627421
7856457
B
9921185946
8575189634
1183
0829335063
8520183
C
9955720475
9174749665
118
0884380649
5450116
D
1022494888
1054151374
12
1026487576
lt01
E
1003068795
9253307262
1199
0918551075
3480297
F
8952017188
8148352848
1198
0906576684
4096805
G
4940393083
4349637713
1186
0862852934
6406294
H
4840176398
4349559364
1188
0880930756
5580958
I
4991209221
4362736266
1189
0856667235
6817707
Sample ID
Initial Aq Conc (ppb)
Equil Aq Conc (ppb)
pH
Fraction Aq
Kd
A
96551461
80911855
1188
08380179
9713902
B
93561763
74410368
1185
07953075
1234203
C
91141226
75881085
1185
0832566
9452625
D
10423492
08195966
1197
07862975
1111505
E
0983206
08251481
12
08392422
7678853
F
09051484
08066411
1206
089117
4923541
G
49501567
44733496
1196
09036784
5072867
H
48890671
43558824
1196
08909435
5665444
I
48544638
43264547
1194
08912323
5739026
Sample ID
Initial Aq Conc (ppb)
Equil Aq Conc (ppb)
pH
Fraction Aq
Kd
A
9655146069
820460082
1181
0849764546
8998984
B
9356176321
7703053505
1183
0823312135
1051242
C
9114122586
7978297395
118
0875377451
7062663
D
1042349157
0853053814
12
0818395456
9099556
E
0983206046
0871198263
1199
0886079033
5196709
F
0905148405
0803451372
1198
0887646013
5098696
G
4950156706
4275082341
1186
0863625658
7213934
H
4889067068
4173762594
1188
0853693053
7687519
I
4854463762
4147024058
1189
0854270268
7771045
Sample ID
Initial Aq Conc (ppb)
Equil Aq Conc (ppb)
pH
Fraction Aq
Kd
A
92641652
NA
1188
NA
NA
B
93525373
00001935
1185
2069E-05
2067199
C
93635416
4119E-05
1185
44E-06
9247818
D
09931106
BDL
1197
NA
NA
E
09772472
BDL
12
NA
NA
F
09624413
00066817
1206
00069424
562421
G
40591285
00003289
1196
8103E-05
5148274
H
40651615
00025316
1196
00006228
6625737
I
41168197
00001018
1194
2474E-05
1692126
Sample ID
Initial Aq Conc (ppb)
Equil Aq Conc (ppb)
pH
Fraction Aq
Kd
A
9264165178
402285E-05
1181
434238E-06
9980817
B
9352537276
0000110618
1183
118276E-05
3616813
C
9363541597
705331E-05
118
753273E-06
5401186
D
0993110568
BDL
12
NA
NA
E
0977247222
300794E-05
1199
307797E-05
1280331
F
0962441315
BDL
1198
NA
NA
G
4059128499
BDL
1186
NA
NA
H
4065161486
705198E-05
1188
173473E-05
2380003
I
4116819691
0000110748
1189
269014E-05
1555864
Sample ID
Initial Aq Conc (ppb)
Equil Aq Conc (ppb)
pH
Fraction Aq
Kd
A
10465806
00330348
1188
00031565
1368879
B
10443676
00114086
1185
00010924
3911924
C
10490805
00062925
1185
00005998
6779161
D
11312466
00044912
1197
00039702
1013734
E
11740374
00029871
12
00025443
1544978
F
11016949
00040505
1206
00036766
1065501
G
54486873
00020968
1196
00003848
1083704
H
53422347
00019612
1196
00003671
1124225
I
53884548
00017107
1194
00003175
1317955
Sample ID
Initial Aq Conc (ppb)
Equil Aq Conc (ppb)
pH
Fraction Aq
Kd
A
1046580588
0026580976
1181
0002539793
1702263
B
104436762
0010478566
1183
0001003341
4259487
C
1049080459
0006700641
118
0000638716
6366025
D
113124665
0004242148
12
0003749977
1073492
E
1174037402
0003429046
1199
000292073
1345371
F
1101694915
0002227889
1198
0002022238
1940359
G
5448687281
0002419858
1186
0000444118
9389651
H
5342234695
0001490989
1188
0000279095
1478928
I
5388454776
0002074015
1189
00003849
1087042
Sample ID
Initial Aq Conc (ppb)
Equil Aq Conc (ppb)
pH
Fraction Aq
Kd
A
99465302
84929996
1109
08193535
8778888
B
9842972
84531183
1111
08242284
8832374
C
13706339
12003449
1109
08375266
8112402
D
93278954
90828797
1126
09697134
127742
E
99391723
89516549
1122
08967768
4514156
F
94413691
7623566
113
08041979
9687715
G
48411705
41571485
1119
08419192
7557309
H
48280436
42801299
1123
08692468
6227932
I
50026381
38002219
1128
07445689
139756
Sample ID
Initial Aq Conc (ppb)
Equil Aq Conc (ppb)
pH
Fraction Aq
Kd
A
9946530213
668522424
1101
0644950246
219202
B
9842972041
6827479432
1105
0665719094
2079681
C
1370633906
128925931
1101
0899565656
4668908
D
9327895369
9578419326
1134
1022618541
lt01
E
9939172266
8563510014
1135
0857892433
6496328
F
9441369098
830634865
114
0876223604
5620694
G
4841170487
4341708968
112
0879296934
5525112
H
4828043618
4502906342
1123
0914490246
3871429
I
500263811
3959869628
1125
0775848285
1176974
Sample ID
Initial Aq Conc (ppb)
Equil Aq Conc (ppb)
pH
Fraction Aq
Kd
A
92565975
78650338
1109
08496679
9123867
B
92206051
80394456
1111
08719
7715476
C
93283226
8120385
1109
08705086
8226739
D
10419458
09591407
1126
09205284
3667817
E
10237347
09375635
1122
09158266
3841864
F
09739518
08407776
113
08632641
6565308
G
48802911
40565827
1119
08312174
8828343
H
48377972
42645053
1123
08814973
6371143
I
47388271
36819451
1128
07769739
1278797
Sample ID
Initial Aq Conc (ppb)
Equil Aq Conc (ppb)
pH
Fraction Aq
Kd
A
9256597482
8294548724
1101
0896068857
6565531
B
9220605132
8284935394
1105
0898524042
631461
C
9328322619
8280953522
1101
0887721604
7274366
D
1041945759
0974835903
1134
0935591795
2958653
E
1023734743
0961438092
1135
0939147663
2759052
F
097395176
0832434488
114
0854697864
7034554
G
4880291057
4145068165
112
0849348557
7809823
H
4837797242
4288579455
1123
0886473583
6107532
I
4738827116
3781772577
1125
0798039786
1137228
Sample ID
Initial Aq Conc (ppb)
Equil Aq Conc (ppb)
pH
Fraction Aq
Kd
A
92169263
00043124
1109
00004679
8986273
B
91704328
00012261
1111
00001337
3088793
C
90961638
00008395
1109
9229E-05
4640933
D
09683149
0000481
1126
00004967
8159477
E
09943148
00005631
1122
00005664
7048587
F
09697777
00003397
113
00003503
115357
G
39296612
0000686
1119
00001746
2271251
H
39110079
00004796
1123
00001226
3374884
I
4054091
00011432
1128
0000282
1477611
Initial Aq Conc (ppb)
Equil Aq Conc (ppb)
pH
Fraction Aq
Kd
921692635
0005957077
1101
0000646319
6504188
9170432784
000306662
1105
0000334403
1234776
9096163751
0002111663
1101
0000232149
1844719
0968314926
0000867507
1134
0000895894
4522352
0994314793
0000898163
1135
0000903298
4417852
0969777681
0000484972
114
0000500086
8079696
3929661216
0001578688
112
0000401736
9867172
3911007939
0001115352
1123
0000285183
1451014
4054091025
0001146601
1125
0000282826
1473233
Sample ID
Initial Aq Conc (ppb)
Equil Aq Conc (ppb)
pH
Fraction Aq
Kd
A
1062367
00011705
1109
00001102
3812373
B
10656118
00008583
1111
8055E-05
5121474
C
10147985
00007166
1109
7062E-05
6055484
D
10356941
0000788
1126
00007609
5324505
E
11326184
00008703
1122
00007684
5193416
F
10055058
00005765
113
00005734
7045016
G
53641636
00007065
1119
00001317
3011367
H
53703939
00007858
1123
00001463
2829396
I
54943036
00008239
1128
000015
2779478
Sample ID
Initial Aq Conc (ppb)
Equil Aq Conc (ppb)
pH
Fraction Aq
Kd
A
1062367044
0001733701
1101
0000163192
2573806
B
1065611835
000212538
1105
0000199452
2067996
C
1014798459
0001323578
1101
0000130428
3278433
D
1035694085
0001381959
1134
0001334331
3034426
E
1132618376
0001099997
1135
0000971199
4108091
F
1005505809
0001101291
114
0001095261
3686045
G
5364163602
0001194136
112
0000222614
178142
H
5370393851
0001095256
1123
0000203943
2029741
I
5494303637
0001659554
1125
000030205
1379743
Sample ID
Initial Aq Conc (ppb)
Equil Aq Conc (ppb)
pH
Fraction Aq
A
1033097
3255083399
1202
0315080133
B
103346555
6520607126
117
0630945767
C
103572814
7637322674
1174
0737386806
D
99819327
BDL
1186
NA
E
988004231
BDL
1186
NA
F
997357004
BDL
1185
NA
G
100361501
3438150241
115
0342576606
H
948633967
2530184962
1148
0026671878
Sample ID
Initial Aq Conc (ppb)
Equil Aq Conc (ppb)
pH
Fraction Aq
A
1033096997
518501178
1206
0501890122
B
1033465548
7276930444
1168
0704128982
C
1035728144
8600139369
1171
0830347174
D
9981932702
8482630391
1196
008497984
E
9880042315
5447287368
1184
0055134251
F
9973570039
9041153475
1185
0090651125
G
1003615011
4353607551
1152
043379259
H
9486339671
5683679634
1154
0059914359
Sample ID
Initial Aq Conc (ppb)
Equil Aq Conc (ppb)
pH
Fraction Aq
A
997029348
9681302845
1202
0971014832
B
103579558
1039736502
117
100380473
C
975618104
9652179907
1174
0989339975
D
099094639
1047989563
1186
1057564341
E
100084829
1047120027
1186
1046232522
F
100021942
1027134282
1185
1026908959
G
10156504
9612163266
115
0946404712
H
100142794
1000804551
1148
0999377496
Sample ID
Initial Aq Conc (ppb)
Equil Aq Conc (ppb)
pH
Fraction Aq
A
9970293475
8758010503
1206
0878410503
B
1035795579
9223444824
1168
0890469607
C
9756181039
868137711
1171
088983354
D
0990946387
09571545
1196
0965899379
E
1000848286
0958642075
1184
0957829561
F
1000219419
0954324935
1185
0954115584
G
1015650402
086718206
1152
0085381944
H
1001427944
0917354471
1154
0916046409
Sample ID
Initial Aq Conc (ppb)
Equil Aq Conc (ppb)
pH
Fraction Aq
A
968977174
4815179672
1202
0496934273
B
984732216
811967814
117
0824556972
C
974937568
5125187481
1174
0525693916
D
115411106
0064698249
1186
0056058946
E
099838327
0006926236
1186
0006937452
F
097322096
0012723741
1185
0013073846
G
976092992
0397124158
115
0040685074
H
098258508
003846849
1148
0039150289
Sample ID
Initial Aq Conc (ppb)
Equil Aq Conc (ppb)
pH
Fraction Aq
A
9689771741
5635730545
1206
058161644
B
9847322158
8815567839
1168
0895224884
C
9749375678
8872066318
1171
0910013791
D
1154111059
1139541421
1196
0987375879
E
0998383266
0716244157
1184
0717404009
F
0973220964
0598731247
1185
0615205867
G
9760929917
0375956436
1152
0038516457
H
0982585077
001870128
1154
0019032734
Sample ID
Initial Aq Conc (ppb)
Equil Aq Conc (ppb)
pH
Fraction Aq
A
109812427
0278151513
1202
0025329694
B
109851807
1179747464
117
0107394452
C
109563323
1149191187
1174
0104888311
D
108433735
0061646445
1186
0056851721
E
106285304
0051767732
1186
0048706387
F
107280706
004514876
1185
0042084697
G
104755438
0271974836
115
0025962837
H
098857645
0056143201
1148
0275117656
Sample ID
Initial Aq Conc (ppb)
Equil Aq Conc (ppb)
pH
Fraction Aq
A
1098124271
0588738002
1206
0053613058
B
1098518068
3623675578
1168
0329869456
C
1095633227
3667254562
1171
033471553
D
1084337349
0224089715
1196
0206660515
E
1062853037
0217987352
1184
0205096419
F
1072807061
0187059704
1185
0174364721
G
1047554375
0245110331
1152
002339834
H
098857645
0053735822
1154
0054356769
Cement
Oxidizing Kd
Std Dev
of Replicates
Reducing Kd
Std Dev
of Replicates
Aged Cement
495
380
9
747
482
7
Vault 2
766
353
9
725
419
6
TR545
864
321
9
786
361
7
TR547
817
198
9
371
238
6
Cement
Oxidizing Kd
Std Dev
of Replicates
Reducing Kd
Std Dev
of Replicates
Aged Cement
330
133
9
557
203
8
Vault 2
508
266
9
5569
203
8
TR545
477
239
9
437E+03
366E+03
9
TR547
275
0948
8
316E+01
182E+01
9
Cement
Oxidizing Solubility (M)
Std Dev
of Replicates
Reducing Solubility (M)
Std Dev
of Replicates
Aged Cement
349E-12
506E-12
9
424E-13
139E-13
3
Vault 2
462E-12
510E-12
9
143E-12
184E-12
9
TR545
680E-12
109E-11
6
780E-13
422E-13
7
TR547
534E-13
240E-13
6
407E-13
298E-13
7
Cement
Oxidizing Solubility (M)
Std Dev
of Replicates
Reducing Solubility (M)
Std Dev
of Replicates
Aged Cement
208E-12
565E-13
9
171E-12
661E-13
9
Vault 2
335E-12
671E-13
9
960E-12
808E-12
9
TR545
312E-11
414E-11
9
344E-12
144E-12
9
TR547
409E-12
154E-12
8
107E-12
575E-13
9
Experiment
Initial Concentration 99Tc 237Np 242Pu
Initial Concentration 127I
Solids-Present
1 ppb
100 ppb
Solids-Present
5 ppb
500 ppb
Solids-Present
10 ppb
1000 ppb
Solids-Free
1 ppb
100 ppb
Solids-Free
10 ppb
1000 ppb
Isotope
Detection Limit
99Tc
0000013 ppb
127I
0244 ppb
237Np
0000026 ppb
242Pu
0000044 ppb
Sample
Percent Reducing Slag (dry wt-) (c)
Percent Portland Cement
(dry wt-) (c)
Percent Fly Ash
(dry wt-) (c)
Percent Aggregatesand ( dry wt-) (c)
Reducing Equivalents (microeqg)
Aged Cement
0
10
45
45
855 plusmn 101(a)
Vault 2 Cement
17
10
45
0
178(b)
TR547
45
10
45
0
607(b)
TR545
90
10
0
0
681(b)
Blast furnace slag
100
0
0
0
819(b)
(a) Kaplan et al (2008)
(b) Roberts and Kaplan (2009)
(c) All percentages of saltstone formulations are reported on a dry weight percentage basis that is the weight of the ingredients before water was added
(d) Based on Table 8 in Dixon et al (2008 SRNL-STI-2008-00421) which shows the following quantity (lbscu yd) for saltstone Vault 2 Mix 1 concrete formulation 201 cement (1271 wt-) 268 slag (1695 wt-) 447 silica fume (283 wt-) 1563 fly ash (989 wt-) 911 fine sand (5762 wt-) The large aggregate was removed before the sorption tests were conducted The large aggregate accounted for 75 wt- of the original field sample not the sample used in these test before water was added to the mix
DDI water
Distilled deionized water
ICP-MS
Inductively coupled plasma ndash mass spectrometer
Kd
Distribution coefficient
LSC
liquid scintillation counting
NOM
Natural organic matter
PA
Performance Assessment
ppb
parts per billion
ppq
parts per quadrillion
QAQC
Quality AssuranceQuality Control
SA
Special Analyses
SRNL
Savannah River National Laboratory
SRS
Savannah River Site
Present data (d)
This document
Stage 1(c)
Young
Stage 2
Medium
Stage 3
Old
Stage 1
Young
Stage 2
Medium
Stage 3
Old
Reducing Concrete (mLg)
I
5
9
0
5
9
0
Np
4000
4000
3000
10-13 M(a)
10-13 M (a)
5000
Pu
10000
10000
1000
10-12 M (a)
10-12 M (a)
2000
Tc
5000
5000
5000
5000
5000
1000 (b)
Oxidizing Concrete (mLg)
I
8
15
4
8
15
4
Np
1600
1600
250
10-12 M (a)
10-12 M (a)
5000
Pu
10000
10000
1000
10-12 M (a)
10-12 M (a)
2000
Tc
08
08
05
08
08
05
(a) Apparent solubility (units = M = molL) Below this concentration Kd value of 10000 mLg is to be used
(b) A decrease in Tc Kd values with respect to previous values will be used because of the observation that Tc(IV) oxidizes readily under SRS conditions to Tc(VII)
(c) Stages 1 2 and 3 are conceptually based on mineral composition changes The 1st 2n and 3rd stages are expected to last 50 500 and 7000 pore volumes respectively A 2-ft slab of cement may be expected to last 740 yr in the 1st stage 7400 yr in the 2nd and 103600 yr in the 3rd stage
(d) Kaplan (2007) Kaplan and Coates (2008) and Kaplan et al 2008
DISCLAIMER
This work was prepared under an agreement with and funded by the US Government Neither the US Government or its employees nor any of its contractors subcontractors or their employees makes any express or implied
1 warranty or assumes any legal liability for the accuracy completeness or for the use or results of such use of any information product or process disclosed or
2 representation that such use or results of such use would not infringe privately owned rights or
3 endorsement or recommendation of any specifically identified commercial product process or service
Any views and opinions of authors expressed in this work do not necessarily state or reflect those of the United States Government or its contractors or subcontractors
Printed in the United States of America
Prepared forUS Department of Energy
KeywordsIodine Neptunium Plutonium Technetium I Np Pu Tc Saltstone Redox Distribution Coefficients Kd Apparent Solubility Values Glovebox
Retention Permanent
Iodine Neptunium Plutonium and Technetium Sorption to Saltstone and Cement Formulations Under Oxidizing and Reducing Conditions
Michael S Lilley(a) Brian A Powell(a) and Daniel I Kaplan
December 16 2009
(a) Department of Environmental Engineering and Earth Sciences
Clemson University Clemson SC
Savannah River National Laboratory
Savannah River Nuclear Solutions
Aiken SC 29808
Prepared for the US Department of Energy undercontract number DE-AC09-08SR22470
SRNL-STI-2009-00636 Revision 0
ii
DISCLAIMER
This work was prepared under an agreement with and funded by the US Government Neither the US Government or its employees nor any of its contractors subcontractors or their employees makes any express or implied
1 warranty or assumes any legal liability for the accuracy completeness or for the use or results of such use of any information product or process disclosed or 2 representation that such use or results of such use would not infringe privately owned rights or 3 endorsement or recommendation of any specifically identified commercial product process or service
Any views and opinions of authors expressed in this work do not necessarily state or reflect those of the United States Government or its contractors or subcontractors
Printed in the United States of America
Prepared for
US Department of Energy
SRNL-STI-2009-00636 Revision 0
iv
EXECUTIVE SUMMARY
Sorption of 99Tc 127I 237Np and 242Pu to two saltstone and two cementitious materials was examined Np and Pu sorbed very strongly to all four cementitious formulations and appeared to reach steady state within 24 h Based on the sorption behavior there were some indications that partial reduction of Pu(IV) to Pu(III) and Np(V) to Np(IV) occurs in these systems However the Kd values for both Pu and Np remain gt105 mLg throughout the experiments This value compares favorably with previously reported Kd values for Pu but is significantly higher than the previously reported value of 3000-4000 mLg for Np (Kaplan et al 2008)
In all experiments regardless of the total concentration of Np and Pu in the system a relatively constant aqueous phase concentration of both Np and Pu was observed Therefore it appears that the aqueous concentrations of Np and Pu are solubility controlled rather than sorption controlled The measured concentrations for Np and Pu ranged from 10-11 molL to 10-13 molL These values are consistent with precipitation of actinide hydrous oxide solid phases consequently these tests strongly suggest that solubility (as described by solubility constants) and not sorption (as described by Kd values) will controlling Np and Pu aqueous concentration near the Saltstone Disposal Facility
Sorption of both Tc and I do not appear to have reached steady state during the four day equilibration times used in these experiments Similar to Np and Pu surface mediated redox processes were affecting Tc and I sorption However this observation was based on changes in sorption behavior not direct determination of Tc or I oxidation states Calculated I Kd values of 766 and 725 mLg for simulated Vault 2 concrete under oxidizing and reducing conditions respectively in the present work compare favorably with values of 894 and 715 mLg under similar conditions reported by Kaplan et al (2008) Although it appears steady state was not reached in Tc systems conditional Kd values were calculated and were found to be a factor of ~5 higher than values previously reported by Kaplan et al (2008) The fraction of reducing slag within each saltstone formulation appears to have an effect on Tc sorption Tc Kd values under oxidizing conditions ranged from 275 to 508 mLg Saltstone formulations under reducing conditions had Kd values between 32 (0 dry wt- slag) and 4370 mLg (45 dry wt- slag) but the system had not achieved steady state conditions at the time of measurement thus greater sorption may likely occur under natural conditions Cementitious formulation did not influence Pu Np or I sorption These data support the following changes in the SRS ldquobest Kdrdquo geochemical data package used as input to SRS performance assessment calculations
Present data (d) This document Stage 1(c)
Young Stage 2 Medium
Stage 3 Old
Stage 1 Young
Stage 2 Medium
Stage 3 Old
Reducing Concrete (mLg) I 5 9 0 5 9 0
Np 4000 4000 3000 10-13 M(a) 10-13 M (a) 5000 Pu 10000 10000 1000 10-12 M (a) 10-12 M (a) 2000 Tc 5000 5000 5000 5000 5000 1000 (b)
Oxidizing Concrete (mLg) I 8 15 4 8 15 4
Np 1600 1600 250 10-12 M (a) 10-12 M (a) 5000 Pu 10000 10000 1000 10-12 M (a) 10-12 M (a) 2000 Tc 08 08 05 08 08 05
(a) Apparent solubility (units = M = molL) Below this concentration Kd value of 10000 mLg is to be used (b) A decrease in Tc Kd values with respect to previous values will be used because of the observation that Tc(IV) oxidizes readily under SRS conditions to Tc(VII) (c) Stages 1 2 and 3 are conceptually based on mineral composition changes The 1st 2n and 3rd stages are expected to last 50 500 and 7000 pore volumes respectively A 2-ft slab of cement may be expected to last 740 yr in the 1st stage 7400 yr in the 2nd and 103600 yr in the 3rd stage (d) Kaplan (2007) Kaplan and Coates (2008) and Kaplan et al 2008
31 Preparation of ICP-MS Standards Stock Solutions and Working Solutions 15 311 242Pu 15 312 237Np 16 313 99Tc 17 314 127I 18 315 Cementitious Materials Selected for Experiments 19
32 ICP-MS Detection Limits 20 33 Experimental Methods 20 34 Experimental Protocol for Sorption Experiments under Aerobic Conditions 21 35 Experimental Protocol for Sorption Experiments under Anerobic Conditions 22 36 Examination of Sorption to Vial Walls for Solids and No Solids Controls 23 37 Data Analysis 23
40 Results and Discussion 24 41 Radionuclide Sorption to Cementitious Formulations under Oxidizing Conditions 24 42 Radionuclide Sorption to Vial Walls Under Oxidizing Conditions 28 43 Radionuclide Sorption to Cementitious Formulations under Reducing Conditions 32 44 Radionuclide Sorption to Vial Walls under Reducing Conditions 38
50 Comparison of Radionuclide Sorption under Oxidizing and Reducing Conditions 40 60 Comparison of Radionuclide Sorption and Solubility under Oxidizing and Reducing Conditions46 70 Summary and Recommendations for Future Work 48
71 Comparison with Previous Data 48 72 Suggested Future Work 48
80 References 49 90 Appendix A Data Tables of Radionuclide Sorption to Saltstone under Oxidizing Conditions 51
91 Data Tables for No Solid Controls 51 92 Data Tables for Vault 2 54 93 Data tables for saltstone TR545 57 94 Data Tables for Saltstone TR547 59
SRNL-STI-2009-00636 Revision 0
vi
95 Data Tables for Aged Cement 62 96 Data Tables for Sorption to Vial Walls 65
100 Appendix B Data Tables of Radionuclide Sorption to Saltstone Under Reducing Conditions 66 101 Data Tables for No-Solid Controls 66 102 Data Tables for Vault 2 69 103 Data Tables for TR545 72 104 Data Tables for TR547 75 105 Data Tables for Aged Cement 78 106 Data Tables for Sorption to Vial Walls 80
110 Appendix C Dixon et al (2009) FY09 PACA Maintenance Program Additional Saltstone
Property Testing SRNL L3100-2009-00019 Rev 0 82
SRNL-STI-2009-00636 Revision 0
vii
LIST OF TABLES
Table 31 Characteristics of saltstone formulations used in this work Kaplan et al (2008) 19
Table 32 Detection limits for each isotope based on representative calibration curves generated in PlasmaLab software associated with the ICP-MS 20
Table 33 Experimental Matrix of Sorption Experiments under Aerobic Conditions 22
Table 61 Comparison of plutonium apparent solubility values under oxidizing and reducing conditions 46
Table 62 Comparison of neptunium apparent solubility values under oxidizing and reducing conditions 47
Table 63 Comparison of technetium Kd values under oxidizing and reducing conditions 47
Table 64 Comparison of iodine Kd values under oxidizing and reducing conditions 48
Table 91 Plutonium no solids control after one day 51
Table 92 Plutonium no solids control after four days 51
Table 93 Neptunium no solids control after one day 52
Table 94 Neptunium no solids control after four days 52
Table 95 Technetium no solids control after one day 52
Table 96 Technetium no solids control after four days 53
Table 97 Iodine no solids control after one day 53
Table 98 Iodine no solids control after four days 53
Table 99 Vault 2- plutonium after one day 54
Table 910 Vault 2- plutonium after four days 54
Table 911 Vault 2- neptunium after one day 54
Table 912 Vault 2- neptunium after four days 55
Table 913 Vault 2- technetium after one day 55
Table 914 Vault 2- technetium after four days 55
Table 915 Vault 2- iodine after one day 56
Table 916 Vault 2- iodine after four days 56
Table 917 TR545- plutonium after one day 56
Table 918 TR545- plutonium after four days 57
SRNL-STI-2009-00636 Revision 0
viii
Table 919 TR545- neptunium after one day 57
Table 920 TR545- neptunium after four days 57
Table 921 TR545- technetium after one day 58
Table 922 TR545- technetium after four days 58
Table 923 TR545- iodine after one day 58
Table 924 TR545- iodine after four days 59
Table 925 TR547- plutonium after one day 59
Table 926 TR547- plutonium after four days 60
Table 927 TR547- neptunium after one day 60
Table 928 TR547- neptunium after four days 60
Table 929 TR547- technetium after one day 61
Table 930 TR547- technetium after four days 61
Table 931 TR547- iodine after one day 61
Table 932 TR547- iodine after four days 62
Table 933 Aged cement- plutonium after one day 62
Table 934 Aged cement- plutonium after four days 63
Table 935 Aged cement- neptunium after one day 63
Table 936 Aged cement- neptunium after four days 63
Table 937 Aged cement- technetium after one day 64
Table 938 Aged cement- technetium after four days 64
Table 939 Aged cement- iodine after one day 64
Table 940 Aged cement- iodine after four days 65
Table 941 Plutonium sorbed to vial wall in no solids control 65
Table 942 Neptunium sorbed to vial wall in no solids control 65
Table 101 Plutonium no solids control after one day 66
Table 102 Plutonium no solids control after four days 67
Table 103 Neptunium no solids control after one day 67
Table 104 Neptunium no solids control after four days 67
Table 105 Technetium no solids control after one day 67
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Table 106 Technetium no solids control after four days 68
Table 107 Iodine no solids control after one day 68
Table 108 Iodine no solids control after four days 68
Table 109 Vault 2- plutonium after one day 69
Table 1010 Vault 2- plutonium after four days 69
Table 1011 Vault 2- neptunium after one day 70
Table 1012 Vault 2- neptunium after four days 70
Table 1013 Vault 2- technetium after one day 70
Table 1014 Vault 2- technetium after four days 71
Table 1015 Vault 2- iodine after one day 71
Table 1016 Vault 2- iodine after four days 71
Table 1017 TR545- plutonium after one day 72
Table 1018 TR545- plutonium after four days 72
Table 1019 TR545- neptunium after one day 73
Table 1020 TR545- neptunium after four days 73
Table 1021 TR545- technetium after one day 73
Table 1022 TR545- technetium after four days 74
Table 1023 TR545- iodine after one day 74
Table 1024 TR545- iodine after four days 74
Table 1025 TR547- plutonium after one day 75
Table 1026 TR547- plutonium after four days 75
Table 1027 TR547- neptunium after one day 76
Table 1028 TR547- neptunium after four days 76
Table 1029 TR547- technetium after one day 76
Table 1030 TR547- technetium after four days 77
Table 1031 TR547- iodine after one day 77
Table 1032 TR547- iodine after four days 77
Table 1033 Aged cement- plutonium after one day 78
Table 1034 Aged cement- plutonium after four days 78
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Table 1035 Aged cement- neptunium after one day 78
Table 1036 Aged cement- neptunium after four days 79
Table 1037 Aged cement- technetium after one day 79
Table 1038 Aged cement- technetium after four days 79
Table 1039 Aged cement- iodine after one day 80
Table 1040 Aged cement- iodine after four days 80
Table 1041 Plutonium sorbed to vial wall in no solids control 80
Table 1042 Neptunium sorbed to vial wall in no solids control 81
Table 1043 Technetium sorbed to vial wall in no solids control 81
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LIST OF FIGURES
Figure 31 Screen capture of a typical 242Pu calibration curve using Thermo PlasmaLab software to control the data collection and analysis R2=0999872 Intercept Conc (Detection Limit) = 0000044 ppb 16
Figure 32 Screen capture of a typical 237Np calibration curve using Thermo PlasmaLab software to control the data collection and analysis R2=0999981 Intercept Conc (Detection Limit) = 0000026 ppb 17
Figure 33 Screen capture of a typical 99Tc calibration curve using Thermo PlasmaLab software to control the data collection and analysis R2=0999984 Intercept Conc (Detection Limit) = 0000013 ppb 18
Figure 34 Screen capture of a typical 127I calibration curve using Thermo PlasmaLab software to control the data collection and analysis R2=0999991 Intercept Conc (Detection Limit) = 024 ppb 19
Figure 41 Plutonium Kd Values under Oxidizing Conditions Plutonium Kd values for various saltstone formulations measured after one-day equilibration (1d) and four-day equilibration (4d under oxidizing conditions Total plutonium concentrations in each system were 1 ppb 5 ppb and 10 ppb Sample prepared in triplicate and error bars represent standard deviation of samples except as follows value for dataset TR547-4d 10 ppb is reported based on duplicate samples 25
Figure 42 Plutonium solubility for various saltstone formulations measured after one-day equilibration (1d) and four-day equilibration (4d) under oxidizing conditions Total plutonium concentrations in each system were 1 ppb 5 ppb and 10 ppb as noted Samples prepared in triplicate and an average of all samples (9) was used to determine average solubility The error bars represent standard deviation of samples 25
Figure 43 Neptunium Kd values under oxidizing conditions Neptunium Kd values for various saltstone formulations measured after one-day equilibration (1d) and four-day equilibration (4d) under oxidizing conditions Total plutonium concentrations in each system were 1 ppb 5 ppb and 10 ppb as noted Samples prepared in triplicate and error bars represent standard deviation of samples except as follows value for datasets TR545-1d 1ppb TR545-4d 1 ppb TR547 4d 1 ppb TR545-4d 10 ppb TR547-1d 1ppb TR547-4d 10 ppb are reported based on a single sample and for dataset TR545-1d 5ppb is reported based on duplicate samples Kd values limited to gt106 were at instrumental background 26
Figure 44 Average solubility of Np under oxidizing conditions Neptunium solubility for various saltstone formulations measured after one-day equilibration (1d) and four-day equilibration (4d) under oxidizing conditions Total Np concentrations in each system were 1 ppb 5 ppb and 10 ppb Samples prepared in triplicate and an average of all samples (9) was used to determine average solubility except as follows TR545-1d is based on 6 samples TR545- 4d on 5 samples TR547-1d on 7 samples and TR547- 4d on 5 samples The error bars represent standard deviation 27
Figure 45 Technetium Kd values under oxidizing conditions Tc Kd values for various saltstone formulations measured after one-day equilibration (1d) and four-day equilibration (4d) under oxidizing conditions Total Tc concentrations in each system were 1 ppb 5 ppb and 10 ppb as noted above Samples were prepared in triplicate and the error bars represent standard deviation
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xii
of samples except as follows data sets for Vault 2-1d 1ppb were duplicates and TR547- 4d 10 ppb is based on a single dataset 27
Figure 46 Iodine Kd Values under Oxidizing Conditions Iodine Kd values for various cementitious formulations measured after one-day equilibration (1d) and four-day equilibration (4d) under oxidizing conditions Total iodine concentrations in the systems were 100ppb 500 ppb and 1000 ppb as noted above Samples were prepared in triplicate and the error bars represent standard deviation of samples except as follows duplicates were used for dataset TR545- 1d 100ppb 28
Figure 47 Plutonium Neptunium and Technetium Aqueous Fractions Fraction of Pu Np and Tc remaining in the aqueous phase for the No Solids controls after a one-day equilibration (1d) and four-day equilibration (4d) under oxidizing conditions The total concentration for each radionuclide 10 ppb as noted above Samples were prepared in triplicate and the error bars represent the standard deviation of the samples 29
Figure 48 Iodine Aqueous Fraction Iodine aqueous fraction for the no-solids controls after a one-day equilibration (1d) and four-day equilibration (4d) under oxidizing conditions The total concentration of iodine was 1000 ppb as noted above Samples were prepared in triplicate and the error bars represent the standard deviation of the samples 29
Figure 49 Percent Pu and Np sorbed to vial walls of the no solids controls after the aqueous phases were discarded and the vials were washed Both the 10 ppb (blueleft) and 1 ppb (redright)) datasets were prepared in triplicate and the error bars show the standard deviation 31
Figure 410 Percent Pu sorbed to vial walls after the solids and aqueous phases were removed and the vials were washed The graph illustrates one sample from each of the 1 ppb (redleft) 5 ppb (greenmiddle) and 10 ppb (blueright) systems Therefore no error bars are present 31
Figure 411 Percent Np sorbed to vial walls after the solids and aqueous phases were removed and the vials were washed The graph illustrates one sample from each of the 1 ppb (redleft) 5 ppb (greenmiddle) and 10 ppb (blueright) systems Therefore no error bars are present 32
Figure 412 Pu Kd Values under Reducing Conditions Plutonium Kd values for various cementitious formulations measured after one-day equilibration (1d) and four-day equilibration (4d) under reducing conditions Total plutonium concentrations in each system were 1ppb 5 ppb and 10 ppb Samples prepared in triplicate and error bars represent standard deviation 33
Figure 413 Average Solubility of Plutonium under Reducing Conditions Plutonium solubility for various cementitious formulations measured after one-day equilibration (1d) and four-day equilibration (4d) under reducing conditions Total plutonium concentrations in each system were 1ppb 5 ppb and 10 ppb as noted Samples prepared in triplicate and an average of all samples (9) was used to determine average solubility The error bars represent standard deviation of samples 33
Figure 414 Np Kd Values under Reducing Conditions Neptunium Kd values for various cementitious formulations measured after one-day equilibration (1d) and four-day equilibration (4d) under reducing conditions Total Np concentrations in each system were 1 ppb 5 ppb and 10 ppb Samples were prepared in triplicate and the error bars represent standard deviation Kd values limited to gt106 were at instrumental background 34
Figure 415 Average Solubility of Neptunium under Reducing Conditions Neptunium solubility for various cementitious formulations measured after one day equilibration (1d) and four day
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xiii
equilibration (4d) under reducing conditions Total plutonium concentrations in each system were 1ppb 5 ppb and 10 ppb Samples prepared in triplicate and an average of all samples (9) was used to determine average solubility The error bars represent standard deviation 35
Figure 416 Tc Kd Values under Reducing Conditions Tc Kd values for various cementitious formulations measured after one-day equilibration (1d) and four-day equilibration (4d) under reducing conditions Total Tc concentrations in each system were 1 ppb 5 ppb and 10 ppb Sample prepared in triplicate and error bars represent standard deviation except as follows TR547-1d 1 ppb is based on a single dataset and datasets Vault 2-1d 5 ppb Vault 2- 4d 1 ppb Aged Cement-1d 5 ppb and Aged Cement-4d 1 ppb are duplicates 36
Figure 417 Data from Figure 416 replotted on a reduced linear scale for easier viewing Each sample was prepared in triplicate except as follows TR547-1d 1 ppb is based on a single dataset Vault 2-1d 5 ppb Vault 2- 4d 1 ppb Aged Cement-1d 5 ppb and Aged Cement-4d 1 ppb are duplicate datasets 36
Figure 418 Iodine Kd Values under Reducing Conditions I Kd Values for various cementitious formulations measured after one day equilibration (1d) and four day equilibration (4d) under reducing conditions Total iodine concentrations in each system were 100 ppb 500 ppb and 1000 ppb as noted Sample prepared in triplicate and error bars represent standard deviation of samples except as follows Vault 2-4 d 100 ppb is a single dataset while the datasets for Vault 2-1 d 100 ppb 4 d 1000 ppb TR545-4 d 1000 ppb 100 ppb TR547-4 d 1000 ppb 500 ppb 100 ppb and Aged Cement- 4 d 1000 ppb and 100 ppb are all based on duplicates 38
Figure 419 Plutonium Neptunium and Technetium No-Solids Aqueous Fractions under Reducing Conditions Pu Np and Tc aqueous fractions of No Solids controls after a one-day equilibration (1d) and four-day equilibration (4 d) under reducing conditions Total concentration for each radionuclide was 1 ppb and 10 ppb Samples were prepared in triplicate and the error bars represent the standard deviation 39
Figure 420 Percent of Pu Np and Tc sorbed to the vial walls of the No Solids control samples under reducing conditions Each the 1 ppb and 10 ppb samples were prepared in triplicate and the error bars represent the standard deviations of triplicate samples 39
Figure 421 Iodine No-Solids Aqueous Fractions under Reducing Conditions I aqueous fractions of No-Solids controls after a one-day equilibration (1d) and four-day equilibration (4d) under reducing conditions The total concentration for each system was 100 ppb and 1000 ppb Samples were prepared in triplicate and the error bars represent the standard deviation 40
Figure 51 Comparison of Tc I Np and Pu sorption to Vault 2 solid under oxidizing and reducing conditions 42
Figure 52 Comparison of Tc I Np and Pu sorption to TR 545 solid under oxidizing and reducing conditions 43
Figure 53 Comparison of Tc I Np and Pu sorption to TR547 solid under oxidizing and reducing conditions 44
Figure 54 Comparison of Tc I Np and Pu sorption to Aged Cement under oxidizing and reducing conditions 45
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LIST OF ABBREVIATIONS
DDI water Distilled deionized water ICP-MS Inductively coupled plasma ndash mass spectrometer
Kd Distribution coefficient LSC liquid scintillation counting NOM Natural organic matter PA Performance Assessment ppb parts per billion ppq parts per quadrillion QAQC Quality AssuranceQuality Control SA Special Analyses SRNL Savannah River National Laboratory SRS Savannah River Site
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10 Introduction Performance Assessments (PA) are risk calculations designed to determine (1) the maximum
amount of radioactivity that can be safely buried in a subsurface facility and (2) the potential human risk associated with disposing of radioactive waste in a subsurface facility Special Analyses (SAs) are similar to PAs except that they are designed to address specific issues related to PAs such as a new discovery since the PA was issued Commonly parameters describing the extent that a radionuclide interacts with solids at the source vadose zone and aquifer influence the extent of calculated human risk The two parameters that the SRS use to represent radionuclidesolid interactions are Kd and apparent solubility values together these parameters are referred to as sorption values Sorption values vary with radionuclides groundwater chemistry and the type of solid phase (and for cementitious materials by the age of the material during the calculation) In this work Kd and apparent solubility values are reported for 99Tc 127I 237Np and 242Pu sorption to various cementitious formulations
20 Objectives
The objectives of this work were to 1 Determine the influence of cementitious formulation on technetium (Tc) iodine (I) neptunium
(Np) and plutonium (Pu) sorption under oxidizing conditions The specific formulations that were evaluated included 1) an aged cement recovered from a 30-year old outdoor concrete pad on the SRS 2) Vault 2 concrete 3) TR545 saltstone and 4) TR547 saltstone (additional details are presented in Section 30 Materials and Methods)
2 Measure Tc I Np and Pu sorption to the cementitious formulations under reducing conditions
30 Materials and Methods
31 Preparation of ICP-MS Standards Stock Solutions and Working Solutions
311 242Pu
A National Institute of Standards and Technology Standard Reference Material (NIST SRM 434H) was used to prepare a stock 242Pu solution by dilution in 2 Aristar Optima HNO3 All volume additions were monitored gravimetrically This working solution was then used to make a set of 001 005 1 2 5 10 parts per billion (ppb) standards by dilution using 2 HNO3 Again all volume additions were monitored gravimetrically These standards were used to calibrate the Thermo Scientific X Series 2 inductively coupled plasma ndash mass spectrometer (ICP-MS) for quantification of 242Pu A representative calibration curve for 242Pu is shown in Figure 31 The instrument performance was monitored using 209Bi 232Th and 238U as internal standards The recovery of each sample during analysis was corrected based on the internal standard recovery The internal standard recoveries remained within standard quality assurancequality control QAQC protocols for the instrument (between 80 and 120)
A 242Pu stock solution was prepared by dissolving 1mg of Pu(NO3)4 obtained as a Certified Reference Material from New Brunswick Laboratory (CRM 130) This CRM is gt999 242Pu by atom percent The CRM was dissolved in 20mL of 8M HNO3 (Aristar Optima Grade) Because no chemicals or heat have been introduced to manipulate the Pu oxidation state it can be assumed that Pu(IV) is the predominant oxidation state in this stock solution A working solution to be used in spiking 242Pu experiments was prepared by diluting 25 mL of the CRM stock solution with 100 mL 10 M Aristar Optima HNO3 The concentration of 242Pu in this stock solution was determined using ICP-MS calibrated using the NIST SRM standards The concentration of Pu in this stock solution was 1065 ppb The total Pu
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concentration was also determined using liquid scintillation counting using the isotopic ratios reported for CRM 130 These compared favorably with the ICP-MS results but are reported here as a rigorous standardization because the isotopic ratios of CRM 130 have not yet been certified
Figure 31 Screen capture of a typical 242Pu calibration curve using Thermo PlasmaLab software to control the data collection and analysis R2=0999872 Intercept Conc (Detection Limit) = 0000044 ppb
312 237Np
A National Institute of Standards and Technology Standard Reference Material (NIST SRM 4341) was used to prepare a stock 237Np solution by dilution in 2 Aristar Optima HNO3 All volume additions were monitored gravimetrically This working solution was then used to make a set of 001 005 1 2 5 10 ppb standards by dilution using 2 HNO3 Again all volume additions were monitored gravimetrically These standards were used to calibrate the Thermo Scientific X Series 2 ICP-MS for quantification of 237Np A representative calibration curve for 237Np is shown in Figure 32 The instrument performance was monitored using 209Bi 232Th and 238U as internal standards The recovery of each sample during analysis was corrected based on the internal standard recovery The internal standard recoveries remained within standard QAQC protocols for the instrument (between 80 and 120)
A compiled 237Np stock solution from the Environmental Engineering and Earth Science (EEampES) inventory (primarily purchased from Isotope Products Valencia CA) was evaporated to dryness then the residue was brought up in approximately 5mL 80 M HNO3 Then 10 M hydroxylamine hydrochloride (NH2OHHCl EMD Chemicals ACS grade) and water were added to achieve a 3M HNO303M NH2OHHCl solution This solution was purified by extraction chromatography using Eichrom TEVA resin packed in a Bio-Rad poly-prep column The 3M HNO303 M NH2OHHCl neptunium solution was loaded on a 2 mL column and washed with 3 column volumes of 3 M HNO3 The Np(IV) was eluted with 002 M HCl + 02 M HF The effluent was evaporated to dryness then redissolved in 10 M HNO3 Additional 10 M HNO3 was added to maintain a approximately 10 mL then the solution was evaporated to incipient dryness and redissolved in a 50 mL of 10 M HNO3 An aliquot of the stock solution was evaporated to dryness on a stainless steel planchet and counted on the EGampG Ortec Alpha Spectrometer (Octete PC Detectors) No other alpha energies besides 237Np were observed The approximate concentration was determined using liquid scintillation counting and little 233Pa was observed The fuming in HNO3 as performed at the end of the purification procedure will drive Np to the soluble pentavalent state This is the stable oxidation state of Np under the experimental conditions Therefore experiments performed here can be assumed to be initially Np(V) The exact Np
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concentration in this solution was determined using ICP-MS calibrated with a NIST standard as discussed in section 312 below
A 237Np working solution (Working Solution 1) was created by pipetting an aliquot of the 237Np stock solution into a 100 mL Nalgene Teflon bottle and diluting with 2 BDH Aristar Ultra HNO3 to give a working solution concentration of 820 ppb All volumes were monitored gravimetrically Analysis on the ICP-MS calibrated against NIST Standards as described below gave a concentration of 820 ppb in Working Solution 1
Figure 32 Screen capture of a typical 237Np calibration curve using Thermo PlasmaLab software to control the data collection and analysis R2=0999981 Intercept Conc (Detection Limit) = 0000026 ppb
313 99Tc
A 99Tc working solution was prepared by diluting a stock solution of 99Tc (from the EEampES inventory purchased from Isotope Products Valencia CA) in distilled-deionized water (DDI Resistivity gt18 MΩcm) The oxidation state of Tc was not measured However based on the aqueous concentration in the DDI water solution Tc(VII) is the expected oxidation state The reduced Tc(IV) oxidation state would not be soluble under these conditions The expected concentration of 950 ppb based on the dilution was verified using liquid scintillation counting The 99Tc working solution was used to make 001 005 1 2 5 and 10 ppb standards by dilution using 2 HNO3 These standards were used to calibrate the Thermo Scientific X Series 2 ICP-MS for quantification of 99Tc A screen shot of a representative calibration curve is shown in Figure 33 The instrument performance was monitored by interpolating between 89Y and 115In internal standards The recovery of each sample during analysis was corrected based on the internal standard recovery The internal standard recoveries remained within standard QAQC protocols for the instrument (between 80 and 120)
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Figure 33 Screen capture of a typical 99Tc calibration curve using Thermo PlasmaLab software to control the data collection and analysis R2=0999984 Intercept Conc (Detection Limit) = 0000013 ppb
314 127I
A 100 microgmL iodate (IO3-) stock solution from High Purity Standards (Charleston SC) was used
to make 1 5 10 50 and 100 ppb standards by dilution using the ldquotraprdquo solution (discussed in Section 32 below) These standards were used to calibrate the Thermo Scientific X Series 2 ICP-MS for quantification of 127I A screen shot of a representative calibration curve is shown in Figure 34 The use of a reducing basic trap solution for iodine analysis limits the number of available internal standards that can be used to monitor ICP-MS instrument performance during iodine analysis Experiments are underway to identify acceptable internal standards However the data presented in this work did not use any internal standards prior to rigorous testing and analysis of representative standards As with the analyses for all isotopes (Tc I Np and Pu) spiked QAQC samples were frequently analyzed throughout the analysis as a check on instrument performance While these values cannot be used to correct individual samples in the same manner that the internal standards can they can be used to ensure accurate measurements of each isotope In almost all cases QAQC standards were within 10 of the expected value Because the average internal standard recovery ranges between 80 and 120 for the ICP-MS the iodine QAQC standard appears to be acceptable However a significant amount of ongoing work is testing various internal standards to improve the accuracy of iodine analysis using ICP-MS In one experiment (discussed in detail below) the QAQC standards deviated by an average value of 195 This will be specifically discussed below
Because experiments were performed with 127I concentrations up to 1000 ppb the 100 microgmL (ppm) stock iodate solution from High Purity Standards was used as the working solution
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Figure 34 Screen capture of a typical 127I calibration curve using Thermo PlasmaLab software to control the data collection and analysis R2=0999991 Intercept Conc (Detection Limit) = 024 ppb
315 Cementitious Materials Selected for Experiments There were four cementitious materials selected for this sorption study The first referred to as Aged Cement is a 30 year old sample that does not contain any reducing slag The aggregate from the Vault 2 cement had its aggregate removed prior to conducted tests in an effort to make subsamples more uniform This was necessary because some of the aggregate were larger than the 05 g subsamples used in individual sorption tests The Vault 2 cementitious material contained 17 dry wt- reducing slag on a dry weight basis before the water was added to the mix (Table 31) The TR547 and TR545 saltstone formulations contain 45 dry wt- and 90 dry wt- reducing slag respectively
Table 31 Characteristics of saltstone formulations used in this work Kaplan et al (2008)
Sample Percent Reducing Slag (dry wt-) (c)
Percent Portland Cement
(dry wt-) (c)
Percent Fly Ash
(dry wt-) (c)
Percent Aggregatesand ( dry wt-) (c)
Reducing Equivalents
(microeqg)
Aged Cement 0 10 45 45 855 plusmn 101(a)
Vault 2 Cement 17 10 45 0 178(b)
TR547 45 10 45 0 607(b) TR545 90 10 0 0 681(b) Blast furnace slag 100 0 0 0 819(b) (a) Kaplan et al (2008) (b) Roberts and Kaplan (2009) (c) All percentages of saltstone formulations are reported on a dry weight percentage basis that is the weight of the ingredients before water was added (d) Based on Table 8 in Dixon et al (2008 SRNL-STI-2008-00421) which shows the following quantity (lbscu yd) for saltstone Vault 2 Mix 1 concrete formulation 201 cement (1271 wt-) 268 slag (1695 wt-) 447 silica fume (283 wt-) 1563 fly ash (989 wt-) 911 fine sand (5762 wt-) The large aggregate was removed before the sorption tests were conducted The large aggregate accounted for 75 wt- of the original field sample not the sample used in these test before water was added to the mix TR547 is referred to as the Baseline by Dixon et al (2008) and is described in more detail in Appendix C (Mix 2) by Dixon et al (2008) (Control-BFSPC) and 1 (Baseline)
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TR545 saltstone contains 90 reducing slag and it is Mix 1 in Dixon et al (2008) and is described as
ldquoA control mix will be based on the baseline mix modified by exclusion of the Class F fly ash Consequently the cementitious materials premix will be a mixture of 90 blast furnace slag and 10 Portland cement The degree of reaction will be much greater than with the normal premix and therefore should result in a lower porosity and a lower permeability This bounding test at 060 wcm ratio is expected to yield a hydraulic conductivity at or below the detection limit for the Mactec permeameter measurement system Therefore this test should demonstrate the lowest level of detection of the Mactec system as well as show a resolvable difference between measurements of the control mix and the control mix with the normal premix compositionrdquo
32 ICP-MS Detection Limits
The PlasmaLab software platform determines a detection limit for each isotope based upon the intercept concentration A new calibration curve was generated for each experimental run and curves were very similar Using representative calibrations curves the detection limits for each isotope were as listed in Table 32 Note the higher detection limit for 127I is primarily due to the higher background count rate observed on the instrument This is believed to be due to the minimum purity levels of chemicals required for the iodine ldquotraprdquo solution as discussed in Section 33 below Therefore experiments were run with initial iodate concentrations higher than Tc Np and Pu to maintain analytical sensitivity
Table 32 Detection limits for each isotope based on representative calibration curves generated in PlasmaLab software associated with the ICP-MS
33 Experimental Methods
The experimental methods used in this work followed closely those previously described for experiments examining radionuclide sorption to saltstone (Kaplan et al 2007 Kaplan et al 2008) Brief descriptions of each method are provided below
Preparation of Calcite Solution Using a hotstirring plate 10 L of distilled-deionized (DDI)
water was heated to 3-100C above room temperature Then 001 g CaCO3 (EM Science ACS grade) was added to the solution and the resulting suspension was mixed for 24 hours at the elevated temperature The solution was then vacuum filtered through a 045-microm filter to ensure no solid CaCO3 remained in solution
Preparation of 2 HNO3 Analysis of Tc Np and Pu on the ICP-MS required dilution in 2
HNO3 This was prepared by adding 28 mL of Aristar Optima HNO3 from a clean graduated cylinder (designated to 2 HNO3) into a 1 L volumetric flask (designated to 2 HNO3) partially filled with DDI water and then further diluted to volume
Preparation of Trap Solution for Iodine Analysis Analysis of I required the use of a reducing
basic solution that was capable of reducing iodate to iodine and holding the iodine in solution This minimized the loss of I during sample analysis A 1 L trap solution was prepared by weighing out 00500 g NaHSO3 (Fisher Scientific ACS Grade) on a calibrated Sartorous LA 230S scale and adding it to a 1L volumetric flask Then 40 mL of 25 ww tetramethylammonium hydroxide (Alfa Aesar electronic grade) and 10 mL CFA-C solution (Spectrasol Inc) were added to the volumetric flask via a calibrated 1000-5000 microL Eppendorf Research pipette The solution was then diluted to volume with DDI water
34 Experimental Protocol for Sorption Experiments under Aerobic Conditions
Falcon BlueMax 15mL polypropylene vials were labeled and weighed to within 0001 g on a calibrated Sartorious LA 230S scale The scale was then zeroed and 025 +- 001 g of a given solid were added to each tube and the weight was recorded to within 0001g
For each of the four solids three sets of triplicate samples were prepared The three sets of samples were used to allow for experiments to be run with varying concentrations of each isotope Target initial concentrations for 99Tc 237Np and 242Pu samples were 1 ppb 5 ppb and 10 ppb Target initial concentrations for the 127I samples were 100 ppb 500 ppb and 1000 ppb A set of no solids controls at initial concentrations of 1 ppb and 10 ppb for 99Tc 237Np and 242Pu and initial concentrations of 100 ppb and 1000 ppb 127I were also prepared by adding the calcite solution to pre-weighed pre-labeled centrifuge tubes as discussed above
The solids were equilibrated with the calcite solution before spiking with the radionuclides This was done by adding 10 plusmn 01 mL of calcite solution to each tube and recording the mass The samples were then placed on a Thermo Scientific shaker overnight After 24 hours the solutions were allowed to settle for 1 hour The pH was then measured and the samples were then centrifuged for 15 minutes at 8000 rpm to further separate the solids The aqueous phase was then decanted and 10 plusmn 01 mL of calcite solution was added to each tube The weight of the tube (labeled tube + solid + calcite solution) was measured to within 0001g During this washing process the pH was monitored and held steady throughout the process The pH ranged from 11-12 depending on the particular saltstone used During the experiments the exact pH for all samples at all equilibration times was measured and is reported in Appendix A and B
The resulting suspensions were then spiked with 127I 237Np 242Pu and 99Tc It is important to note that all four isotopes were added to the same vial Use of the ICP-MS to determine the concentration of each isotope allows for a single solution to contain all analytes of concern This allowed for a greater variability in the sample set and increased replicates as opposed to running individual sorption tests for each isotope For the systems with initial 99Tc 237Np and 242Pu concentrations of 10 ppb and initial 127I concentration of 100 ppb a 100 microL aliquot of each radionuclide working solution was added to the first three tubes for each solid The addition was made with the tube resting on a tared analytical balance so that the exact mass of each radionuclide solution added was recorded and the solution was gently swirled before the next radionuclide was added The 5 ppb 237Np 242Pu and 99Tc and 500 ppb 127I samples were prepared in the same manner but adding 50 microL of the respective spike solutions The final three tubes with initial 237Np 242Pu and 99Tc concentrations of 1 ppb and 100 ppb 127I were prepared by using 10 microL of the spike solutions for all four solids as well as a set of solid-free controls (No-Solids Controls) For clarity this experimental matrix is shown in Table 33 below
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Table 33 Experimental Matrix of Sorption Experiments under Aerobic Conditions
After spiking the radionuclides a precalculated amount of 10M NaOH was added to each sample
to counter the acidic radionuclide spike solutions and the pH of one of the triplicate samples was measured to ensure the proper pH range was reached The samples were then placed on and end-over-end shaker to mix at approximately 8 rpm After 24 hours the samples were removed from the shaker and the pH of each sample was measured using an Orion Ross semi-micro glass electrode calibrated against pH 4 7 and 10 buffers (Thermo) The samples were then shaken and a transfer pipette was used to transfer 35 mL of a homogenous suspension to a 5mL syringe The solution was then passed through a 100 nm nylon syringe filter The first 025-050 mL of filtrate was discarded and the remaining filtrate was collected in a clean polyethylene vial Then 10 mL of the filtrate was removed and diluted in 90 mL 2 HNO3 The mass of each phase was determined and recorded gravimetrically Then 10 mL of the remaining filtrate was transferred to a clean Falcon BlueMax 15mL vial and diluted with 90 mL of trap solution for 127I analysis Again the volume of each phase was monitored gravimetrically After the 24 hour sampling event the samples were put back on the shaker to mix for three additional days On day four the above sampling procedure was repeated
The 237Np 242Pu and 99Tc samples can be run on the Thermo Scientific ICP-MS using the standard setup and procedure which included a standard flow glass nebulizer and bulb spray chamber However for the 127I analysis the ICP-MS must be reconfigured to accommodate the basic reducing trap solution This is to alleviate problems with iodine signal stability over time frequently observed in ICP-MS analysis The reconfigured instrument uses an Elemental Science Microflow PFA-100 Teflon nebulizer with a flow rate of 100microLmin along with a sapphire torch and a Teflon spray chamber This configuration must be run with a low pump speed to prevent back pressure on the system Two 30 minute stability tests were performed using a 50 ppb iodate solution Each experiment consisted of 40 separate measurements After each experiment was completed the uncorrected mass counts were examined and found to stay steady over the sampling period The relative standard deviation ( RSD) over all samples for each experiment was 1866 and 1460 respectively This shows that there was no significant ldquomemoryrdquo or loss of the iodine signal over time and that the reconfigured instrument has a stable iodine signal over time However as will be discussed below some difficulty has been encountered in finding an adequate internal standard for iodine analysis
35 Experimental Protocol for Sorption Experiments under Anerobic Conditions In order to examine the effects of reducing conditions of sorption of each isotope to the various cementitious samples a series of sorption experiments were performed in an anaerobic glovebox under a 2 H2(g) 98 N2(g) atmosphere Based on the measured pH and EH of these systems as discussed below these systems were at the point of reducing water Therefore they are expected to represent a lower end of the possible range for reducing conditions expected in the porewater available within cementitious materials
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Preparation of Calcite for Reducing Conditions Approximately 35 L of DDI water was boiled for 45 minutes Argon was slowly bubbled through the water as it cooled Once it cooled to below 500C approximately 3 g of calcite was added This solution mixed overnight under a continuous Ar flow After 12 hours the solution was moved into an oxygen free glove bag for filtration as described in 3231 After filtration the calcite solution was moved into the glove box
Preparation of Working Solutions under Reducing Conditions The calcite and solid solutions
were prepared in the glove box using the previously mentioned procedure used under aerobic conditions The radionuclide working solutions were transferred to the glovebox and stirred open to the reducing atmosphere for at least three days The concentration of each isotope in the working solutions was measured to determine any change in the concentration due to evaporation while the solutions were equilibrating
The preparation and spiking of samples for sorption experiments was performed exactly as described for the oxidizing conditions except all sample handling was performed in the glovebox After the 1 day and 4 day equilibration the samples were filtered within the glovebox then transferred outside for dilution and ICP-MS analysis similar to the description provided about for the oxidizing conditions For these experiments only 4 mL of either 2 HNO3 or trap solution were used to dilute the filtrate instead of the 90 mL used above for experiments performed under oxidizing conditions
36 Examination of Sorption to Vial Walls for Solids and No Solids Controls
As will be discussed below the solid-free controls samples indicated significant loss of Np and Pu Once the one and four days samples were collected and run on the ICP-MS it was necessary to determine the degree each radionuclide was sorbing to the vial walls The remaining suspensions and controls were emptied into a waste container Then 5 mL of the calcite solution was added to each vial using a calibrated pipette The vials were sonicated for approximately one minute and then emptied into the waste container Another 5 mL of calcite solution was added for the second wash and then discarded into the waste container This procedure was expected to remove any soluble Pu from the system or Pu associated with colloidal particles After each vial was washed 10 mL of 2 HNO3 was added using a calibrated pipette The acid solution is expected to remove any Tc Np or Pu associated with the vial walls This procedure has been shown to complete mass balances of Pu in similar sorption experiments using Pu (Powell et al 2002) This process was performed for both the solid suspension and the no solids controls The samples were then run on the ICP-MS to determine the concentration of 99Tc 237Np and 242Pu sorbed to the vial walls
37 Data Analysis The solubilities of 242Pu and 237Np were calculated by using the formula
nuclide
nuclide
nuclideMSICP
sol Mg
gCC
)(10 6
microminus
minus
= (Equation 31)
Csol = observed nuclide solubility (molnuclidekgsolution) CICP-MS = aqueous concentration of nuclide from ICP-MS measurement (ppb micrognuclidekgsolution) Mnuclide = molecular mass of nuclide (gnuclidemolnuclide)
In order to determine the Kd values one first needs to determine the concentration on the solid by using
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solid
calcitespikeaqspikecalcite
spikestock
solid m
mmCmmmC
C)(
)()(
+⎥⎥⎦
⎤
⎢⎢⎣
⎡minus
+
lowast
= (Equation 32)
Csolid = calculated solid phase concentration of the nuclide (ppb) Cstock = concentration of the nuclide stock solution (ppb) mspike = mass of nuclide spiked into the saltstone suspension (g) mcalcite = total mass of calcite solution used in the saltstone suspension (g) Caq = aqueous concentration of nuclide from ICP-MS measurement (ppb) msolid = mass of the saltstone used in the suspension (g)
The Kd can be calculated using the equation
aq
solidd C
CK = (Equation 33)
Kd = solid-water partitioning coefficient (gsolutiongsolid assuming density of 10 gmL traditional
unit of mLsolutiongsolid can be obtained) This Kd Equation (33) is numerically equivalent to the traditional Kd equation proposed in ASTM D-4646 which has been used in previous saltstone experiments (Kaplan et al 2007 Kaplan et al 2008)
40 Results and Discussion
41 Radionuclide Sorption to Cementitious Formulations under Oxidizing Conditions
Figure 41 shows Pu Kd values ranging from 104 to gt105 mLg Generally for each solid the Kd increases with increasing initial Pu concentrations typical behavior of systems where the aqueous concentrations of the radionuclides are solubility controlled This is not expected because the Kd expression indicates that the Kd value should remain constant with increasing total Pu concentrations It was noted that aqueous phase concentration of Pu remained relatively constant in all samples (see discussion below regarding Pu solubility) Therefore the sorption capacity of each solid phase for Pu has not been overcome For each of these solid phases it appears the solutions had reached equilibrium before the first samples were taken at 24 hours In each case the Kd values for the one day and four day are similar A trend between the solid phases is not discernible The aged cement with no reducing slag was expected to have the lowest Kd values but in actuality it has the highest Kd Also there is no correlation with the concentration of reducing slag The Vault 2 samples with 17 dry wt- reducing slag has a Kd similar to that of the TR547 (45 dry wt- slag) while the saltstone with the most slag TR545 (90 dry wt- slag) has the lowest Kd value Others have observed that Pu Kd values of cementitious materials are similar in the absence and presence of slag (Allard et al 1984 Hoaglund et al 1985)
It was observed that similar aqueous concentrations of Pu were observed regardless of the solid phase present Figure 42 shows the average aqueous phase concentrations measured after one day and four days for all solids As stated above triplicate samples were prepared for each solid phase and each initial concentration Therefore each of the reported solubility values in Figure 42 is an average of nine measurements Using the highest reported value with the expected maximum error (0018 ppb for solid TR545) the maximum expected aqueous concentration of Pu in the pore water associated with the
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saltstone formulations will be approximately 7 x 10-11 molL as calculated using Equation 31 This is on the same order as the solubility of Pu hydrous oxide solid phases (Neck and Kim 2001)
Figure 41 Plutonium Kd Values under Oxidizing Conditions Plutonium Kd values for various saltstone formulations measured after one-day equilibration (1d) and four-day equilibration (4d under oxidizing conditions Total plutonium concentrations in each system were 1 ppb 5 ppb and 10 ppb Sample prepared in triplicate and error bars represent standard deviation of samples except as follows value for dataset TR547-4d 10 ppb is reported based on duplicate samples
Figure 42 Plutonium solubility for various saltstone formulations measured after one-day equilibration (1d) and four-day equilibration (4d) under oxidizing conditions Total plutonium concentrations in each system were 1 ppb 5 ppb and 10 ppb as noted Samples prepared in triplicate and an average of all samples (9) was used to determine average solubility The error bars represent standard deviation of samples
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Overall the Kd values for Np range from 105 to gt106 with only a few outliers The most significant outlier is the 1 ppb solution in the TR545 sample after the four-day equilibration It drops two orders of magnitude while the 5 and 10 ppb solutions remain constant However this result is most likely an analytical artifact from working at the detection limits of the ICP-MS In the one-day equilibration samples only one of the triplicates S-2-E had detectable Np while in the four-day equilibration samples only S-2-F had detectable amounts present The graph also shows that with the exception of the 5 ppb sample in the aged cement Np sorption to TR545 (90 dry-wt- slag) and TR547 (45 dry wt- slag) have Kd values approximately one order of magnitude over the aged cement (no slag) and Vault 2 (17 dry wt- slag) samples
It was observed that similar aqueous concentrations of Np were observed regardless of the solid phase present Figure 44 shows the average aqueous phase concentrations measured after one day and four-day equilibrations for all solids As stated above triplicate samples were prepared for each solid phase and each initial concentration Therefore each of the reported solubility values in Figure 44 is an average of nine measurements of Np concentration unless stated otherwise Using the highest reported value with the expected maximum error (00026 ppb for solid TR545) the maximum expected aqueous concentration of Pu in the pore water associated with the saltstone formulations will be approximately 2 x 10-11 molL
Figure 43 Neptunium Kd values under oxidizing conditions Neptunium Kd values for various saltstone formulations measured after one-day equilibration (1d) and four-day equilibration (4d) under oxidizing conditions Total plutonium concentrations in each system were 1 ppb 5 ppb and 10 ppb as noted Samples prepared in triplicate and error bars represent standard deviation of samples except as follows value for datasets TR545-1d 1ppb TR545-4d 1 ppb TR547 4d 1 ppb TR545-4d 10 ppb TR547-1d 1ppb TR547-4d 10 ppb are reported based on a single sample and for dataset TR545-1d 5ppb is reported based on duplicate samples Kd values limited to gt106 were at instrumental background
The Kd values for Tc are significantly lower than that of Pu or Np As a whole the values are
comparable The values for the one-day and four-day equilibrations solutions in the Vault 2 (17 dry wt- slag) and TR545 (90 dry wt- slag) remained constant within reasonable error with just a slight increase from the one-day to four-day equilibration However the Aged Cement (no slag) and TR547 (45 dry wt- slag) showed a noticeable decrease from day one to day four (Figure 45)
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Figure 44 Average solubility of Np under oxidizing conditions Neptunium solubility for various saltstone formulations measured after one-day equilibration (1d) and four-day equilibration (4d) under oxidizing conditions Total Np concentrations in each system were 1 ppb 5 ppb and 10 ppb Samples prepared in triplicate and an average of all samples (9) was used to determine average solubility except as follows TR545-1d is based on 6 samples TR545- 4d on 5 samples TR547-1d on 7 samples and TR547- 4d on 5 samples The error bars represent standard deviation
Figure 45 Technetium Kd values under oxidizing conditions Tc Kd values for various saltstone formulations measured after one-day equilibration (1d) and four-day equilibration (4d) under oxidizing conditions Total Tc concentrations in each system were 1 ppb 5 ppb and 10 ppb as noted above Samples were prepared in triplicate and the error bars represent standard deviation of samples except as follows data sets for Vault 2-1d 1ppb were duplicates and TR547- 4d 10 ppb is based on a single dataset
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Similar to the Tc Kd values the 127I Kd values are much lower than those of Pu and Np The amount of reducing slag present in each of the solids does not appear to have a drastic effect on the 127I Kd values In fact the initial (one day) Aged Cement (0 slag) samples had a Kd almost two orders of magnitude above those with reducing slag The cause of this behavior is not known but it has been shown that iodate IO3
- the oxidized form of iodine sorbs more strongly than iodide I- to charged surfaces (Schwehr et al 2009 Yoshida et al 1992 Fukui et al 1996) It is possible that the slag is reducing the iodine to the I- form converting it to a species that is less likely to sorb to saltstone Additional work would be required to confirm the oxidation state of iodine when associated with saltstone
Figure 46 Iodine Kd Values under Oxidizing Conditions Iodine Kd values for various cementitious formulations measured after one-day equilibration (1d) and four-day equilibration (4d) under oxidizing conditions Total iodine concentrations in the systems were 100ppb 500 ppb and 1000 ppb as noted above Samples were prepared in triplicate and the error bars represent standard deviation of samples except as follows duplicates were used for dataset TR545- 1d 100ppb
42 Radionuclide Sorption to Vial Walls Under Oxidizing Conditions
Figure 47 shows the aqueous fractions found in the no-solids controls It provides a measure of the solubility of each radionuclide as well as examines the fraction of each radionuclide sorbed to the vial walls After one day only 25 of the Pu remained in solution and the concentration decreased even more after four days The loss of Pu from the aqueous phase may be due to sorption of Pu to the vial walls or precipitation of a Pu hydrous oxide solid (discussed with respect to Figure 49 below) Additional experiments would be required to examine the solubility of the Pu in high pH calcite saturated solutions
After one day about 80 of the Np remained in solution However the aqueous concentration in the initially 1-ppb solution was significantly reduced after four days Approximately 60 of the Np remained soluble in the initially 10-ppb solution Once again this drop could be due to sorption to the vial wall The Tc present after one day ranged from about 88 to about 95 and was virtually 100 after four days These values are consistent with internal standards used to monitor Tc detection performance on the ICP-MS Greater than 50 of the I remained in solution after the one-day and four-day equilibrations As shown in Figure 48 the standard deviation between the triplicate I control samples was
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quite large Additional control samples are required to understand the mechanism by which I is being lost from the aqueous phase in these samples
Figure 47 Plutonium Neptunium and Technetium Aqueous Fractions Fraction of Pu Np and Tc remaining in the aqueous phase for the No Solids controls after a one-day equilibration (1d) and four-day equilibration (4d) under oxidizing conditions The total concentration for each radionuclide 10 ppb as noted above Samples were prepared in triplicate and the error bars represent the standard deviation of the samples
Figure 48 Iodine Aqueous Fraction Iodine aqueous fraction for the no-solids controls after a one-day equilibration (1d) and four-day equilibration (4d) under oxidizing conditions The total concentration of iodine was 1000 ppb as noted above Samples were prepared in triplicate and the error bars represent the standard deviation of the samples
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As discussed above the loss of Np and Pu from the no-solids control (Figure 47) could be due to
precipitation of Np and Pu hydrous oxides or sorption to the vial walls To quantify the differences between these possible sinks the vials were washed as described in Section 36 The data in Figure 49 indicate that significant sorption of Np and Pu to the vial walls may occur When combining the mass of Np represented in Figure 47 and Figure 49 there is almost 100 mass recovery of the Np sorbed to the vial wall and the aqueous fraction measured Therefore no precipitation of Np is expected However because 100 recovery was not achieved for Pu a Pu hydrous oxide phase could be precipitating which was washed out of the vial during the cleaning procedure The data in Figure 47 represent the no-solids control samples where there was no solid phase present for Np or Pu to sorb to besides the vial walls However when a cementitious solid phase is present in the sample there will be competition between the vial walls and the cement for sorption of Np and Pu Based on the affinity of metals for metal oxide surfaces as opposed to the polypropylene surface and the much higher surface site density expected for the cementitious samples it is assumed that the cementitious samples will out-compete the vial walls for sorption sites This thesis was tested by taking one of the triplicate samples from each sorption experiment with a solid phase present removing the solid phase from the tubes and leaching any sorbed Np and Pu from the tubes with acid as described in Section 36 Figure 410 and Figure 411 show that although some of the Pu and Np sorbed to the vial walls of the samples this amount accounted for less than 2 in all samples Therefore sorption of Np and Pu to the vial walls does not appear to be a significant factor in experiments where the solid phase is present Note these results do not discount the possibility that Pu hydrous oxide precipitates were forming in both the no-solid control experiments and experiments with cement formulations present Based on the observation of a constant aqueous phase concentration of Pu regardless of the initial Pu concentration the presence of a solubility limiting Pu phase cannot be discounted based on these data Further experiments examining the solubility of Pu in high pH calcite saturated solutions are required
Like Pu Np shows little affinity for the vial walls in the presence of a solid phase In each case tested there was significantly less than 1 of the total Np sorbed to the vial walls This behavior is consistent with the ~100 mass balance on Np achieve in the solid-free controls The majority of Np remained soluble in the solid-free control experiments Therefore it is expected that sorption of Np to the vial walls was the primary reason for the loss of Np from the aqueous phase in the no-solids systems rather than precipitation of a Np solid phase similar to the process discussed for Pu above This assumption is based on the relative solubility of Np(V) as compared with Pu(IV)
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Figure 49 Percent Pu and Np sorbed to vial walls of the no solids controls after the aqueous phases were discarded and the vials were washed Both the 10 ppb and 1 ppb datasets were prepared in triplicate and the error bars show the standard deviation
Figure 410 Percent Pu sorbed to vial walls after the solids and aqueous phases were removed and the vials were washed The graph illustrates one sample from each of the 1 ppb 5 ppb and 10 ppb systems Therefore no error bars are present
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Figure 411 Percent Np sorbed to vial walls after the solids and aqueous phases were removed and the vials were washed The graph illustrates one sample from each of the 1 ppb 5 ppb and 10 ppb systems Therefore no error bars are present
43 Radionuclide Sorption to Cementitious Formulations under Reducing Conditions
Similar to the Pu Kd values under oxidizing conditions Pu Kd values ranged from 104 to gt105 under reducing conditions (Figure 412) Also similar to the results under oxidizing conditions the Kd increases with increasing initial Pu concentration Again this behavior is indicative of the aqueous phase concentration of Pu being controlled by solubility of Pu rather than by sorption In each case the samples appeared to reach steady state within 24 hours This equilibration is evident because the Kd values after one day and four days are very similar Also it appears that the amount of reducing slag does not make a significant difference in the Kd value In fact the TR547 solid consists of 45 reducing grout but produces approximately the same Kd values of the aged cement which does not have any reducing grout Each of these Kd values are higher than the TR545 which is 90 reducing grout These findings are in agreement with those conducted by Allard et al (1984) and Hoglund et al (1985) who reported that concrete containing reducing agents (slag similar to that used in our study) did not have greater Pu Kd values than those that did not contain slag
Similar aqueous concentrations of Pu were observed regardless of the solid phase present Figure 36 shows the average aqueous phase concentrations measured after one day and four days for all solids As stated above triplicate samples were prepared for each solid phase and each initial concentration Therefore each of the reported solubility values in Figure 412 is an average of up to nine measurements of the Pu aqueous concentrations Using the highest reported value with the expected maximum error (00045 ppb for solid Vault 2) the maximum expected aqueous concentration of Pu in the pore water associated with the cementitious formulations will be approximately 2 x 10-11 molL (calculated from Equation 31) This value is on the same order as the solubility of Pu hydrous oxide solid phases (Neck and Kim 2001) A best value would be 10-12 molL
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Figure 412 Pu Kd Values under Reducing Conditions Plutonium Kd values for various cementitious formulations measured after one-day equilibration (1d) and four-day equilibration (4d) under reducing conditions Total plutonium concentrations in each system were 1ppb 5 ppb and 10 ppb Samples prepared in triplicate and error bars represent standard deviation
Figure 413 Average Solubility of Plutonium under Reducing Conditions Plutonium solubility for various cementitious formulations measured after one-day equilibration (1d) and four-day equilibration (4d) under reducing conditions Total plutonium concentrations in each system were 1ppb 5 ppb and 10 ppb as noted Samples prepared in triplicate and an average of all samples (9) was used to determine average solubility The error bars represent standard deviation of samples
The Np Kd values reported in Figure 414 obtained under reducing conditions are very similar to
those obtained under oxidizing conditions In each case the samples appeared to reach steady state within 24 hours This equilibration is evident because the Kd values between the one-day and fourndashday equilibrations are similar As was the case with Pu the amount of slag present in each solid does not
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seem to have a significant effect on the Kd values Again the aged cement with no slag has as high a Kd as the TR545 with 90 reducing slag
Similar aqueous concentrations of Np were observed regardless of the solid phase present Figure 314 shows the average aqueous phase concentrations measured after one day and four days for all solids All Kd values were gt 105 mLg which is considerably larger than those reported by Kaplan and Coates (2007) who reported Np Kd values to 1300 to 1600 mLg This difference can be attributed to two important experimental differences 1) the experiment was designed to permit larger Kd values to be measured (eg solid to liquid ratios and spike concentrations) and more importantly 2) a more sensitive analytical method ICP-MS was used instead of conventional low-energy gamma spectroscopy or liquid scintillation counting (LSC) analysis As stated above triplicate samples were prepared for each solid phase and each initial concentration Therefore each of the reported solubility values in Figure 415 is an average of up to nine measurements Using the highest reported value (to provide the most conservative most soluble values) with the expected maximum error (00045 ppb for solid TR545) the maximum expected aqueous concentration of Np in the pore water associated with the cementitious formulations will be approximately 2 x 10-11 molL A best value taking into consideration the less-than values which are depicted in Figure 414 as running off the top of the plot would be 10-12 molL
Figure 414 Np Kd Values under Reducing Conditions Neptunium Kd values for various cementitious formulations measured after one-day equilibration (1d) and four-day equilibration (4d) under reducing conditions Total Np concentrations in each system were 1 ppb 5 ppb and 10 ppb Samples were prepared in triplicate and the error bars represent standard deviation Kd values limited to gt106 were at instrumental background
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Figure 415 Average Solubility of Neptunium under Reducing Conditions Neptunium solubility for various cementitious formulations measured after one day equilibration (1d) and four day equilibration (4d) under reducing conditions Total plutonium concentrations in each system were 1ppb 5 ppb and 10 ppb Samples prepared in triplicate and an average of all samples (9) was used to determine average solubility The error bars represent standard deviation
A plot of the Tc Kd values for each cementitious formulations under reducing conditions is shown
in Figure 416 (log y-axis) and Figure 417 (reduced scale linear y-axis) The Kd values for each of the initial Tc concentrations are relatively similar This behavior is consistent with the Kd expression However the increasing Kd values from the one-day to four-day day equilibrations for each solid indicate that steady state was not reached within one day and it is unclear whether steady state was reached after four days A possible explanation for this behavior is that Tc(VII) was being reduced to Tc(IV) in these systems due to the reducing conditions As Tc(VII) was reduced the Kd would increase based on the high affinity of Tc(IV) for solid phases This proposed mechanism was observed by Lukens et al (2005) using an SRS saltstone material similar but not identical to TR547 Using synchrotron X-ray absorption fine structure spectroscopy they observed over a 453 month period that Tc(VII) incorporated into SRS saltstone slowly converted to Tc(IV) and that the nearest neighbor was initially predominantly oxygen and eventually became predominantly sulfur (described as a Tc(IV) phase TcSx) Lacking in Lukens et al (2005) is quantification of the solubility of Tc This analysis still needs to be completed along with re-oxidation studies (ie what is the rate that reduced Tc reoxidizes under ambient natural saltstone conditions)
Unlike Np and Pu Tc Kd values changed with the amount of slag included in the formulation Tc Kd values noticeable increase as the amount of slag in the formulation increased TR547 (45 dry-wt- slag) Kd value is visibly higher than the Aged Cement and Vault 2 Kd values while the most reducing TR545 (90 dry wt- slag) Kd value is significantly higher than the others Following a similar trend the reduction capacity that is the total quantity of reductant in the saltstone on a mass basis (units of milli-equivalents of charge per g) of TR547 had slightly greater or equal reduction capacity to that of TR545 (Roberts and Kaplan 2009)
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Figure 416 Tc Kd Values under Reducing Conditions Tc Kd values for various cementitious formulations measured after one-day equilibration (1d) and four-day equilibration (4d) under reducing conditions Total Tc concentrations in each system were 1 ppb 5 ppb and 10 ppb Sample prepared in triplicate and error bars represent standard deviation except as follows TR547-1d 1 ppb is based on a single dataset and datasets Vault 2-1d 5 ppb Vault 2- 4d 1 ppb Aged Cement-1d 5 ppb and Aged Cement-4d 1 ppb are duplicates
Figure 417 Data from Figure 416 replotted on a reduced linear scale for easier viewing Each sample was prepared in triplicate except as follows TR547-1d 1 ppb is based on a single dataset Vault 2-1d 5 ppb Vault 2- 4d 1 ppb Aged Cement-1d 5 ppb and Aged Cement-4d 1 ppb are duplicate datasets
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The calculated Kd values for I sorption to cementitious samples under reducing conditions are shown in Figure 418 Before discussing the data it should be noted that spiked QAQC samples which were analyzed on the ICP-MS along with the samples used to generate the data in Figure 418 were off by an average of 195 with one outlier of approximately 40 This dataset did not include the use of internal standards as discussed in Section 31 above1 Due to a lack of an internal standard the iodine results presented in this report should be considered with a minimum error estimate of 20
The iodine Kd values under reducing conditions are different from those observed under oxidizing conditions Under oxidizing conditions it appears they are at a steady state by day one However under reducing conditions there is a noticeable difference between days one and four indicating steady state was not reached by day one and possibly not by day four Another interesting observation is that the Kd values are decreasing from day one to four A possible reason for this behavior may be due to redox chemistry of iodine in this system If iodine partially or entirely exists in the form as iodate (IO3
-) it is possible it could be reduced to iodide I- within the reducing cementitious system These two iodine species sorb differently iodate sorbing to minerals more strongly than iodide (Denham et al 2009 Schwehr et al 2009 Fukui et al 1996 Yoshida et al 1992) It is hypothesized that the reducing environment of the saltstone is sufficient to reduce iodate ions to the more weakly binding form of iodine iodide
This is one of the few datasets (along with Tc) in this study where there may be a difference between the various solids The degree of iodate reduction would be expected to increase as the slag content increases As mentioned above reduction of iodate to iodide should result in a decrease in sorption Therefore higher Kd values should be observed for solids with less slag such as the Aged Cement (0 dry wt- slag) and Vault 2 (17 dry wt- slag) This is generally the case in Figure 418 where the highest Kd values are reported for the Aged Cement and the lowest values are for solid TR547 However this trend does not hold completely where the saltstone sample containing 90 slag (TR545) has generally equal or higher Kd values than the saltstone containing 45 dry wt- slag (TR547)
1 Clemson University is presently investigating appropriate internal standards for iodine analyses for ICP-MS Of those tested rhenium and molybdenum have shown some promise
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Figure 418 Iodine Kd Values under Reducing Conditions I Kd Values for various cementitious formulations measured after one day equilibration (1d) and four day equilibration (4d) under reducing conditions Total iodine concentrations in each system were 100 ppb 500 ppb and 1000 ppb as noted Sample prepared in triplicate and error bars represent standard deviation of samples except as follows Vault 2-4 d 100 ppb is a single dataset while the datasets for Vault 2-1 d 100 ppb 4 d 1000 ppb TR545-4 d 1000 ppb 100 ppb TR547-4 d 1000 ppb 500 ppb 100 ppb and Aged Cement- 4 d 1000 ppb and 100 ppb are all based on duplicates
44 Radionuclide Sorption to Vial Walls under Reducing Conditions
The aqueous concentrations for Pu Np and Tc in the no solids controls are shown in Figure 419 The results are similar to those presented for experiments performed under oxidizing conditions above The 1 ppb Pu aqueous fraction is approximately three times greater than the 10 ppb fraction at day one This fraction decreases over time and by day four they are approximately equal when taking error into account This behavior is similar to the aqueous fraction under oxidizing conditions The 1 ppb Np aqueous fraction is significantly higher on both day one and day four than the aqueous fraction of the 10 ppb samples However each remained constant from day one to day four The 10 ppb aqueous fraction is twice as low as under oxidizing conditions which suggests either higher sorption to the vial walls or more precipitating out under the reducing conditions Like Pu and Np Tc shows a decrease from day one to day four especially for the 1 ppb samples The decrease in the 10 ppb sample is minimal and the aqueous fraction remains around 09 This value is slightly lower than that under oxidizing conditions
To examine the degree of sorption to the vial walls the tubes were washed again as performed for the experiments under oxidizing conditions above and similar results were found Ninety percent of the 1 ppb Pu sample was sorbed to the vial wall upon completion of the experiment which gives a 100 mass recovery when comparing this value to that found in Figure 419 However this result is not the case with the 10 ppb samples where approximately 75 of the mass remains unaccounted It is noteworthy that approximately 25 of the Pu from the 10 ppb solution sorbed to the vial walls under both oxidizing
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and reducing conditions Np follows the same trend as Pu while less than 005 of the Tc sorbed to the wall
Figure 419 Plutonium Neptunium and Technetium No-Solids Aqueous Fractions under Reducing Conditions Pu Np and Tc aqueous fractions of No Solids controls after a one-day equilibration (1d) and four-day equilibration (4 d) under reducing conditions Total concentration for each radionuclide was 1 ppb and 10 ppb Samples were prepared in triplicate and the error bars represent the standard deviation
Figure 420 Percent of Pu Np and Tc sorbed to the vial walls of the No Solids control samples under reducing conditions Each the 1 ppb and 10 ppb samples were prepared in triplicate and the error bars represent the standard deviations of triplicate samples
Under reducing conditions the fraction of I remaining in the aqueous phase was around 90 with
almost 100 mass recovery of the 100 ppb I after the four-day equilibration These graphs show that
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under reducing conditions there will only be a small fraction of I sorbing to the vial wall or coming out of solution This result is a much better mass recovery than under oxidizing conditions (Figure 48) which had a mass recovery of approximately 65 after four days This result is also consistent with the interpretation that there may be a iodine speciation change between the two redox treatments
Figure 421 Iodine No-Solids Aqueous Fractions under Reducing Conditions I aqueous fractions of No-Solids controls after a one-day equilibration (1d) and four-day equilibration (4d) under reducing conditions The total concentration for each system was 100 ppb and 1000 ppb Samples were prepared in triplicate and the error bars represent the standard deviation
50 Comparison of Radionuclide Sorption under Oxidizing and Reducing Conditions
In the following figures (Figure 51 through Figure 54) the data shown above has been replotted to allow comparison between the oxidizing and reducing conditions for each cementitious formulation General observations based on these data follow Vault 2 Observations (Figure 51)
bull Pu Kds are greater than 104 under both oxidizing and reducing conditions and Pu Kds are slightly lower under reducing conditions This could possibly be due to reduction of Pu(IV) to Pu(III) However no oxidation state analysis was performed in this work
bull Np Kds are generally greater than 104 under both oxidizing and reducing conditions Interestingly Np Kds are higher under reducing conditions by almost an order of magnitude This could possibly be due to reduction of Np(V) to Np(IV) However no oxidation state analysis was performed in this work
bull Regardless of the initial Np or Pu concentration similar aqueous phase concentrations of Np or Pu were observed in all samples This trend indicates that ldquosorptionrdquo of Np and Pu in these systems may be a combination of adsorption absorption and (co)precipitation processes
bull Tc appears to reach a steady state within four days under oxidizing conditions This behavior does not appear to be the case under reducing conditions After four days similar Kd values are reached under both oxidizing and reducing conditions It is unclear
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whether the Kd value of Tc will continue to increase under reducing conditions consistent with reduction of Tc(VII) to Tc(IV) The similarity in Kd values under both oxidizing and reducing conditions is an interesting observation and certainly warrants additional studies
bull I Kd values are similar under both oxidizing and reducing conditions However reducing condition systems may not be at steady state after four days while systems under oxidizing conditions appeared to reach a steady state The difference in rates may be due to reduction of iodate to iodine
bull For all isotopes examined the sorption behavior to each of the solid phases is very similar
TR545 and TR547 Observations (Figure 52 and Figure 53) bull Similar to the discussion above with respect to Vault 2 Pu Np and Tc all appear to reach
a steady state under oxidizing conditions and approach steady state slower under reducing conditions
bull Np and Pu Kd values are greater than 104 for all systems and time steps The aqueous phase concentrations of Np and Pu appear to be better described as a solubility in terms of the aqueous phase concentration of Np and Pu Similar aqueous phase concentrations of both Np and Pu were reached The data indicate that the initial Np and Pu concentration generally does not affect the aqueous phase concentration at an apparent steady state The presence of each solid phase appears to limit the aqueous phase concentration of both Np and Pu on the order of 10-11 molL
bull Tc shows significantly higher Kd values under reducing conditions versus oxidizing conditions
bull For all isotopes examined the sorption behavior to each of the solid phases is very similar
Aged Cement Observations (Figure 54) bull Pu appears to be close to steady state for each solid by day one with similar Kd values
reached on between day one and day four bull Np has a higher Kd under reducing conditions than oxidizing (105 under oxidizing
conditions and gt105 under reducing conditions) bull Neither set of Tc data was at steady state by day one and rates of sorptiondesorption
reactions appear to be different Tc Kds decrease from day one to four under oxidizing conditions but increase under reducing conditions
bull The Kd values for I under oxidizing conditions were considerably higher than those measured for I with any other solid Similar Kd values obtained for the same solids under reducing conditions indicate that the reported Kd values under oxidizing conditions appear to be suspect However analysis of the raw data gives no indication of an experimental artifact As discussed above these observations may be explained based upon the amount of slag contained within the solids which will affect the reducing capacity (ie No reducing slag is in the aged cement which could be reason the reduction of iodate to iodide (speculated in other samples) is not evident)
bull The difference in sorption behavior of iodine to the aged cement between oxidizing and reducing conditions also indicates that the reducing conditions of the solution may affect I redox behavior in addition to any reactivity expected in the solid phases
SRNL-STI-2009-00636 Revision 0
42
Figure 51 Comparison of Tc I Np and Pu sorption to Vault 2 solid under oxidizing and reducing conditions
SRNL-STI-2009-00636 Revision 0
43
Figure 52 Comparison of Tc I Np and Pu sorption to TR 545 solid under oxidizing and reducing conditions
SRNL-STI-2009-00636 Revision 0
44
Figure 53 Comparison of Tc I Np and Pu sorption to TR547 solid under oxidizing and reducing conditions
SRNL-STI-2009-00636 Revision 0
45
Figure 54 Comparison of Tc I Np and Pu sorption to Aged Cement under oxidizing and reducing conditions
SRNL-STI-2009-00636 Revision 0
46
60 Comparison of Radionuclide Sorption and Solubility under Oxidizing and Reducing Conditions
To further summarize the data the following tables provide either the average solubility
(for Np and Pu) or average Kd (for Tc and I) determined under both oxidizing and reducing conditions for each cementitious formulation Each table lists the average value standard deviation and the number of replicate samples used to calculate the reported values
The solubility of Pu in the presence of each solid under oxidizing and reducing conditions is shown in Table 61 (this is taken from experiments equilibrated for four days not one day) Under oxidizing conditions the apparent solubility values associated with the Aged Cement (0 dry wt- slag) Vault 2 (17 dry wt- slag) and TR547 (45 dry wt- slag) are all similar with only a slight increase in solubility as the amount of reducing slag increases There is a significant increase of almost an order of magnitude for the most reducing saltstone TR545 (90 dry wt- slag) However these samples also have a standard deviation on the same order of magnitude as the solubility itself which when taken into account brings the solubility back into the range of the others Under reducing conditions the apparent solubility values are slightly lower than under oxidizing conditions In this set of samples the Vault 2 saltstone with 10 dry wt- reducing slag had the highest apparent solubility but once again when considering the standard deviation the values are similar
Table 61 Comparison of plutonium apparent solubility values under oxidizing and reducing conditions
Table 62 lists the apparent solubility values of Np in the presence of each cementitious
formulation under both oxidizing and reducing conditions Under oxidizing conditions the cementitious formulation does not appear to have a dramatic effect on the solubility The apparent solubility values are similar to those of Pu under similar conditions except the Np standard deviations are much higher The high standard deviations are an analytical artifact since the measured concentrations were close to or at the detection limit of the ICP-MS There does appear to be a slight decrease in Np solubility under reducing conditions However the statistical significance of this decrease was not calculated
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47
Table 62 Comparison of neptunium apparent solubility values under oxidizing and reducing conditions
Unlike the apparent solubility values of Pu and Np the aqueousatmospheric conditions
and cementitious formulation seem to have an effect on the Tc Kd values (Table 63) Under oxidizing conditions there is not a discernible difference among the different cementitious formulations especially when taking the respective standard deviations into account However when experiments were run under reducing conditions the specific formulation had a noticeable effect The two saltstone samples with the least amount of reducing slag Aged Cement (0 dry-wt- slag) and Vault 2 (17 dry wt- slag) had Kd values which were similar to those observed under oxidizing conditions However the TR547 (45 dry-wt- slag) increased by almost an order of magnitude while the TR545 (90 dry wt- slag) increased by about three orders of magnitude Although the respective standard deviations are large the higher Kd values do appear to be significant
Table 63 Comparison of technetium Kd values under oxidizing and reducing conditions
Unlike Tc I does not seem to be as affected by cementitious formulation and redox status (Table 64) The only treatment (possible outlier) that does not follow this trend is the Aged Cement under oxidizing conditions This Kd value is higher than the others but also has a much higher standard deviation which when accounted for gives a value similar to the others All other treatments had near identical Kd values irrespective of solid phase or redox condition But again the Aged Cement data cannot be discounted at this time given the possibility of the influence that redox may have on iodine speciation and the strong influence I speciation has on sorption to cementitious materials
SRNL-STI-2009-00636 Revision 0
48
Table 64 Comparison of iodine Kd values under oxidizing and reducing conditions
71 Comparison with Previous Data The increased sensitivity of the ICP-MS over conventional low-energy gamma
spectroscopy or liquid scintillation counting (LSC) analysis allowed for much more accurate Kd values and apparent solubility values in this work than were previously obtainable Generally radioanalytical detection methods start with activities on the order of 103 to 104 counts per minute (cpm) and approach background levels of 1 to 5 cpm for strongly sorbing radionuclides Therefore the accuracy of the Kd value will be the difference in analytical sensitivity when the initial aqueous activity decreases by a factor of approximately 5000 (ie the aqueous activity drops from approximately 5000 cpm to the instrument background of 1 cpm following almost complete sorption) As a result the reported Kd values can only be reliably reported up for a Kd of 103 to 104 This constraint is believed to be the difference between the observed Kd values for 237Np of gt 105 observed in this work when compared with the Kd values between 3000 and 4000 reported by Kaplan et al (2008) A similar observation was made for Pu because 242Pu was used for ICP-MS analysis and 238Pu was used in the work of Kaplan et al (2008) This constrint may account for the different Kd value of gt104 reported in Kaplan et al (2008) compared with the value of gt105 observed in this work
In the case of Tc Kaplan et al (2008) reported a Kd of 023 mLg for Vault 2 under oxidizing conditions and 093 mLg under reducing conditions while the above experiment determined the Vault 2 Kd to be 505 mLg under oxidizing conditions and 557 mLg under reducing conditions Unlike the discrepancy in the Kd values for Np Pu and Tc between the above findings and those in Kaplan et al (2008) the reported Kd values for iodine are similar For Vault 2 Kaplan et al (2008) found 125I to have a Kd of 894 mLg under oxidizing conditions and 715 mLg under reducing conditions These values are similar to the Kd values of 766 mLg and 725 mLg observed under oxidizing and reducing conditions respectively in this work These findings appear to confirm the previously accepted Kd values of 0-10 mLg depending on the cementitious formulation
72 Suggested Future Work The above data demonstrate several areas that require further examination The
increasing Tc Kd values over time dataset suggest that steady state had not been achieved It would be beneficial to determine the amount of time required to reach steady state and allow determination of a more accurate Kd value (an assumption of the Kd construct is that it be measured at steady state) Also kinetic studies of both Tc and I are needed to better understand their respective interactions with the different cementitious formulations As for the I additional
SRNL-STI-2009-00636 Revision 0
49
tests should be performed to test the hypothesis that iodine may in part exist as iodate which may initially sorb to the saltstone then undergo reduction to iodine or iodide and then desorbs causing a decrease in Kd
A final area of future work is to examine the possible causes for the similar behavior of each cementitious formulation despite the different slag content This discrepancy is not only observed in the above experiments but also in Kaplan et al (2008) which is illustrated in Table 31 and by recent work in measurements of saltstone reduction capacity (Roberts and Kaplan 2009) The reduction capacity (units in milli-equivalentsg solid) equivalents of the Aged Cement with no slag is 855 plusmn 101 and adding 10 slag gives a reducing equivalent of 2398 plusmn 311 However increasing the slag content to 23 causes the reducing capacity to increase to 8218 plusmn 81 which is almost equivalent to the 8324 plusmn 49 of the 100 slag Understanding the chemistry behind the reducing capacity of each cementitious formulation will help to define what reactions are important for controlling radionuclide release from the saltstone
80 References Allard B L Eliasson S Hoglund and K Andersson 1984 ldquoSorption of Cs I and actinides in
concrete systemsrdquo SKB Technical Report SKBKBS TR-84-15 DKB Stockholm Sweden
Denham M D I Kaplan and C Yeager2009 ldquoGroundwater radioiodine Prevalence biogeochemistry and potential remedial approachesrdquo SRNL-STI-2009-00463 Savannah River National Laboratory Aiken SC
Dixon K L M A Phifer and J R Harbour 2008 ldquoFY09 PACA Maintenance Program Additional Saltstone Property Testingrdquo SRNL-L3100-2009-00019 Rev0 Savannah River National Laboratory Aiken SC
Fukui M Fujikawa Y and Satta N 1996 ldquoFactors affecting interaction of radioiodide and iodate species with soilrdquo Journal of Environmental Radioactivity 31 199-216
Hoglund S L Eliasson B Allard K Andersson and B Torstenfelt 1985 ldquoSorption of some fission products and actinides in concrete systemsrdquo Mat Res Soc Symp Proc 50 683-690
Kaplan D I 2007 Geochemical Data Package for Performance Assessment Calculations Related to the Savannah River Site WSRC-TR-2006-00004 Rev 1 Washington Savannah River Company Aiken SC
Kaplan D I and Coates J 2007 ldquoPartitioning of Dissolved Radionuclides to Concrete under Scenarios Appropriate for Tank Closure Performance Assessmentsrdquo WSRC-STI-2007-00640 Rev 0 Washington Savannah River Company Aiken SC 29808
Kaplan D I Roberts K Coates J Siegfried M Serkiz S 2008 ldquoSaltstone and concrete interactions with radionuclides Sorption (Kd) desorption and reduction capacity measurementsrdquo SRNS-STI-2008-00045 Savannah River National Laboratory Aiken SC 2008
SRNL-STI-2009-00636 Revision 0
50
Neck V and Kim J I 2001 ldquoSolubility and hydrolysis of tetravalent actinidesrdquo Radiochim Acta 89 1
Powell B A Fjeld R A Coates J T Kaplan D I Serkiz S M 2002 ldquoPlutonium Oxidation State Geochemistry in the SRS Subsurface Environmentrdquo WSRC-TR-2003-00035 Westinghouse Savannah River Company US DOE Savannah River Site Aiken SC
Roberts K A and D I Kaplan 2009 Reduction Capacity of Saltstone and Saltstone Componentsrdquo SRNL-STI-2009-00637 Rev0 Savannah River National Laboratory Aiken SC
Schwehr K A Santschi P H D I Kaplan C M Yeager and R Brinkmeyer 2009 ldquoOrgano-iodine formation in soils and aquifer sediments at ambient concentrationsrdquo Environ Sci Technol 437258-7264
Yoshida S Muramatsu Y and Uchida S 1992 ldquoStudies on the sorption of I-(iodide) and IO3-
(iodate) onto andosolsrdquo Water Air and Soil Pollution 63 321-329
SRNL-STI-2009-00636 Revision 0
51
90 Appendix A Data Tables of Radionuclide Sorption to Saltstone under Oxidizing Conditions
The following tables represent data collected for the no solids controls each saltstone and testing of radionuclide sorption to the vial walls The no solids controls tables include the concentration (ppb) of the radionuclide spiked into the sample along with the concentration of the radionuclide (ppb) measured in the aqueous phase after the given equilibration time The pH at the time the sample was taken is also recorded along with the fraction of the radionuclide which stayed in the aqueous phase The tables for the cementitious formulation data include the data above along with the addition of a Kd value The tables of the data for the radionuclides sorbed to the vial walls include the initial concentration (ppb) of the spike the concentration (ppb) of the radionuclide that had sorbed to the vial wall during the experiment and the percentage of the total concentration this represents Important Notes
BDL- Below Detection Limit lt01 denotes no notable sorption occurred
91 Data Tables for No Solid Controls
Table 91 Plutonium no solids control after one day
A 9264165178 402285E‐05 1181 434238E‐06 9980817 B 9352537276 0000110618 1183 118276E‐05 3616813 C 9363541597 705331E‐05 118 753273E‐06 5401186 D 0993110568 BDL 12 NA NA E 0977247222 300794E‐05 1199 307797E‐05 1280331 F 0962441315 BDL 1198 NA NA G 4059128499 BDL 1186 NA NA H 4065161486 705198E‐05 1188 173473E‐05 2380003 I 4116819691 0000110748 1189 269014E‐05 1555864
Table 920 TR545- neptunium after four days
Sample ID
Initial Aq Conc (ppb)
Equil Aq Conc (ppb) pH
Fraction Aq Kd
A 92641652 NA 1188 NA NA B 93525373 00001935 1185 2069E‐05 2067199C 93635416 4119E‐05 1185 44E‐06 9247818D 09931106 BDL 1197 NA NA E 09772472 BDL 12 NA NA F 09624413 00066817 1206 00069424 562421G 40591285 00003289 1196 8103E‐05 5148274H 40651615 00025316 1196 00006228 6625737I 41168197 00001018 1194 2474E‐05 1692126
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58
Table 921 TR545- technetium after one day
Sample ID
Initial Aq Conc (ppb)
Equil Aq Conc (ppb) pH Fraction Aq Kd
A 9655146069 820460082 1181 0849764546 8998984 B 9356176321 7703053505 1183 0823312135 1051242 C 9114122586 7978297395 118 0875377451 7062663 D 1042349157 0853053814 12 0818395456 9099556 E 0983206046 0871198263 1199 0886079033 5196709 F 0905148405 0803451372 1198 0887646013 5098696 G 4950156706 4275082341 1186 0863625658 7213934 H 4889067068 4173762594 1188 0853693053 7687519 I 4854463762 4147024058 1189 0854270268 7771045
A 1048950046 0002141023 1149 0000204111 2112281 B 1039943573 0001770549 1157 0000170254 2460487 C 1084651695 0001127533 1153 0000103953 4014918 D 1088686867 0001201087 1172 0001103244 3564524 E 1119673887 0000783288 1177 0000699568 5709897 F 1045722787 0000914861 1181 000087486 4495324 G 5387981131 0001444832 1169 0000268158 1494715 H 5412748988 0001143483 1169 0000211257 1965749 I 5373948758 00010003 1164 0000186139 2280472
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Table 926 TR547- plutonium after four days
Sample ID
Initial Aq Conc (ppb)
Equil Aq Conc (ppb) pH
Fraction Aq Kd
A 104895 NA 116 NA NA B 10399436 0001828 1165 00001758 2383132C 10846517 00010788 1164 9946E‐05 4196159D 10886869 00009131 1184 00008388 4689778E 11196739 00010624 1189 00009488 4208928F 10457228 00007967 1191 00007619 516258G 53879811 00007915 1173 00001469 2728993H 5412749 00008355 1175 00001544 2690641I 53739488 00006103 1174 00001136 3737892
Table 927 TR547- neptunium after one day
Sample ID
Initial Aq Conc (ppb)
Equil Aq Conc (ppb) pH Fraction Aq Kd
A 9589772032 0000454463 1149 473903E‐05 9116335 B 9293228768 0000260081 1157 27986E‐05 1499475 C 1008725504 0000302018 1153 299405E‐05 1397125 D 0952173007 000019177 1172 0000201403 1954603 E 0992224074 BDL NA NA F 0967815522 402137E‐05 1181 41551E‐05 9474699 G 4068405786 0000222282 1169 546361E‐05 7336986 H 409543171 0000531619 1169 0000129808 3199152 I 4017406611 0000410123 1164 0000102086 4157807
Table 928 TR547- neptunium after four days
Sample ID
Initial Aq Conc (ppb)
Equil Aq Conc (ppb) pH Fraction Aq Kd
A 9589772 NA 116 NA NA B 92932288 00002145 1165 2308E‐05 1818463C 10087255 00001628 1164 1614E‐05 2591215D 0952173 BDL 1184 NA NA E 09922241 BDL NA NA F 09678155 5107E‐05 1191 5277E‐05 7460375G 40684058 00001336 1173 3284E‐05 1220544H 40954317 8151E‐05 1175 199E‐05 2086795I 40174066 00001322 1174 3292E‐05 1289605
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Table 929 TR547- technetium after one day
Sample ID
Initial Aq Conc (ppb)
Equil Aq Conc (ppb) pH Fraction Aq Kd
A 9466799266 8233850788 1149 0869760788 8220086 B 9439556236 817653394 1157 0866198975 8165745 C 9383493063 8086024379 1153 0861728604 8430884 D 1061939876 0919992065 1172 0866331594 6241759 E 0991827343 0836511397 1177 0843404251 7590958 F 0971981155 0839862696 1181 0864073024 6354378 G 4883337077 414858839 1169 0849539633 7903986 H 4691440077 3996173112 1169 0851800949 8038249 I 486993937 4291285586 1164 0881178442 6558707
Table 930 TR547- technetium after four days
Sample ID
Initial Aq Conc (ppb)
Equil Aq Conc (ppb) pH
Fraction Aq Kd
A 94667993 NA 116 NA NA B 94395562 85812109 1165 09090693 5885474C 93834931 84622373 1164 09018217 6279204D 10619399 09580683 1184 09021869 4435663E 09918273 08881507 1189 08954691 4835506F 09719812 09036489 1191 0929698 3138862G 48833371 4490415 1173 09195382 4312104H 46914401 42054182 1175 08964024 5612948I 48699394 43843193 1174 09002821 5536503
Table 931 TR547- iodine after one day
Sample ID
Initial Aq Conc (ppb)
Equil Aq Conc (ppb) pH Fraction Aq Kd
A 9944920441 8813152965 1149 0886196427 738241 B 9956006121 8747156303 1157 0878580848 8007767 C 9822152291 8664470934 1153 0882135674 7988892 D 1002391846 9333490632 1172 0931121963 3368509 E 9918273427 6625075445 1177 0667966607 1551748 F 9918175056 8931364957 1181 0900504872 4773862 G 5166570628 4445386532 1169 0860413387 7961604 H 4847821413 410447427 1169 084666367 8664303 I 4850381381 4266693706 1164 0879661489 6413801
100 Appendix B Data Tables of Radionuclide Sorption to Saltstone Under Reducing Conditions
The following tables represent data collected for the no solids controls each cementitious solid and testing of radionuclide sorption to the vial walls The no solids controls tables include the concentration (ppb) of the radionuclide spiked into the sample along with the concentration of the radionuclide (ppb) measured in the aqueous phase after the given equilibration time The pH at the time the sample was taken is also recorded along with the fraction of the radionuclide which stayed in the aqueous phase The tables for the cementitious solidsrsquo data include the data above along with the addition of a Kd value The tables of the data for the radionuclides sorbed to the vial walls include the initial concentration (ppb) of the spike the concentration (ppb) of the radionuclide that had sorbed to the vial wall during the experiment and the percentage of the total concentration this represents Important Notes
BDL= Below Detection Limit lt01 denotes no notable sorption occurred
101 Data Tables for No-Solid Controls
Table 101 Plutonium no solids control after one day
A 9405892 0007019 111 0000746258 5681206 B 9602498 0003294 1117 0000342992 123554 C 9630619 0002936 1114 0000304893 1396318 D 4945396 0001795 113 0000363011 1171688 E 4964945 0001373 1131 0000276484 1493015 F 4441601 0001516 113 0000341219 1389674 G 1079602 0001109 1142 0001027508 4215519 H 1031512 0000883 1143 0000855983 4820576 I 0939294 0000978 1143 0001040992 4550255
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Table 1011 Vault 2- neptunium after one day
Sample ID Initial Aq Conc (ppb)
Equil Aq Conc (ppb) pH Fraction Aq
A 9425042625 0001709054 1105 0000181331 B 9611386476 0001184125 1110 00001232 C 9579553607 0001155517 1104 0000120623 D 4974000414 0000672325 1125 0000135168 E 4916731623 0000675371 1128 0000137362 F 4373142817 0000570681 1120 0000130497 G 0943366414 0000389738 1129 0000413136 H 1011745587 0000565648 1132 0000559081 I 0865252712 0000379545 1133 0000438653
A 8849444124 0000306309 1150 346133E‐05 1289533 B 8447823057 0000150131 1155 177715E‐05 2711019 C 8590597085 0000199185 1153 231864E‐05 2044057 D 4491250244 517162E‐05 1156 115149E‐05 4020064 E 4391894479 204591E‐05 1158 465838E‐06 9846089 F 4210703646 204376E‐05 1158 485374E‐06 9816203 G 086381524 522216E‐06 1160 604546E‐06 7577764 H 0870501884 BDL 1160 NA NA I 0861953838 BDL 1162 NA NA
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79
Table 1036 Aged cement- neptunium after four days
Sample ID
Initial Aq Conc (ppb)
Equil Aq Conc (ppb) pH Fraction Aq Kd
A 8849444 0000131 1145 148418E‐05 3007445B 8447823 0000111 1146 131529E‐05 3662996C 8590597 656E‐05 1146 76328E‐06 6209405D 449125 BDL 1155 NA NA E 4391894 BDL 1156 NA NA F 4210704 BDL 1155 NA NA G 0863815 BDL 1165 NA NA H 0870502 BDL 1162 NA NA I 0861954 BDL 1164 NA NA
Table 1037 Aged cement- technetium after one day
Sample ID
Initial Aq Conc (ppb)
Equil Aq Conc (ppb) pH Fraction Aq Kd
A 8426518355 833290075 1150 098889012 0476492 B 8638001423 7823321167 1155 0905686487 4413063 C 9323317745 925927516 1153 0993130923 0294664 D 442651005 4300859603 1156 0971614106 1242837 E 4426849405 4336992073 1158 0979701742 0855315 F 3929483125 3938204338 1158 100221943 lt01 G 0817864386 081693181 1160 0998859743 0049487 H 0878958929 0792412508 1160 0901535306 4510199 I 0772205665 0871436364 1162 1128502941 lt01
Table 1038 Aged cement- technetium after four days
110 Appendix C Dixon et al (2009) FY09 PACA Maintenance Program Additional Saltstone Property Testing SRNL L3100-2009-00019 Rev 0
SRNL-STI-2009-00636 Revision 0
83
SRNL L3100-2009-00019 Rev 0
December 16 2008
Keywords Performance Permeability Modulus
L B Romanowski
Waste Determinations From K L Dixon M A Phifer and J R Harbour
FY09 PACA Maintenance Program Additional Saltstone Property Testing
BACKGROUND
Additional tests have been identified for measurement of important hydraulic and physical properties of saltstone The initial phase of this work [1] was completed last year and the results were detailed in an internal report [2] The proposed testing for FY09 includes measurement of saturated hydraulic conductivity porosity bulk density particle density water retention and Youngrsquos modulus of simulated Saltstone grouts For completeness the bleed volumes and gel times for each mix will also be measured
The testing will be based on a projected salt solution composition for the ARPMCU stream that will be fed to the Saltstone Production Facility over the next few years The scope for FY09 will include testing to determine the impact of (1) admixtures (2) organics (3) wcm ratio (4) aluminate concentration and (5) temperature of curing on the hydraulic properties of saltstone mixes Samples of selected batches prepared as part of this task will be provided to Dan Kaplan for measurement of Kd through leaching tests The eleven mixes that will be batched and tested are detailed in Table 1
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84
Table 1 The Eleven Mixes That will be Batched and Tested
BFS is Blast Furnace Slag FA is Fly Ash and PC is Portland Cement
TEST DETAILS
Test 1 Control (Mix 1)
A control mix will be based on the baseline mix modified by exclusion of the Class F fly ash Consequently the cementitious materials premix will be a mixture of 90 blast furnace slag and 10 portland cement The degree of reaction will be much greater than with the normal premix and therefore should result in a lower porosity and a lower permeability This bounding test at 060 wcm ratio is expected to yield a hydraulic conductivity at or below the detection limit for the Mactec permeameter measurement system Therefore this test should demonstrate the lowest level of detection of the Mactec system as well as show a resolvable difference between measurements of the control mix and the control mix with the normal premix composition
Test 2 ndashImpact of Admixtures (Mixes 2 and 3)
Recent saltstone batches have required both a set retarder (Daratard 17) and an antifoam agent (Q2) for processing of the saltstone Therefore the baseline mix will be prepared with and without nominal levels of these two admixtures to determine whether these admixtures appreciably affect the hydraulic and physical properties of saltstone at these nominal concentrations
Test 3ndashImpact of Organics (Mixes 2 and 4)
The solvent extraction process is expected to result in some carryover of organics [3]
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85
Consequently a test will be performed on the impact of Caustic Side Solvent Extraction (CSSX) organics at 100 microliters per 1600 gram batch The CSSX solvent consists of 075 M 1-(2233-tetrafluoropropoxy)-3-(4-sec-butylphenoxy)-2-propanol (Cs-7SB) and 0003 M tri-n-octylamine (TOA) in an Isoparreg L diluent Test 4ndashImpact of Combination of Admixtures and Organics (Mixes 2 5 10 and 11)
This test will determine the impact of a combination of admixtures (Test 2) and organics (Test 3) together in the mix vs the baseline case without admixtures and organics
Test 5ndash Impact of wcm Ratio (Mixes 2 6 and 7)
It is well known that decreasing the wcm ratio in a mix will improve permeability in normal portland cement water mixes This test will measure the variation in permeability for the case of the MCU salt solution at three different wcm ratios The initial selection of wcm ratios is 055 060 and 065 However if the mix at an as-batched 065 wcm ratio has significant bleed water and the resulting actual wcm ratio is close to 060 then the three ratios will be adjusted to provide a more evenly spaced set of values However the baseline mix at 060 will be included as one of the three mixes
Test 6 ndash Impact of Aluminate Concentration (Mixes 8 9 and 10)
The DWPF has modified its process flowsheet to include a caustic washing of HLW sludge to remove some of the aluminum from the HLW prior to vitrification The resulting aluminate stream will then be blended with tank 50 material and fed to the SPF This increased aluminate concentration in the salt solution has significant impact on heat of hydration and set times and consequently it is likely that it will also impact permeability Therefore a set of three samples will be made at wcm ratios of 055 060 and 065 (as in Test 3) with a higher level of aluminate (028 M) for testing
Test 7 ndash Impact of Increased Curing Temperature (Mix 11)
In an ongoing task there is evidence that Youngrsquos modulus (a performance indicator) [4] is reduced by increasing the curing temperature of the mix Since the vault temperature increases during curing as a result of the exothermic hydration reactions one of the baseline mixes with a combination of admixtures and organics will be cured at 60
o
C rather than the normal 22
o
C to determine the impact of curing temperature on the permeability
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SCHEDULE
The schedule for the task of batching and testing of the samples is provided in Table 2 This schedule is based on the fact that the cementitious materials will be available for the testing as needed
Table 2 Additional Saltstone Hydraulic and Physical Property Tests
Item Schedule Start Work 12108 Test Plan Complete 1509 Preparation of 1st set of Samples Complete 11909 90-Day Cure Period for 1st set of Samples Complete 42009
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87
SRNL-STI-2009-00636 Revision 0
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DISTRIBUTION Savannah River Site
A B Barnes 999-W Rm 336 H H Burns 999-W Rm 381 B T Butcher 773-43A Rm 212 A D Cozzi 999-W Rm 337 D A Crowley 773-43A Rm 216 M E Denham 773-42A Rm 218 J C Griffin 773-A Rm A-231 J R Harbour 999-W Rm 348 C A Langton 773-43A Rm 219 M H Layton 705-1C Rm 14 D I Kaplan (3 copies) 773-43A Rm 215 S L Marra 773A Rm A-230 A M Murray 773-A Rm 229 K A Roberts 773-43A Rm 225 T C Robinson 705-1C Rm 13 L B Romanowski 705-1C Rm 19 K H Rosenberger 705-1C Rm 16 F M Smith 705-1C Rm 24 RPA File (2 copies) 773-43A Rm 213
Clemson University Environmental Engineering and Earth Sciences 372 Computer Court LG Rich Environmental Laboratory Anderson SC 29625
Sorption of 99Tc 127I 237Np and 242Pu to two saltstone and two cementitious materials was examined Np and Pu sorbed very strongly to all four cementitious formulations and appeared to reach steady state within 24 h Based on the sorption behavior there were some indications that partial reduction of Pu(IV) to Pu(III) and Np(V) to Np(IV) occurs in these systems However the Kd values for both Pu and Np remain gt105 mLg throughout the experiments This value compares favorably with previously reported Kd values for Pu but is significantly higher than the previously reported value of 3000-4000 mLg for Np (Kaplan et al 2008)
In all experiments regardless of the total concentration of Np and Pu in the system a relatively constant aqueous phase concentration of both Np and Pu was observed Therefore it appears that the aqueous concentrations of Np and Pu are solubility controlled rather than sorption controlled The measured concentrations for Np and Pu ranged from 10-11 molL to 10-13 molL These values are consistent with precipitation of actinide hydrous oxide solid phases consequently these tests strongly suggest that solubility (as described by solubility constants) and not sorption (as described by Kd values) will controlling Np and Pu aqueous concentration near the Saltstone Disposal Facility
Sorption of both Tc and I do not appear to have reached steady state during the four day equilibration times used in these experiments Similar to Np and Pu surface mediated redox processes were affecting Tc and I sorption However this observation was based on changes in sorption behavior not direct determination of Tc or I oxidation states Calculated I Kd values of 766 and 725 mLg for simulated Vault 2 concrete under oxidizing and reducing conditions respectively in the present work compare favorably with values of 894 and 715 mLg under similar conditions reported by Kaplan et al (2008) Although it appears steady state was not reached in Tc systems conditional Kd values were calculated and were found to be a factor of ~5 higher than values previously reported by Kaplan et al (2008) The fraction of reducing slag within each saltstone formulation appears to have an effect on Tc sorption Tc Kd values under oxidizing conditions ranged from 275 to 508 mLg Saltstone formulations under reducing conditions had Kd values between 32 (0 dry wt- slag) and 4370 mLg (45 dry wt- slag) but the system had not achieved steady state conditions at the time of measurement thus greater sorption may likely occur under natural conditions Cementitious formulation did not influence Pu Np or I sorption These data support the following changes in the SRS ldquobest Kdrdquo geochemical data package used as input to SRS performance assessment calculations
Present data (d) This document Stage 1(c)
Young Stage 2 Medium
Stage 3 Old
Stage 1 Young
Stage 2 Medium
Stage 3 Old
Reducing Concrete (mLg) I 5 9 0 5 9 0
Np 4000 4000 3000 10-13 M(a) 10-13 M (a) 5000 Pu 10000 10000 1000 10-12 M (a) 10-12 M (a) 2000 Tc 5000 5000 5000 5000 5000 1000 (b)
Oxidizing Concrete (mLg) I 8 15 4 8 15 4
Np 1600 1600 250 10-12 M (a) 10-12 M (a) 5000 Pu 10000 10000 1000 10-12 M (a) 10-12 M (a) 2000 Tc 08 08 05 08 08 05
(a) Apparent solubility (units = M = molL) Below this concentration Kd value of 10000 mLg is to be used (b) A decrease in Tc Kd values with respect to previous values will be used because of the observation that Tc(IV) oxidizes readily under SRS conditions to Tc(VII) (c) Stages 1 2 and 3 are conceptually based on mineral composition changes The 1st 2n and 3rd stages are expected to last 50 500 and 7000 pore volumes respectively A 2-ft slab of cement may be expected to last 740 yr in the 1st stage 7400 yr in the 2nd and 103600 yr in the 3rd stage (d) Kaplan (2007) Kaplan and Coates (2008) and Kaplan et al 2008
31 Preparation of ICP-MS Standards Stock Solutions and Working Solutions 15 311 242Pu 15 312 237Np 16 313 99Tc 17 314 127I 18 315 Cementitious Materials Selected for Experiments 19
32 ICP-MS Detection Limits 20 33 Experimental Methods 20 34 Experimental Protocol for Sorption Experiments under Aerobic Conditions 21 35 Experimental Protocol for Sorption Experiments under Anerobic Conditions 22 36 Examination of Sorption to Vial Walls for Solids and No Solids Controls 23 37 Data Analysis 23
40 Results and Discussion 24 41 Radionuclide Sorption to Cementitious Formulations under Oxidizing Conditions 24 42 Radionuclide Sorption to Vial Walls Under Oxidizing Conditions 28 43 Radionuclide Sorption to Cementitious Formulations under Reducing Conditions 32 44 Radionuclide Sorption to Vial Walls under Reducing Conditions 38
50 Comparison of Radionuclide Sorption under Oxidizing and Reducing Conditions 40 60 Comparison of Radionuclide Sorption and Solubility under Oxidizing and Reducing Conditions46 70 Summary and Recommendations for Future Work 48
71 Comparison with Previous Data 48 72 Suggested Future Work 48
80 References 49 90 Appendix A Data Tables of Radionuclide Sorption to Saltstone under Oxidizing Conditions 51
91 Data Tables for No Solid Controls 51 92 Data Tables for Vault 2 54 93 Data tables for saltstone TR545 57 94 Data Tables for Saltstone TR547 59
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95 Data Tables for Aged Cement 62 96 Data Tables for Sorption to Vial Walls 65
100 Appendix B Data Tables of Radionuclide Sorption to Saltstone Under Reducing Conditions 66 101 Data Tables for No-Solid Controls 66 102 Data Tables for Vault 2 69 103 Data Tables for TR545 72 104 Data Tables for TR547 75 105 Data Tables for Aged Cement 78 106 Data Tables for Sorption to Vial Walls 80
110 Appendix C Dixon et al (2009) FY09 PACA Maintenance Program Additional Saltstone
Property Testing SRNL L3100-2009-00019 Rev 0 82
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LIST OF TABLES
Table 31 Characteristics of saltstone formulations used in this work Kaplan et al (2008) 19
Table 32 Detection limits for each isotope based on representative calibration curves generated in PlasmaLab software associated with the ICP-MS 20
Table 33 Experimental Matrix of Sorption Experiments under Aerobic Conditions 22
Table 61 Comparison of plutonium apparent solubility values under oxidizing and reducing conditions 46
Table 62 Comparison of neptunium apparent solubility values under oxidizing and reducing conditions 47
Table 63 Comparison of technetium Kd values under oxidizing and reducing conditions 47
Table 64 Comparison of iodine Kd values under oxidizing and reducing conditions 48
Table 91 Plutonium no solids control after one day 51
Table 92 Plutonium no solids control after four days 51
Table 93 Neptunium no solids control after one day 52
Table 94 Neptunium no solids control after four days 52
Table 95 Technetium no solids control after one day 52
Table 96 Technetium no solids control after four days 53
Table 97 Iodine no solids control after one day 53
Table 98 Iodine no solids control after four days 53
Table 99 Vault 2- plutonium after one day 54
Table 910 Vault 2- plutonium after four days 54
Table 911 Vault 2- neptunium after one day 54
Table 912 Vault 2- neptunium after four days 55
Table 913 Vault 2- technetium after one day 55
Table 914 Vault 2- technetium after four days 55
Table 915 Vault 2- iodine after one day 56
Table 916 Vault 2- iodine after four days 56
Table 917 TR545- plutonium after one day 56
Table 918 TR545- plutonium after four days 57
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Table 919 TR545- neptunium after one day 57
Table 920 TR545- neptunium after four days 57
Table 921 TR545- technetium after one day 58
Table 922 TR545- technetium after four days 58
Table 923 TR545- iodine after one day 58
Table 924 TR545- iodine after four days 59
Table 925 TR547- plutonium after one day 59
Table 926 TR547- plutonium after four days 60
Table 927 TR547- neptunium after one day 60
Table 928 TR547- neptunium after four days 60
Table 929 TR547- technetium after one day 61
Table 930 TR547- technetium after four days 61
Table 931 TR547- iodine after one day 61
Table 932 TR547- iodine after four days 62
Table 933 Aged cement- plutonium after one day 62
Table 934 Aged cement- plutonium after four days 63
Table 935 Aged cement- neptunium after one day 63
Table 936 Aged cement- neptunium after four days 63
Table 937 Aged cement- technetium after one day 64
Table 938 Aged cement- technetium after four days 64
Table 939 Aged cement- iodine after one day 64
Table 940 Aged cement- iodine after four days 65
Table 941 Plutonium sorbed to vial wall in no solids control 65
Table 942 Neptunium sorbed to vial wall in no solids control 65
Table 101 Plutonium no solids control after one day 66
Table 102 Plutonium no solids control after four days 67
Table 103 Neptunium no solids control after one day 67
Table 104 Neptunium no solids control after four days 67
Table 105 Technetium no solids control after one day 67
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Table 106 Technetium no solids control after four days 68
Table 107 Iodine no solids control after one day 68
Table 108 Iodine no solids control after four days 68
Table 109 Vault 2- plutonium after one day 69
Table 1010 Vault 2- plutonium after four days 69
Table 1011 Vault 2- neptunium after one day 70
Table 1012 Vault 2- neptunium after four days 70
Table 1013 Vault 2- technetium after one day 70
Table 1014 Vault 2- technetium after four days 71
Table 1015 Vault 2- iodine after one day 71
Table 1016 Vault 2- iodine after four days 71
Table 1017 TR545- plutonium after one day 72
Table 1018 TR545- plutonium after four days 72
Table 1019 TR545- neptunium after one day 73
Table 1020 TR545- neptunium after four days 73
Table 1021 TR545- technetium after one day 73
Table 1022 TR545- technetium after four days 74
Table 1023 TR545- iodine after one day 74
Table 1024 TR545- iodine after four days 74
Table 1025 TR547- plutonium after one day 75
Table 1026 TR547- plutonium after four days 75
Table 1027 TR547- neptunium after one day 76
Table 1028 TR547- neptunium after four days 76
Table 1029 TR547- technetium after one day 76
Table 1030 TR547- technetium after four days 77
Table 1031 TR547- iodine after one day 77
Table 1032 TR547- iodine after four days 77
Table 1033 Aged cement- plutonium after one day 78
Table 1034 Aged cement- plutonium after four days 78
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Table 1035 Aged cement- neptunium after one day 78
Table 1036 Aged cement- neptunium after four days 79
Table 1037 Aged cement- technetium after one day 79
Table 1038 Aged cement- technetium after four days 79
Table 1039 Aged cement- iodine after one day 80
Table 1040 Aged cement- iodine after four days 80
Table 1041 Plutonium sorbed to vial wall in no solids control 80
Table 1042 Neptunium sorbed to vial wall in no solids control 81
Table 1043 Technetium sorbed to vial wall in no solids control 81
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LIST OF FIGURES
Figure 31 Screen capture of a typical 242Pu calibration curve using Thermo PlasmaLab software to control the data collection and analysis R2=0999872 Intercept Conc (Detection Limit) = 0000044 ppb 16
Figure 32 Screen capture of a typical 237Np calibration curve using Thermo PlasmaLab software to control the data collection and analysis R2=0999981 Intercept Conc (Detection Limit) = 0000026 ppb 17
Figure 33 Screen capture of a typical 99Tc calibration curve using Thermo PlasmaLab software to control the data collection and analysis R2=0999984 Intercept Conc (Detection Limit) = 0000013 ppb 18
Figure 34 Screen capture of a typical 127I calibration curve using Thermo PlasmaLab software to control the data collection and analysis R2=0999991 Intercept Conc (Detection Limit) = 024 ppb 19
Figure 41 Plutonium Kd Values under Oxidizing Conditions Plutonium Kd values for various saltstone formulations measured after one-day equilibration (1d) and four-day equilibration (4d under oxidizing conditions Total plutonium concentrations in each system were 1 ppb 5 ppb and 10 ppb Sample prepared in triplicate and error bars represent standard deviation of samples except as follows value for dataset TR547-4d 10 ppb is reported based on duplicate samples 25
Figure 42 Plutonium solubility for various saltstone formulations measured after one-day equilibration (1d) and four-day equilibration (4d) under oxidizing conditions Total plutonium concentrations in each system were 1 ppb 5 ppb and 10 ppb as noted Samples prepared in triplicate and an average of all samples (9) was used to determine average solubility The error bars represent standard deviation of samples 25
Figure 43 Neptunium Kd values under oxidizing conditions Neptunium Kd values for various saltstone formulations measured after one-day equilibration (1d) and four-day equilibration (4d) under oxidizing conditions Total plutonium concentrations in each system were 1 ppb 5 ppb and 10 ppb as noted Samples prepared in triplicate and error bars represent standard deviation of samples except as follows value for datasets TR545-1d 1ppb TR545-4d 1 ppb TR547 4d 1 ppb TR545-4d 10 ppb TR547-1d 1ppb TR547-4d 10 ppb are reported based on a single sample and for dataset TR545-1d 5ppb is reported based on duplicate samples Kd values limited to gt106 were at instrumental background 26
Figure 44 Average solubility of Np under oxidizing conditions Neptunium solubility for various saltstone formulations measured after one-day equilibration (1d) and four-day equilibration (4d) under oxidizing conditions Total Np concentrations in each system were 1 ppb 5 ppb and 10 ppb Samples prepared in triplicate and an average of all samples (9) was used to determine average solubility except as follows TR545-1d is based on 6 samples TR545- 4d on 5 samples TR547-1d on 7 samples and TR547- 4d on 5 samples The error bars represent standard deviation 27
Figure 45 Technetium Kd values under oxidizing conditions Tc Kd values for various saltstone formulations measured after one-day equilibration (1d) and four-day equilibration (4d) under oxidizing conditions Total Tc concentrations in each system were 1 ppb 5 ppb and 10 ppb as noted above Samples were prepared in triplicate and the error bars represent standard deviation
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of samples except as follows data sets for Vault 2-1d 1ppb were duplicates and TR547- 4d 10 ppb is based on a single dataset 27
Figure 46 Iodine Kd Values under Oxidizing Conditions Iodine Kd values for various cementitious formulations measured after one-day equilibration (1d) and four-day equilibration (4d) under oxidizing conditions Total iodine concentrations in the systems were 100ppb 500 ppb and 1000 ppb as noted above Samples were prepared in triplicate and the error bars represent standard deviation of samples except as follows duplicates were used for dataset TR545- 1d 100ppb 28
Figure 47 Plutonium Neptunium and Technetium Aqueous Fractions Fraction of Pu Np and Tc remaining in the aqueous phase for the No Solids controls after a one-day equilibration (1d) and four-day equilibration (4d) under oxidizing conditions The total concentration for each radionuclide 10 ppb as noted above Samples were prepared in triplicate and the error bars represent the standard deviation of the samples 29
Figure 48 Iodine Aqueous Fraction Iodine aqueous fraction for the no-solids controls after a one-day equilibration (1d) and four-day equilibration (4d) under oxidizing conditions The total concentration of iodine was 1000 ppb as noted above Samples were prepared in triplicate and the error bars represent the standard deviation of the samples 29
Figure 49 Percent Pu and Np sorbed to vial walls of the no solids controls after the aqueous phases were discarded and the vials were washed Both the 10 ppb (blueleft) and 1 ppb (redright)) datasets were prepared in triplicate and the error bars show the standard deviation 31
Figure 410 Percent Pu sorbed to vial walls after the solids and aqueous phases were removed and the vials were washed The graph illustrates one sample from each of the 1 ppb (redleft) 5 ppb (greenmiddle) and 10 ppb (blueright) systems Therefore no error bars are present 31
Figure 411 Percent Np sorbed to vial walls after the solids and aqueous phases were removed and the vials were washed The graph illustrates one sample from each of the 1 ppb (redleft) 5 ppb (greenmiddle) and 10 ppb (blueright) systems Therefore no error bars are present 32
Figure 412 Pu Kd Values under Reducing Conditions Plutonium Kd values for various cementitious formulations measured after one-day equilibration (1d) and four-day equilibration (4d) under reducing conditions Total plutonium concentrations in each system were 1ppb 5 ppb and 10 ppb Samples prepared in triplicate and error bars represent standard deviation 33
Figure 413 Average Solubility of Plutonium under Reducing Conditions Plutonium solubility for various cementitious formulations measured after one-day equilibration (1d) and four-day equilibration (4d) under reducing conditions Total plutonium concentrations in each system were 1ppb 5 ppb and 10 ppb as noted Samples prepared in triplicate and an average of all samples (9) was used to determine average solubility The error bars represent standard deviation of samples 33
Figure 414 Np Kd Values under Reducing Conditions Neptunium Kd values for various cementitious formulations measured after one-day equilibration (1d) and four-day equilibration (4d) under reducing conditions Total Np concentrations in each system were 1 ppb 5 ppb and 10 ppb Samples were prepared in triplicate and the error bars represent standard deviation Kd values limited to gt106 were at instrumental background 34
Figure 415 Average Solubility of Neptunium under Reducing Conditions Neptunium solubility for various cementitious formulations measured after one day equilibration (1d) and four day
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equilibration (4d) under reducing conditions Total plutonium concentrations in each system were 1ppb 5 ppb and 10 ppb Samples prepared in triplicate and an average of all samples (9) was used to determine average solubility The error bars represent standard deviation 35
Figure 416 Tc Kd Values under Reducing Conditions Tc Kd values for various cementitious formulations measured after one-day equilibration (1d) and four-day equilibration (4d) under reducing conditions Total Tc concentrations in each system were 1 ppb 5 ppb and 10 ppb Sample prepared in triplicate and error bars represent standard deviation except as follows TR547-1d 1 ppb is based on a single dataset and datasets Vault 2-1d 5 ppb Vault 2- 4d 1 ppb Aged Cement-1d 5 ppb and Aged Cement-4d 1 ppb are duplicates 36
Figure 417 Data from Figure 416 replotted on a reduced linear scale for easier viewing Each sample was prepared in triplicate except as follows TR547-1d 1 ppb is based on a single dataset Vault 2-1d 5 ppb Vault 2- 4d 1 ppb Aged Cement-1d 5 ppb and Aged Cement-4d 1 ppb are duplicate datasets 36
Figure 418 Iodine Kd Values under Reducing Conditions I Kd Values for various cementitious formulations measured after one day equilibration (1d) and four day equilibration (4d) under reducing conditions Total iodine concentrations in each system were 100 ppb 500 ppb and 1000 ppb as noted Sample prepared in triplicate and error bars represent standard deviation of samples except as follows Vault 2-4 d 100 ppb is a single dataset while the datasets for Vault 2-1 d 100 ppb 4 d 1000 ppb TR545-4 d 1000 ppb 100 ppb TR547-4 d 1000 ppb 500 ppb 100 ppb and Aged Cement- 4 d 1000 ppb and 100 ppb are all based on duplicates 38
Figure 419 Plutonium Neptunium and Technetium No-Solids Aqueous Fractions under Reducing Conditions Pu Np and Tc aqueous fractions of No Solids controls after a one-day equilibration (1d) and four-day equilibration (4 d) under reducing conditions Total concentration for each radionuclide was 1 ppb and 10 ppb Samples were prepared in triplicate and the error bars represent the standard deviation 39
Figure 420 Percent of Pu Np and Tc sorbed to the vial walls of the No Solids control samples under reducing conditions Each the 1 ppb and 10 ppb samples were prepared in triplicate and the error bars represent the standard deviations of triplicate samples 39
Figure 421 Iodine No-Solids Aqueous Fractions under Reducing Conditions I aqueous fractions of No-Solids controls after a one-day equilibration (1d) and four-day equilibration (4d) under reducing conditions The total concentration for each system was 100 ppb and 1000 ppb Samples were prepared in triplicate and the error bars represent the standard deviation 40
Figure 51 Comparison of Tc I Np and Pu sorption to Vault 2 solid under oxidizing and reducing conditions 42
Figure 52 Comparison of Tc I Np and Pu sorption to TR 545 solid under oxidizing and reducing conditions 43
Figure 53 Comparison of Tc I Np and Pu sorption to TR547 solid under oxidizing and reducing conditions 44
Figure 54 Comparison of Tc I Np and Pu sorption to Aged Cement under oxidizing and reducing conditions 45
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LIST OF ABBREVIATIONS
DDI water Distilled deionized water ICP-MS Inductively coupled plasma ndash mass spectrometer
Kd Distribution coefficient LSC liquid scintillation counting NOM Natural organic matter PA Performance Assessment ppb parts per billion ppq parts per quadrillion QAQC Quality AssuranceQuality Control SA Special Analyses SRNL Savannah River National Laboratory SRS Savannah River Site
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10 Introduction Performance Assessments (PA) are risk calculations designed to determine (1) the maximum
amount of radioactivity that can be safely buried in a subsurface facility and (2) the potential human risk associated with disposing of radioactive waste in a subsurface facility Special Analyses (SAs) are similar to PAs except that they are designed to address specific issues related to PAs such as a new discovery since the PA was issued Commonly parameters describing the extent that a radionuclide interacts with solids at the source vadose zone and aquifer influence the extent of calculated human risk The two parameters that the SRS use to represent radionuclidesolid interactions are Kd and apparent solubility values together these parameters are referred to as sorption values Sorption values vary with radionuclides groundwater chemistry and the type of solid phase (and for cementitious materials by the age of the material during the calculation) In this work Kd and apparent solubility values are reported for 99Tc 127I 237Np and 242Pu sorption to various cementitious formulations
20 Objectives
The objectives of this work were to 1 Determine the influence of cementitious formulation on technetium (Tc) iodine (I) neptunium
(Np) and plutonium (Pu) sorption under oxidizing conditions The specific formulations that were evaluated included 1) an aged cement recovered from a 30-year old outdoor concrete pad on the SRS 2) Vault 2 concrete 3) TR545 saltstone and 4) TR547 saltstone (additional details are presented in Section 30 Materials and Methods)
2 Measure Tc I Np and Pu sorption to the cementitious formulations under reducing conditions
30 Materials and Methods
31 Preparation of ICP-MS Standards Stock Solutions and Working Solutions
311 242Pu
A National Institute of Standards and Technology Standard Reference Material (NIST SRM 434H) was used to prepare a stock 242Pu solution by dilution in 2 Aristar Optima HNO3 All volume additions were monitored gravimetrically This working solution was then used to make a set of 001 005 1 2 5 10 parts per billion (ppb) standards by dilution using 2 HNO3 Again all volume additions were monitored gravimetrically These standards were used to calibrate the Thermo Scientific X Series 2 inductively coupled plasma ndash mass spectrometer (ICP-MS) for quantification of 242Pu A representative calibration curve for 242Pu is shown in Figure 31 The instrument performance was monitored using 209Bi 232Th and 238U as internal standards The recovery of each sample during analysis was corrected based on the internal standard recovery The internal standard recoveries remained within standard quality assurancequality control QAQC protocols for the instrument (between 80 and 120)
A 242Pu stock solution was prepared by dissolving 1mg of Pu(NO3)4 obtained as a Certified Reference Material from New Brunswick Laboratory (CRM 130) This CRM is gt999 242Pu by atom percent The CRM was dissolved in 20mL of 8M HNO3 (Aristar Optima Grade) Because no chemicals or heat have been introduced to manipulate the Pu oxidation state it can be assumed that Pu(IV) is the predominant oxidation state in this stock solution A working solution to be used in spiking 242Pu experiments was prepared by diluting 25 mL of the CRM stock solution with 100 mL 10 M Aristar Optima HNO3 The concentration of 242Pu in this stock solution was determined using ICP-MS calibrated using the NIST SRM standards The concentration of Pu in this stock solution was 1065 ppb The total Pu
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concentration was also determined using liquid scintillation counting using the isotopic ratios reported for CRM 130 These compared favorably with the ICP-MS results but are reported here as a rigorous standardization because the isotopic ratios of CRM 130 have not yet been certified
Figure 31 Screen capture of a typical 242Pu calibration curve using Thermo PlasmaLab software to control the data collection and analysis R2=0999872 Intercept Conc (Detection Limit) = 0000044 ppb
312 237Np
A National Institute of Standards and Technology Standard Reference Material (NIST SRM 4341) was used to prepare a stock 237Np solution by dilution in 2 Aristar Optima HNO3 All volume additions were monitored gravimetrically This working solution was then used to make a set of 001 005 1 2 5 10 ppb standards by dilution using 2 HNO3 Again all volume additions were monitored gravimetrically These standards were used to calibrate the Thermo Scientific X Series 2 ICP-MS for quantification of 237Np A representative calibration curve for 237Np is shown in Figure 32 The instrument performance was monitored using 209Bi 232Th and 238U as internal standards The recovery of each sample during analysis was corrected based on the internal standard recovery The internal standard recoveries remained within standard QAQC protocols for the instrument (between 80 and 120)
A compiled 237Np stock solution from the Environmental Engineering and Earth Science (EEampES) inventory (primarily purchased from Isotope Products Valencia CA) was evaporated to dryness then the residue was brought up in approximately 5mL 80 M HNO3 Then 10 M hydroxylamine hydrochloride (NH2OHHCl EMD Chemicals ACS grade) and water were added to achieve a 3M HNO303M NH2OHHCl solution This solution was purified by extraction chromatography using Eichrom TEVA resin packed in a Bio-Rad poly-prep column The 3M HNO303 M NH2OHHCl neptunium solution was loaded on a 2 mL column and washed with 3 column volumes of 3 M HNO3 The Np(IV) was eluted with 002 M HCl + 02 M HF The effluent was evaporated to dryness then redissolved in 10 M HNO3 Additional 10 M HNO3 was added to maintain a approximately 10 mL then the solution was evaporated to incipient dryness and redissolved in a 50 mL of 10 M HNO3 An aliquot of the stock solution was evaporated to dryness on a stainless steel planchet and counted on the EGampG Ortec Alpha Spectrometer (Octete PC Detectors) No other alpha energies besides 237Np were observed The approximate concentration was determined using liquid scintillation counting and little 233Pa was observed The fuming in HNO3 as performed at the end of the purification procedure will drive Np to the soluble pentavalent state This is the stable oxidation state of Np under the experimental conditions Therefore experiments performed here can be assumed to be initially Np(V) The exact Np
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concentration in this solution was determined using ICP-MS calibrated with a NIST standard as discussed in section 312 below
A 237Np working solution (Working Solution 1) was created by pipetting an aliquot of the 237Np stock solution into a 100 mL Nalgene Teflon bottle and diluting with 2 BDH Aristar Ultra HNO3 to give a working solution concentration of 820 ppb All volumes were monitored gravimetrically Analysis on the ICP-MS calibrated against NIST Standards as described below gave a concentration of 820 ppb in Working Solution 1
Figure 32 Screen capture of a typical 237Np calibration curve using Thermo PlasmaLab software to control the data collection and analysis R2=0999981 Intercept Conc (Detection Limit) = 0000026 ppb
313 99Tc
A 99Tc working solution was prepared by diluting a stock solution of 99Tc (from the EEampES inventory purchased from Isotope Products Valencia CA) in distilled-deionized water (DDI Resistivity gt18 MΩcm) The oxidation state of Tc was not measured However based on the aqueous concentration in the DDI water solution Tc(VII) is the expected oxidation state The reduced Tc(IV) oxidation state would not be soluble under these conditions The expected concentration of 950 ppb based on the dilution was verified using liquid scintillation counting The 99Tc working solution was used to make 001 005 1 2 5 and 10 ppb standards by dilution using 2 HNO3 These standards were used to calibrate the Thermo Scientific X Series 2 ICP-MS for quantification of 99Tc A screen shot of a representative calibration curve is shown in Figure 33 The instrument performance was monitored by interpolating between 89Y and 115In internal standards The recovery of each sample during analysis was corrected based on the internal standard recovery The internal standard recoveries remained within standard QAQC protocols for the instrument (between 80 and 120)
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Figure 33 Screen capture of a typical 99Tc calibration curve using Thermo PlasmaLab software to control the data collection and analysis R2=0999984 Intercept Conc (Detection Limit) = 0000013 ppb
314 127I
A 100 microgmL iodate (IO3-) stock solution from High Purity Standards (Charleston SC) was used
to make 1 5 10 50 and 100 ppb standards by dilution using the ldquotraprdquo solution (discussed in Section 32 below) These standards were used to calibrate the Thermo Scientific X Series 2 ICP-MS for quantification of 127I A screen shot of a representative calibration curve is shown in Figure 34 The use of a reducing basic trap solution for iodine analysis limits the number of available internal standards that can be used to monitor ICP-MS instrument performance during iodine analysis Experiments are underway to identify acceptable internal standards However the data presented in this work did not use any internal standards prior to rigorous testing and analysis of representative standards As with the analyses for all isotopes (Tc I Np and Pu) spiked QAQC samples were frequently analyzed throughout the analysis as a check on instrument performance While these values cannot be used to correct individual samples in the same manner that the internal standards can they can be used to ensure accurate measurements of each isotope In almost all cases QAQC standards were within 10 of the expected value Because the average internal standard recovery ranges between 80 and 120 for the ICP-MS the iodine QAQC standard appears to be acceptable However a significant amount of ongoing work is testing various internal standards to improve the accuracy of iodine analysis using ICP-MS In one experiment (discussed in detail below) the QAQC standards deviated by an average value of 195 This will be specifically discussed below
Because experiments were performed with 127I concentrations up to 1000 ppb the 100 microgmL (ppm) stock iodate solution from High Purity Standards was used as the working solution
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Figure 34 Screen capture of a typical 127I calibration curve using Thermo PlasmaLab software to control the data collection and analysis R2=0999991 Intercept Conc (Detection Limit) = 024 ppb
315 Cementitious Materials Selected for Experiments There were four cementitious materials selected for this sorption study The first referred to as Aged Cement is a 30 year old sample that does not contain any reducing slag The aggregate from the Vault 2 cement had its aggregate removed prior to conducted tests in an effort to make subsamples more uniform This was necessary because some of the aggregate were larger than the 05 g subsamples used in individual sorption tests The Vault 2 cementitious material contained 17 dry wt- reducing slag on a dry weight basis before the water was added to the mix (Table 31) The TR547 and TR545 saltstone formulations contain 45 dry wt- and 90 dry wt- reducing slag respectively
Table 31 Characteristics of saltstone formulations used in this work Kaplan et al (2008)
Sample Percent Reducing Slag (dry wt-) (c)
Percent Portland Cement
(dry wt-) (c)
Percent Fly Ash
(dry wt-) (c)
Percent Aggregatesand ( dry wt-) (c)
Reducing Equivalents
(microeqg)
Aged Cement 0 10 45 45 855 plusmn 101(a)
Vault 2 Cement 17 10 45 0 178(b)
TR547 45 10 45 0 607(b) TR545 90 10 0 0 681(b) Blast furnace slag 100 0 0 0 819(b) (a) Kaplan et al (2008) (b) Roberts and Kaplan (2009) (c) All percentages of saltstone formulations are reported on a dry weight percentage basis that is the weight of the ingredients before water was added (d) Based on Table 8 in Dixon et al (2008 SRNL-STI-2008-00421) which shows the following quantity (lbscu yd) for saltstone Vault 2 Mix 1 concrete formulation 201 cement (1271 wt-) 268 slag (1695 wt-) 447 silica fume (283 wt-) 1563 fly ash (989 wt-) 911 fine sand (5762 wt-) The large aggregate was removed before the sorption tests were conducted The large aggregate accounted for 75 wt- of the original field sample not the sample used in these test before water was added to the mix TR547 is referred to as the Baseline by Dixon et al (2008) and is described in more detail in Appendix C (Mix 2) by Dixon et al (2008) (Control-BFSPC) and 1 (Baseline)
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TR545 saltstone contains 90 reducing slag and it is Mix 1 in Dixon et al (2008) and is described as
ldquoA control mix will be based on the baseline mix modified by exclusion of the Class F fly ash Consequently the cementitious materials premix will be a mixture of 90 blast furnace slag and 10 Portland cement The degree of reaction will be much greater than with the normal premix and therefore should result in a lower porosity and a lower permeability This bounding test at 060 wcm ratio is expected to yield a hydraulic conductivity at or below the detection limit for the Mactec permeameter measurement system Therefore this test should demonstrate the lowest level of detection of the Mactec system as well as show a resolvable difference between measurements of the control mix and the control mix with the normal premix compositionrdquo
32 ICP-MS Detection Limits
The PlasmaLab software platform determines a detection limit for each isotope based upon the intercept concentration A new calibration curve was generated for each experimental run and curves were very similar Using representative calibrations curves the detection limits for each isotope were as listed in Table 32 Note the higher detection limit for 127I is primarily due to the higher background count rate observed on the instrument This is believed to be due to the minimum purity levels of chemicals required for the iodine ldquotraprdquo solution as discussed in Section 33 below Therefore experiments were run with initial iodate concentrations higher than Tc Np and Pu to maintain analytical sensitivity
Table 32 Detection limits for each isotope based on representative calibration curves generated in PlasmaLab software associated with the ICP-MS
33 Experimental Methods
The experimental methods used in this work followed closely those previously described for experiments examining radionuclide sorption to saltstone (Kaplan et al 2007 Kaplan et al 2008) Brief descriptions of each method are provided below
Preparation of Calcite Solution Using a hotstirring plate 10 L of distilled-deionized (DDI)
water was heated to 3-100C above room temperature Then 001 g CaCO3 (EM Science ACS grade) was added to the solution and the resulting suspension was mixed for 24 hours at the elevated temperature The solution was then vacuum filtered through a 045-microm filter to ensure no solid CaCO3 remained in solution
Preparation of 2 HNO3 Analysis of Tc Np and Pu on the ICP-MS required dilution in 2
HNO3 This was prepared by adding 28 mL of Aristar Optima HNO3 from a clean graduated cylinder (designated to 2 HNO3) into a 1 L volumetric flask (designated to 2 HNO3) partially filled with DDI water and then further diluted to volume
Preparation of Trap Solution for Iodine Analysis Analysis of I required the use of a reducing
basic solution that was capable of reducing iodate to iodine and holding the iodine in solution This minimized the loss of I during sample analysis A 1 L trap solution was prepared by weighing out 00500 g NaHSO3 (Fisher Scientific ACS Grade) on a calibrated Sartorous LA 230S scale and adding it to a 1L volumetric flask Then 40 mL of 25 ww tetramethylammonium hydroxide (Alfa Aesar electronic grade) and 10 mL CFA-C solution (Spectrasol Inc) were added to the volumetric flask via a calibrated 1000-5000 microL Eppendorf Research pipette The solution was then diluted to volume with DDI water
34 Experimental Protocol for Sorption Experiments under Aerobic Conditions
Falcon BlueMax 15mL polypropylene vials were labeled and weighed to within 0001 g on a calibrated Sartorious LA 230S scale The scale was then zeroed and 025 +- 001 g of a given solid were added to each tube and the weight was recorded to within 0001g
For each of the four solids three sets of triplicate samples were prepared The three sets of samples were used to allow for experiments to be run with varying concentrations of each isotope Target initial concentrations for 99Tc 237Np and 242Pu samples were 1 ppb 5 ppb and 10 ppb Target initial concentrations for the 127I samples were 100 ppb 500 ppb and 1000 ppb A set of no solids controls at initial concentrations of 1 ppb and 10 ppb for 99Tc 237Np and 242Pu and initial concentrations of 100 ppb and 1000 ppb 127I were also prepared by adding the calcite solution to pre-weighed pre-labeled centrifuge tubes as discussed above
The solids were equilibrated with the calcite solution before spiking with the radionuclides This was done by adding 10 plusmn 01 mL of calcite solution to each tube and recording the mass The samples were then placed on a Thermo Scientific shaker overnight After 24 hours the solutions were allowed to settle for 1 hour The pH was then measured and the samples were then centrifuged for 15 minutes at 8000 rpm to further separate the solids The aqueous phase was then decanted and 10 plusmn 01 mL of calcite solution was added to each tube The weight of the tube (labeled tube + solid + calcite solution) was measured to within 0001g During this washing process the pH was monitored and held steady throughout the process The pH ranged from 11-12 depending on the particular saltstone used During the experiments the exact pH for all samples at all equilibration times was measured and is reported in Appendix A and B
The resulting suspensions were then spiked with 127I 237Np 242Pu and 99Tc It is important to note that all four isotopes were added to the same vial Use of the ICP-MS to determine the concentration of each isotope allows for a single solution to contain all analytes of concern This allowed for a greater variability in the sample set and increased replicates as opposed to running individual sorption tests for each isotope For the systems with initial 99Tc 237Np and 242Pu concentrations of 10 ppb and initial 127I concentration of 100 ppb a 100 microL aliquot of each radionuclide working solution was added to the first three tubes for each solid The addition was made with the tube resting on a tared analytical balance so that the exact mass of each radionuclide solution added was recorded and the solution was gently swirled before the next radionuclide was added The 5 ppb 237Np 242Pu and 99Tc and 500 ppb 127I samples were prepared in the same manner but adding 50 microL of the respective spike solutions The final three tubes with initial 237Np 242Pu and 99Tc concentrations of 1 ppb and 100 ppb 127I were prepared by using 10 microL of the spike solutions for all four solids as well as a set of solid-free controls (No-Solids Controls) For clarity this experimental matrix is shown in Table 33 below
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Table 33 Experimental Matrix of Sorption Experiments under Aerobic Conditions
After spiking the radionuclides a precalculated amount of 10M NaOH was added to each sample
to counter the acidic radionuclide spike solutions and the pH of one of the triplicate samples was measured to ensure the proper pH range was reached The samples were then placed on and end-over-end shaker to mix at approximately 8 rpm After 24 hours the samples were removed from the shaker and the pH of each sample was measured using an Orion Ross semi-micro glass electrode calibrated against pH 4 7 and 10 buffers (Thermo) The samples were then shaken and a transfer pipette was used to transfer 35 mL of a homogenous suspension to a 5mL syringe The solution was then passed through a 100 nm nylon syringe filter The first 025-050 mL of filtrate was discarded and the remaining filtrate was collected in a clean polyethylene vial Then 10 mL of the filtrate was removed and diluted in 90 mL 2 HNO3 The mass of each phase was determined and recorded gravimetrically Then 10 mL of the remaining filtrate was transferred to a clean Falcon BlueMax 15mL vial and diluted with 90 mL of trap solution for 127I analysis Again the volume of each phase was monitored gravimetrically After the 24 hour sampling event the samples were put back on the shaker to mix for three additional days On day four the above sampling procedure was repeated
The 237Np 242Pu and 99Tc samples can be run on the Thermo Scientific ICP-MS using the standard setup and procedure which included a standard flow glass nebulizer and bulb spray chamber However for the 127I analysis the ICP-MS must be reconfigured to accommodate the basic reducing trap solution This is to alleviate problems with iodine signal stability over time frequently observed in ICP-MS analysis The reconfigured instrument uses an Elemental Science Microflow PFA-100 Teflon nebulizer with a flow rate of 100microLmin along with a sapphire torch and a Teflon spray chamber This configuration must be run with a low pump speed to prevent back pressure on the system Two 30 minute stability tests were performed using a 50 ppb iodate solution Each experiment consisted of 40 separate measurements After each experiment was completed the uncorrected mass counts were examined and found to stay steady over the sampling period The relative standard deviation ( RSD) over all samples for each experiment was 1866 and 1460 respectively This shows that there was no significant ldquomemoryrdquo or loss of the iodine signal over time and that the reconfigured instrument has a stable iodine signal over time However as will be discussed below some difficulty has been encountered in finding an adequate internal standard for iodine analysis
35 Experimental Protocol for Sorption Experiments under Anerobic Conditions In order to examine the effects of reducing conditions of sorption of each isotope to the various cementitious samples a series of sorption experiments were performed in an anaerobic glovebox under a 2 H2(g) 98 N2(g) atmosphere Based on the measured pH and EH of these systems as discussed below these systems were at the point of reducing water Therefore they are expected to represent a lower end of the possible range for reducing conditions expected in the porewater available within cementitious materials
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Preparation of Calcite for Reducing Conditions Approximately 35 L of DDI water was boiled for 45 minutes Argon was slowly bubbled through the water as it cooled Once it cooled to below 500C approximately 3 g of calcite was added This solution mixed overnight under a continuous Ar flow After 12 hours the solution was moved into an oxygen free glove bag for filtration as described in 3231 After filtration the calcite solution was moved into the glove box
Preparation of Working Solutions under Reducing Conditions The calcite and solid solutions
were prepared in the glove box using the previously mentioned procedure used under aerobic conditions The radionuclide working solutions were transferred to the glovebox and stirred open to the reducing atmosphere for at least three days The concentration of each isotope in the working solutions was measured to determine any change in the concentration due to evaporation while the solutions were equilibrating
The preparation and spiking of samples for sorption experiments was performed exactly as described for the oxidizing conditions except all sample handling was performed in the glovebox After the 1 day and 4 day equilibration the samples were filtered within the glovebox then transferred outside for dilution and ICP-MS analysis similar to the description provided about for the oxidizing conditions For these experiments only 4 mL of either 2 HNO3 or trap solution were used to dilute the filtrate instead of the 90 mL used above for experiments performed under oxidizing conditions
36 Examination of Sorption to Vial Walls for Solids and No Solids Controls
As will be discussed below the solid-free controls samples indicated significant loss of Np and Pu Once the one and four days samples were collected and run on the ICP-MS it was necessary to determine the degree each radionuclide was sorbing to the vial walls The remaining suspensions and controls were emptied into a waste container Then 5 mL of the calcite solution was added to each vial using a calibrated pipette The vials were sonicated for approximately one minute and then emptied into the waste container Another 5 mL of calcite solution was added for the second wash and then discarded into the waste container This procedure was expected to remove any soluble Pu from the system or Pu associated with colloidal particles After each vial was washed 10 mL of 2 HNO3 was added using a calibrated pipette The acid solution is expected to remove any Tc Np or Pu associated with the vial walls This procedure has been shown to complete mass balances of Pu in similar sorption experiments using Pu (Powell et al 2002) This process was performed for both the solid suspension and the no solids controls The samples were then run on the ICP-MS to determine the concentration of 99Tc 237Np and 242Pu sorbed to the vial walls
37 Data Analysis The solubilities of 242Pu and 237Np were calculated by using the formula
nuclide
nuclide
nuclideMSICP
sol Mg
gCC
)(10 6
microminus
minus
= (Equation 31)
Csol = observed nuclide solubility (molnuclidekgsolution) CICP-MS = aqueous concentration of nuclide from ICP-MS measurement (ppb micrognuclidekgsolution) Mnuclide = molecular mass of nuclide (gnuclidemolnuclide)
In order to determine the Kd values one first needs to determine the concentration on the solid by using
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solid
calcitespikeaqspikecalcite
spikestock
solid m
mmCmmmC
C)(
)()(
+⎥⎥⎦
⎤
⎢⎢⎣
⎡minus
+
lowast
= (Equation 32)
Csolid = calculated solid phase concentration of the nuclide (ppb) Cstock = concentration of the nuclide stock solution (ppb) mspike = mass of nuclide spiked into the saltstone suspension (g) mcalcite = total mass of calcite solution used in the saltstone suspension (g) Caq = aqueous concentration of nuclide from ICP-MS measurement (ppb) msolid = mass of the saltstone used in the suspension (g)
The Kd can be calculated using the equation
aq
solidd C
CK = (Equation 33)
Kd = solid-water partitioning coefficient (gsolutiongsolid assuming density of 10 gmL traditional
unit of mLsolutiongsolid can be obtained) This Kd Equation (33) is numerically equivalent to the traditional Kd equation proposed in ASTM D-4646 which has been used in previous saltstone experiments (Kaplan et al 2007 Kaplan et al 2008)
40 Results and Discussion
41 Radionuclide Sorption to Cementitious Formulations under Oxidizing Conditions
Figure 41 shows Pu Kd values ranging from 104 to gt105 mLg Generally for each solid the Kd increases with increasing initial Pu concentrations typical behavior of systems where the aqueous concentrations of the radionuclides are solubility controlled This is not expected because the Kd expression indicates that the Kd value should remain constant with increasing total Pu concentrations It was noted that aqueous phase concentration of Pu remained relatively constant in all samples (see discussion below regarding Pu solubility) Therefore the sorption capacity of each solid phase for Pu has not been overcome For each of these solid phases it appears the solutions had reached equilibrium before the first samples were taken at 24 hours In each case the Kd values for the one day and four day are similar A trend between the solid phases is not discernible The aged cement with no reducing slag was expected to have the lowest Kd values but in actuality it has the highest Kd Also there is no correlation with the concentration of reducing slag The Vault 2 samples with 17 dry wt- reducing slag has a Kd similar to that of the TR547 (45 dry wt- slag) while the saltstone with the most slag TR545 (90 dry wt- slag) has the lowest Kd value Others have observed that Pu Kd values of cementitious materials are similar in the absence and presence of slag (Allard et al 1984 Hoaglund et al 1985)
It was observed that similar aqueous concentrations of Pu were observed regardless of the solid phase present Figure 42 shows the average aqueous phase concentrations measured after one day and four days for all solids As stated above triplicate samples were prepared for each solid phase and each initial concentration Therefore each of the reported solubility values in Figure 42 is an average of nine measurements Using the highest reported value with the expected maximum error (0018 ppb for solid TR545) the maximum expected aqueous concentration of Pu in the pore water associated with the
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saltstone formulations will be approximately 7 x 10-11 molL as calculated using Equation 31 This is on the same order as the solubility of Pu hydrous oxide solid phases (Neck and Kim 2001)
Figure 41 Plutonium Kd Values under Oxidizing Conditions Plutonium Kd values for various saltstone formulations measured after one-day equilibration (1d) and four-day equilibration (4d under oxidizing conditions Total plutonium concentrations in each system were 1 ppb 5 ppb and 10 ppb Sample prepared in triplicate and error bars represent standard deviation of samples except as follows value for dataset TR547-4d 10 ppb is reported based on duplicate samples
Figure 42 Plutonium solubility for various saltstone formulations measured after one-day equilibration (1d) and four-day equilibration (4d) under oxidizing conditions Total plutonium concentrations in each system were 1 ppb 5 ppb and 10 ppb as noted Samples prepared in triplicate and an average of all samples (9) was used to determine average solubility The error bars represent standard deviation of samples
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Overall the Kd values for Np range from 105 to gt106 with only a few outliers The most significant outlier is the 1 ppb solution in the TR545 sample after the four-day equilibration It drops two orders of magnitude while the 5 and 10 ppb solutions remain constant However this result is most likely an analytical artifact from working at the detection limits of the ICP-MS In the one-day equilibration samples only one of the triplicates S-2-E had detectable Np while in the four-day equilibration samples only S-2-F had detectable amounts present The graph also shows that with the exception of the 5 ppb sample in the aged cement Np sorption to TR545 (90 dry-wt- slag) and TR547 (45 dry wt- slag) have Kd values approximately one order of magnitude over the aged cement (no slag) and Vault 2 (17 dry wt- slag) samples
It was observed that similar aqueous concentrations of Np were observed regardless of the solid phase present Figure 44 shows the average aqueous phase concentrations measured after one day and four-day equilibrations for all solids As stated above triplicate samples were prepared for each solid phase and each initial concentration Therefore each of the reported solubility values in Figure 44 is an average of nine measurements of Np concentration unless stated otherwise Using the highest reported value with the expected maximum error (00026 ppb for solid TR545) the maximum expected aqueous concentration of Pu in the pore water associated with the saltstone formulations will be approximately 2 x 10-11 molL
Figure 43 Neptunium Kd values under oxidizing conditions Neptunium Kd values for various saltstone formulations measured after one-day equilibration (1d) and four-day equilibration (4d) under oxidizing conditions Total plutonium concentrations in each system were 1 ppb 5 ppb and 10 ppb as noted Samples prepared in triplicate and error bars represent standard deviation of samples except as follows value for datasets TR545-1d 1ppb TR545-4d 1 ppb TR547 4d 1 ppb TR545-4d 10 ppb TR547-1d 1ppb TR547-4d 10 ppb are reported based on a single sample and for dataset TR545-1d 5ppb is reported based on duplicate samples Kd values limited to gt106 were at instrumental background
The Kd values for Tc are significantly lower than that of Pu or Np As a whole the values are
comparable The values for the one-day and four-day equilibrations solutions in the Vault 2 (17 dry wt- slag) and TR545 (90 dry wt- slag) remained constant within reasonable error with just a slight increase from the one-day to four-day equilibration However the Aged Cement (no slag) and TR547 (45 dry wt- slag) showed a noticeable decrease from day one to day four (Figure 45)
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Figure 44 Average solubility of Np under oxidizing conditions Neptunium solubility for various saltstone formulations measured after one-day equilibration (1d) and four-day equilibration (4d) under oxidizing conditions Total Np concentrations in each system were 1 ppb 5 ppb and 10 ppb Samples prepared in triplicate and an average of all samples (9) was used to determine average solubility except as follows TR545-1d is based on 6 samples TR545- 4d on 5 samples TR547-1d on 7 samples and TR547- 4d on 5 samples The error bars represent standard deviation
Figure 45 Technetium Kd values under oxidizing conditions Tc Kd values for various saltstone formulations measured after one-day equilibration (1d) and four-day equilibration (4d) under oxidizing conditions Total Tc concentrations in each system were 1 ppb 5 ppb and 10 ppb as noted above Samples were prepared in triplicate and the error bars represent standard deviation of samples except as follows data sets for Vault 2-1d 1ppb were duplicates and TR547- 4d 10 ppb is based on a single dataset
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Similar to the Tc Kd values the 127I Kd values are much lower than those of Pu and Np The amount of reducing slag present in each of the solids does not appear to have a drastic effect on the 127I Kd values In fact the initial (one day) Aged Cement (0 slag) samples had a Kd almost two orders of magnitude above those with reducing slag The cause of this behavior is not known but it has been shown that iodate IO3
- the oxidized form of iodine sorbs more strongly than iodide I- to charged surfaces (Schwehr et al 2009 Yoshida et al 1992 Fukui et al 1996) It is possible that the slag is reducing the iodine to the I- form converting it to a species that is less likely to sorb to saltstone Additional work would be required to confirm the oxidation state of iodine when associated with saltstone
Figure 46 Iodine Kd Values under Oxidizing Conditions Iodine Kd values for various cementitious formulations measured after one-day equilibration (1d) and four-day equilibration (4d) under oxidizing conditions Total iodine concentrations in the systems were 100ppb 500 ppb and 1000 ppb as noted above Samples were prepared in triplicate and the error bars represent standard deviation of samples except as follows duplicates were used for dataset TR545- 1d 100ppb
42 Radionuclide Sorption to Vial Walls Under Oxidizing Conditions
Figure 47 shows the aqueous fractions found in the no-solids controls It provides a measure of the solubility of each radionuclide as well as examines the fraction of each radionuclide sorbed to the vial walls After one day only 25 of the Pu remained in solution and the concentration decreased even more after four days The loss of Pu from the aqueous phase may be due to sorption of Pu to the vial walls or precipitation of a Pu hydrous oxide solid (discussed with respect to Figure 49 below) Additional experiments would be required to examine the solubility of the Pu in high pH calcite saturated solutions
After one day about 80 of the Np remained in solution However the aqueous concentration in the initially 1-ppb solution was significantly reduced after four days Approximately 60 of the Np remained soluble in the initially 10-ppb solution Once again this drop could be due to sorption to the vial wall The Tc present after one day ranged from about 88 to about 95 and was virtually 100 after four days These values are consistent with internal standards used to monitor Tc detection performance on the ICP-MS Greater than 50 of the I remained in solution after the one-day and four-day equilibrations As shown in Figure 48 the standard deviation between the triplicate I control samples was
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quite large Additional control samples are required to understand the mechanism by which I is being lost from the aqueous phase in these samples
Figure 47 Plutonium Neptunium and Technetium Aqueous Fractions Fraction of Pu Np and Tc remaining in the aqueous phase for the No Solids controls after a one-day equilibration (1d) and four-day equilibration (4d) under oxidizing conditions The total concentration for each radionuclide 10 ppb as noted above Samples were prepared in triplicate and the error bars represent the standard deviation of the samples
Figure 48 Iodine Aqueous Fraction Iodine aqueous fraction for the no-solids controls after a one-day equilibration (1d) and four-day equilibration (4d) under oxidizing conditions The total concentration of iodine was 1000 ppb as noted above Samples were prepared in triplicate and the error bars represent the standard deviation of the samples
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As discussed above the loss of Np and Pu from the no-solids control (Figure 47) could be due to
precipitation of Np and Pu hydrous oxides or sorption to the vial walls To quantify the differences between these possible sinks the vials were washed as described in Section 36 The data in Figure 49 indicate that significant sorption of Np and Pu to the vial walls may occur When combining the mass of Np represented in Figure 47 and Figure 49 there is almost 100 mass recovery of the Np sorbed to the vial wall and the aqueous fraction measured Therefore no precipitation of Np is expected However because 100 recovery was not achieved for Pu a Pu hydrous oxide phase could be precipitating which was washed out of the vial during the cleaning procedure The data in Figure 47 represent the no-solids control samples where there was no solid phase present for Np or Pu to sorb to besides the vial walls However when a cementitious solid phase is present in the sample there will be competition between the vial walls and the cement for sorption of Np and Pu Based on the affinity of metals for metal oxide surfaces as opposed to the polypropylene surface and the much higher surface site density expected for the cementitious samples it is assumed that the cementitious samples will out-compete the vial walls for sorption sites This thesis was tested by taking one of the triplicate samples from each sorption experiment with a solid phase present removing the solid phase from the tubes and leaching any sorbed Np and Pu from the tubes with acid as described in Section 36 Figure 410 and Figure 411 show that although some of the Pu and Np sorbed to the vial walls of the samples this amount accounted for less than 2 in all samples Therefore sorption of Np and Pu to the vial walls does not appear to be a significant factor in experiments where the solid phase is present Note these results do not discount the possibility that Pu hydrous oxide precipitates were forming in both the no-solid control experiments and experiments with cement formulations present Based on the observation of a constant aqueous phase concentration of Pu regardless of the initial Pu concentration the presence of a solubility limiting Pu phase cannot be discounted based on these data Further experiments examining the solubility of Pu in high pH calcite saturated solutions are required
Like Pu Np shows little affinity for the vial walls in the presence of a solid phase In each case tested there was significantly less than 1 of the total Np sorbed to the vial walls This behavior is consistent with the ~100 mass balance on Np achieve in the solid-free controls The majority of Np remained soluble in the solid-free control experiments Therefore it is expected that sorption of Np to the vial walls was the primary reason for the loss of Np from the aqueous phase in the no-solids systems rather than precipitation of a Np solid phase similar to the process discussed for Pu above This assumption is based on the relative solubility of Np(V) as compared with Pu(IV)
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Figure 49 Percent Pu and Np sorbed to vial walls of the no solids controls after the aqueous phases were discarded and the vials were washed Both the 10 ppb and 1 ppb datasets were prepared in triplicate and the error bars show the standard deviation
Figure 410 Percent Pu sorbed to vial walls after the solids and aqueous phases were removed and the vials were washed The graph illustrates one sample from each of the 1 ppb 5 ppb and 10 ppb systems Therefore no error bars are present
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Figure 411 Percent Np sorbed to vial walls after the solids and aqueous phases were removed and the vials were washed The graph illustrates one sample from each of the 1 ppb 5 ppb and 10 ppb systems Therefore no error bars are present
43 Radionuclide Sorption to Cementitious Formulations under Reducing Conditions
Similar to the Pu Kd values under oxidizing conditions Pu Kd values ranged from 104 to gt105 under reducing conditions (Figure 412) Also similar to the results under oxidizing conditions the Kd increases with increasing initial Pu concentration Again this behavior is indicative of the aqueous phase concentration of Pu being controlled by solubility of Pu rather than by sorption In each case the samples appeared to reach steady state within 24 hours This equilibration is evident because the Kd values after one day and four days are very similar Also it appears that the amount of reducing slag does not make a significant difference in the Kd value In fact the TR547 solid consists of 45 reducing grout but produces approximately the same Kd values of the aged cement which does not have any reducing grout Each of these Kd values are higher than the TR545 which is 90 reducing grout These findings are in agreement with those conducted by Allard et al (1984) and Hoglund et al (1985) who reported that concrete containing reducing agents (slag similar to that used in our study) did not have greater Pu Kd values than those that did not contain slag
Similar aqueous concentrations of Pu were observed regardless of the solid phase present Figure 36 shows the average aqueous phase concentrations measured after one day and four days for all solids As stated above triplicate samples were prepared for each solid phase and each initial concentration Therefore each of the reported solubility values in Figure 412 is an average of up to nine measurements of the Pu aqueous concentrations Using the highest reported value with the expected maximum error (00045 ppb for solid Vault 2) the maximum expected aqueous concentration of Pu in the pore water associated with the cementitious formulations will be approximately 2 x 10-11 molL (calculated from Equation 31) This value is on the same order as the solubility of Pu hydrous oxide solid phases (Neck and Kim 2001) A best value would be 10-12 molL
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Figure 412 Pu Kd Values under Reducing Conditions Plutonium Kd values for various cementitious formulations measured after one-day equilibration (1d) and four-day equilibration (4d) under reducing conditions Total plutonium concentrations in each system were 1ppb 5 ppb and 10 ppb Samples prepared in triplicate and error bars represent standard deviation
Figure 413 Average Solubility of Plutonium under Reducing Conditions Plutonium solubility for various cementitious formulations measured after one-day equilibration (1d) and four-day equilibration (4d) under reducing conditions Total plutonium concentrations in each system were 1ppb 5 ppb and 10 ppb as noted Samples prepared in triplicate and an average of all samples (9) was used to determine average solubility The error bars represent standard deviation of samples
The Np Kd values reported in Figure 414 obtained under reducing conditions are very similar to
those obtained under oxidizing conditions In each case the samples appeared to reach steady state within 24 hours This equilibration is evident because the Kd values between the one-day and fourndashday equilibrations are similar As was the case with Pu the amount of slag present in each solid does not
SRNL-STI-2009-00636 Revision 0
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seem to have a significant effect on the Kd values Again the aged cement with no slag has as high a Kd as the TR545 with 90 reducing slag
Similar aqueous concentrations of Np were observed regardless of the solid phase present Figure 314 shows the average aqueous phase concentrations measured after one day and four days for all solids All Kd values were gt 105 mLg which is considerably larger than those reported by Kaplan and Coates (2007) who reported Np Kd values to 1300 to 1600 mLg This difference can be attributed to two important experimental differences 1) the experiment was designed to permit larger Kd values to be measured (eg solid to liquid ratios and spike concentrations) and more importantly 2) a more sensitive analytical method ICP-MS was used instead of conventional low-energy gamma spectroscopy or liquid scintillation counting (LSC) analysis As stated above triplicate samples were prepared for each solid phase and each initial concentration Therefore each of the reported solubility values in Figure 415 is an average of up to nine measurements Using the highest reported value (to provide the most conservative most soluble values) with the expected maximum error (00045 ppb for solid TR545) the maximum expected aqueous concentration of Np in the pore water associated with the cementitious formulations will be approximately 2 x 10-11 molL A best value taking into consideration the less-than values which are depicted in Figure 414 as running off the top of the plot would be 10-12 molL
Figure 414 Np Kd Values under Reducing Conditions Neptunium Kd values for various cementitious formulations measured after one-day equilibration (1d) and four-day equilibration (4d) under reducing conditions Total Np concentrations in each system were 1 ppb 5 ppb and 10 ppb Samples were prepared in triplicate and the error bars represent standard deviation Kd values limited to gt106 were at instrumental background
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Figure 415 Average Solubility of Neptunium under Reducing Conditions Neptunium solubility for various cementitious formulations measured after one day equilibration (1d) and four day equilibration (4d) under reducing conditions Total plutonium concentrations in each system were 1ppb 5 ppb and 10 ppb Samples prepared in triplicate and an average of all samples (9) was used to determine average solubility The error bars represent standard deviation
A plot of the Tc Kd values for each cementitious formulations under reducing conditions is shown
in Figure 416 (log y-axis) and Figure 417 (reduced scale linear y-axis) The Kd values for each of the initial Tc concentrations are relatively similar This behavior is consistent with the Kd expression However the increasing Kd values from the one-day to four-day day equilibrations for each solid indicate that steady state was not reached within one day and it is unclear whether steady state was reached after four days A possible explanation for this behavior is that Tc(VII) was being reduced to Tc(IV) in these systems due to the reducing conditions As Tc(VII) was reduced the Kd would increase based on the high affinity of Tc(IV) for solid phases This proposed mechanism was observed by Lukens et al (2005) using an SRS saltstone material similar but not identical to TR547 Using synchrotron X-ray absorption fine structure spectroscopy they observed over a 453 month period that Tc(VII) incorporated into SRS saltstone slowly converted to Tc(IV) and that the nearest neighbor was initially predominantly oxygen and eventually became predominantly sulfur (described as a Tc(IV) phase TcSx) Lacking in Lukens et al (2005) is quantification of the solubility of Tc This analysis still needs to be completed along with re-oxidation studies (ie what is the rate that reduced Tc reoxidizes under ambient natural saltstone conditions)
Unlike Np and Pu Tc Kd values changed with the amount of slag included in the formulation Tc Kd values noticeable increase as the amount of slag in the formulation increased TR547 (45 dry-wt- slag) Kd value is visibly higher than the Aged Cement and Vault 2 Kd values while the most reducing TR545 (90 dry wt- slag) Kd value is significantly higher than the others Following a similar trend the reduction capacity that is the total quantity of reductant in the saltstone on a mass basis (units of milli-equivalents of charge per g) of TR547 had slightly greater or equal reduction capacity to that of TR545 (Roberts and Kaplan 2009)
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36
Figure 416 Tc Kd Values under Reducing Conditions Tc Kd values for various cementitious formulations measured after one-day equilibration (1d) and four-day equilibration (4d) under reducing conditions Total Tc concentrations in each system were 1 ppb 5 ppb and 10 ppb Sample prepared in triplicate and error bars represent standard deviation except as follows TR547-1d 1 ppb is based on a single dataset and datasets Vault 2-1d 5 ppb Vault 2- 4d 1 ppb Aged Cement-1d 5 ppb and Aged Cement-4d 1 ppb are duplicates
Figure 417 Data from Figure 416 replotted on a reduced linear scale for easier viewing Each sample was prepared in triplicate except as follows TR547-1d 1 ppb is based on a single dataset Vault 2-1d 5 ppb Vault 2- 4d 1 ppb Aged Cement-1d 5 ppb and Aged Cement-4d 1 ppb are duplicate datasets
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37
The calculated Kd values for I sorption to cementitious samples under reducing conditions are shown in Figure 418 Before discussing the data it should be noted that spiked QAQC samples which were analyzed on the ICP-MS along with the samples used to generate the data in Figure 418 were off by an average of 195 with one outlier of approximately 40 This dataset did not include the use of internal standards as discussed in Section 31 above1 Due to a lack of an internal standard the iodine results presented in this report should be considered with a minimum error estimate of 20
The iodine Kd values under reducing conditions are different from those observed under oxidizing conditions Under oxidizing conditions it appears they are at a steady state by day one However under reducing conditions there is a noticeable difference between days one and four indicating steady state was not reached by day one and possibly not by day four Another interesting observation is that the Kd values are decreasing from day one to four A possible reason for this behavior may be due to redox chemistry of iodine in this system If iodine partially or entirely exists in the form as iodate (IO3
-) it is possible it could be reduced to iodide I- within the reducing cementitious system These two iodine species sorb differently iodate sorbing to minerals more strongly than iodide (Denham et al 2009 Schwehr et al 2009 Fukui et al 1996 Yoshida et al 1992) It is hypothesized that the reducing environment of the saltstone is sufficient to reduce iodate ions to the more weakly binding form of iodine iodide
This is one of the few datasets (along with Tc) in this study where there may be a difference between the various solids The degree of iodate reduction would be expected to increase as the slag content increases As mentioned above reduction of iodate to iodide should result in a decrease in sorption Therefore higher Kd values should be observed for solids with less slag such as the Aged Cement (0 dry wt- slag) and Vault 2 (17 dry wt- slag) This is generally the case in Figure 418 where the highest Kd values are reported for the Aged Cement and the lowest values are for solid TR547 However this trend does not hold completely where the saltstone sample containing 90 slag (TR545) has generally equal or higher Kd values than the saltstone containing 45 dry wt- slag (TR547)
1 Clemson University is presently investigating appropriate internal standards for iodine analyses for ICP-MS Of those tested rhenium and molybdenum have shown some promise
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38
Figure 418 Iodine Kd Values under Reducing Conditions I Kd Values for various cementitious formulations measured after one day equilibration (1d) and four day equilibration (4d) under reducing conditions Total iodine concentrations in each system were 100 ppb 500 ppb and 1000 ppb as noted Sample prepared in triplicate and error bars represent standard deviation of samples except as follows Vault 2-4 d 100 ppb is a single dataset while the datasets for Vault 2-1 d 100 ppb 4 d 1000 ppb TR545-4 d 1000 ppb 100 ppb TR547-4 d 1000 ppb 500 ppb 100 ppb and Aged Cement- 4 d 1000 ppb and 100 ppb are all based on duplicates
44 Radionuclide Sorption to Vial Walls under Reducing Conditions
The aqueous concentrations for Pu Np and Tc in the no solids controls are shown in Figure 419 The results are similar to those presented for experiments performed under oxidizing conditions above The 1 ppb Pu aqueous fraction is approximately three times greater than the 10 ppb fraction at day one This fraction decreases over time and by day four they are approximately equal when taking error into account This behavior is similar to the aqueous fraction under oxidizing conditions The 1 ppb Np aqueous fraction is significantly higher on both day one and day four than the aqueous fraction of the 10 ppb samples However each remained constant from day one to day four The 10 ppb aqueous fraction is twice as low as under oxidizing conditions which suggests either higher sorption to the vial walls or more precipitating out under the reducing conditions Like Pu and Np Tc shows a decrease from day one to day four especially for the 1 ppb samples The decrease in the 10 ppb sample is minimal and the aqueous fraction remains around 09 This value is slightly lower than that under oxidizing conditions
To examine the degree of sorption to the vial walls the tubes were washed again as performed for the experiments under oxidizing conditions above and similar results were found Ninety percent of the 1 ppb Pu sample was sorbed to the vial wall upon completion of the experiment which gives a 100 mass recovery when comparing this value to that found in Figure 419 However this result is not the case with the 10 ppb samples where approximately 75 of the mass remains unaccounted It is noteworthy that approximately 25 of the Pu from the 10 ppb solution sorbed to the vial walls under both oxidizing
SRNL-STI-2009-00636 Revision 0
39
and reducing conditions Np follows the same trend as Pu while less than 005 of the Tc sorbed to the wall
Figure 419 Plutonium Neptunium and Technetium No-Solids Aqueous Fractions under Reducing Conditions Pu Np and Tc aqueous fractions of No Solids controls after a one-day equilibration (1d) and four-day equilibration (4 d) under reducing conditions Total concentration for each radionuclide was 1 ppb and 10 ppb Samples were prepared in triplicate and the error bars represent the standard deviation
Figure 420 Percent of Pu Np and Tc sorbed to the vial walls of the No Solids control samples under reducing conditions Each the 1 ppb and 10 ppb samples were prepared in triplicate and the error bars represent the standard deviations of triplicate samples
Under reducing conditions the fraction of I remaining in the aqueous phase was around 90 with
almost 100 mass recovery of the 100 ppb I after the four-day equilibration These graphs show that
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40
under reducing conditions there will only be a small fraction of I sorbing to the vial wall or coming out of solution This result is a much better mass recovery than under oxidizing conditions (Figure 48) which had a mass recovery of approximately 65 after four days This result is also consistent with the interpretation that there may be a iodine speciation change between the two redox treatments
Figure 421 Iodine No-Solids Aqueous Fractions under Reducing Conditions I aqueous fractions of No-Solids controls after a one-day equilibration (1d) and four-day equilibration (4d) under reducing conditions The total concentration for each system was 100 ppb and 1000 ppb Samples were prepared in triplicate and the error bars represent the standard deviation
50 Comparison of Radionuclide Sorption under Oxidizing and Reducing Conditions
In the following figures (Figure 51 through Figure 54) the data shown above has been replotted to allow comparison between the oxidizing and reducing conditions for each cementitious formulation General observations based on these data follow Vault 2 Observations (Figure 51)
bull Pu Kds are greater than 104 under both oxidizing and reducing conditions and Pu Kds are slightly lower under reducing conditions This could possibly be due to reduction of Pu(IV) to Pu(III) However no oxidation state analysis was performed in this work
bull Np Kds are generally greater than 104 under both oxidizing and reducing conditions Interestingly Np Kds are higher under reducing conditions by almost an order of magnitude This could possibly be due to reduction of Np(V) to Np(IV) However no oxidation state analysis was performed in this work
bull Regardless of the initial Np or Pu concentration similar aqueous phase concentrations of Np or Pu were observed in all samples This trend indicates that ldquosorptionrdquo of Np and Pu in these systems may be a combination of adsorption absorption and (co)precipitation processes
bull Tc appears to reach a steady state within four days under oxidizing conditions This behavior does not appear to be the case under reducing conditions After four days similar Kd values are reached under both oxidizing and reducing conditions It is unclear
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41
whether the Kd value of Tc will continue to increase under reducing conditions consistent with reduction of Tc(VII) to Tc(IV) The similarity in Kd values under both oxidizing and reducing conditions is an interesting observation and certainly warrants additional studies
bull I Kd values are similar under both oxidizing and reducing conditions However reducing condition systems may not be at steady state after four days while systems under oxidizing conditions appeared to reach a steady state The difference in rates may be due to reduction of iodate to iodine
bull For all isotopes examined the sorption behavior to each of the solid phases is very similar
TR545 and TR547 Observations (Figure 52 and Figure 53) bull Similar to the discussion above with respect to Vault 2 Pu Np and Tc all appear to reach
a steady state under oxidizing conditions and approach steady state slower under reducing conditions
bull Np and Pu Kd values are greater than 104 for all systems and time steps The aqueous phase concentrations of Np and Pu appear to be better described as a solubility in terms of the aqueous phase concentration of Np and Pu Similar aqueous phase concentrations of both Np and Pu were reached The data indicate that the initial Np and Pu concentration generally does not affect the aqueous phase concentration at an apparent steady state The presence of each solid phase appears to limit the aqueous phase concentration of both Np and Pu on the order of 10-11 molL
bull Tc shows significantly higher Kd values under reducing conditions versus oxidizing conditions
bull For all isotopes examined the sorption behavior to each of the solid phases is very similar
Aged Cement Observations (Figure 54) bull Pu appears to be close to steady state for each solid by day one with similar Kd values
reached on between day one and day four bull Np has a higher Kd under reducing conditions than oxidizing (105 under oxidizing
conditions and gt105 under reducing conditions) bull Neither set of Tc data was at steady state by day one and rates of sorptiondesorption
reactions appear to be different Tc Kds decrease from day one to four under oxidizing conditions but increase under reducing conditions
bull The Kd values for I under oxidizing conditions were considerably higher than those measured for I with any other solid Similar Kd values obtained for the same solids under reducing conditions indicate that the reported Kd values under oxidizing conditions appear to be suspect However analysis of the raw data gives no indication of an experimental artifact As discussed above these observations may be explained based upon the amount of slag contained within the solids which will affect the reducing capacity (ie No reducing slag is in the aged cement which could be reason the reduction of iodate to iodide (speculated in other samples) is not evident)
bull The difference in sorption behavior of iodine to the aged cement between oxidizing and reducing conditions also indicates that the reducing conditions of the solution may affect I redox behavior in addition to any reactivity expected in the solid phases
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42
Figure 51 Comparison of Tc I Np and Pu sorption to Vault 2 solid under oxidizing and reducing conditions
SRNL-STI-2009-00636 Revision 0
43
Figure 52 Comparison of Tc I Np and Pu sorption to TR 545 solid under oxidizing and reducing conditions
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44
Figure 53 Comparison of Tc I Np and Pu sorption to TR547 solid under oxidizing and reducing conditions
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45
Figure 54 Comparison of Tc I Np and Pu sorption to Aged Cement under oxidizing and reducing conditions
SRNL-STI-2009-00636 Revision 0
46
60 Comparison of Radionuclide Sorption and Solubility under Oxidizing and Reducing Conditions
To further summarize the data the following tables provide either the average solubility
(for Np and Pu) or average Kd (for Tc and I) determined under both oxidizing and reducing conditions for each cementitious formulation Each table lists the average value standard deviation and the number of replicate samples used to calculate the reported values
The solubility of Pu in the presence of each solid under oxidizing and reducing conditions is shown in Table 61 (this is taken from experiments equilibrated for four days not one day) Under oxidizing conditions the apparent solubility values associated with the Aged Cement (0 dry wt- slag) Vault 2 (17 dry wt- slag) and TR547 (45 dry wt- slag) are all similar with only a slight increase in solubility as the amount of reducing slag increases There is a significant increase of almost an order of magnitude for the most reducing saltstone TR545 (90 dry wt- slag) However these samples also have a standard deviation on the same order of magnitude as the solubility itself which when taken into account brings the solubility back into the range of the others Under reducing conditions the apparent solubility values are slightly lower than under oxidizing conditions In this set of samples the Vault 2 saltstone with 10 dry wt- reducing slag had the highest apparent solubility but once again when considering the standard deviation the values are similar
Table 61 Comparison of plutonium apparent solubility values under oxidizing and reducing conditions
Table 62 lists the apparent solubility values of Np in the presence of each cementitious
formulation under both oxidizing and reducing conditions Under oxidizing conditions the cementitious formulation does not appear to have a dramatic effect on the solubility The apparent solubility values are similar to those of Pu under similar conditions except the Np standard deviations are much higher The high standard deviations are an analytical artifact since the measured concentrations were close to or at the detection limit of the ICP-MS There does appear to be a slight decrease in Np solubility under reducing conditions However the statistical significance of this decrease was not calculated
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47
Table 62 Comparison of neptunium apparent solubility values under oxidizing and reducing conditions
Unlike the apparent solubility values of Pu and Np the aqueousatmospheric conditions
and cementitious formulation seem to have an effect on the Tc Kd values (Table 63) Under oxidizing conditions there is not a discernible difference among the different cementitious formulations especially when taking the respective standard deviations into account However when experiments were run under reducing conditions the specific formulation had a noticeable effect The two saltstone samples with the least amount of reducing slag Aged Cement (0 dry-wt- slag) and Vault 2 (17 dry wt- slag) had Kd values which were similar to those observed under oxidizing conditions However the TR547 (45 dry-wt- slag) increased by almost an order of magnitude while the TR545 (90 dry wt- slag) increased by about three orders of magnitude Although the respective standard deviations are large the higher Kd values do appear to be significant
Table 63 Comparison of technetium Kd values under oxidizing and reducing conditions
Unlike Tc I does not seem to be as affected by cementitious formulation and redox status (Table 64) The only treatment (possible outlier) that does not follow this trend is the Aged Cement under oxidizing conditions This Kd value is higher than the others but also has a much higher standard deviation which when accounted for gives a value similar to the others All other treatments had near identical Kd values irrespective of solid phase or redox condition But again the Aged Cement data cannot be discounted at this time given the possibility of the influence that redox may have on iodine speciation and the strong influence I speciation has on sorption to cementitious materials
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48
Table 64 Comparison of iodine Kd values under oxidizing and reducing conditions
71 Comparison with Previous Data The increased sensitivity of the ICP-MS over conventional low-energy gamma
spectroscopy or liquid scintillation counting (LSC) analysis allowed for much more accurate Kd values and apparent solubility values in this work than were previously obtainable Generally radioanalytical detection methods start with activities on the order of 103 to 104 counts per minute (cpm) and approach background levels of 1 to 5 cpm for strongly sorbing radionuclides Therefore the accuracy of the Kd value will be the difference in analytical sensitivity when the initial aqueous activity decreases by a factor of approximately 5000 (ie the aqueous activity drops from approximately 5000 cpm to the instrument background of 1 cpm following almost complete sorption) As a result the reported Kd values can only be reliably reported up for a Kd of 103 to 104 This constraint is believed to be the difference between the observed Kd values for 237Np of gt 105 observed in this work when compared with the Kd values between 3000 and 4000 reported by Kaplan et al (2008) A similar observation was made for Pu because 242Pu was used for ICP-MS analysis and 238Pu was used in the work of Kaplan et al (2008) This constrint may account for the different Kd value of gt104 reported in Kaplan et al (2008) compared with the value of gt105 observed in this work
In the case of Tc Kaplan et al (2008) reported a Kd of 023 mLg for Vault 2 under oxidizing conditions and 093 mLg under reducing conditions while the above experiment determined the Vault 2 Kd to be 505 mLg under oxidizing conditions and 557 mLg under reducing conditions Unlike the discrepancy in the Kd values for Np Pu and Tc between the above findings and those in Kaplan et al (2008) the reported Kd values for iodine are similar For Vault 2 Kaplan et al (2008) found 125I to have a Kd of 894 mLg under oxidizing conditions and 715 mLg under reducing conditions These values are similar to the Kd values of 766 mLg and 725 mLg observed under oxidizing and reducing conditions respectively in this work These findings appear to confirm the previously accepted Kd values of 0-10 mLg depending on the cementitious formulation
72 Suggested Future Work The above data demonstrate several areas that require further examination The
increasing Tc Kd values over time dataset suggest that steady state had not been achieved It would be beneficial to determine the amount of time required to reach steady state and allow determination of a more accurate Kd value (an assumption of the Kd construct is that it be measured at steady state) Also kinetic studies of both Tc and I are needed to better understand their respective interactions with the different cementitious formulations As for the I additional
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49
tests should be performed to test the hypothesis that iodine may in part exist as iodate which may initially sorb to the saltstone then undergo reduction to iodine or iodide and then desorbs causing a decrease in Kd
A final area of future work is to examine the possible causes for the similar behavior of each cementitious formulation despite the different slag content This discrepancy is not only observed in the above experiments but also in Kaplan et al (2008) which is illustrated in Table 31 and by recent work in measurements of saltstone reduction capacity (Roberts and Kaplan 2009) The reduction capacity (units in milli-equivalentsg solid) equivalents of the Aged Cement with no slag is 855 plusmn 101 and adding 10 slag gives a reducing equivalent of 2398 plusmn 311 However increasing the slag content to 23 causes the reducing capacity to increase to 8218 plusmn 81 which is almost equivalent to the 8324 plusmn 49 of the 100 slag Understanding the chemistry behind the reducing capacity of each cementitious formulation will help to define what reactions are important for controlling radionuclide release from the saltstone
80 References Allard B L Eliasson S Hoglund and K Andersson 1984 ldquoSorption of Cs I and actinides in
concrete systemsrdquo SKB Technical Report SKBKBS TR-84-15 DKB Stockholm Sweden
Denham M D I Kaplan and C Yeager2009 ldquoGroundwater radioiodine Prevalence biogeochemistry and potential remedial approachesrdquo SRNL-STI-2009-00463 Savannah River National Laboratory Aiken SC
Dixon K L M A Phifer and J R Harbour 2008 ldquoFY09 PACA Maintenance Program Additional Saltstone Property Testingrdquo SRNL-L3100-2009-00019 Rev0 Savannah River National Laboratory Aiken SC
Fukui M Fujikawa Y and Satta N 1996 ldquoFactors affecting interaction of radioiodide and iodate species with soilrdquo Journal of Environmental Radioactivity 31 199-216
Hoglund S L Eliasson B Allard K Andersson and B Torstenfelt 1985 ldquoSorption of some fission products and actinides in concrete systemsrdquo Mat Res Soc Symp Proc 50 683-690
Kaplan D I 2007 Geochemical Data Package for Performance Assessment Calculations Related to the Savannah River Site WSRC-TR-2006-00004 Rev 1 Washington Savannah River Company Aiken SC
Kaplan D I and Coates J 2007 ldquoPartitioning of Dissolved Radionuclides to Concrete under Scenarios Appropriate for Tank Closure Performance Assessmentsrdquo WSRC-STI-2007-00640 Rev 0 Washington Savannah River Company Aiken SC 29808
Kaplan D I Roberts K Coates J Siegfried M Serkiz S 2008 ldquoSaltstone and concrete interactions with radionuclides Sorption (Kd) desorption and reduction capacity measurementsrdquo SRNS-STI-2008-00045 Savannah River National Laboratory Aiken SC 2008
SRNL-STI-2009-00636 Revision 0
50
Neck V and Kim J I 2001 ldquoSolubility and hydrolysis of tetravalent actinidesrdquo Radiochim Acta 89 1
Powell B A Fjeld R A Coates J T Kaplan D I Serkiz S M 2002 ldquoPlutonium Oxidation State Geochemistry in the SRS Subsurface Environmentrdquo WSRC-TR-2003-00035 Westinghouse Savannah River Company US DOE Savannah River Site Aiken SC
Roberts K A and D I Kaplan 2009 Reduction Capacity of Saltstone and Saltstone Componentsrdquo SRNL-STI-2009-00637 Rev0 Savannah River National Laboratory Aiken SC
Schwehr K A Santschi P H D I Kaplan C M Yeager and R Brinkmeyer 2009 ldquoOrgano-iodine formation in soils and aquifer sediments at ambient concentrationsrdquo Environ Sci Technol 437258-7264
Yoshida S Muramatsu Y and Uchida S 1992 ldquoStudies on the sorption of I-(iodide) and IO3-
(iodate) onto andosolsrdquo Water Air and Soil Pollution 63 321-329
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51
90 Appendix A Data Tables of Radionuclide Sorption to Saltstone under Oxidizing Conditions
The following tables represent data collected for the no solids controls each saltstone and testing of radionuclide sorption to the vial walls The no solids controls tables include the concentration (ppb) of the radionuclide spiked into the sample along with the concentration of the radionuclide (ppb) measured in the aqueous phase after the given equilibration time The pH at the time the sample was taken is also recorded along with the fraction of the radionuclide which stayed in the aqueous phase The tables for the cementitious formulation data include the data above along with the addition of a Kd value The tables of the data for the radionuclides sorbed to the vial walls include the initial concentration (ppb) of the spike the concentration (ppb) of the radionuclide that had sorbed to the vial wall during the experiment and the percentage of the total concentration this represents Important Notes
BDL- Below Detection Limit lt01 denotes no notable sorption occurred
91 Data Tables for No Solid Controls
Table 91 Plutonium no solids control after one day
A 9264165178 402285E‐05 1181 434238E‐06 9980817 B 9352537276 0000110618 1183 118276E‐05 3616813 C 9363541597 705331E‐05 118 753273E‐06 5401186 D 0993110568 BDL 12 NA NA E 0977247222 300794E‐05 1199 307797E‐05 1280331 F 0962441315 BDL 1198 NA NA G 4059128499 BDL 1186 NA NA H 4065161486 705198E‐05 1188 173473E‐05 2380003 I 4116819691 0000110748 1189 269014E‐05 1555864
Table 920 TR545- neptunium after four days
Sample ID
Initial Aq Conc (ppb)
Equil Aq Conc (ppb) pH
Fraction Aq Kd
A 92641652 NA 1188 NA NA B 93525373 00001935 1185 2069E‐05 2067199C 93635416 4119E‐05 1185 44E‐06 9247818D 09931106 BDL 1197 NA NA E 09772472 BDL 12 NA NA F 09624413 00066817 1206 00069424 562421G 40591285 00003289 1196 8103E‐05 5148274H 40651615 00025316 1196 00006228 6625737I 41168197 00001018 1194 2474E‐05 1692126
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58
Table 921 TR545- technetium after one day
Sample ID
Initial Aq Conc (ppb)
Equil Aq Conc (ppb) pH Fraction Aq Kd
A 9655146069 820460082 1181 0849764546 8998984 B 9356176321 7703053505 1183 0823312135 1051242 C 9114122586 7978297395 118 0875377451 7062663 D 1042349157 0853053814 12 0818395456 9099556 E 0983206046 0871198263 1199 0886079033 5196709 F 0905148405 0803451372 1198 0887646013 5098696 G 4950156706 4275082341 1186 0863625658 7213934 H 4889067068 4173762594 1188 0853693053 7687519 I 4854463762 4147024058 1189 0854270268 7771045
A 1048950046 0002141023 1149 0000204111 2112281 B 1039943573 0001770549 1157 0000170254 2460487 C 1084651695 0001127533 1153 0000103953 4014918 D 1088686867 0001201087 1172 0001103244 3564524 E 1119673887 0000783288 1177 0000699568 5709897 F 1045722787 0000914861 1181 000087486 4495324 G 5387981131 0001444832 1169 0000268158 1494715 H 5412748988 0001143483 1169 0000211257 1965749 I 5373948758 00010003 1164 0000186139 2280472
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60
Table 926 TR547- plutonium after four days
Sample ID
Initial Aq Conc (ppb)
Equil Aq Conc (ppb) pH
Fraction Aq Kd
A 104895 NA 116 NA NA B 10399436 0001828 1165 00001758 2383132C 10846517 00010788 1164 9946E‐05 4196159D 10886869 00009131 1184 00008388 4689778E 11196739 00010624 1189 00009488 4208928F 10457228 00007967 1191 00007619 516258G 53879811 00007915 1173 00001469 2728993H 5412749 00008355 1175 00001544 2690641I 53739488 00006103 1174 00001136 3737892
Table 927 TR547- neptunium after one day
Sample ID
Initial Aq Conc (ppb)
Equil Aq Conc (ppb) pH Fraction Aq Kd
A 9589772032 0000454463 1149 473903E‐05 9116335 B 9293228768 0000260081 1157 27986E‐05 1499475 C 1008725504 0000302018 1153 299405E‐05 1397125 D 0952173007 000019177 1172 0000201403 1954603 E 0992224074 BDL NA NA F 0967815522 402137E‐05 1181 41551E‐05 9474699 G 4068405786 0000222282 1169 546361E‐05 7336986 H 409543171 0000531619 1169 0000129808 3199152 I 4017406611 0000410123 1164 0000102086 4157807
Table 928 TR547- neptunium after four days
Sample ID
Initial Aq Conc (ppb)
Equil Aq Conc (ppb) pH Fraction Aq Kd
A 9589772 NA 116 NA NA B 92932288 00002145 1165 2308E‐05 1818463C 10087255 00001628 1164 1614E‐05 2591215D 0952173 BDL 1184 NA NA E 09922241 BDL NA NA F 09678155 5107E‐05 1191 5277E‐05 7460375G 40684058 00001336 1173 3284E‐05 1220544H 40954317 8151E‐05 1175 199E‐05 2086795I 40174066 00001322 1174 3292E‐05 1289605
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61
Table 929 TR547- technetium after one day
Sample ID
Initial Aq Conc (ppb)
Equil Aq Conc (ppb) pH Fraction Aq Kd
A 9466799266 8233850788 1149 0869760788 8220086 B 9439556236 817653394 1157 0866198975 8165745 C 9383493063 8086024379 1153 0861728604 8430884 D 1061939876 0919992065 1172 0866331594 6241759 E 0991827343 0836511397 1177 0843404251 7590958 F 0971981155 0839862696 1181 0864073024 6354378 G 4883337077 414858839 1169 0849539633 7903986 H 4691440077 3996173112 1169 0851800949 8038249 I 486993937 4291285586 1164 0881178442 6558707
Table 930 TR547- technetium after four days
Sample ID
Initial Aq Conc (ppb)
Equil Aq Conc (ppb) pH
Fraction Aq Kd
A 94667993 NA 116 NA NA B 94395562 85812109 1165 09090693 5885474C 93834931 84622373 1164 09018217 6279204D 10619399 09580683 1184 09021869 4435663E 09918273 08881507 1189 08954691 4835506F 09719812 09036489 1191 0929698 3138862G 48833371 4490415 1173 09195382 4312104H 46914401 42054182 1175 08964024 5612948I 48699394 43843193 1174 09002821 5536503
Table 931 TR547- iodine after one day
Sample ID
Initial Aq Conc (ppb)
Equil Aq Conc (ppb) pH Fraction Aq Kd
A 9944920441 8813152965 1149 0886196427 738241 B 9956006121 8747156303 1157 0878580848 8007767 C 9822152291 8664470934 1153 0882135674 7988892 D 1002391846 9333490632 1172 0931121963 3368509 E 9918273427 6625075445 1177 0667966607 1551748 F 9918175056 8931364957 1181 0900504872 4773862 G 5166570628 4445386532 1169 0860413387 7961604 H 4847821413 410447427 1169 084666367 8664303 I 4850381381 4266693706 1164 0879661489 6413801
100 Appendix B Data Tables of Radionuclide Sorption to Saltstone Under Reducing Conditions
The following tables represent data collected for the no solids controls each cementitious solid and testing of radionuclide sorption to the vial walls The no solids controls tables include the concentration (ppb) of the radionuclide spiked into the sample along with the concentration of the radionuclide (ppb) measured in the aqueous phase after the given equilibration time The pH at the time the sample was taken is also recorded along with the fraction of the radionuclide which stayed in the aqueous phase The tables for the cementitious solidsrsquo data include the data above along with the addition of a Kd value The tables of the data for the radionuclides sorbed to the vial walls include the initial concentration (ppb) of the spike the concentration (ppb) of the radionuclide that had sorbed to the vial wall during the experiment and the percentage of the total concentration this represents Important Notes
BDL= Below Detection Limit lt01 denotes no notable sorption occurred
101 Data Tables for No-Solid Controls
Table 101 Plutonium no solids control after one day
A 9405892 0007019 111 0000746258 5681206 B 9602498 0003294 1117 0000342992 123554 C 9630619 0002936 1114 0000304893 1396318 D 4945396 0001795 113 0000363011 1171688 E 4964945 0001373 1131 0000276484 1493015 F 4441601 0001516 113 0000341219 1389674 G 1079602 0001109 1142 0001027508 4215519 H 1031512 0000883 1143 0000855983 4820576 I 0939294 0000978 1143 0001040992 4550255
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Table 1011 Vault 2- neptunium after one day
Sample ID Initial Aq Conc (ppb)
Equil Aq Conc (ppb) pH Fraction Aq
A 9425042625 0001709054 1105 0000181331 B 9611386476 0001184125 1110 00001232 C 9579553607 0001155517 1104 0000120623 D 4974000414 0000672325 1125 0000135168 E 4916731623 0000675371 1128 0000137362 F 4373142817 0000570681 1120 0000130497 G 0943366414 0000389738 1129 0000413136 H 1011745587 0000565648 1132 0000559081 I 0865252712 0000379545 1133 0000438653
A 8849444124 0000306309 1150 346133E‐05 1289533 B 8447823057 0000150131 1155 177715E‐05 2711019 C 8590597085 0000199185 1153 231864E‐05 2044057 D 4491250244 517162E‐05 1156 115149E‐05 4020064 E 4391894479 204591E‐05 1158 465838E‐06 9846089 F 4210703646 204376E‐05 1158 485374E‐06 9816203 G 086381524 522216E‐06 1160 604546E‐06 7577764 H 0870501884 BDL 1160 NA NA I 0861953838 BDL 1162 NA NA
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Table 1036 Aged cement- neptunium after four days
Sample ID
Initial Aq Conc (ppb)
Equil Aq Conc (ppb) pH Fraction Aq Kd
A 8849444 0000131 1145 148418E‐05 3007445B 8447823 0000111 1146 131529E‐05 3662996C 8590597 656E‐05 1146 76328E‐06 6209405D 449125 BDL 1155 NA NA E 4391894 BDL 1156 NA NA F 4210704 BDL 1155 NA NA G 0863815 BDL 1165 NA NA H 0870502 BDL 1162 NA NA I 0861954 BDL 1164 NA NA
Table 1037 Aged cement- technetium after one day
Sample ID
Initial Aq Conc (ppb)
Equil Aq Conc (ppb) pH Fraction Aq Kd
A 8426518355 833290075 1150 098889012 0476492 B 8638001423 7823321167 1155 0905686487 4413063 C 9323317745 925927516 1153 0993130923 0294664 D 442651005 4300859603 1156 0971614106 1242837 E 4426849405 4336992073 1158 0979701742 0855315 F 3929483125 3938204338 1158 100221943 lt01 G 0817864386 081693181 1160 0998859743 0049487 H 0878958929 0792412508 1160 0901535306 4510199 I 0772205665 0871436364 1162 1128502941 lt01
Table 1038 Aged cement- technetium after four days
110 Appendix C Dixon et al (2009) FY09 PACA Maintenance Program Additional Saltstone Property Testing SRNL L3100-2009-00019 Rev 0
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SRNL L3100-2009-00019 Rev 0
December 16 2008
Keywords Performance Permeability Modulus
L B Romanowski
Waste Determinations From K L Dixon M A Phifer and J R Harbour
FY09 PACA Maintenance Program Additional Saltstone Property Testing
BACKGROUND
Additional tests have been identified for measurement of important hydraulic and physical properties of saltstone The initial phase of this work [1] was completed last year and the results were detailed in an internal report [2] The proposed testing for FY09 includes measurement of saturated hydraulic conductivity porosity bulk density particle density water retention and Youngrsquos modulus of simulated Saltstone grouts For completeness the bleed volumes and gel times for each mix will also be measured
The testing will be based on a projected salt solution composition for the ARPMCU stream that will be fed to the Saltstone Production Facility over the next few years The scope for FY09 will include testing to determine the impact of (1) admixtures (2) organics (3) wcm ratio (4) aluminate concentration and (5) temperature of curing on the hydraulic properties of saltstone mixes Samples of selected batches prepared as part of this task will be provided to Dan Kaplan for measurement of Kd through leaching tests The eleven mixes that will be batched and tested are detailed in Table 1
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Table 1 The Eleven Mixes That will be Batched and Tested
BFS is Blast Furnace Slag FA is Fly Ash and PC is Portland Cement
TEST DETAILS
Test 1 Control (Mix 1)
A control mix will be based on the baseline mix modified by exclusion of the Class F fly ash Consequently the cementitious materials premix will be a mixture of 90 blast furnace slag and 10 portland cement The degree of reaction will be much greater than with the normal premix and therefore should result in a lower porosity and a lower permeability This bounding test at 060 wcm ratio is expected to yield a hydraulic conductivity at or below the detection limit for the Mactec permeameter measurement system Therefore this test should demonstrate the lowest level of detection of the Mactec system as well as show a resolvable difference between measurements of the control mix and the control mix with the normal premix composition
Test 2 ndashImpact of Admixtures (Mixes 2 and 3)
Recent saltstone batches have required both a set retarder (Daratard 17) and an antifoam agent (Q2) for processing of the saltstone Therefore the baseline mix will be prepared with and without nominal levels of these two admixtures to determine whether these admixtures appreciably affect the hydraulic and physical properties of saltstone at these nominal concentrations
Test 3ndashImpact of Organics (Mixes 2 and 4)
The solvent extraction process is expected to result in some carryover of organics [3]
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Consequently a test will be performed on the impact of Caustic Side Solvent Extraction (CSSX) organics at 100 microliters per 1600 gram batch The CSSX solvent consists of 075 M 1-(2233-tetrafluoropropoxy)-3-(4-sec-butylphenoxy)-2-propanol (Cs-7SB) and 0003 M tri-n-octylamine (TOA) in an Isoparreg L diluent Test 4ndashImpact of Combination of Admixtures and Organics (Mixes 2 5 10 and 11)
This test will determine the impact of a combination of admixtures (Test 2) and organics (Test 3) together in the mix vs the baseline case without admixtures and organics
Test 5ndash Impact of wcm Ratio (Mixes 2 6 and 7)
It is well known that decreasing the wcm ratio in a mix will improve permeability in normal portland cement water mixes This test will measure the variation in permeability for the case of the MCU salt solution at three different wcm ratios The initial selection of wcm ratios is 055 060 and 065 However if the mix at an as-batched 065 wcm ratio has significant bleed water and the resulting actual wcm ratio is close to 060 then the three ratios will be adjusted to provide a more evenly spaced set of values However the baseline mix at 060 will be included as one of the three mixes
Test 6 ndash Impact of Aluminate Concentration (Mixes 8 9 and 10)
The DWPF has modified its process flowsheet to include a caustic washing of HLW sludge to remove some of the aluminum from the HLW prior to vitrification The resulting aluminate stream will then be blended with tank 50 material and fed to the SPF This increased aluminate concentration in the salt solution has significant impact on heat of hydration and set times and consequently it is likely that it will also impact permeability Therefore a set of three samples will be made at wcm ratios of 055 060 and 065 (as in Test 3) with a higher level of aluminate (028 M) for testing
Test 7 ndash Impact of Increased Curing Temperature (Mix 11)
In an ongoing task there is evidence that Youngrsquos modulus (a performance indicator) [4] is reduced by increasing the curing temperature of the mix Since the vault temperature increases during curing as a result of the exothermic hydration reactions one of the baseline mixes with a combination of admixtures and organics will be cured at 60
o
C rather than the normal 22
o
C to determine the impact of curing temperature on the permeability
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SCHEDULE
The schedule for the task of batching and testing of the samples is provided in Table 2 This schedule is based on the fact that the cementitious materials will be available for the testing as needed
Table 2 Additional Saltstone Hydraulic and Physical Property Tests
Item Schedule Start Work 12108 Test Plan Complete 1509 Preparation of 1st set of Samples Complete 11909 90-Day Cure Period for 1st set of Samples Complete 42009
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DISTRIBUTION Savannah River Site
A B Barnes 999-W Rm 336 H H Burns 999-W Rm 381 B T Butcher 773-43A Rm 212 A D Cozzi 999-W Rm 337 D A Crowley 773-43A Rm 216 M E Denham 773-42A Rm 218 J C Griffin 773-A Rm A-231 J R Harbour 999-W Rm 348 C A Langton 773-43A Rm 219 M H Layton 705-1C Rm 14 D I Kaplan (3 copies) 773-43A Rm 215 S L Marra 773A Rm A-230 A M Murray 773-A Rm 229 K A Roberts 773-43A Rm 225 T C Robinson 705-1C Rm 13 L B Romanowski 705-1C Rm 19 K H Rosenberger 705-1C Rm 16 F M Smith 705-1C Rm 24 RPA File (2 copies) 773-43A Rm 213
Clemson University Environmental Engineering and Earth Sciences 372 Computer Court LG Rich Environmental Laboratory Anderson SC 29625
31 Preparation of ICP-MS Standards Stock Solutions and Working Solutions 15 311 242Pu 15 312 237Np 16 313 99Tc 17 314 127I 18 315 Cementitious Materials Selected for Experiments 19
32 ICP-MS Detection Limits 20 33 Experimental Methods 20 34 Experimental Protocol for Sorption Experiments under Aerobic Conditions 21 35 Experimental Protocol for Sorption Experiments under Anerobic Conditions 22 36 Examination of Sorption to Vial Walls for Solids and No Solids Controls 23 37 Data Analysis 23
40 Results and Discussion 24 41 Radionuclide Sorption to Cementitious Formulations under Oxidizing Conditions 24 42 Radionuclide Sorption to Vial Walls Under Oxidizing Conditions 28 43 Radionuclide Sorption to Cementitious Formulations under Reducing Conditions 32 44 Radionuclide Sorption to Vial Walls under Reducing Conditions 38
50 Comparison of Radionuclide Sorption under Oxidizing and Reducing Conditions 40 60 Comparison of Radionuclide Sorption and Solubility under Oxidizing and Reducing Conditions46 70 Summary and Recommendations for Future Work 48
71 Comparison with Previous Data 48 72 Suggested Future Work 48
80 References 49 90 Appendix A Data Tables of Radionuclide Sorption to Saltstone under Oxidizing Conditions 51
91 Data Tables for No Solid Controls 51 92 Data Tables for Vault 2 54 93 Data tables for saltstone TR545 57 94 Data Tables for Saltstone TR547 59
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95 Data Tables for Aged Cement 62 96 Data Tables for Sorption to Vial Walls 65
100 Appendix B Data Tables of Radionuclide Sorption to Saltstone Under Reducing Conditions 66 101 Data Tables for No-Solid Controls 66 102 Data Tables for Vault 2 69 103 Data Tables for TR545 72 104 Data Tables for TR547 75 105 Data Tables for Aged Cement 78 106 Data Tables for Sorption to Vial Walls 80
110 Appendix C Dixon et al (2009) FY09 PACA Maintenance Program Additional Saltstone
Property Testing SRNL L3100-2009-00019 Rev 0 82
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LIST OF TABLES
Table 31 Characteristics of saltstone formulations used in this work Kaplan et al (2008) 19
Table 32 Detection limits for each isotope based on representative calibration curves generated in PlasmaLab software associated with the ICP-MS 20
Table 33 Experimental Matrix of Sorption Experiments under Aerobic Conditions 22
Table 61 Comparison of plutonium apparent solubility values under oxidizing and reducing conditions 46
Table 62 Comparison of neptunium apparent solubility values under oxidizing and reducing conditions 47
Table 63 Comparison of technetium Kd values under oxidizing and reducing conditions 47
Table 64 Comparison of iodine Kd values under oxidizing and reducing conditions 48
Table 91 Plutonium no solids control after one day 51
Table 92 Plutonium no solids control after four days 51
Table 93 Neptunium no solids control after one day 52
Table 94 Neptunium no solids control after four days 52
Table 95 Technetium no solids control after one day 52
Table 96 Technetium no solids control after four days 53
Table 97 Iodine no solids control after one day 53
Table 98 Iodine no solids control after four days 53
Table 99 Vault 2- plutonium after one day 54
Table 910 Vault 2- plutonium after four days 54
Table 911 Vault 2- neptunium after one day 54
Table 912 Vault 2- neptunium after four days 55
Table 913 Vault 2- technetium after one day 55
Table 914 Vault 2- technetium after four days 55
Table 915 Vault 2- iodine after one day 56
Table 916 Vault 2- iodine after four days 56
Table 917 TR545- plutonium after one day 56
Table 918 TR545- plutonium after four days 57
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Table 919 TR545- neptunium after one day 57
Table 920 TR545- neptunium after four days 57
Table 921 TR545- technetium after one day 58
Table 922 TR545- technetium after four days 58
Table 923 TR545- iodine after one day 58
Table 924 TR545- iodine after four days 59
Table 925 TR547- plutonium after one day 59
Table 926 TR547- plutonium after four days 60
Table 927 TR547- neptunium after one day 60
Table 928 TR547- neptunium after four days 60
Table 929 TR547- technetium after one day 61
Table 930 TR547- technetium after four days 61
Table 931 TR547- iodine after one day 61
Table 932 TR547- iodine after four days 62
Table 933 Aged cement- plutonium after one day 62
Table 934 Aged cement- plutonium after four days 63
Table 935 Aged cement- neptunium after one day 63
Table 936 Aged cement- neptunium after four days 63
Table 937 Aged cement- technetium after one day 64
Table 938 Aged cement- technetium after four days 64
Table 939 Aged cement- iodine after one day 64
Table 940 Aged cement- iodine after four days 65
Table 941 Plutonium sorbed to vial wall in no solids control 65
Table 942 Neptunium sorbed to vial wall in no solids control 65
Table 101 Plutonium no solids control after one day 66
Table 102 Plutonium no solids control after four days 67
Table 103 Neptunium no solids control after one day 67
Table 104 Neptunium no solids control after four days 67
Table 105 Technetium no solids control after one day 67
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Table 106 Technetium no solids control after four days 68
Table 107 Iodine no solids control after one day 68
Table 108 Iodine no solids control after four days 68
Table 109 Vault 2- plutonium after one day 69
Table 1010 Vault 2- plutonium after four days 69
Table 1011 Vault 2- neptunium after one day 70
Table 1012 Vault 2- neptunium after four days 70
Table 1013 Vault 2- technetium after one day 70
Table 1014 Vault 2- technetium after four days 71
Table 1015 Vault 2- iodine after one day 71
Table 1016 Vault 2- iodine after four days 71
Table 1017 TR545- plutonium after one day 72
Table 1018 TR545- plutonium after four days 72
Table 1019 TR545- neptunium after one day 73
Table 1020 TR545- neptunium after four days 73
Table 1021 TR545- technetium after one day 73
Table 1022 TR545- technetium after four days 74
Table 1023 TR545- iodine after one day 74
Table 1024 TR545- iodine after four days 74
Table 1025 TR547- plutonium after one day 75
Table 1026 TR547- plutonium after four days 75
Table 1027 TR547- neptunium after one day 76
Table 1028 TR547- neptunium after four days 76
Table 1029 TR547- technetium after one day 76
Table 1030 TR547- technetium after four days 77
Table 1031 TR547- iodine after one day 77
Table 1032 TR547- iodine after four days 77
Table 1033 Aged cement- plutonium after one day 78
Table 1034 Aged cement- plutonium after four days 78
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Table 1035 Aged cement- neptunium after one day 78
Table 1036 Aged cement- neptunium after four days 79
Table 1037 Aged cement- technetium after one day 79
Table 1038 Aged cement- technetium after four days 79
Table 1039 Aged cement- iodine after one day 80
Table 1040 Aged cement- iodine after four days 80
Table 1041 Plutonium sorbed to vial wall in no solids control 80
Table 1042 Neptunium sorbed to vial wall in no solids control 81
Table 1043 Technetium sorbed to vial wall in no solids control 81
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LIST OF FIGURES
Figure 31 Screen capture of a typical 242Pu calibration curve using Thermo PlasmaLab software to control the data collection and analysis R2=0999872 Intercept Conc (Detection Limit) = 0000044 ppb 16
Figure 32 Screen capture of a typical 237Np calibration curve using Thermo PlasmaLab software to control the data collection and analysis R2=0999981 Intercept Conc (Detection Limit) = 0000026 ppb 17
Figure 33 Screen capture of a typical 99Tc calibration curve using Thermo PlasmaLab software to control the data collection and analysis R2=0999984 Intercept Conc (Detection Limit) = 0000013 ppb 18
Figure 34 Screen capture of a typical 127I calibration curve using Thermo PlasmaLab software to control the data collection and analysis R2=0999991 Intercept Conc (Detection Limit) = 024 ppb 19
Figure 41 Plutonium Kd Values under Oxidizing Conditions Plutonium Kd values for various saltstone formulations measured after one-day equilibration (1d) and four-day equilibration (4d under oxidizing conditions Total plutonium concentrations in each system were 1 ppb 5 ppb and 10 ppb Sample prepared in triplicate and error bars represent standard deviation of samples except as follows value for dataset TR547-4d 10 ppb is reported based on duplicate samples 25
Figure 42 Plutonium solubility for various saltstone formulations measured after one-day equilibration (1d) and four-day equilibration (4d) under oxidizing conditions Total plutonium concentrations in each system were 1 ppb 5 ppb and 10 ppb as noted Samples prepared in triplicate and an average of all samples (9) was used to determine average solubility The error bars represent standard deviation of samples 25
Figure 43 Neptunium Kd values under oxidizing conditions Neptunium Kd values for various saltstone formulations measured after one-day equilibration (1d) and four-day equilibration (4d) under oxidizing conditions Total plutonium concentrations in each system were 1 ppb 5 ppb and 10 ppb as noted Samples prepared in triplicate and error bars represent standard deviation of samples except as follows value for datasets TR545-1d 1ppb TR545-4d 1 ppb TR547 4d 1 ppb TR545-4d 10 ppb TR547-1d 1ppb TR547-4d 10 ppb are reported based on a single sample and for dataset TR545-1d 5ppb is reported based on duplicate samples Kd values limited to gt106 were at instrumental background 26
Figure 44 Average solubility of Np under oxidizing conditions Neptunium solubility for various saltstone formulations measured after one-day equilibration (1d) and four-day equilibration (4d) under oxidizing conditions Total Np concentrations in each system were 1 ppb 5 ppb and 10 ppb Samples prepared in triplicate and an average of all samples (9) was used to determine average solubility except as follows TR545-1d is based on 6 samples TR545- 4d on 5 samples TR547-1d on 7 samples and TR547- 4d on 5 samples The error bars represent standard deviation 27
Figure 45 Technetium Kd values under oxidizing conditions Tc Kd values for various saltstone formulations measured after one-day equilibration (1d) and four-day equilibration (4d) under oxidizing conditions Total Tc concentrations in each system were 1 ppb 5 ppb and 10 ppb as noted above Samples were prepared in triplicate and the error bars represent standard deviation
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of samples except as follows data sets for Vault 2-1d 1ppb were duplicates and TR547- 4d 10 ppb is based on a single dataset 27
Figure 46 Iodine Kd Values under Oxidizing Conditions Iodine Kd values for various cementitious formulations measured after one-day equilibration (1d) and four-day equilibration (4d) under oxidizing conditions Total iodine concentrations in the systems were 100ppb 500 ppb and 1000 ppb as noted above Samples were prepared in triplicate and the error bars represent standard deviation of samples except as follows duplicates were used for dataset TR545- 1d 100ppb 28
Figure 47 Plutonium Neptunium and Technetium Aqueous Fractions Fraction of Pu Np and Tc remaining in the aqueous phase for the No Solids controls after a one-day equilibration (1d) and four-day equilibration (4d) under oxidizing conditions The total concentration for each radionuclide 10 ppb as noted above Samples were prepared in triplicate and the error bars represent the standard deviation of the samples 29
Figure 48 Iodine Aqueous Fraction Iodine aqueous fraction for the no-solids controls after a one-day equilibration (1d) and four-day equilibration (4d) under oxidizing conditions The total concentration of iodine was 1000 ppb as noted above Samples were prepared in triplicate and the error bars represent the standard deviation of the samples 29
Figure 49 Percent Pu and Np sorbed to vial walls of the no solids controls after the aqueous phases were discarded and the vials were washed Both the 10 ppb (blueleft) and 1 ppb (redright)) datasets were prepared in triplicate and the error bars show the standard deviation 31
Figure 410 Percent Pu sorbed to vial walls after the solids and aqueous phases were removed and the vials were washed The graph illustrates one sample from each of the 1 ppb (redleft) 5 ppb (greenmiddle) and 10 ppb (blueright) systems Therefore no error bars are present 31
Figure 411 Percent Np sorbed to vial walls after the solids and aqueous phases were removed and the vials were washed The graph illustrates one sample from each of the 1 ppb (redleft) 5 ppb (greenmiddle) and 10 ppb (blueright) systems Therefore no error bars are present 32
Figure 412 Pu Kd Values under Reducing Conditions Plutonium Kd values for various cementitious formulations measured after one-day equilibration (1d) and four-day equilibration (4d) under reducing conditions Total plutonium concentrations in each system were 1ppb 5 ppb and 10 ppb Samples prepared in triplicate and error bars represent standard deviation 33
Figure 413 Average Solubility of Plutonium under Reducing Conditions Plutonium solubility for various cementitious formulations measured after one-day equilibration (1d) and four-day equilibration (4d) under reducing conditions Total plutonium concentrations in each system were 1ppb 5 ppb and 10 ppb as noted Samples prepared in triplicate and an average of all samples (9) was used to determine average solubility The error bars represent standard deviation of samples 33
Figure 414 Np Kd Values under Reducing Conditions Neptunium Kd values for various cementitious formulations measured after one-day equilibration (1d) and four-day equilibration (4d) under reducing conditions Total Np concentrations in each system were 1 ppb 5 ppb and 10 ppb Samples were prepared in triplicate and the error bars represent standard deviation Kd values limited to gt106 were at instrumental background 34
Figure 415 Average Solubility of Neptunium under Reducing Conditions Neptunium solubility for various cementitious formulations measured after one day equilibration (1d) and four day
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equilibration (4d) under reducing conditions Total plutonium concentrations in each system were 1ppb 5 ppb and 10 ppb Samples prepared in triplicate and an average of all samples (9) was used to determine average solubility The error bars represent standard deviation 35
Figure 416 Tc Kd Values under Reducing Conditions Tc Kd values for various cementitious formulations measured after one-day equilibration (1d) and four-day equilibration (4d) under reducing conditions Total Tc concentrations in each system were 1 ppb 5 ppb and 10 ppb Sample prepared in triplicate and error bars represent standard deviation except as follows TR547-1d 1 ppb is based on a single dataset and datasets Vault 2-1d 5 ppb Vault 2- 4d 1 ppb Aged Cement-1d 5 ppb and Aged Cement-4d 1 ppb are duplicates 36
Figure 417 Data from Figure 416 replotted on a reduced linear scale for easier viewing Each sample was prepared in triplicate except as follows TR547-1d 1 ppb is based on a single dataset Vault 2-1d 5 ppb Vault 2- 4d 1 ppb Aged Cement-1d 5 ppb and Aged Cement-4d 1 ppb are duplicate datasets 36
Figure 418 Iodine Kd Values under Reducing Conditions I Kd Values for various cementitious formulations measured after one day equilibration (1d) and four day equilibration (4d) under reducing conditions Total iodine concentrations in each system were 100 ppb 500 ppb and 1000 ppb as noted Sample prepared in triplicate and error bars represent standard deviation of samples except as follows Vault 2-4 d 100 ppb is a single dataset while the datasets for Vault 2-1 d 100 ppb 4 d 1000 ppb TR545-4 d 1000 ppb 100 ppb TR547-4 d 1000 ppb 500 ppb 100 ppb and Aged Cement- 4 d 1000 ppb and 100 ppb are all based on duplicates 38
Figure 419 Plutonium Neptunium and Technetium No-Solids Aqueous Fractions under Reducing Conditions Pu Np and Tc aqueous fractions of No Solids controls after a one-day equilibration (1d) and four-day equilibration (4 d) under reducing conditions Total concentration for each radionuclide was 1 ppb and 10 ppb Samples were prepared in triplicate and the error bars represent the standard deviation 39
Figure 420 Percent of Pu Np and Tc sorbed to the vial walls of the No Solids control samples under reducing conditions Each the 1 ppb and 10 ppb samples were prepared in triplicate and the error bars represent the standard deviations of triplicate samples 39
Figure 421 Iodine No-Solids Aqueous Fractions under Reducing Conditions I aqueous fractions of No-Solids controls after a one-day equilibration (1d) and four-day equilibration (4d) under reducing conditions The total concentration for each system was 100 ppb and 1000 ppb Samples were prepared in triplicate and the error bars represent the standard deviation 40
Figure 51 Comparison of Tc I Np and Pu sorption to Vault 2 solid under oxidizing and reducing conditions 42
Figure 52 Comparison of Tc I Np and Pu sorption to TR 545 solid under oxidizing and reducing conditions 43
Figure 53 Comparison of Tc I Np and Pu sorption to TR547 solid under oxidizing and reducing conditions 44
Figure 54 Comparison of Tc I Np and Pu sorption to Aged Cement under oxidizing and reducing conditions 45
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LIST OF ABBREVIATIONS
DDI water Distilled deionized water ICP-MS Inductively coupled plasma ndash mass spectrometer
Kd Distribution coefficient LSC liquid scintillation counting NOM Natural organic matter PA Performance Assessment ppb parts per billion ppq parts per quadrillion QAQC Quality AssuranceQuality Control SA Special Analyses SRNL Savannah River National Laboratory SRS Savannah River Site
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10 Introduction Performance Assessments (PA) are risk calculations designed to determine (1) the maximum
amount of radioactivity that can be safely buried in a subsurface facility and (2) the potential human risk associated with disposing of radioactive waste in a subsurface facility Special Analyses (SAs) are similar to PAs except that they are designed to address specific issues related to PAs such as a new discovery since the PA was issued Commonly parameters describing the extent that a radionuclide interacts with solids at the source vadose zone and aquifer influence the extent of calculated human risk The two parameters that the SRS use to represent radionuclidesolid interactions are Kd and apparent solubility values together these parameters are referred to as sorption values Sorption values vary with radionuclides groundwater chemistry and the type of solid phase (and for cementitious materials by the age of the material during the calculation) In this work Kd and apparent solubility values are reported for 99Tc 127I 237Np and 242Pu sorption to various cementitious formulations
20 Objectives
The objectives of this work were to 1 Determine the influence of cementitious formulation on technetium (Tc) iodine (I) neptunium
(Np) and plutonium (Pu) sorption under oxidizing conditions The specific formulations that were evaluated included 1) an aged cement recovered from a 30-year old outdoor concrete pad on the SRS 2) Vault 2 concrete 3) TR545 saltstone and 4) TR547 saltstone (additional details are presented in Section 30 Materials and Methods)
2 Measure Tc I Np and Pu sorption to the cementitious formulations under reducing conditions
30 Materials and Methods
31 Preparation of ICP-MS Standards Stock Solutions and Working Solutions
311 242Pu
A National Institute of Standards and Technology Standard Reference Material (NIST SRM 434H) was used to prepare a stock 242Pu solution by dilution in 2 Aristar Optima HNO3 All volume additions were monitored gravimetrically This working solution was then used to make a set of 001 005 1 2 5 10 parts per billion (ppb) standards by dilution using 2 HNO3 Again all volume additions were monitored gravimetrically These standards were used to calibrate the Thermo Scientific X Series 2 inductively coupled plasma ndash mass spectrometer (ICP-MS) for quantification of 242Pu A representative calibration curve for 242Pu is shown in Figure 31 The instrument performance was monitored using 209Bi 232Th and 238U as internal standards The recovery of each sample during analysis was corrected based on the internal standard recovery The internal standard recoveries remained within standard quality assurancequality control QAQC protocols for the instrument (between 80 and 120)
A 242Pu stock solution was prepared by dissolving 1mg of Pu(NO3)4 obtained as a Certified Reference Material from New Brunswick Laboratory (CRM 130) This CRM is gt999 242Pu by atom percent The CRM was dissolved in 20mL of 8M HNO3 (Aristar Optima Grade) Because no chemicals or heat have been introduced to manipulate the Pu oxidation state it can be assumed that Pu(IV) is the predominant oxidation state in this stock solution A working solution to be used in spiking 242Pu experiments was prepared by diluting 25 mL of the CRM stock solution with 100 mL 10 M Aristar Optima HNO3 The concentration of 242Pu in this stock solution was determined using ICP-MS calibrated using the NIST SRM standards The concentration of Pu in this stock solution was 1065 ppb The total Pu
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16
concentration was also determined using liquid scintillation counting using the isotopic ratios reported for CRM 130 These compared favorably with the ICP-MS results but are reported here as a rigorous standardization because the isotopic ratios of CRM 130 have not yet been certified
Figure 31 Screen capture of a typical 242Pu calibration curve using Thermo PlasmaLab software to control the data collection and analysis R2=0999872 Intercept Conc (Detection Limit) = 0000044 ppb
312 237Np
A National Institute of Standards and Technology Standard Reference Material (NIST SRM 4341) was used to prepare a stock 237Np solution by dilution in 2 Aristar Optima HNO3 All volume additions were monitored gravimetrically This working solution was then used to make a set of 001 005 1 2 5 10 ppb standards by dilution using 2 HNO3 Again all volume additions were monitored gravimetrically These standards were used to calibrate the Thermo Scientific X Series 2 ICP-MS for quantification of 237Np A representative calibration curve for 237Np is shown in Figure 32 The instrument performance was monitored using 209Bi 232Th and 238U as internal standards The recovery of each sample during analysis was corrected based on the internal standard recovery The internal standard recoveries remained within standard QAQC protocols for the instrument (between 80 and 120)
A compiled 237Np stock solution from the Environmental Engineering and Earth Science (EEampES) inventory (primarily purchased from Isotope Products Valencia CA) was evaporated to dryness then the residue was brought up in approximately 5mL 80 M HNO3 Then 10 M hydroxylamine hydrochloride (NH2OHHCl EMD Chemicals ACS grade) and water were added to achieve a 3M HNO303M NH2OHHCl solution This solution was purified by extraction chromatography using Eichrom TEVA resin packed in a Bio-Rad poly-prep column The 3M HNO303 M NH2OHHCl neptunium solution was loaded on a 2 mL column and washed with 3 column volumes of 3 M HNO3 The Np(IV) was eluted with 002 M HCl + 02 M HF The effluent was evaporated to dryness then redissolved in 10 M HNO3 Additional 10 M HNO3 was added to maintain a approximately 10 mL then the solution was evaporated to incipient dryness and redissolved in a 50 mL of 10 M HNO3 An aliquot of the stock solution was evaporated to dryness on a stainless steel planchet and counted on the EGampG Ortec Alpha Spectrometer (Octete PC Detectors) No other alpha energies besides 237Np were observed The approximate concentration was determined using liquid scintillation counting and little 233Pa was observed The fuming in HNO3 as performed at the end of the purification procedure will drive Np to the soluble pentavalent state This is the stable oxidation state of Np under the experimental conditions Therefore experiments performed here can be assumed to be initially Np(V) The exact Np
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17
concentration in this solution was determined using ICP-MS calibrated with a NIST standard as discussed in section 312 below
A 237Np working solution (Working Solution 1) was created by pipetting an aliquot of the 237Np stock solution into a 100 mL Nalgene Teflon bottle and diluting with 2 BDH Aristar Ultra HNO3 to give a working solution concentration of 820 ppb All volumes were monitored gravimetrically Analysis on the ICP-MS calibrated against NIST Standards as described below gave a concentration of 820 ppb in Working Solution 1
Figure 32 Screen capture of a typical 237Np calibration curve using Thermo PlasmaLab software to control the data collection and analysis R2=0999981 Intercept Conc (Detection Limit) = 0000026 ppb
313 99Tc
A 99Tc working solution was prepared by diluting a stock solution of 99Tc (from the EEampES inventory purchased from Isotope Products Valencia CA) in distilled-deionized water (DDI Resistivity gt18 MΩcm) The oxidation state of Tc was not measured However based on the aqueous concentration in the DDI water solution Tc(VII) is the expected oxidation state The reduced Tc(IV) oxidation state would not be soluble under these conditions The expected concentration of 950 ppb based on the dilution was verified using liquid scintillation counting The 99Tc working solution was used to make 001 005 1 2 5 and 10 ppb standards by dilution using 2 HNO3 These standards were used to calibrate the Thermo Scientific X Series 2 ICP-MS for quantification of 99Tc A screen shot of a representative calibration curve is shown in Figure 33 The instrument performance was monitored by interpolating between 89Y and 115In internal standards The recovery of each sample during analysis was corrected based on the internal standard recovery The internal standard recoveries remained within standard QAQC protocols for the instrument (between 80 and 120)
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Figure 33 Screen capture of a typical 99Tc calibration curve using Thermo PlasmaLab software to control the data collection and analysis R2=0999984 Intercept Conc (Detection Limit) = 0000013 ppb
314 127I
A 100 microgmL iodate (IO3-) stock solution from High Purity Standards (Charleston SC) was used
to make 1 5 10 50 and 100 ppb standards by dilution using the ldquotraprdquo solution (discussed in Section 32 below) These standards were used to calibrate the Thermo Scientific X Series 2 ICP-MS for quantification of 127I A screen shot of a representative calibration curve is shown in Figure 34 The use of a reducing basic trap solution for iodine analysis limits the number of available internal standards that can be used to monitor ICP-MS instrument performance during iodine analysis Experiments are underway to identify acceptable internal standards However the data presented in this work did not use any internal standards prior to rigorous testing and analysis of representative standards As with the analyses for all isotopes (Tc I Np and Pu) spiked QAQC samples were frequently analyzed throughout the analysis as a check on instrument performance While these values cannot be used to correct individual samples in the same manner that the internal standards can they can be used to ensure accurate measurements of each isotope In almost all cases QAQC standards were within 10 of the expected value Because the average internal standard recovery ranges between 80 and 120 for the ICP-MS the iodine QAQC standard appears to be acceptable However a significant amount of ongoing work is testing various internal standards to improve the accuracy of iodine analysis using ICP-MS In one experiment (discussed in detail below) the QAQC standards deviated by an average value of 195 This will be specifically discussed below
Because experiments were performed with 127I concentrations up to 1000 ppb the 100 microgmL (ppm) stock iodate solution from High Purity Standards was used as the working solution
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Figure 34 Screen capture of a typical 127I calibration curve using Thermo PlasmaLab software to control the data collection and analysis R2=0999991 Intercept Conc (Detection Limit) = 024 ppb
315 Cementitious Materials Selected for Experiments There were four cementitious materials selected for this sorption study The first referred to as Aged Cement is a 30 year old sample that does not contain any reducing slag The aggregate from the Vault 2 cement had its aggregate removed prior to conducted tests in an effort to make subsamples more uniform This was necessary because some of the aggregate were larger than the 05 g subsamples used in individual sorption tests The Vault 2 cementitious material contained 17 dry wt- reducing slag on a dry weight basis before the water was added to the mix (Table 31) The TR547 and TR545 saltstone formulations contain 45 dry wt- and 90 dry wt- reducing slag respectively
Table 31 Characteristics of saltstone formulations used in this work Kaplan et al (2008)
Sample Percent Reducing Slag (dry wt-) (c)
Percent Portland Cement
(dry wt-) (c)
Percent Fly Ash
(dry wt-) (c)
Percent Aggregatesand ( dry wt-) (c)
Reducing Equivalents
(microeqg)
Aged Cement 0 10 45 45 855 plusmn 101(a)
Vault 2 Cement 17 10 45 0 178(b)
TR547 45 10 45 0 607(b) TR545 90 10 0 0 681(b) Blast furnace slag 100 0 0 0 819(b) (a) Kaplan et al (2008) (b) Roberts and Kaplan (2009) (c) All percentages of saltstone formulations are reported on a dry weight percentage basis that is the weight of the ingredients before water was added (d) Based on Table 8 in Dixon et al (2008 SRNL-STI-2008-00421) which shows the following quantity (lbscu yd) for saltstone Vault 2 Mix 1 concrete formulation 201 cement (1271 wt-) 268 slag (1695 wt-) 447 silica fume (283 wt-) 1563 fly ash (989 wt-) 911 fine sand (5762 wt-) The large aggregate was removed before the sorption tests were conducted The large aggregate accounted for 75 wt- of the original field sample not the sample used in these test before water was added to the mix TR547 is referred to as the Baseline by Dixon et al (2008) and is described in more detail in Appendix C (Mix 2) by Dixon et al (2008) (Control-BFSPC) and 1 (Baseline)
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TR545 saltstone contains 90 reducing slag and it is Mix 1 in Dixon et al (2008) and is described as
ldquoA control mix will be based on the baseline mix modified by exclusion of the Class F fly ash Consequently the cementitious materials premix will be a mixture of 90 blast furnace slag and 10 Portland cement The degree of reaction will be much greater than with the normal premix and therefore should result in a lower porosity and a lower permeability This bounding test at 060 wcm ratio is expected to yield a hydraulic conductivity at or below the detection limit for the Mactec permeameter measurement system Therefore this test should demonstrate the lowest level of detection of the Mactec system as well as show a resolvable difference between measurements of the control mix and the control mix with the normal premix compositionrdquo
32 ICP-MS Detection Limits
The PlasmaLab software platform determines a detection limit for each isotope based upon the intercept concentration A new calibration curve was generated for each experimental run and curves were very similar Using representative calibrations curves the detection limits for each isotope were as listed in Table 32 Note the higher detection limit for 127I is primarily due to the higher background count rate observed on the instrument This is believed to be due to the minimum purity levels of chemicals required for the iodine ldquotraprdquo solution as discussed in Section 33 below Therefore experiments were run with initial iodate concentrations higher than Tc Np and Pu to maintain analytical sensitivity
Table 32 Detection limits for each isotope based on representative calibration curves generated in PlasmaLab software associated with the ICP-MS
33 Experimental Methods
The experimental methods used in this work followed closely those previously described for experiments examining radionuclide sorption to saltstone (Kaplan et al 2007 Kaplan et al 2008) Brief descriptions of each method are provided below
Preparation of Calcite Solution Using a hotstirring plate 10 L of distilled-deionized (DDI)
water was heated to 3-100C above room temperature Then 001 g CaCO3 (EM Science ACS grade) was added to the solution and the resulting suspension was mixed for 24 hours at the elevated temperature The solution was then vacuum filtered through a 045-microm filter to ensure no solid CaCO3 remained in solution
Preparation of 2 HNO3 Analysis of Tc Np and Pu on the ICP-MS required dilution in 2
HNO3 This was prepared by adding 28 mL of Aristar Optima HNO3 from a clean graduated cylinder (designated to 2 HNO3) into a 1 L volumetric flask (designated to 2 HNO3) partially filled with DDI water and then further diluted to volume
Preparation of Trap Solution for Iodine Analysis Analysis of I required the use of a reducing
basic solution that was capable of reducing iodate to iodine and holding the iodine in solution This minimized the loss of I during sample analysis A 1 L trap solution was prepared by weighing out 00500 g NaHSO3 (Fisher Scientific ACS Grade) on a calibrated Sartorous LA 230S scale and adding it to a 1L volumetric flask Then 40 mL of 25 ww tetramethylammonium hydroxide (Alfa Aesar electronic grade) and 10 mL CFA-C solution (Spectrasol Inc) were added to the volumetric flask via a calibrated 1000-5000 microL Eppendorf Research pipette The solution was then diluted to volume with DDI water
34 Experimental Protocol for Sorption Experiments under Aerobic Conditions
Falcon BlueMax 15mL polypropylene vials were labeled and weighed to within 0001 g on a calibrated Sartorious LA 230S scale The scale was then zeroed and 025 +- 001 g of a given solid were added to each tube and the weight was recorded to within 0001g
For each of the four solids three sets of triplicate samples were prepared The three sets of samples were used to allow for experiments to be run with varying concentrations of each isotope Target initial concentrations for 99Tc 237Np and 242Pu samples were 1 ppb 5 ppb and 10 ppb Target initial concentrations for the 127I samples were 100 ppb 500 ppb and 1000 ppb A set of no solids controls at initial concentrations of 1 ppb and 10 ppb for 99Tc 237Np and 242Pu and initial concentrations of 100 ppb and 1000 ppb 127I were also prepared by adding the calcite solution to pre-weighed pre-labeled centrifuge tubes as discussed above
The solids were equilibrated with the calcite solution before spiking with the radionuclides This was done by adding 10 plusmn 01 mL of calcite solution to each tube and recording the mass The samples were then placed on a Thermo Scientific shaker overnight After 24 hours the solutions were allowed to settle for 1 hour The pH was then measured and the samples were then centrifuged for 15 minutes at 8000 rpm to further separate the solids The aqueous phase was then decanted and 10 plusmn 01 mL of calcite solution was added to each tube The weight of the tube (labeled tube + solid + calcite solution) was measured to within 0001g During this washing process the pH was monitored and held steady throughout the process The pH ranged from 11-12 depending on the particular saltstone used During the experiments the exact pH for all samples at all equilibration times was measured and is reported in Appendix A and B
The resulting suspensions were then spiked with 127I 237Np 242Pu and 99Tc It is important to note that all four isotopes were added to the same vial Use of the ICP-MS to determine the concentration of each isotope allows for a single solution to contain all analytes of concern This allowed for a greater variability in the sample set and increased replicates as opposed to running individual sorption tests for each isotope For the systems with initial 99Tc 237Np and 242Pu concentrations of 10 ppb and initial 127I concentration of 100 ppb a 100 microL aliquot of each radionuclide working solution was added to the first three tubes for each solid The addition was made with the tube resting on a tared analytical balance so that the exact mass of each radionuclide solution added was recorded and the solution was gently swirled before the next radionuclide was added The 5 ppb 237Np 242Pu and 99Tc and 500 ppb 127I samples were prepared in the same manner but adding 50 microL of the respective spike solutions The final three tubes with initial 237Np 242Pu and 99Tc concentrations of 1 ppb and 100 ppb 127I were prepared by using 10 microL of the spike solutions for all four solids as well as a set of solid-free controls (No-Solids Controls) For clarity this experimental matrix is shown in Table 33 below
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Table 33 Experimental Matrix of Sorption Experiments under Aerobic Conditions
After spiking the radionuclides a precalculated amount of 10M NaOH was added to each sample
to counter the acidic radionuclide spike solutions and the pH of one of the triplicate samples was measured to ensure the proper pH range was reached The samples were then placed on and end-over-end shaker to mix at approximately 8 rpm After 24 hours the samples were removed from the shaker and the pH of each sample was measured using an Orion Ross semi-micro glass electrode calibrated against pH 4 7 and 10 buffers (Thermo) The samples were then shaken and a transfer pipette was used to transfer 35 mL of a homogenous suspension to a 5mL syringe The solution was then passed through a 100 nm nylon syringe filter The first 025-050 mL of filtrate was discarded and the remaining filtrate was collected in a clean polyethylene vial Then 10 mL of the filtrate was removed and diluted in 90 mL 2 HNO3 The mass of each phase was determined and recorded gravimetrically Then 10 mL of the remaining filtrate was transferred to a clean Falcon BlueMax 15mL vial and diluted with 90 mL of trap solution for 127I analysis Again the volume of each phase was monitored gravimetrically After the 24 hour sampling event the samples were put back on the shaker to mix for three additional days On day four the above sampling procedure was repeated
The 237Np 242Pu and 99Tc samples can be run on the Thermo Scientific ICP-MS using the standard setup and procedure which included a standard flow glass nebulizer and bulb spray chamber However for the 127I analysis the ICP-MS must be reconfigured to accommodate the basic reducing trap solution This is to alleviate problems with iodine signal stability over time frequently observed in ICP-MS analysis The reconfigured instrument uses an Elemental Science Microflow PFA-100 Teflon nebulizer with a flow rate of 100microLmin along with a sapphire torch and a Teflon spray chamber This configuration must be run with a low pump speed to prevent back pressure on the system Two 30 minute stability tests were performed using a 50 ppb iodate solution Each experiment consisted of 40 separate measurements After each experiment was completed the uncorrected mass counts were examined and found to stay steady over the sampling period The relative standard deviation ( RSD) over all samples for each experiment was 1866 and 1460 respectively This shows that there was no significant ldquomemoryrdquo or loss of the iodine signal over time and that the reconfigured instrument has a stable iodine signal over time However as will be discussed below some difficulty has been encountered in finding an adequate internal standard for iodine analysis
35 Experimental Protocol for Sorption Experiments under Anerobic Conditions In order to examine the effects of reducing conditions of sorption of each isotope to the various cementitious samples a series of sorption experiments were performed in an anaerobic glovebox under a 2 H2(g) 98 N2(g) atmosphere Based on the measured pH and EH of these systems as discussed below these systems were at the point of reducing water Therefore they are expected to represent a lower end of the possible range for reducing conditions expected in the porewater available within cementitious materials
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Preparation of Calcite for Reducing Conditions Approximately 35 L of DDI water was boiled for 45 minutes Argon was slowly bubbled through the water as it cooled Once it cooled to below 500C approximately 3 g of calcite was added This solution mixed overnight under a continuous Ar flow After 12 hours the solution was moved into an oxygen free glove bag for filtration as described in 3231 After filtration the calcite solution was moved into the glove box
Preparation of Working Solutions under Reducing Conditions The calcite and solid solutions
were prepared in the glove box using the previously mentioned procedure used under aerobic conditions The radionuclide working solutions were transferred to the glovebox and stirred open to the reducing atmosphere for at least three days The concentration of each isotope in the working solutions was measured to determine any change in the concentration due to evaporation while the solutions were equilibrating
The preparation and spiking of samples for sorption experiments was performed exactly as described for the oxidizing conditions except all sample handling was performed in the glovebox After the 1 day and 4 day equilibration the samples were filtered within the glovebox then transferred outside for dilution and ICP-MS analysis similar to the description provided about for the oxidizing conditions For these experiments only 4 mL of either 2 HNO3 or trap solution were used to dilute the filtrate instead of the 90 mL used above for experiments performed under oxidizing conditions
36 Examination of Sorption to Vial Walls for Solids and No Solids Controls
As will be discussed below the solid-free controls samples indicated significant loss of Np and Pu Once the one and four days samples were collected and run on the ICP-MS it was necessary to determine the degree each radionuclide was sorbing to the vial walls The remaining suspensions and controls were emptied into a waste container Then 5 mL of the calcite solution was added to each vial using a calibrated pipette The vials were sonicated for approximately one minute and then emptied into the waste container Another 5 mL of calcite solution was added for the second wash and then discarded into the waste container This procedure was expected to remove any soluble Pu from the system or Pu associated with colloidal particles After each vial was washed 10 mL of 2 HNO3 was added using a calibrated pipette The acid solution is expected to remove any Tc Np or Pu associated with the vial walls This procedure has been shown to complete mass balances of Pu in similar sorption experiments using Pu (Powell et al 2002) This process was performed for both the solid suspension and the no solids controls The samples were then run on the ICP-MS to determine the concentration of 99Tc 237Np and 242Pu sorbed to the vial walls
37 Data Analysis The solubilities of 242Pu and 237Np were calculated by using the formula
nuclide
nuclide
nuclideMSICP
sol Mg
gCC
)(10 6
microminus
minus
= (Equation 31)
Csol = observed nuclide solubility (molnuclidekgsolution) CICP-MS = aqueous concentration of nuclide from ICP-MS measurement (ppb micrognuclidekgsolution) Mnuclide = molecular mass of nuclide (gnuclidemolnuclide)
In order to determine the Kd values one first needs to determine the concentration on the solid by using
SRNL-STI-2009-00636 Revision 0
24
solid
calcitespikeaqspikecalcite
spikestock
solid m
mmCmmmC
C)(
)()(
+⎥⎥⎦
⎤
⎢⎢⎣
⎡minus
+
lowast
= (Equation 32)
Csolid = calculated solid phase concentration of the nuclide (ppb) Cstock = concentration of the nuclide stock solution (ppb) mspike = mass of nuclide spiked into the saltstone suspension (g) mcalcite = total mass of calcite solution used in the saltstone suspension (g) Caq = aqueous concentration of nuclide from ICP-MS measurement (ppb) msolid = mass of the saltstone used in the suspension (g)
The Kd can be calculated using the equation
aq
solidd C
CK = (Equation 33)
Kd = solid-water partitioning coefficient (gsolutiongsolid assuming density of 10 gmL traditional
unit of mLsolutiongsolid can be obtained) This Kd Equation (33) is numerically equivalent to the traditional Kd equation proposed in ASTM D-4646 which has been used in previous saltstone experiments (Kaplan et al 2007 Kaplan et al 2008)
40 Results and Discussion
41 Radionuclide Sorption to Cementitious Formulations under Oxidizing Conditions
Figure 41 shows Pu Kd values ranging from 104 to gt105 mLg Generally for each solid the Kd increases with increasing initial Pu concentrations typical behavior of systems where the aqueous concentrations of the radionuclides are solubility controlled This is not expected because the Kd expression indicates that the Kd value should remain constant with increasing total Pu concentrations It was noted that aqueous phase concentration of Pu remained relatively constant in all samples (see discussion below regarding Pu solubility) Therefore the sorption capacity of each solid phase for Pu has not been overcome For each of these solid phases it appears the solutions had reached equilibrium before the first samples were taken at 24 hours In each case the Kd values for the one day and four day are similar A trend between the solid phases is not discernible The aged cement with no reducing slag was expected to have the lowest Kd values but in actuality it has the highest Kd Also there is no correlation with the concentration of reducing slag The Vault 2 samples with 17 dry wt- reducing slag has a Kd similar to that of the TR547 (45 dry wt- slag) while the saltstone with the most slag TR545 (90 dry wt- slag) has the lowest Kd value Others have observed that Pu Kd values of cementitious materials are similar in the absence and presence of slag (Allard et al 1984 Hoaglund et al 1985)
It was observed that similar aqueous concentrations of Pu were observed regardless of the solid phase present Figure 42 shows the average aqueous phase concentrations measured after one day and four days for all solids As stated above triplicate samples were prepared for each solid phase and each initial concentration Therefore each of the reported solubility values in Figure 42 is an average of nine measurements Using the highest reported value with the expected maximum error (0018 ppb for solid TR545) the maximum expected aqueous concentration of Pu in the pore water associated with the
SRNL-STI-2009-00636 Revision 0
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saltstone formulations will be approximately 7 x 10-11 molL as calculated using Equation 31 This is on the same order as the solubility of Pu hydrous oxide solid phases (Neck and Kim 2001)
Figure 41 Plutonium Kd Values under Oxidizing Conditions Plutonium Kd values for various saltstone formulations measured after one-day equilibration (1d) and four-day equilibration (4d under oxidizing conditions Total plutonium concentrations in each system were 1 ppb 5 ppb and 10 ppb Sample prepared in triplicate and error bars represent standard deviation of samples except as follows value for dataset TR547-4d 10 ppb is reported based on duplicate samples
Figure 42 Plutonium solubility for various saltstone formulations measured after one-day equilibration (1d) and four-day equilibration (4d) under oxidizing conditions Total plutonium concentrations in each system were 1 ppb 5 ppb and 10 ppb as noted Samples prepared in triplicate and an average of all samples (9) was used to determine average solubility The error bars represent standard deviation of samples
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Overall the Kd values for Np range from 105 to gt106 with only a few outliers The most significant outlier is the 1 ppb solution in the TR545 sample after the four-day equilibration It drops two orders of magnitude while the 5 and 10 ppb solutions remain constant However this result is most likely an analytical artifact from working at the detection limits of the ICP-MS In the one-day equilibration samples only one of the triplicates S-2-E had detectable Np while in the four-day equilibration samples only S-2-F had detectable amounts present The graph also shows that with the exception of the 5 ppb sample in the aged cement Np sorption to TR545 (90 dry-wt- slag) and TR547 (45 dry wt- slag) have Kd values approximately one order of magnitude over the aged cement (no slag) and Vault 2 (17 dry wt- slag) samples
It was observed that similar aqueous concentrations of Np were observed regardless of the solid phase present Figure 44 shows the average aqueous phase concentrations measured after one day and four-day equilibrations for all solids As stated above triplicate samples were prepared for each solid phase and each initial concentration Therefore each of the reported solubility values in Figure 44 is an average of nine measurements of Np concentration unless stated otherwise Using the highest reported value with the expected maximum error (00026 ppb for solid TR545) the maximum expected aqueous concentration of Pu in the pore water associated with the saltstone formulations will be approximately 2 x 10-11 molL
Figure 43 Neptunium Kd values under oxidizing conditions Neptunium Kd values for various saltstone formulations measured after one-day equilibration (1d) and four-day equilibration (4d) under oxidizing conditions Total plutonium concentrations in each system were 1 ppb 5 ppb and 10 ppb as noted Samples prepared in triplicate and error bars represent standard deviation of samples except as follows value for datasets TR545-1d 1ppb TR545-4d 1 ppb TR547 4d 1 ppb TR545-4d 10 ppb TR547-1d 1ppb TR547-4d 10 ppb are reported based on a single sample and for dataset TR545-1d 5ppb is reported based on duplicate samples Kd values limited to gt106 were at instrumental background
The Kd values for Tc are significantly lower than that of Pu or Np As a whole the values are
comparable The values for the one-day and four-day equilibrations solutions in the Vault 2 (17 dry wt- slag) and TR545 (90 dry wt- slag) remained constant within reasonable error with just a slight increase from the one-day to four-day equilibration However the Aged Cement (no slag) and TR547 (45 dry wt- slag) showed a noticeable decrease from day one to day four (Figure 45)
SRNL-STI-2009-00636 Revision 0
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Figure 44 Average solubility of Np under oxidizing conditions Neptunium solubility for various saltstone formulations measured after one-day equilibration (1d) and four-day equilibration (4d) under oxidizing conditions Total Np concentrations in each system were 1 ppb 5 ppb and 10 ppb Samples prepared in triplicate and an average of all samples (9) was used to determine average solubility except as follows TR545-1d is based on 6 samples TR545- 4d on 5 samples TR547-1d on 7 samples and TR547- 4d on 5 samples The error bars represent standard deviation
Figure 45 Technetium Kd values under oxidizing conditions Tc Kd values for various saltstone formulations measured after one-day equilibration (1d) and four-day equilibration (4d) under oxidizing conditions Total Tc concentrations in each system were 1 ppb 5 ppb and 10 ppb as noted above Samples were prepared in triplicate and the error bars represent standard deviation of samples except as follows data sets for Vault 2-1d 1ppb were duplicates and TR547- 4d 10 ppb is based on a single dataset
SRNL-STI-2009-00636 Revision 0
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Similar to the Tc Kd values the 127I Kd values are much lower than those of Pu and Np The amount of reducing slag present in each of the solids does not appear to have a drastic effect on the 127I Kd values In fact the initial (one day) Aged Cement (0 slag) samples had a Kd almost two orders of magnitude above those with reducing slag The cause of this behavior is not known but it has been shown that iodate IO3
- the oxidized form of iodine sorbs more strongly than iodide I- to charged surfaces (Schwehr et al 2009 Yoshida et al 1992 Fukui et al 1996) It is possible that the slag is reducing the iodine to the I- form converting it to a species that is less likely to sorb to saltstone Additional work would be required to confirm the oxidation state of iodine when associated with saltstone
Figure 46 Iodine Kd Values under Oxidizing Conditions Iodine Kd values for various cementitious formulations measured after one-day equilibration (1d) and four-day equilibration (4d) under oxidizing conditions Total iodine concentrations in the systems were 100ppb 500 ppb and 1000 ppb as noted above Samples were prepared in triplicate and the error bars represent standard deviation of samples except as follows duplicates were used for dataset TR545- 1d 100ppb
42 Radionuclide Sorption to Vial Walls Under Oxidizing Conditions
Figure 47 shows the aqueous fractions found in the no-solids controls It provides a measure of the solubility of each radionuclide as well as examines the fraction of each radionuclide sorbed to the vial walls After one day only 25 of the Pu remained in solution and the concentration decreased even more after four days The loss of Pu from the aqueous phase may be due to sorption of Pu to the vial walls or precipitation of a Pu hydrous oxide solid (discussed with respect to Figure 49 below) Additional experiments would be required to examine the solubility of the Pu in high pH calcite saturated solutions
After one day about 80 of the Np remained in solution However the aqueous concentration in the initially 1-ppb solution was significantly reduced after four days Approximately 60 of the Np remained soluble in the initially 10-ppb solution Once again this drop could be due to sorption to the vial wall The Tc present after one day ranged from about 88 to about 95 and was virtually 100 after four days These values are consistent with internal standards used to monitor Tc detection performance on the ICP-MS Greater than 50 of the I remained in solution after the one-day and four-day equilibrations As shown in Figure 48 the standard deviation between the triplicate I control samples was
SRNL-STI-2009-00636 Revision 0
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quite large Additional control samples are required to understand the mechanism by which I is being lost from the aqueous phase in these samples
Figure 47 Plutonium Neptunium and Technetium Aqueous Fractions Fraction of Pu Np and Tc remaining in the aqueous phase for the No Solids controls after a one-day equilibration (1d) and four-day equilibration (4d) under oxidizing conditions The total concentration for each radionuclide 10 ppb as noted above Samples were prepared in triplicate and the error bars represent the standard deviation of the samples
Figure 48 Iodine Aqueous Fraction Iodine aqueous fraction for the no-solids controls after a one-day equilibration (1d) and four-day equilibration (4d) under oxidizing conditions The total concentration of iodine was 1000 ppb as noted above Samples were prepared in triplicate and the error bars represent the standard deviation of the samples
SRNL-STI-2009-00636 Revision 0
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As discussed above the loss of Np and Pu from the no-solids control (Figure 47) could be due to
precipitation of Np and Pu hydrous oxides or sorption to the vial walls To quantify the differences between these possible sinks the vials were washed as described in Section 36 The data in Figure 49 indicate that significant sorption of Np and Pu to the vial walls may occur When combining the mass of Np represented in Figure 47 and Figure 49 there is almost 100 mass recovery of the Np sorbed to the vial wall and the aqueous fraction measured Therefore no precipitation of Np is expected However because 100 recovery was not achieved for Pu a Pu hydrous oxide phase could be precipitating which was washed out of the vial during the cleaning procedure The data in Figure 47 represent the no-solids control samples where there was no solid phase present for Np or Pu to sorb to besides the vial walls However when a cementitious solid phase is present in the sample there will be competition between the vial walls and the cement for sorption of Np and Pu Based on the affinity of metals for metal oxide surfaces as opposed to the polypropylene surface and the much higher surface site density expected for the cementitious samples it is assumed that the cementitious samples will out-compete the vial walls for sorption sites This thesis was tested by taking one of the triplicate samples from each sorption experiment with a solid phase present removing the solid phase from the tubes and leaching any sorbed Np and Pu from the tubes with acid as described in Section 36 Figure 410 and Figure 411 show that although some of the Pu and Np sorbed to the vial walls of the samples this amount accounted for less than 2 in all samples Therefore sorption of Np and Pu to the vial walls does not appear to be a significant factor in experiments where the solid phase is present Note these results do not discount the possibility that Pu hydrous oxide precipitates were forming in both the no-solid control experiments and experiments with cement formulations present Based on the observation of a constant aqueous phase concentration of Pu regardless of the initial Pu concentration the presence of a solubility limiting Pu phase cannot be discounted based on these data Further experiments examining the solubility of Pu in high pH calcite saturated solutions are required
Like Pu Np shows little affinity for the vial walls in the presence of a solid phase In each case tested there was significantly less than 1 of the total Np sorbed to the vial walls This behavior is consistent with the ~100 mass balance on Np achieve in the solid-free controls The majority of Np remained soluble in the solid-free control experiments Therefore it is expected that sorption of Np to the vial walls was the primary reason for the loss of Np from the aqueous phase in the no-solids systems rather than precipitation of a Np solid phase similar to the process discussed for Pu above This assumption is based on the relative solubility of Np(V) as compared with Pu(IV)
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31
Figure 49 Percent Pu and Np sorbed to vial walls of the no solids controls after the aqueous phases were discarded and the vials were washed Both the 10 ppb and 1 ppb datasets were prepared in triplicate and the error bars show the standard deviation
Figure 410 Percent Pu sorbed to vial walls after the solids and aqueous phases were removed and the vials were washed The graph illustrates one sample from each of the 1 ppb 5 ppb and 10 ppb systems Therefore no error bars are present
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Figure 411 Percent Np sorbed to vial walls after the solids and aqueous phases were removed and the vials were washed The graph illustrates one sample from each of the 1 ppb 5 ppb and 10 ppb systems Therefore no error bars are present
43 Radionuclide Sorption to Cementitious Formulations under Reducing Conditions
Similar to the Pu Kd values under oxidizing conditions Pu Kd values ranged from 104 to gt105 under reducing conditions (Figure 412) Also similar to the results under oxidizing conditions the Kd increases with increasing initial Pu concentration Again this behavior is indicative of the aqueous phase concentration of Pu being controlled by solubility of Pu rather than by sorption In each case the samples appeared to reach steady state within 24 hours This equilibration is evident because the Kd values after one day and four days are very similar Also it appears that the amount of reducing slag does not make a significant difference in the Kd value In fact the TR547 solid consists of 45 reducing grout but produces approximately the same Kd values of the aged cement which does not have any reducing grout Each of these Kd values are higher than the TR545 which is 90 reducing grout These findings are in agreement with those conducted by Allard et al (1984) and Hoglund et al (1985) who reported that concrete containing reducing agents (slag similar to that used in our study) did not have greater Pu Kd values than those that did not contain slag
Similar aqueous concentrations of Pu were observed regardless of the solid phase present Figure 36 shows the average aqueous phase concentrations measured after one day and four days for all solids As stated above triplicate samples were prepared for each solid phase and each initial concentration Therefore each of the reported solubility values in Figure 412 is an average of up to nine measurements of the Pu aqueous concentrations Using the highest reported value with the expected maximum error (00045 ppb for solid Vault 2) the maximum expected aqueous concentration of Pu in the pore water associated with the cementitious formulations will be approximately 2 x 10-11 molL (calculated from Equation 31) This value is on the same order as the solubility of Pu hydrous oxide solid phases (Neck and Kim 2001) A best value would be 10-12 molL
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Figure 412 Pu Kd Values under Reducing Conditions Plutonium Kd values for various cementitious formulations measured after one-day equilibration (1d) and four-day equilibration (4d) under reducing conditions Total plutonium concentrations in each system were 1ppb 5 ppb and 10 ppb Samples prepared in triplicate and error bars represent standard deviation
Figure 413 Average Solubility of Plutonium under Reducing Conditions Plutonium solubility for various cementitious formulations measured after one-day equilibration (1d) and four-day equilibration (4d) under reducing conditions Total plutonium concentrations in each system were 1ppb 5 ppb and 10 ppb as noted Samples prepared in triplicate and an average of all samples (9) was used to determine average solubility The error bars represent standard deviation of samples
The Np Kd values reported in Figure 414 obtained under reducing conditions are very similar to
those obtained under oxidizing conditions In each case the samples appeared to reach steady state within 24 hours This equilibration is evident because the Kd values between the one-day and fourndashday equilibrations are similar As was the case with Pu the amount of slag present in each solid does not
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seem to have a significant effect on the Kd values Again the aged cement with no slag has as high a Kd as the TR545 with 90 reducing slag
Similar aqueous concentrations of Np were observed regardless of the solid phase present Figure 314 shows the average aqueous phase concentrations measured after one day and four days for all solids All Kd values were gt 105 mLg which is considerably larger than those reported by Kaplan and Coates (2007) who reported Np Kd values to 1300 to 1600 mLg This difference can be attributed to two important experimental differences 1) the experiment was designed to permit larger Kd values to be measured (eg solid to liquid ratios and spike concentrations) and more importantly 2) a more sensitive analytical method ICP-MS was used instead of conventional low-energy gamma spectroscopy or liquid scintillation counting (LSC) analysis As stated above triplicate samples were prepared for each solid phase and each initial concentration Therefore each of the reported solubility values in Figure 415 is an average of up to nine measurements Using the highest reported value (to provide the most conservative most soluble values) with the expected maximum error (00045 ppb for solid TR545) the maximum expected aqueous concentration of Np in the pore water associated with the cementitious formulations will be approximately 2 x 10-11 molL A best value taking into consideration the less-than values which are depicted in Figure 414 as running off the top of the plot would be 10-12 molL
Figure 414 Np Kd Values under Reducing Conditions Neptunium Kd values for various cementitious formulations measured after one-day equilibration (1d) and four-day equilibration (4d) under reducing conditions Total Np concentrations in each system were 1 ppb 5 ppb and 10 ppb Samples were prepared in triplicate and the error bars represent standard deviation Kd values limited to gt106 were at instrumental background
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35
Figure 415 Average Solubility of Neptunium under Reducing Conditions Neptunium solubility for various cementitious formulations measured after one day equilibration (1d) and four day equilibration (4d) under reducing conditions Total plutonium concentrations in each system were 1ppb 5 ppb and 10 ppb Samples prepared in triplicate and an average of all samples (9) was used to determine average solubility The error bars represent standard deviation
A plot of the Tc Kd values for each cementitious formulations under reducing conditions is shown
in Figure 416 (log y-axis) and Figure 417 (reduced scale linear y-axis) The Kd values for each of the initial Tc concentrations are relatively similar This behavior is consistent with the Kd expression However the increasing Kd values from the one-day to four-day day equilibrations for each solid indicate that steady state was not reached within one day and it is unclear whether steady state was reached after four days A possible explanation for this behavior is that Tc(VII) was being reduced to Tc(IV) in these systems due to the reducing conditions As Tc(VII) was reduced the Kd would increase based on the high affinity of Tc(IV) for solid phases This proposed mechanism was observed by Lukens et al (2005) using an SRS saltstone material similar but not identical to TR547 Using synchrotron X-ray absorption fine structure spectroscopy they observed over a 453 month period that Tc(VII) incorporated into SRS saltstone slowly converted to Tc(IV) and that the nearest neighbor was initially predominantly oxygen and eventually became predominantly sulfur (described as a Tc(IV) phase TcSx) Lacking in Lukens et al (2005) is quantification of the solubility of Tc This analysis still needs to be completed along with re-oxidation studies (ie what is the rate that reduced Tc reoxidizes under ambient natural saltstone conditions)
Unlike Np and Pu Tc Kd values changed with the amount of slag included in the formulation Tc Kd values noticeable increase as the amount of slag in the formulation increased TR547 (45 dry-wt- slag) Kd value is visibly higher than the Aged Cement and Vault 2 Kd values while the most reducing TR545 (90 dry wt- slag) Kd value is significantly higher than the others Following a similar trend the reduction capacity that is the total quantity of reductant in the saltstone on a mass basis (units of milli-equivalents of charge per g) of TR547 had slightly greater or equal reduction capacity to that of TR545 (Roberts and Kaplan 2009)
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Figure 416 Tc Kd Values under Reducing Conditions Tc Kd values for various cementitious formulations measured after one-day equilibration (1d) and four-day equilibration (4d) under reducing conditions Total Tc concentrations in each system were 1 ppb 5 ppb and 10 ppb Sample prepared in triplicate and error bars represent standard deviation except as follows TR547-1d 1 ppb is based on a single dataset and datasets Vault 2-1d 5 ppb Vault 2- 4d 1 ppb Aged Cement-1d 5 ppb and Aged Cement-4d 1 ppb are duplicates
Figure 417 Data from Figure 416 replotted on a reduced linear scale for easier viewing Each sample was prepared in triplicate except as follows TR547-1d 1 ppb is based on a single dataset Vault 2-1d 5 ppb Vault 2- 4d 1 ppb Aged Cement-1d 5 ppb and Aged Cement-4d 1 ppb are duplicate datasets
SRNL-STI-2009-00636 Revision 0
37
The calculated Kd values for I sorption to cementitious samples under reducing conditions are shown in Figure 418 Before discussing the data it should be noted that spiked QAQC samples which were analyzed on the ICP-MS along with the samples used to generate the data in Figure 418 were off by an average of 195 with one outlier of approximately 40 This dataset did not include the use of internal standards as discussed in Section 31 above1 Due to a lack of an internal standard the iodine results presented in this report should be considered with a minimum error estimate of 20
The iodine Kd values under reducing conditions are different from those observed under oxidizing conditions Under oxidizing conditions it appears they are at a steady state by day one However under reducing conditions there is a noticeable difference between days one and four indicating steady state was not reached by day one and possibly not by day four Another interesting observation is that the Kd values are decreasing from day one to four A possible reason for this behavior may be due to redox chemistry of iodine in this system If iodine partially or entirely exists in the form as iodate (IO3
-) it is possible it could be reduced to iodide I- within the reducing cementitious system These two iodine species sorb differently iodate sorbing to minerals more strongly than iodide (Denham et al 2009 Schwehr et al 2009 Fukui et al 1996 Yoshida et al 1992) It is hypothesized that the reducing environment of the saltstone is sufficient to reduce iodate ions to the more weakly binding form of iodine iodide
This is one of the few datasets (along with Tc) in this study where there may be a difference between the various solids The degree of iodate reduction would be expected to increase as the slag content increases As mentioned above reduction of iodate to iodide should result in a decrease in sorption Therefore higher Kd values should be observed for solids with less slag such as the Aged Cement (0 dry wt- slag) and Vault 2 (17 dry wt- slag) This is generally the case in Figure 418 where the highest Kd values are reported for the Aged Cement and the lowest values are for solid TR547 However this trend does not hold completely where the saltstone sample containing 90 slag (TR545) has generally equal or higher Kd values than the saltstone containing 45 dry wt- slag (TR547)
1 Clemson University is presently investigating appropriate internal standards for iodine analyses for ICP-MS Of those tested rhenium and molybdenum have shown some promise
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38
Figure 418 Iodine Kd Values under Reducing Conditions I Kd Values for various cementitious formulations measured after one day equilibration (1d) and four day equilibration (4d) under reducing conditions Total iodine concentrations in each system were 100 ppb 500 ppb and 1000 ppb as noted Sample prepared in triplicate and error bars represent standard deviation of samples except as follows Vault 2-4 d 100 ppb is a single dataset while the datasets for Vault 2-1 d 100 ppb 4 d 1000 ppb TR545-4 d 1000 ppb 100 ppb TR547-4 d 1000 ppb 500 ppb 100 ppb and Aged Cement- 4 d 1000 ppb and 100 ppb are all based on duplicates
44 Radionuclide Sorption to Vial Walls under Reducing Conditions
The aqueous concentrations for Pu Np and Tc in the no solids controls are shown in Figure 419 The results are similar to those presented for experiments performed under oxidizing conditions above The 1 ppb Pu aqueous fraction is approximately three times greater than the 10 ppb fraction at day one This fraction decreases over time and by day four they are approximately equal when taking error into account This behavior is similar to the aqueous fraction under oxidizing conditions The 1 ppb Np aqueous fraction is significantly higher on both day one and day four than the aqueous fraction of the 10 ppb samples However each remained constant from day one to day four The 10 ppb aqueous fraction is twice as low as under oxidizing conditions which suggests either higher sorption to the vial walls or more precipitating out under the reducing conditions Like Pu and Np Tc shows a decrease from day one to day four especially for the 1 ppb samples The decrease in the 10 ppb sample is minimal and the aqueous fraction remains around 09 This value is slightly lower than that under oxidizing conditions
To examine the degree of sorption to the vial walls the tubes were washed again as performed for the experiments under oxidizing conditions above and similar results were found Ninety percent of the 1 ppb Pu sample was sorbed to the vial wall upon completion of the experiment which gives a 100 mass recovery when comparing this value to that found in Figure 419 However this result is not the case with the 10 ppb samples where approximately 75 of the mass remains unaccounted It is noteworthy that approximately 25 of the Pu from the 10 ppb solution sorbed to the vial walls under both oxidizing
SRNL-STI-2009-00636 Revision 0
39
and reducing conditions Np follows the same trend as Pu while less than 005 of the Tc sorbed to the wall
Figure 419 Plutonium Neptunium and Technetium No-Solids Aqueous Fractions under Reducing Conditions Pu Np and Tc aqueous fractions of No Solids controls after a one-day equilibration (1d) and four-day equilibration (4 d) under reducing conditions Total concentration for each radionuclide was 1 ppb and 10 ppb Samples were prepared in triplicate and the error bars represent the standard deviation
Figure 420 Percent of Pu Np and Tc sorbed to the vial walls of the No Solids control samples under reducing conditions Each the 1 ppb and 10 ppb samples were prepared in triplicate and the error bars represent the standard deviations of triplicate samples
Under reducing conditions the fraction of I remaining in the aqueous phase was around 90 with
almost 100 mass recovery of the 100 ppb I after the four-day equilibration These graphs show that
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40
under reducing conditions there will only be a small fraction of I sorbing to the vial wall or coming out of solution This result is a much better mass recovery than under oxidizing conditions (Figure 48) which had a mass recovery of approximately 65 after four days This result is also consistent with the interpretation that there may be a iodine speciation change between the two redox treatments
Figure 421 Iodine No-Solids Aqueous Fractions under Reducing Conditions I aqueous fractions of No-Solids controls after a one-day equilibration (1d) and four-day equilibration (4d) under reducing conditions The total concentration for each system was 100 ppb and 1000 ppb Samples were prepared in triplicate and the error bars represent the standard deviation
50 Comparison of Radionuclide Sorption under Oxidizing and Reducing Conditions
In the following figures (Figure 51 through Figure 54) the data shown above has been replotted to allow comparison between the oxidizing and reducing conditions for each cementitious formulation General observations based on these data follow Vault 2 Observations (Figure 51)
bull Pu Kds are greater than 104 under both oxidizing and reducing conditions and Pu Kds are slightly lower under reducing conditions This could possibly be due to reduction of Pu(IV) to Pu(III) However no oxidation state analysis was performed in this work
bull Np Kds are generally greater than 104 under both oxidizing and reducing conditions Interestingly Np Kds are higher under reducing conditions by almost an order of magnitude This could possibly be due to reduction of Np(V) to Np(IV) However no oxidation state analysis was performed in this work
bull Regardless of the initial Np or Pu concentration similar aqueous phase concentrations of Np or Pu were observed in all samples This trend indicates that ldquosorptionrdquo of Np and Pu in these systems may be a combination of adsorption absorption and (co)precipitation processes
bull Tc appears to reach a steady state within four days under oxidizing conditions This behavior does not appear to be the case under reducing conditions After four days similar Kd values are reached under both oxidizing and reducing conditions It is unclear
SRNL-STI-2009-00636 Revision 0
41
whether the Kd value of Tc will continue to increase under reducing conditions consistent with reduction of Tc(VII) to Tc(IV) The similarity in Kd values under both oxidizing and reducing conditions is an interesting observation and certainly warrants additional studies
bull I Kd values are similar under both oxidizing and reducing conditions However reducing condition systems may not be at steady state after four days while systems under oxidizing conditions appeared to reach a steady state The difference in rates may be due to reduction of iodate to iodine
bull For all isotopes examined the sorption behavior to each of the solid phases is very similar
TR545 and TR547 Observations (Figure 52 and Figure 53) bull Similar to the discussion above with respect to Vault 2 Pu Np and Tc all appear to reach
a steady state under oxidizing conditions and approach steady state slower under reducing conditions
bull Np and Pu Kd values are greater than 104 for all systems and time steps The aqueous phase concentrations of Np and Pu appear to be better described as a solubility in terms of the aqueous phase concentration of Np and Pu Similar aqueous phase concentrations of both Np and Pu were reached The data indicate that the initial Np and Pu concentration generally does not affect the aqueous phase concentration at an apparent steady state The presence of each solid phase appears to limit the aqueous phase concentration of both Np and Pu on the order of 10-11 molL
bull Tc shows significantly higher Kd values under reducing conditions versus oxidizing conditions
bull For all isotopes examined the sorption behavior to each of the solid phases is very similar
Aged Cement Observations (Figure 54) bull Pu appears to be close to steady state for each solid by day one with similar Kd values
reached on between day one and day four bull Np has a higher Kd under reducing conditions than oxidizing (105 under oxidizing
conditions and gt105 under reducing conditions) bull Neither set of Tc data was at steady state by day one and rates of sorptiondesorption
reactions appear to be different Tc Kds decrease from day one to four under oxidizing conditions but increase under reducing conditions
bull The Kd values for I under oxidizing conditions were considerably higher than those measured for I with any other solid Similar Kd values obtained for the same solids under reducing conditions indicate that the reported Kd values under oxidizing conditions appear to be suspect However analysis of the raw data gives no indication of an experimental artifact As discussed above these observations may be explained based upon the amount of slag contained within the solids which will affect the reducing capacity (ie No reducing slag is in the aged cement which could be reason the reduction of iodate to iodide (speculated in other samples) is not evident)
bull The difference in sorption behavior of iodine to the aged cement between oxidizing and reducing conditions also indicates that the reducing conditions of the solution may affect I redox behavior in addition to any reactivity expected in the solid phases
SRNL-STI-2009-00636 Revision 0
42
Figure 51 Comparison of Tc I Np and Pu sorption to Vault 2 solid under oxidizing and reducing conditions
SRNL-STI-2009-00636 Revision 0
43
Figure 52 Comparison of Tc I Np and Pu sorption to TR 545 solid under oxidizing and reducing conditions
SRNL-STI-2009-00636 Revision 0
44
Figure 53 Comparison of Tc I Np and Pu sorption to TR547 solid under oxidizing and reducing conditions
SRNL-STI-2009-00636 Revision 0
45
Figure 54 Comparison of Tc I Np and Pu sorption to Aged Cement under oxidizing and reducing conditions
SRNL-STI-2009-00636 Revision 0
46
60 Comparison of Radionuclide Sorption and Solubility under Oxidizing and Reducing Conditions
To further summarize the data the following tables provide either the average solubility
(for Np and Pu) or average Kd (for Tc and I) determined under both oxidizing and reducing conditions for each cementitious formulation Each table lists the average value standard deviation and the number of replicate samples used to calculate the reported values
The solubility of Pu in the presence of each solid under oxidizing and reducing conditions is shown in Table 61 (this is taken from experiments equilibrated for four days not one day) Under oxidizing conditions the apparent solubility values associated with the Aged Cement (0 dry wt- slag) Vault 2 (17 dry wt- slag) and TR547 (45 dry wt- slag) are all similar with only a slight increase in solubility as the amount of reducing slag increases There is a significant increase of almost an order of magnitude for the most reducing saltstone TR545 (90 dry wt- slag) However these samples also have a standard deviation on the same order of magnitude as the solubility itself which when taken into account brings the solubility back into the range of the others Under reducing conditions the apparent solubility values are slightly lower than under oxidizing conditions In this set of samples the Vault 2 saltstone with 10 dry wt- reducing slag had the highest apparent solubility but once again when considering the standard deviation the values are similar
Table 61 Comparison of plutonium apparent solubility values under oxidizing and reducing conditions
Table 62 lists the apparent solubility values of Np in the presence of each cementitious
formulation under both oxidizing and reducing conditions Under oxidizing conditions the cementitious formulation does not appear to have a dramatic effect on the solubility The apparent solubility values are similar to those of Pu under similar conditions except the Np standard deviations are much higher The high standard deviations are an analytical artifact since the measured concentrations were close to or at the detection limit of the ICP-MS There does appear to be a slight decrease in Np solubility under reducing conditions However the statistical significance of this decrease was not calculated
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47
Table 62 Comparison of neptunium apparent solubility values under oxidizing and reducing conditions
Unlike the apparent solubility values of Pu and Np the aqueousatmospheric conditions
and cementitious formulation seem to have an effect on the Tc Kd values (Table 63) Under oxidizing conditions there is not a discernible difference among the different cementitious formulations especially when taking the respective standard deviations into account However when experiments were run under reducing conditions the specific formulation had a noticeable effect The two saltstone samples with the least amount of reducing slag Aged Cement (0 dry-wt- slag) and Vault 2 (17 dry wt- slag) had Kd values which were similar to those observed under oxidizing conditions However the TR547 (45 dry-wt- slag) increased by almost an order of magnitude while the TR545 (90 dry wt- slag) increased by about three orders of magnitude Although the respective standard deviations are large the higher Kd values do appear to be significant
Table 63 Comparison of technetium Kd values under oxidizing and reducing conditions
Unlike Tc I does not seem to be as affected by cementitious formulation and redox status (Table 64) The only treatment (possible outlier) that does not follow this trend is the Aged Cement under oxidizing conditions This Kd value is higher than the others but also has a much higher standard deviation which when accounted for gives a value similar to the others All other treatments had near identical Kd values irrespective of solid phase or redox condition But again the Aged Cement data cannot be discounted at this time given the possibility of the influence that redox may have on iodine speciation and the strong influence I speciation has on sorption to cementitious materials
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48
Table 64 Comparison of iodine Kd values under oxidizing and reducing conditions
71 Comparison with Previous Data The increased sensitivity of the ICP-MS over conventional low-energy gamma
spectroscopy or liquid scintillation counting (LSC) analysis allowed for much more accurate Kd values and apparent solubility values in this work than were previously obtainable Generally radioanalytical detection methods start with activities on the order of 103 to 104 counts per minute (cpm) and approach background levels of 1 to 5 cpm for strongly sorbing radionuclides Therefore the accuracy of the Kd value will be the difference in analytical sensitivity when the initial aqueous activity decreases by a factor of approximately 5000 (ie the aqueous activity drops from approximately 5000 cpm to the instrument background of 1 cpm following almost complete sorption) As a result the reported Kd values can only be reliably reported up for a Kd of 103 to 104 This constraint is believed to be the difference between the observed Kd values for 237Np of gt 105 observed in this work when compared with the Kd values between 3000 and 4000 reported by Kaplan et al (2008) A similar observation was made for Pu because 242Pu was used for ICP-MS analysis and 238Pu was used in the work of Kaplan et al (2008) This constrint may account for the different Kd value of gt104 reported in Kaplan et al (2008) compared with the value of gt105 observed in this work
In the case of Tc Kaplan et al (2008) reported a Kd of 023 mLg for Vault 2 under oxidizing conditions and 093 mLg under reducing conditions while the above experiment determined the Vault 2 Kd to be 505 mLg under oxidizing conditions and 557 mLg under reducing conditions Unlike the discrepancy in the Kd values for Np Pu and Tc between the above findings and those in Kaplan et al (2008) the reported Kd values for iodine are similar For Vault 2 Kaplan et al (2008) found 125I to have a Kd of 894 mLg under oxidizing conditions and 715 mLg under reducing conditions These values are similar to the Kd values of 766 mLg and 725 mLg observed under oxidizing and reducing conditions respectively in this work These findings appear to confirm the previously accepted Kd values of 0-10 mLg depending on the cementitious formulation
72 Suggested Future Work The above data demonstrate several areas that require further examination The
increasing Tc Kd values over time dataset suggest that steady state had not been achieved It would be beneficial to determine the amount of time required to reach steady state and allow determination of a more accurate Kd value (an assumption of the Kd construct is that it be measured at steady state) Also kinetic studies of both Tc and I are needed to better understand their respective interactions with the different cementitious formulations As for the I additional
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49
tests should be performed to test the hypothesis that iodine may in part exist as iodate which may initially sorb to the saltstone then undergo reduction to iodine or iodide and then desorbs causing a decrease in Kd
A final area of future work is to examine the possible causes for the similar behavior of each cementitious formulation despite the different slag content This discrepancy is not only observed in the above experiments but also in Kaplan et al (2008) which is illustrated in Table 31 and by recent work in measurements of saltstone reduction capacity (Roberts and Kaplan 2009) The reduction capacity (units in milli-equivalentsg solid) equivalents of the Aged Cement with no slag is 855 plusmn 101 and adding 10 slag gives a reducing equivalent of 2398 plusmn 311 However increasing the slag content to 23 causes the reducing capacity to increase to 8218 plusmn 81 which is almost equivalent to the 8324 plusmn 49 of the 100 slag Understanding the chemistry behind the reducing capacity of each cementitious formulation will help to define what reactions are important for controlling radionuclide release from the saltstone
80 References Allard B L Eliasson S Hoglund and K Andersson 1984 ldquoSorption of Cs I and actinides in
concrete systemsrdquo SKB Technical Report SKBKBS TR-84-15 DKB Stockholm Sweden
Denham M D I Kaplan and C Yeager2009 ldquoGroundwater radioiodine Prevalence biogeochemistry and potential remedial approachesrdquo SRNL-STI-2009-00463 Savannah River National Laboratory Aiken SC
Dixon K L M A Phifer and J R Harbour 2008 ldquoFY09 PACA Maintenance Program Additional Saltstone Property Testingrdquo SRNL-L3100-2009-00019 Rev0 Savannah River National Laboratory Aiken SC
Fukui M Fujikawa Y and Satta N 1996 ldquoFactors affecting interaction of radioiodide and iodate species with soilrdquo Journal of Environmental Radioactivity 31 199-216
Hoglund S L Eliasson B Allard K Andersson and B Torstenfelt 1985 ldquoSorption of some fission products and actinides in concrete systemsrdquo Mat Res Soc Symp Proc 50 683-690
Kaplan D I 2007 Geochemical Data Package for Performance Assessment Calculations Related to the Savannah River Site WSRC-TR-2006-00004 Rev 1 Washington Savannah River Company Aiken SC
Kaplan D I and Coates J 2007 ldquoPartitioning of Dissolved Radionuclides to Concrete under Scenarios Appropriate for Tank Closure Performance Assessmentsrdquo WSRC-STI-2007-00640 Rev 0 Washington Savannah River Company Aiken SC 29808
Kaplan D I Roberts K Coates J Siegfried M Serkiz S 2008 ldquoSaltstone and concrete interactions with radionuclides Sorption (Kd) desorption and reduction capacity measurementsrdquo SRNS-STI-2008-00045 Savannah River National Laboratory Aiken SC 2008
SRNL-STI-2009-00636 Revision 0
50
Neck V and Kim J I 2001 ldquoSolubility and hydrolysis of tetravalent actinidesrdquo Radiochim Acta 89 1
Powell B A Fjeld R A Coates J T Kaplan D I Serkiz S M 2002 ldquoPlutonium Oxidation State Geochemistry in the SRS Subsurface Environmentrdquo WSRC-TR-2003-00035 Westinghouse Savannah River Company US DOE Savannah River Site Aiken SC
Roberts K A and D I Kaplan 2009 Reduction Capacity of Saltstone and Saltstone Componentsrdquo SRNL-STI-2009-00637 Rev0 Savannah River National Laboratory Aiken SC
Schwehr K A Santschi P H D I Kaplan C M Yeager and R Brinkmeyer 2009 ldquoOrgano-iodine formation in soils and aquifer sediments at ambient concentrationsrdquo Environ Sci Technol 437258-7264
Yoshida S Muramatsu Y and Uchida S 1992 ldquoStudies on the sorption of I-(iodide) and IO3-
(iodate) onto andosolsrdquo Water Air and Soil Pollution 63 321-329
SRNL-STI-2009-00636 Revision 0
51
90 Appendix A Data Tables of Radionuclide Sorption to Saltstone under Oxidizing Conditions
The following tables represent data collected for the no solids controls each saltstone and testing of radionuclide sorption to the vial walls The no solids controls tables include the concentration (ppb) of the radionuclide spiked into the sample along with the concentration of the radionuclide (ppb) measured in the aqueous phase after the given equilibration time The pH at the time the sample was taken is also recorded along with the fraction of the radionuclide which stayed in the aqueous phase The tables for the cementitious formulation data include the data above along with the addition of a Kd value The tables of the data for the radionuclides sorbed to the vial walls include the initial concentration (ppb) of the spike the concentration (ppb) of the radionuclide that had sorbed to the vial wall during the experiment and the percentage of the total concentration this represents Important Notes
BDL- Below Detection Limit lt01 denotes no notable sorption occurred
91 Data Tables for No Solid Controls
Table 91 Plutonium no solids control after one day
A 9264165178 402285E‐05 1181 434238E‐06 9980817 B 9352537276 0000110618 1183 118276E‐05 3616813 C 9363541597 705331E‐05 118 753273E‐06 5401186 D 0993110568 BDL 12 NA NA E 0977247222 300794E‐05 1199 307797E‐05 1280331 F 0962441315 BDL 1198 NA NA G 4059128499 BDL 1186 NA NA H 4065161486 705198E‐05 1188 173473E‐05 2380003 I 4116819691 0000110748 1189 269014E‐05 1555864
Table 920 TR545- neptunium after four days
Sample ID
Initial Aq Conc (ppb)
Equil Aq Conc (ppb) pH
Fraction Aq Kd
A 92641652 NA 1188 NA NA B 93525373 00001935 1185 2069E‐05 2067199C 93635416 4119E‐05 1185 44E‐06 9247818D 09931106 BDL 1197 NA NA E 09772472 BDL 12 NA NA F 09624413 00066817 1206 00069424 562421G 40591285 00003289 1196 8103E‐05 5148274H 40651615 00025316 1196 00006228 6625737I 41168197 00001018 1194 2474E‐05 1692126
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Table 921 TR545- technetium after one day
Sample ID
Initial Aq Conc (ppb)
Equil Aq Conc (ppb) pH Fraction Aq Kd
A 9655146069 820460082 1181 0849764546 8998984 B 9356176321 7703053505 1183 0823312135 1051242 C 9114122586 7978297395 118 0875377451 7062663 D 1042349157 0853053814 12 0818395456 9099556 E 0983206046 0871198263 1199 0886079033 5196709 F 0905148405 0803451372 1198 0887646013 5098696 G 4950156706 4275082341 1186 0863625658 7213934 H 4889067068 4173762594 1188 0853693053 7687519 I 4854463762 4147024058 1189 0854270268 7771045
A 1048950046 0002141023 1149 0000204111 2112281 B 1039943573 0001770549 1157 0000170254 2460487 C 1084651695 0001127533 1153 0000103953 4014918 D 1088686867 0001201087 1172 0001103244 3564524 E 1119673887 0000783288 1177 0000699568 5709897 F 1045722787 0000914861 1181 000087486 4495324 G 5387981131 0001444832 1169 0000268158 1494715 H 5412748988 0001143483 1169 0000211257 1965749 I 5373948758 00010003 1164 0000186139 2280472
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Table 926 TR547- plutonium after four days
Sample ID
Initial Aq Conc (ppb)
Equil Aq Conc (ppb) pH
Fraction Aq Kd
A 104895 NA 116 NA NA B 10399436 0001828 1165 00001758 2383132C 10846517 00010788 1164 9946E‐05 4196159D 10886869 00009131 1184 00008388 4689778E 11196739 00010624 1189 00009488 4208928F 10457228 00007967 1191 00007619 516258G 53879811 00007915 1173 00001469 2728993H 5412749 00008355 1175 00001544 2690641I 53739488 00006103 1174 00001136 3737892
Table 927 TR547- neptunium after one day
Sample ID
Initial Aq Conc (ppb)
Equil Aq Conc (ppb) pH Fraction Aq Kd
A 9589772032 0000454463 1149 473903E‐05 9116335 B 9293228768 0000260081 1157 27986E‐05 1499475 C 1008725504 0000302018 1153 299405E‐05 1397125 D 0952173007 000019177 1172 0000201403 1954603 E 0992224074 BDL NA NA F 0967815522 402137E‐05 1181 41551E‐05 9474699 G 4068405786 0000222282 1169 546361E‐05 7336986 H 409543171 0000531619 1169 0000129808 3199152 I 4017406611 0000410123 1164 0000102086 4157807
Table 928 TR547- neptunium after four days
Sample ID
Initial Aq Conc (ppb)
Equil Aq Conc (ppb) pH Fraction Aq Kd
A 9589772 NA 116 NA NA B 92932288 00002145 1165 2308E‐05 1818463C 10087255 00001628 1164 1614E‐05 2591215D 0952173 BDL 1184 NA NA E 09922241 BDL NA NA F 09678155 5107E‐05 1191 5277E‐05 7460375G 40684058 00001336 1173 3284E‐05 1220544H 40954317 8151E‐05 1175 199E‐05 2086795I 40174066 00001322 1174 3292E‐05 1289605
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Table 929 TR547- technetium after one day
Sample ID
Initial Aq Conc (ppb)
Equil Aq Conc (ppb) pH Fraction Aq Kd
A 9466799266 8233850788 1149 0869760788 8220086 B 9439556236 817653394 1157 0866198975 8165745 C 9383493063 8086024379 1153 0861728604 8430884 D 1061939876 0919992065 1172 0866331594 6241759 E 0991827343 0836511397 1177 0843404251 7590958 F 0971981155 0839862696 1181 0864073024 6354378 G 4883337077 414858839 1169 0849539633 7903986 H 4691440077 3996173112 1169 0851800949 8038249 I 486993937 4291285586 1164 0881178442 6558707
Table 930 TR547- technetium after four days
Sample ID
Initial Aq Conc (ppb)
Equil Aq Conc (ppb) pH
Fraction Aq Kd
A 94667993 NA 116 NA NA B 94395562 85812109 1165 09090693 5885474C 93834931 84622373 1164 09018217 6279204D 10619399 09580683 1184 09021869 4435663E 09918273 08881507 1189 08954691 4835506F 09719812 09036489 1191 0929698 3138862G 48833371 4490415 1173 09195382 4312104H 46914401 42054182 1175 08964024 5612948I 48699394 43843193 1174 09002821 5536503
Table 931 TR547- iodine after one day
Sample ID
Initial Aq Conc (ppb)
Equil Aq Conc (ppb) pH Fraction Aq Kd
A 9944920441 8813152965 1149 0886196427 738241 B 9956006121 8747156303 1157 0878580848 8007767 C 9822152291 8664470934 1153 0882135674 7988892 D 1002391846 9333490632 1172 0931121963 3368509 E 9918273427 6625075445 1177 0667966607 1551748 F 9918175056 8931364957 1181 0900504872 4773862 G 5166570628 4445386532 1169 0860413387 7961604 H 4847821413 410447427 1169 084666367 8664303 I 4850381381 4266693706 1164 0879661489 6413801
100 Appendix B Data Tables of Radionuclide Sorption to Saltstone Under Reducing Conditions
The following tables represent data collected for the no solids controls each cementitious solid and testing of radionuclide sorption to the vial walls The no solids controls tables include the concentration (ppb) of the radionuclide spiked into the sample along with the concentration of the radionuclide (ppb) measured in the aqueous phase after the given equilibration time The pH at the time the sample was taken is also recorded along with the fraction of the radionuclide which stayed in the aqueous phase The tables for the cementitious solidsrsquo data include the data above along with the addition of a Kd value The tables of the data for the radionuclides sorbed to the vial walls include the initial concentration (ppb) of the spike the concentration (ppb) of the radionuclide that had sorbed to the vial wall during the experiment and the percentage of the total concentration this represents Important Notes
BDL= Below Detection Limit lt01 denotes no notable sorption occurred
101 Data Tables for No-Solid Controls
Table 101 Plutonium no solids control after one day
A 9405892 0007019 111 0000746258 5681206 B 9602498 0003294 1117 0000342992 123554 C 9630619 0002936 1114 0000304893 1396318 D 4945396 0001795 113 0000363011 1171688 E 4964945 0001373 1131 0000276484 1493015 F 4441601 0001516 113 0000341219 1389674 G 1079602 0001109 1142 0001027508 4215519 H 1031512 0000883 1143 0000855983 4820576 I 0939294 0000978 1143 0001040992 4550255
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Table 1011 Vault 2- neptunium after one day
Sample ID Initial Aq Conc (ppb)
Equil Aq Conc (ppb) pH Fraction Aq
A 9425042625 0001709054 1105 0000181331 B 9611386476 0001184125 1110 00001232 C 9579553607 0001155517 1104 0000120623 D 4974000414 0000672325 1125 0000135168 E 4916731623 0000675371 1128 0000137362 F 4373142817 0000570681 1120 0000130497 G 0943366414 0000389738 1129 0000413136 H 1011745587 0000565648 1132 0000559081 I 0865252712 0000379545 1133 0000438653
A 8849444124 0000306309 1150 346133E‐05 1289533 B 8447823057 0000150131 1155 177715E‐05 2711019 C 8590597085 0000199185 1153 231864E‐05 2044057 D 4491250244 517162E‐05 1156 115149E‐05 4020064 E 4391894479 204591E‐05 1158 465838E‐06 9846089 F 4210703646 204376E‐05 1158 485374E‐06 9816203 G 086381524 522216E‐06 1160 604546E‐06 7577764 H 0870501884 BDL 1160 NA NA I 0861953838 BDL 1162 NA NA
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Table 1036 Aged cement- neptunium after four days
Sample ID
Initial Aq Conc (ppb)
Equil Aq Conc (ppb) pH Fraction Aq Kd
A 8849444 0000131 1145 148418E‐05 3007445B 8447823 0000111 1146 131529E‐05 3662996C 8590597 656E‐05 1146 76328E‐06 6209405D 449125 BDL 1155 NA NA E 4391894 BDL 1156 NA NA F 4210704 BDL 1155 NA NA G 0863815 BDL 1165 NA NA H 0870502 BDL 1162 NA NA I 0861954 BDL 1164 NA NA
Table 1037 Aged cement- technetium after one day
Sample ID
Initial Aq Conc (ppb)
Equil Aq Conc (ppb) pH Fraction Aq Kd
A 8426518355 833290075 1150 098889012 0476492 B 8638001423 7823321167 1155 0905686487 4413063 C 9323317745 925927516 1153 0993130923 0294664 D 442651005 4300859603 1156 0971614106 1242837 E 4426849405 4336992073 1158 0979701742 0855315 F 3929483125 3938204338 1158 100221943 lt01 G 0817864386 081693181 1160 0998859743 0049487 H 0878958929 0792412508 1160 0901535306 4510199 I 0772205665 0871436364 1162 1128502941 lt01
Table 1038 Aged cement- technetium after four days
110 Appendix C Dixon et al (2009) FY09 PACA Maintenance Program Additional Saltstone Property Testing SRNL L3100-2009-00019 Rev 0
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SRNL L3100-2009-00019 Rev 0
December 16 2008
Keywords Performance Permeability Modulus
L B Romanowski
Waste Determinations From K L Dixon M A Phifer and J R Harbour
FY09 PACA Maintenance Program Additional Saltstone Property Testing
BACKGROUND
Additional tests have been identified for measurement of important hydraulic and physical properties of saltstone The initial phase of this work [1] was completed last year and the results were detailed in an internal report [2] The proposed testing for FY09 includes measurement of saturated hydraulic conductivity porosity bulk density particle density water retention and Youngrsquos modulus of simulated Saltstone grouts For completeness the bleed volumes and gel times for each mix will also be measured
The testing will be based on a projected salt solution composition for the ARPMCU stream that will be fed to the Saltstone Production Facility over the next few years The scope for FY09 will include testing to determine the impact of (1) admixtures (2) organics (3) wcm ratio (4) aluminate concentration and (5) temperature of curing on the hydraulic properties of saltstone mixes Samples of selected batches prepared as part of this task will be provided to Dan Kaplan for measurement of Kd through leaching tests The eleven mixes that will be batched and tested are detailed in Table 1
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Table 1 The Eleven Mixes That will be Batched and Tested
BFS is Blast Furnace Slag FA is Fly Ash and PC is Portland Cement
TEST DETAILS
Test 1 Control (Mix 1)
A control mix will be based on the baseline mix modified by exclusion of the Class F fly ash Consequently the cementitious materials premix will be a mixture of 90 blast furnace slag and 10 portland cement The degree of reaction will be much greater than with the normal premix and therefore should result in a lower porosity and a lower permeability This bounding test at 060 wcm ratio is expected to yield a hydraulic conductivity at or below the detection limit for the Mactec permeameter measurement system Therefore this test should demonstrate the lowest level of detection of the Mactec system as well as show a resolvable difference between measurements of the control mix and the control mix with the normal premix composition
Test 2 ndashImpact of Admixtures (Mixes 2 and 3)
Recent saltstone batches have required both a set retarder (Daratard 17) and an antifoam agent (Q2) for processing of the saltstone Therefore the baseline mix will be prepared with and without nominal levels of these two admixtures to determine whether these admixtures appreciably affect the hydraulic and physical properties of saltstone at these nominal concentrations
Test 3ndashImpact of Organics (Mixes 2 and 4)
The solvent extraction process is expected to result in some carryover of organics [3]
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Consequently a test will be performed on the impact of Caustic Side Solvent Extraction (CSSX) organics at 100 microliters per 1600 gram batch The CSSX solvent consists of 075 M 1-(2233-tetrafluoropropoxy)-3-(4-sec-butylphenoxy)-2-propanol (Cs-7SB) and 0003 M tri-n-octylamine (TOA) in an Isoparreg L diluent Test 4ndashImpact of Combination of Admixtures and Organics (Mixes 2 5 10 and 11)
This test will determine the impact of a combination of admixtures (Test 2) and organics (Test 3) together in the mix vs the baseline case without admixtures and organics
Test 5ndash Impact of wcm Ratio (Mixes 2 6 and 7)
It is well known that decreasing the wcm ratio in a mix will improve permeability in normal portland cement water mixes This test will measure the variation in permeability for the case of the MCU salt solution at three different wcm ratios The initial selection of wcm ratios is 055 060 and 065 However if the mix at an as-batched 065 wcm ratio has significant bleed water and the resulting actual wcm ratio is close to 060 then the three ratios will be adjusted to provide a more evenly spaced set of values However the baseline mix at 060 will be included as one of the three mixes
Test 6 ndash Impact of Aluminate Concentration (Mixes 8 9 and 10)
The DWPF has modified its process flowsheet to include a caustic washing of HLW sludge to remove some of the aluminum from the HLW prior to vitrification The resulting aluminate stream will then be blended with tank 50 material and fed to the SPF This increased aluminate concentration in the salt solution has significant impact on heat of hydration and set times and consequently it is likely that it will also impact permeability Therefore a set of three samples will be made at wcm ratios of 055 060 and 065 (as in Test 3) with a higher level of aluminate (028 M) for testing
Test 7 ndash Impact of Increased Curing Temperature (Mix 11)
In an ongoing task there is evidence that Youngrsquos modulus (a performance indicator) [4] is reduced by increasing the curing temperature of the mix Since the vault temperature increases during curing as a result of the exothermic hydration reactions one of the baseline mixes with a combination of admixtures and organics will be cured at 60
o
C rather than the normal 22
o
C to determine the impact of curing temperature on the permeability
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SCHEDULE
The schedule for the task of batching and testing of the samples is provided in Table 2 This schedule is based on the fact that the cementitious materials will be available for the testing as needed
Table 2 Additional Saltstone Hydraulic and Physical Property Tests
Item Schedule Start Work 12108 Test Plan Complete 1509 Preparation of 1st set of Samples Complete 11909 90-Day Cure Period for 1st set of Samples Complete 42009
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DISTRIBUTION Savannah River Site
A B Barnes 999-W Rm 336 H H Burns 999-W Rm 381 B T Butcher 773-43A Rm 212 A D Cozzi 999-W Rm 337 D A Crowley 773-43A Rm 216 M E Denham 773-42A Rm 218 J C Griffin 773-A Rm A-231 J R Harbour 999-W Rm 348 C A Langton 773-43A Rm 219 M H Layton 705-1C Rm 14 D I Kaplan (3 copies) 773-43A Rm 215 S L Marra 773A Rm A-230 A M Murray 773-A Rm 229 K A Roberts 773-43A Rm 225 T C Robinson 705-1C Rm 13 L B Romanowski 705-1C Rm 19 K H Rosenberger 705-1C Rm 16 F M Smith 705-1C Rm 24 RPA File (2 copies) 773-43A Rm 213
Clemson University Environmental Engineering and Earth Sciences 372 Computer Court LG Rich Environmental Laboratory Anderson SC 29625
95 Data Tables for Aged Cement 62 96 Data Tables for Sorption to Vial Walls 65
100 Appendix B Data Tables of Radionuclide Sorption to Saltstone Under Reducing Conditions 66 101 Data Tables for No-Solid Controls 66 102 Data Tables for Vault 2 69 103 Data Tables for TR545 72 104 Data Tables for TR547 75 105 Data Tables for Aged Cement 78 106 Data Tables for Sorption to Vial Walls 80
110 Appendix C Dixon et al (2009) FY09 PACA Maintenance Program Additional Saltstone
Property Testing SRNL L3100-2009-00019 Rev 0 82
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LIST OF TABLES
Table 31 Characteristics of saltstone formulations used in this work Kaplan et al (2008) 19
Table 32 Detection limits for each isotope based on representative calibration curves generated in PlasmaLab software associated with the ICP-MS 20
Table 33 Experimental Matrix of Sorption Experiments under Aerobic Conditions 22
Table 61 Comparison of plutonium apparent solubility values under oxidizing and reducing conditions 46
Table 62 Comparison of neptunium apparent solubility values under oxidizing and reducing conditions 47
Table 63 Comparison of technetium Kd values under oxidizing and reducing conditions 47
Table 64 Comparison of iodine Kd values under oxidizing and reducing conditions 48
Table 91 Plutonium no solids control after one day 51
Table 92 Plutonium no solids control after four days 51
Table 93 Neptunium no solids control after one day 52
Table 94 Neptunium no solids control after four days 52
Table 95 Technetium no solids control after one day 52
Table 96 Technetium no solids control after four days 53
Table 97 Iodine no solids control after one day 53
Table 98 Iodine no solids control after four days 53
Table 99 Vault 2- plutonium after one day 54
Table 910 Vault 2- plutonium after four days 54
Table 911 Vault 2- neptunium after one day 54
Table 912 Vault 2- neptunium after four days 55
Table 913 Vault 2- technetium after one day 55
Table 914 Vault 2- technetium after four days 55
Table 915 Vault 2- iodine after one day 56
Table 916 Vault 2- iodine after four days 56
Table 917 TR545- plutonium after one day 56
Table 918 TR545- plutonium after four days 57
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Table 919 TR545- neptunium after one day 57
Table 920 TR545- neptunium after four days 57
Table 921 TR545- technetium after one day 58
Table 922 TR545- technetium after four days 58
Table 923 TR545- iodine after one day 58
Table 924 TR545- iodine after four days 59
Table 925 TR547- plutonium after one day 59
Table 926 TR547- plutonium after four days 60
Table 927 TR547- neptunium after one day 60
Table 928 TR547- neptunium after four days 60
Table 929 TR547- technetium after one day 61
Table 930 TR547- technetium after four days 61
Table 931 TR547- iodine after one day 61
Table 932 TR547- iodine after four days 62
Table 933 Aged cement- plutonium after one day 62
Table 934 Aged cement- plutonium after four days 63
Table 935 Aged cement- neptunium after one day 63
Table 936 Aged cement- neptunium after four days 63
Table 937 Aged cement- technetium after one day 64
Table 938 Aged cement- technetium after four days 64
Table 939 Aged cement- iodine after one day 64
Table 940 Aged cement- iodine after four days 65
Table 941 Plutonium sorbed to vial wall in no solids control 65
Table 942 Neptunium sorbed to vial wall in no solids control 65
Table 101 Plutonium no solids control after one day 66
Table 102 Plutonium no solids control after four days 67
Table 103 Neptunium no solids control after one day 67
Table 104 Neptunium no solids control after four days 67
Table 105 Technetium no solids control after one day 67
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Table 106 Technetium no solids control after four days 68
Table 107 Iodine no solids control after one day 68
Table 108 Iodine no solids control after four days 68
Table 109 Vault 2- plutonium after one day 69
Table 1010 Vault 2- plutonium after four days 69
Table 1011 Vault 2- neptunium after one day 70
Table 1012 Vault 2- neptunium after four days 70
Table 1013 Vault 2- technetium after one day 70
Table 1014 Vault 2- technetium after four days 71
Table 1015 Vault 2- iodine after one day 71
Table 1016 Vault 2- iodine after four days 71
Table 1017 TR545- plutonium after one day 72
Table 1018 TR545- plutonium after four days 72
Table 1019 TR545- neptunium after one day 73
Table 1020 TR545- neptunium after four days 73
Table 1021 TR545- technetium after one day 73
Table 1022 TR545- technetium after four days 74
Table 1023 TR545- iodine after one day 74
Table 1024 TR545- iodine after four days 74
Table 1025 TR547- plutonium after one day 75
Table 1026 TR547- plutonium after four days 75
Table 1027 TR547- neptunium after one day 76
Table 1028 TR547- neptunium after four days 76
Table 1029 TR547- technetium after one day 76
Table 1030 TR547- technetium after four days 77
Table 1031 TR547- iodine after one day 77
Table 1032 TR547- iodine after four days 77
Table 1033 Aged cement- plutonium after one day 78
Table 1034 Aged cement- plutonium after four days 78
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Table 1035 Aged cement- neptunium after one day 78
Table 1036 Aged cement- neptunium after four days 79
Table 1037 Aged cement- technetium after one day 79
Table 1038 Aged cement- technetium after four days 79
Table 1039 Aged cement- iodine after one day 80
Table 1040 Aged cement- iodine after four days 80
Table 1041 Plutonium sorbed to vial wall in no solids control 80
Table 1042 Neptunium sorbed to vial wall in no solids control 81
Table 1043 Technetium sorbed to vial wall in no solids control 81
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LIST OF FIGURES
Figure 31 Screen capture of a typical 242Pu calibration curve using Thermo PlasmaLab software to control the data collection and analysis R2=0999872 Intercept Conc (Detection Limit) = 0000044 ppb 16
Figure 32 Screen capture of a typical 237Np calibration curve using Thermo PlasmaLab software to control the data collection and analysis R2=0999981 Intercept Conc (Detection Limit) = 0000026 ppb 17
Figure 33 Screen capture of a typical 99Tc calibration curve using Thermo PlasmaLab software to control the data collection and analysis R2=0999984 Intercept Conc (Detection Limit) = 0000013 ppb 18
Figure 34 Screen capture of a typical 127I calibration curve using Thermo PlasmaLab software to control the data collection and analysis R2=0999991 Intercept Conc (Detection Limit) = 024 ppb 19
Figure 41 Plutonium Kd Values under Oxidizing Conditions Plutonium Kd values for various saltstone formulations measured after one-day equilibration (1d) and four-day equilibration (4d under oxidizing conditions Total plutonium concentrations in each system were 1 ppb 5 ppb and 10 ppb Sample prepared in triplicate and error bars represent standard deviation of samples except as follows value for dataset TR547-4d 10 ppb is reported based on duplicate samples 25
Figure 42 Plutonium solubility for various saltstone formulations measured after one-day equilibration (1d) and four-day equilibration (4d) under oxidizing conditions Total plutonium concentrations in each system were 1 ppb 5 ppb and 10 ppb as noted Samples prepared in triplicate and an average of all samples (9) was used to determine average solubility The error bars represent standard deviation of samples 25
Figure 43 Neptunium Kd values under oxidizing conditions Neptunium Kd values for various saltstone formulations measured after one-day equilibration (1d) and four-day equilibration (4d) under oxidizing conditions Total plutonium concentrations in each system were 1 ppb 5 ppb and 10 ppb as noted Samples prepared in triplicate and error bars represent standard deviation of samples except as follows value for datasets TR545-1d 1ppb TR545-4d 1 ppb TR547 4d 1 ppb TR545-4d 10 ppb TR547-1d 1ppb TR547-4d 10 ppb are reported based on a single sample and for dataset TR545-1d 5ppb is reported based on duplicate samples Kd values limited to gt106 were at instrumental background 26
Figure 44 Average solubility of Np under oxidizing conditions Neptunium solubility for various saltstone formulations measured after one-day equilibration (1d) and four-day equilibration (4d) under oxidizing conditions Total Np concentrations in each system were 1 ppb 5 ppb and 10 ppb Samples prepared in triplicate and an average of all samples (9) was used to determine average solubility except as follows TR545-1d is based on 6 samples TR545- 4d on 5 samples TR547-1d on 7 samples and TR547- 4d on 5 samples The error bars represent standard deviation 27
Figure 45 Technetium Kd values under oxidizing conditions Tc Kd values for various saltstone formulations measured after one-day equilibration (1d) and four-day equilibration (4d) under oxidizing conditions Total Tc concentrations in each system were 1 ppb 5 ppb and 10 ppb as noted above Samples were prepared in triplicate and the error bars represent standard deviation
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of samples except as follows data sets for Vault 2-1d 1ppb were duplicates and TR547- 4d 10 ppb is based on a single dataset 27
Figure 46 Iodine Kd Values under Oxidizing Conditions Iodine Kd values for various cementitious formulations measured after one-day equilibration (1d) and four-day equilibration (4d) under oxidizing conditions Total iodine concentrations in the systems were 100ppb 500 ppb and 1000 ppb as noted above Samples were prepared in triplicate and the error bars represent standard deviation of samples except as follows duplicates were used for dataset TR545- 1d 100ppb 28
Figure 47 Plutonium Neptunium and Technetium Aqueous Fractions Fraction of Pu Np and Tc remaining in the aqueous phase for the No Solids controls after a one-day equilibration (1d) and four-day equilibration (4d) under oxidizing conditions The total concentration for each radionuclide 10 ppb as noted above Samples were prepared in triplicate and the error bars represent the standard deviation of the samples 29
Figure 48 Iodine Aqueous Fraction Iodine aqueous fraction for the no-solids controls after a one-day equilibration (1d) and four-day equilibration (4d) under oxidizing conditions The total concentration of iodine was 1000 ppb as noted above Samples were prepared in triplicate and the error bars represent the standard deviation of the samples 29
Figure 49 Percent Pu and Np sorbed to vial walls of the no solids controls after the aqueous phases were discarded and the vials were washed Both the 10 ppb (blueleft) and 1 ppb (redright)) datasets were prepared in triplicate and the error bars show the standard deviation 31
Figure 410 Percent Pu sorbed to vial walls after the solids and aqueous phases were removed and the vials were washed The graph illustrates one sample from each of the 1 ppb (redleft) 5 ppb (greenmiddle) and 10 ppb (blueright) systems Therefore no error bars are present 31
Figure 411 Percent Np sorbed to vial walls after the solids and aqueous phases were removed and the vials were washed The graph illustrates one sample from each of the 1 ppb (redleft) 5 ppb (greenmiddle) and 10 ppb (blueright) systems Therefore no error bars are present 32
Figure 412 Pu Kd Values under Reducing Conditions Plutonium Kd values for various cementitious formulations measured after one-day equilibration (1d) and four-day equilibration (4d) under reducing conditions Total plutonium concentrations in each system were 1ppb 5 ppb and 10 ppb Samples prepared in triplicate and error bars represent standard deviation 33
Figure 413 Average Solubility of Plutonium under Reducing Conditions Plutonium solubility for various cementitious formulations measured after one-day equilibration (1d) and four-day equilibration (4d) under reducing conditions Total plutonium concentrations in each system were 1ppb 5 ppb and 10 ppb as noted Samples prepared in triplicate and an average of all samples (9) was used to determine average solubility The error bars represent standard deviation of samples 33
Figure 414 Np Kd Values under Reducing Conditions Neptunium Kd values for various cementitious formulations measured after one-day equilibration (1d) and four-day equilibration (4d) under reducing conditions Total Np concentrations in each system were 1 ppb 5 ppb and 10 ppb Samples were prepared in triplicate and the error bars represent standard deviation Kd values limited to gt106 were at instrumental background 34
Figure 415 Average Solubility of Neptunium under Reducing Conditions Neptunium solubility for various cementitious formulations measured after one day equilibration (1d) and four day
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equilibration (4d) under reducing conditions Total plutonium concentrations in each system were 1ppb 5 ppb and 10 ppb Samples prepared in triplicate and an average of all samples (9) was used to determine average solubility The error bars represent standard deviation 35
Figure 416 Tc Kd Values under Reducing Conditions Tc Kd values for various cementitious formulations measured after one-day equilibration (1d) and four-day equilibration (4d) under reducing conditions Total Tc concentrations in each system were 1 ppb 5 ppb and 10 ppb Sample prepared in triplicate and error bars represent standard deviation except as follows TR547-1d 1 ppb is based on a single dataset and datasets Vault 2-1d 5 ppb Vault 2- 4d 1 ppb Aged Cement-1d 5 ppb and Aged Cement-4d 1 ppb are duplicates 36
Figure 417 Data from Figure 416 replotted on a reduced linear scale for easier viewing Each sample was prepared in triplicate except as follows TR547-1d 1 ppb is based on a single dataset Vault 2-1d 5 ppb Vault 2- 4d 1 ppb Aged Cement-1d 5 ppb and Aged Cement-4d 1 ppb are duplicate datasets 36
Figure 418 Iodine Kd Values under Reducing Conditions I Kd Values for various cementitious formulations measured after one day equilibration (1d) and four day equilibration (4d) under reducing conditions Total iodine concentrations in each system were 100 ppb 500 ppb and 1000 ppb as noted Sample prepared in triplicate and error bars represent standard deviation of samples except as follows Vault 2-4 d 100 ppb is a single dataset while the datasets for Vault 2-1 d 100 ppb 4 d 1000 ppb TR545-4 d 1000 ppb 100 ppb TR547-4 d 1000 ppb 500 ppb 100 ppb and Aged Cement- 4 d 1000 ppb and 100 ppb are all based on duplicates 38
Figure 419 Plutonium Neptunium and Technetium No-Solids Aqueous Fractions under Reducing Conditions Pu Np and Tc aqueous fractions of No Solids controls after a one-day equilibration (1d) and four-day equilibration (4 d) under reducing conditions Total concentration for each radionuclide was 1 ppb and 10 ppb Samples were prepared in triplicate and the error bars represent the standard deviation 39
Figure 420 Percent of Pu Np and Tc sorbed to the vial walls of the No Solids control samples under reducing conditions Each the 1 ppb and 10 ppb samples were prepared in triplicate and the error bars represent the standard deviations of triplicate samples 39
Figure 421 Iodine No-Solids Aqueous Fractions under Reducing Conditions I aqueous fractions of No-Solids controls after a one-day equilibration (1d) and four-day equilibration (4d) under reducing conditions The total concentration for each system was 100 ppb and 1000 ppb Samples were prepared in triplicate and the error bars represent the standard deviation 40
Figure 51 Comparison of Tc I Np and Pu sorption to Vault 2 solid under oxidizing and reducing conditions 42
Figure 52 Comparison of Tc I Np and Pu sorption to TR 545 solid under oxidizing and reducing conditions 43
Figure 53 Comparison of Tc I Np and Pu sorption to TR547 solid under oxidizing and reducing conditions 44
Figure 54 Comparison of Tc I Np and Pu sorption to Aged Cement under oxidizing and reducing conditions 45
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xiv
LIST OF ABBREVIATIONS
DDI water Distilled deionized water ICP-MS Inductively coupled plasma ndash mass spectrometer
Kd Distribution coefficient LSC liquid scintillation counting NOM Natural organic matter PA Performance Assessment ppb parts per billion ppq parts per quadrillion QAQC Quality AssuranceQuality Control SA Special Analyses SRNL Savannah River National Laboratory SRS Savannah River Site
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15
10 Introduction Performance Assessments (PA) are risk calculations designed to determine (1) the maximum
amount of radioactivity that can be safely buried in a subsurface facility and (2) the potential human risk associated with disposing of radioactive waste in a subsurface facility Special Analyses (SAs) are similar to PAs except that they are designed to address specific issues related to PAs such as a new discovery since the PA was issued Commonly parameters describing the extent that a radionuclide interacts with solids at the source vadose zone and aquifer influence the extent of calculated human risk The two parameters that the SRS use to represent radionuclidesolid interactions are Kd and apparent solubility values together these parameters are referred to as sorption values Sorption values vary with radionuclides groundwater chemistry and the type of solid phase (and for cementitious materials by the age of the material during the calculation) In this work Kd and apparent solubility values are reported for 99Tc 127I 237Np and 242Pu sorption to various cementitious formulations
20 Objectives
The objectives of this work were to 1 Determine the influence of cementitious formulation on technetium (Tc) iodine (I) neptunium
(Np) and plutonium (Pu) sorption under oxidizing conditions The specific formulations that were evaluated included 1) an aged cement recovered from a 30-year old outdoor concrete pad on the SRS 2) Vault 2 concrete 3) TR545 saltstone and 4) TR547 saltstone (additional details are presented in Section 30 Materials and Methods)
2 Measure Tc I Np and Pu sorption to the cementitious formulations under reducing conditions
30 Materials and Methods
31 Preparation of ICP-MS Standards Stock Solutions and Working Solutions
311 242Pu
A National Institute of Standards and Technology Standard Reference Material (NIST SRM 434H) was used to prepare a stock 242Pu solution by dilution in 2 Aristar Optima HNO3 All volume additions were monitored gravimetrically This working solution was then used to make a set of 001 005 1 2 5 10 parts per billion (ppb) standards by dilution using 2 HNO3 Again all volume additions were monitored gravimetrically These standards were used to calibrate the Thermo Scientific X Series 2 inductively coupled plasma ndash mass spectrometer (ICP-MS) for quantification of 242Pu A representative calibration curve for 242Pu is shown in Figure 31 The instrument performance was monitored using 209Bi 232Th and 238U as internal standards The recovery of each sample during analysis was corrected based on the internal standard recovery The internal standard recoveries remained within standard quality assurancequality control QAQC protocols for the instrument (between 80 and 120)
A 242Pu stock solution was prepared by dissolving 1mg of Pu(NO3)4 obtained as a Certified Reference Material from New Brunswick Laboratory (CRM 130) This CRM is gt999 242Pu by atom percent The CRM was dissolved in 20mL of 8M HNO3 (Aristar Optima Grade) Because no chemicals or heat have been introduced to manipulate the Pu oxidation state it can be assumed that Pu(IV) is the predominant oxidation state in this stock solution A working solution to be used in spiking 242Pu experiments was prepared by diluting 25 mL of the CRM stock solution with 100 mL 10 M Aristar Optima HNO3 The concentration of 242Pu in this stock solution was determined using ICP-MS calibrated using the NIST SRM standards The concentration of Pu in this stock solution was 1065 ppb The total Pu
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concentration was also determined using liquid scintillation counting using the isotopic ratios reported for CRM 130 These compared favorably with the ICP-MS results but are reported here as a rigorous standardization because the isotopic ratios of CRM 130 have not yet been certified
Figure 31 Screen capture of a typical 242Pu calibration curve using Thermo PlasmaLab software to control the data collection and analysis R2=0999872 Intercept Conc (Detection Limit) = 0000044 ppb
312 237Np
A National Institute of Standards and Technology Standard Reference Material (NIST SRM 4341) was used to prepare a stock 237Np solution by dilution in 2 Aristar Optima HNO3 All volume additions were monitored gravimetrically This working solution was then used to make a set of 001 005 1 2 5 10 ppb standards by dilution using 2 HNO3 Again all volume additions were monitored gravimetrically These standards were used to calibrate the Thermo Scientific X Series 2 ICP-MS for quantification of 237Np A representative calibration curve for 237Np is shown in Figure 32 The instrument performance was monitored using 209Bi 232Th and 238U as internal standards The recovery of each sample during analysis was corrected based on the internal standard recovery The internal standard recoveries remained within standard QAQC protocols for the instrument (between 80 and 120)
A compiled 237Np stock solution from the Environmental Engineering and Earth Science (EEampES) inventory (primarily purchased from Isotope Products Valencia CA) was evaporated to dryness then the residue was brought up in approximately 5mL 80 M HNO3 Then 10 M hydroxylamine hydrochloride (NH2OHHCl EMD Chemicals ACS grade) and water were added to achieve a 3M HNO303M NH2OHHCl solution This solution was purified by extraction chromatography using Eichrom TEVA resin packed in a Bio-Rad poly-prep column The 3M HNO303 M NH2OHHCl neptunium solution was loaded on a 2 mL column and washed with 3 column volumes of 3 M HNO3 The Np(IV) was eluted with 002 M HCl + 02 M HF The effluent was evaporated to dryness then redissolved in 10 M HNO3 Additional 10 M HNO3 was added to maintain a approximately 10 mL then the solution was evaporated to incipient dryness and redissolved in a 50 mL of 10 M HNO3 An aliquot of the stock solution was evaporated to dryness on a stainless steel planchet and counted on the EGampG Ortec Alpha Spectrometer (Octete PC Detectors) No other alpha energies besides 237Np were observed The approximate concentration was determined using liquid scintillation counting and little 233Pa was observed The fuming in HNO3 as performed at the end of the purification procedure will drive Np to the soluble pentavalent state This is the stable oxidation state of Np under the experimental conditions Therefore experiments performed here can be assumed to be initially Np(V) The exact Np
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concentration in this solution was determined using ICP-MS calibrated with a NIST standard as discussed in section 312 below
A 237Np working solution (Working Solution 1) was created by pipetting an aliquot of the 237Np stock solution into a 100 mL Nalgene Teflon bottle and diluting with 2 BDH Aristar Ultra HNO3 to give a working solution concentration of 820 ppb All volumes were monitored gravimetrically Analysis on the ICP-MS calibrated against NIST Standards as described below gave a concentration of 820 ppb in Working Solution 1
Figure 32 Screen capture of a typical 237Np calibration curve using Thermo PlasmaLab software to control the data collection and analysis R2=0999981 Intercept Conc (Detection Limit) = 0000026 ppb
313 99Tc
A 99Tc working solution was prepared by diluting a stock solution of 99Tc (from the EEampES inventory purchased from Isotope Products Valencia CA) in distilled-deionized water (DDI Resistivity gt18 MΩcm) The oxidation state of Tc was not measured However based on the aqueous concentration in the DDI water solution Tc(VII) is the expected oxidation state The reduced Tc(IV) oxidation state would not be soluble under these conditions The expected concentration of 950 ppb based on the dilution was verified using liquid scintillation counting The 99Tc working solution was used to make 001 005 1 2 5 and 10 ppb standards by dilution using 2 HNO3 These standards were used to calibrate the Thermo Scientific X Series 2 ICP-MS for quantification of 99Tc A screen shot of a representative calibration curve is shown in Figure 33 The instrument performance was monitored by interpolating between 89Y and 115In internal standards The recovery of each sample during analysis was corrected based on the internal standard recovery The internal standard recoveries remained within standard QAQC protocols for the instrument (between 80 and 120)
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Figure 33 Screen capture of a typical 99Tc calibration curve using Thermo PlasmaLab software to control the data collection and analysis R2=0999984 Intercept Conc (Detection Limit) = 0000013 ppb
314 127I
A 100 microgmL iodate (IO3-) stock solution from High Purity Standards (Charleston SC) was used
to make 1 5 10 50 and 100 ppb standards by dilution using the ldquotraprdquo solution (discussed in Section 32 below) These standards were used to calibrate the Thermo Scientific X Series 2 ICP-MS for quantification of 127I A screen shot of a representative calibration curve is shown in Figure 34 The use of a reducing basic trap solution for iodine analysis limits the number of available internal standards that can be used to monitor ICP-MS instrument performance during iodine analysis Experiments are underway to identify acceptable internal standards However the data presented in this work did not use any internal standards prior to rigorous testing and analysis of representative standards As with the analyses for all isotopes (Tc I Np and Pu) spiked QAQC samples were frequently analyzed throughout the analysis as a check on instrument performance While these values cannot be used to correct individual samples in the same manner that the internal standards can they can be used to ensure accurate measurements of each isotope In almost all cases QAQC standards were within 10 of the expected value Because the average internal standard recovery ranges between 80 and 120 for the ICP-MS the iodine QAQC standard appears to be acceptable However a significant amount of ongoing work is testing various internal standards to improve the accuracy of iodine analysis using ICP-MS In one experiment (discussed in detail below) the QAQC standards deviated by an average value of 195 This will be specifically discussed below
Because experiments were performed with 127I concentrations up to 1000 ppb the 100 microgmL (ppm) stock iodate solution from High Purity Standards was used as the working solution
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Figure 34 Screen capture of a typical 127I calibration curve using Thermo PlasmaLab software to control the data collection and analysis R2=0999991 Intercept Conc (Detection Limit) = 024 ppb
315 Cementitious Materials Selected for Experiments There were four cementitious materials selected for this sorption study The first referred to as Aged Cement is a 30 year old sample that does not contain any reducing slag The aggregate from the Vault 2 cement had its aggregate removed prior to conducted tests in an effort to make subsamples more uniform This was necessary because some of the aggregate were larger than the 05 g subsamples used in individual sorption tests The Vault 2 cementitious material contained 17 dry wt- reducing slag on a dry weight basis before the water was added to the mix (Table 31) The TR547 and TR545 saltstone formulations contain 45 dry wt- and 90 dry wt- reducing slag respectively
Table 31 Characteristics of saltstone formulations used in this work Kaplan et al (2008)
Sample Percent Reducing Slag (dry wt-) (c)
Percent Portland Cement
(dry wt-) (c)
Percent Fly Ash
(dry wt-) (c)
Percent Aggregatesand ( dry wt-) (c)
Reducing Equivalents
(microeqg)
Aged Cement 0 10 45 45 855 plusmn 101(a)
Vault 2 Cement 17 10 45 0 178(b)
TR547 45 10 45 0 607(b) TR545 90 10 0 0 681(b) Blast furnace slag 100 0 0 0 819(b) (a) Kaplan et al (2008) (b) Roberts and Kaplan (2009) (c) All percentages of saltstone formulations are reported on a dry weight percentage basis that is the weight of the ingredients before water was added (d) Based on Table 8 in Dixon et al (2008 SRNL-STI-2008-00421) which shows the following quantity (lbscu yd) for saltstone Vault 2 Mix 1 concrete formulation 201 cement (1271 wt-) 268 slag (1695 wt-) 447 silica fume (283 wt-) 1563 fly ash (989 wt-) 911 fine sand (5762 wt-) The large aggregate was removed before the sorption tests were conducted The large aggregate accounted for 75 wt- of the original field sample not the sample used in these test before water was added to the mix TR547 is referred to as the Baseline by Dixon et al (2008) and is described in more detail in Appendix C (Mix 2) by Dixon et al (2008) (Control-BFSPC) and 1 (Baseline)
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TR545 saltstone contains 90 reducing slag and it is Mix 1 in Dixon et al (2008) and is described as
ldquoA control mix will be based on the baseline mix modified by exclusion of the Class F fly ash Consequently the cementitious materials premix will be a mixture of 90 blast furnace slag and 10 Portland cement The degree of reaction will be much greater than with the normal premix and therefore should result in a lower porosity and a lower permeability This bounding test at 060 wcm ratio is expected to yield a hydraulic conductivity at or below the detection limit for the Mactec permeameter measurement system Therefore this test should demonstrate the lowest level of detection of the Mactec system as well as show a resolvable difference between measurements of the control mix and the control mix with the normal premix compositionrdquo
32 ICP-MS Detection Limits
The PlasmaLab software platform determines a detection limit for each isotope based upon the intercept concentration A new calibration curve was generated for each experimental run and curves were very similar Using representative calibrations curves the detection limits for each isotope were as listed in Table 32 Note the higher detection limit for 127I is primarily due to the higher background count rate observed on the instrument This is believed to be due to the minimum purity levels of chemicals required for the iodine ldquotraprdquo solution as discussed in Section 33 below Therefore experiments were run with initial iodate concentrations higher than Tc Np and Pu to maintain analytical sensitivity
Table 32 Detection limits for each isotope based on representative calibration curves generated in PlasmaLab software associated with the ICP-MS
33 Experimental Methods
The experimental methods used in this work followed closely those previously described for experiments examining radionuclide sorption to saltstone (Kaplan et al 2007 Kaplan et al 2008) Brief descriptions of each method are provided below
Preparation of Calcite Solution Using a hotstirring plate 10 L of distilled-deionized (DDI)
water was heated to 3-100C above room temperature Then 001 g CaCO3 (EM Science ACS grade) was added to the solution and the resulting suspension was mixed for 24 hours at the elevated temperature The solution was then vacuum filtered through a 045-microm filter to ensure no solid CaCO3 remained in solution
Preparation of 2 HNO3 Analysis of Tc Np and Pu on the ICP-MS required dilution in 2
HNO3 This was prepared by adding 28 mL of Aristar Optima HNO3 from a clean graduated cylinder (designated to 2 HNO3) into a 1 L volumetric flask (designated to 2 HNO3) partially filled with DDI water and then further diluted to volume
Preparation of Trap Solution for Iodine Analysis Analysis of I required the use of a reducing
basic solution that was capable of reducing iodate to iodine and holding the iodine in solution This minimized the loss of I during sample analysis A 1 L trap solution was prepared by weighing out 00500 g NaHSO3 (Fisher Scientific ACS Grade) on a calibrated Sartorous LA 230S scale and adding it to a 1L volumetric flask Then 40 mL of 25 ww tetramethylammonium hydroxide (Alfa Aesar electronic grade) and 10 mL CFA-C solution (Spectrasol Inc) were added to the volumetric flask via a calibrated 1000-5000 microL Eppendorf Research pipette The solution was then diluted to volume with DDI water
34 Experimental Protocol for Sorption Experiments under Aerobic Conditions
Falcon BlueMax 15mL polypropylene vials were labeled and weighed to within 0001 g on a calibrated Sartorious LA 230S scale The scale was then zeroed and 025 +- 001 g of a given solid were added to each tube and the weight was recorded to within 0001g
For each of the four solids three sets of triplicate samples were prepared The three sets of samples were used to allow for experiments to be run with varying concentrations of each isotope Target initial concentrations for 99Tc 237Np and 242Pu samples were 1 ppb 5 ppb and 10 ppb Target initial concentrations for the 127I samples were 100 ppb 500 ppb and 1000 ppb A set of no solids controls at initial concentrations of 1 ppb and 10 ppb for 99Tc 237Np and 242Pu and initial concentrations of 100 ppb and 1000 ppb 127I were also prepared by adding the calcite solution to pre-weighed pre-labeled centrifuge tubes as discussed above
The solids were equilibrated with the calcite solution before spiking with the radionuclides This was done by adding 10 plusmn 01 mL of calcite solution to each tube and recording the mass The samples were then placed on a Thermo Scientific shaker overnight After 24 hours the solutions were allowed to settle for 1 hour The pH was then measured and the samples were then centrifuged for 15 minutes at 8000 rpm to further separate the solids The aqueous phase was then decanted and 10 plusmn 01 mL of calcite solution was added to each tube The weight of the tube (labeled tube + solid + calcite solution) was measured to within 0001g During this washing process the pH was monitored and held steady throughout the process The pH ranged from 11-12 depending on the particular saltstone used During the experiments the exact pH for all samples at all equilibration times was measured and is reported in Appendix A and B
The resulting suspensions were then spiked with 127I 237Np 242Pu and 99Tc It is important to note that all four isotopes were added to the same vial Use of the ICP-MS to determine the concentration of each isotope allows for a single solution to contain all analytes of concern This allowed for a greater variability in the sample set and increased replicates as opposed to running individual sorption tests for each isotope For the systems with initial 99Tc 237Np and 242Pu concentrations of 10 ppb and initial 127I concentration of 100 ppb a 100 microL aliquot of each radionuclide working solution was added to the first three tubes for each solid The addition was made with the tube resting on a tared analytical balance so that the exact mass of each radionuclide solution added was recorded and the solution was gently swirled before the next radionuclide was added The 5 ppb 237Np 242Pu and 99Tc and 500 ppb 127I samples were prepared in the same manner but adding 50 microL of the respective spike solutions The final three tubes with initial 237Np 242Pu and 99Tc concentrations of 1 ppb and 100 ppb 127I were prepared by using 10 microL of the spike solutions for all four solids as well as a set of solid-free controls (No-Solids Controls) For clarity this experimental matrix is shown in Table 33 below
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Table 33 Experimental Matrix of Sorption Experiments under Aerobic Conditions
After spiking the radionuclides a precalculated amount of 10M NaOH was added to each sample
to counter the acidic radionuclide spike solutions and the pH of one of the triplicate samples was measured to ensure the proper pH range was reached The samples were then placed on and end-over-end shaker to mix at approximately 8 rpm After 24 hours the samples were removed from the shaker and the pH of each sample was measured using an Orion Ross semi-micro glass electrode calibrated against pH 4 7 and 10 buffers (Thermo) The samples were then shaken and a transfer pipette was used to transfer 35 mL of a homogenous suspension to a 5mL syringe The solution was then passed through a 100 nm nylon syringe filter The first 025-050 mL of filtrate was discarded and the remaining filtrate was collected in a clean polyethylene vial Then 10 mL of the filtrate was removed and diluted in 90 mL 2 HNO3 The mass of each phase was determined and recorded gravimetrically Then 10 mL of the remaining filtrate was transferred to a clean Falcon BlueMax 15mL vial and diluted with 90 mL of trap solution for 127I analysis Again the volume of each phase was monitored gravimetrically After the 24 hour sampling event the samples were put back on the shaker to mix for three additional days On day four the above sampling procedure was repeated
The 237Np 242Pu and 99Tc samples can be run on the Thermo Scientific ICP-MS using the standard setup and procedure which included a standard flow glass nebulizer and bulb spray chamber However for the 127I analysis the ICP-MS must be reconfigured to accommodate the basic reducing trap solution This is to alleviate problems with iodine signal stability over time frequently observed in ICP-MS analysis The reconfigured instrument uses an Elemental Science Microflow PFA-100 Teflon nebulizer with a flow rate of 100microLmin along with a sapphire torch and a Teflon spray chamber This configuration must be run with a low pump speed to prevent back pressure on the system Two 30 minute stability tests were performed using a 50 ppb iodate solution Each experiment consisted of 40 separate measurements After each experiment was completed the uncorrected mass counts were examined and found to stay steady over the sampling period The relative standard deviation ( RSD) over all samples for each experiment was 1866 and 1460 respectively This shows that there was no significant ldquomemoryrdquo or loss of the iodine signal over time and that the reconfigured instrument has a stable iodine signal over time However as will be discussed below some difficulty has been encountered in finding an adequate internal standard for iodine analysis
35 Experimental Protocol for Sorption Experiments under Anerobic Conditions In order to examine the effects of reducing conditions of sorption of each isotope to the various cementitious samples a series of sorption experiments were performed in an anaerobic glovebox under a 2 H2(g) 98 N2(g) atmosphere Based on the measured pH and EH of these systems as discussed below these systems were at the point of reducing water Therefore they are expected to represent a lower end of the possible range for reducing conditions expected in the porewater available within cementitious materials
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Preparation of Calcite for Reducing Conditions Approximately 35 L of DDI water was boiled for 45 minutes Argon was slowly bubbled through the water as it cooled Once it cooled to below 500C approximately 3 g of calcite was added This solution mixed overnight under a continuous Ar flow After 12 hours the solution was moved into an oxygen free glove bag for filtration as described in 3231 After filtration the calcite solution was moved into the glove box
Preparation of Working Solutions under Reducing Conditions The calcite and solid solutions
were prepared in the glove box using the previously mentioned procedure used under aerobic conditions The radionuclide working solutions were transferred to the glovebox and stirred open to the reducing atmosphere for at least three days The concentration of each isotope in the working solutions was measured to determine any change in the concentration due to evaporation while the solutions were equilibrating
The preparation and spiking of samples for sorption experiments was performed exactly as described for the oxidizing conditions except all sample handling was performed in the glovebox After the 1 day and 4 day equilibration the samples were filtered within the glovebox then transferred outside for dilution and ICP-MS analysis similar to the description provided about for the oxidizing conditions For these experiments only 4 mL of either 2 HNO3 or trap solution were used to dilute the filtrate instead of the 90 mL used above for experiments performed under oxidizing conditions
36 Examination of Sorption to Vial Walls for Solids and No Solids Controls
As will be discussed below the solid-free controls samples indicated significant loss of Np and Pu Once the one and four days samples were collected and run on the ICP-MS it was necessary to determine the degree each radionuclide was sorbing to the vial walls The remaining suspensions and controls were emptied into a waste container Then 5 mL of the calcite solution was added to each vial using a calibrated pipette The vials were sonicated for approximately one minute and then emptied into the waste container Another 5 mL of calcite solution was added for the second wash and then discarded into the waste container This procedure was expected to remove any soluble Pu from the system or Pu associated with colloidal particles After each vial was washed 10 mL of 2 HNO3 was added using a calibrated pipette The acid solution is expected to remove any Tc Np or Pu associated with the vial walls This procedure has been shown to complete mass balances of Pu in similar sorption experiments using Pu (Powell et al 2002) This process was performed for both the solid suspension and the no solids controls The samples were then run on the ICP-MS to determine the concentration of 99Tc 237Np and 242Pu sorbed to the vial walls
37 Data Analysis The solubilities of 242Pu and 237Np were calculated by using the formula
nuclide
nuclide
nuclideMSICP
sol Mg
gCC
)(10 6
microminus
minus
= (Equation 31)
Csol = observed nuclide solubility (molnuclidekgsolution) CICP-MS = aqueous concentration of nuclide from ICP-MS measurement (ppb micrognuclidekgsolution) Mnuclide = molecular mass of nuclide (gnuclidemolnuclide)
In order to determine the Kd values one first needs to determine the concentration on the solid by using
SRNL-STI-2009-00636 Revision 0
24
solid
calcitespikeaqspikecalcite
spikestock
solid m
mmCmmmC
C)(
)()(
+⎥⎥⎦
⎤
⎢⎢⎣
⎡minus
+
lowast
= (Equation 32)
Csolid = calculated solid phase concentration of the nuclide (ppb) Cstock = concentration of the nuclide stock solution (ppb) mspike = mass of nuclide spiked into the saltstone suspension (g) mcalcite = total mass of calcite solution used in the saltstone suspension (g) Caq = aqueous concentration of nuclide from ICP-MS measurement (ppb) msolid = mass of the saltstone used in the suspension (g)
The Kd can be calculated using the equation
aq
solidd C
CK = (Equation 33)
Kd = solid-water partitioning coefficient (gsolutiongsolid assuming density of 10 gmL traditional
unit of mLsolutiongsolid can be obtained) This Kd Equation (33) is numerically equivalent to the traditional Kd equation proposed in ASTM D-4646 which has been used in previous saltstone experiments (Kaplan et al 2007 Kaplan et al 2008)
40 Results and Discussion
41 Radionuclide Sorption to Cementitious Formulations under Oxidizing Conditions
Figure 41 shows Pu Kd values ranging from 104 to gt105 mLg Generally for each solid the Kd increases with increasing initial Pu concentrations typical behavior of systems where the aqueous concentrations of the radionuclides are solubility controlled This is not expected because the Kd expression indicates that the Kd value should remain constant with increasing total Pu concentrations It was noted that aqueous phase concentration of Pu remained relatively constant in all samples (see discussion below regarding Pu solubility) Therefore the sorption capacity of each solid phase for Pu has not been overcome For each of these solid phases it appears the solutions had reached equilibrium before the first samples were taken at 24 hours In each case the Kd values for the one day and four day are similar A trend between the solid phases is not discernible The aged cement with no reducing slag was expected to have the lowest Kd values but in actuality it has the highest Kd Also there is no correlation with the concentration of reducing slag The Vault 2 samples with 17 dry wt- reducing slag has a Kd similar to that of the TR547 (45 dry wt- slag) while the saltstone with the most slag TR545 (90 dry wt- slag) has the lowest Kd value Others have observed that Pu Kd values of cementitious materials are similar in the absence and presence of slag (Allard et al 1984 Hoaglund et al 1985)
It was observed that similar aqueous concentrations of Pu were observed regardless of the solid phase present Figure 42 shows the average aqueous phase concentrations measured after one day and four days for all solids As stated above triplicate samples were prepared for each solid phase and each initial concentration Therefore each of the reported solubility values in Figure 42 is an average of nine measurements Using the highest reported value with the expected maximum error (0018 ppb for solid TR545) the maximum expected aqueous concentration of Pu in the pore water associated with the
SRNL-STI-2009-00636 Revision 0
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saltstone formulations will be approximately 7 x 10-11 molL as calculated using Equation 31 This is on the same order as the solubility of Pu hydrous oxide solid phases (Neck and Kim 2001)
Figure 41 Plutonium Kd Values under Oxidizing Conditions Plutonium Kd values for various saltstone formulations measured after one-day equilibration (1d) and four-day equilibration (4d under oxidizing conditions Total plutonium concentrations in each system were 1 ppb 5 ppb and 10 ppb Sample prepared in triplicate and error bars represent standard deviation of samples except as follows value for dataset TR547-4d 10 ppb is reported based on duplicate samples
Figure 42 Plutonium solubility for various saltstone formulations measured after one-day equilibration (1d) and four-day equilibration (4d) under oxidizing conditions Total plutonium concentrations in each system were 1 ppb 5 ppb and 10 ppb as noted Samples prepared in triplicate and an average of all samples (9) was used to determine average solubility The error bars represent standard deviation of samples
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Overall the Kd values for Np range from 105 to gt106 with only a few outliers The most significant outlier is the 1 ppb solution in the TR545 sample after the four-day equilibration It drops two orders of magnitude while the 5 and 10 ppb solutions remain constant However this result is most likely an analytical artifact from working at the detection limits of the ICP-MS In the one-day equilibration samples only one of the triplicates S-2-E had detectable Np while in the four-day equilibration samples only S-2-F had detectable amounts present The graph also shows that with the exception of the 5 ppb sample in the aged cement Np sorption to TR545 (90 dry-wt- slag) and TR547 (45 dry wt- slag) have Kd values approximately one order of magnitude over the aged cement (no slag) and Vault 2 (17 dry wt- slag) samples
It was observed that similar aqueous concentrations of Np were observed regardless of the solid phase present Figure 44 shows the average aqueous phase concentrations measured after one day and four-day equilibrations for all solids As stated above triplicate samples were prepared for each solid phase and each initial concentration Therefore each of the reported solubility values in Figure 44 is an average of nine measurements of Np concentration unless stated otherwise Using the highest reported value with the expected maximum error (00026 ppb for solid TR545) the maximum expected aqueous concentration of Pu in the pore water associated with the saltstone formulations will be approximately 2 x 10-11 molL
Figure 43 Neptunium Kd values under oxidizing conditions Neptunium Kd values for various saltstone formulations measured after one-day equilibration (1d) and four-day equilibration (4d) under oxidizing conditions Total plutonium concentrations in each system were 1 ppb 5 ppb and 10 ppb as noted Samples prepared in triplicate and error bars represent standard deviation of samples except as follows value for datasets TR545-1d 1ppb TR545-4d 1 ppb TR547 4d 1 ppb TR545-4d 10 ppb TR547-1d 1ppb TR547-4d 10 ppb are reported based on a single sample and for dataset TR545-1d 5ppb is reported based on duplicate samples Kd values limited to gt106 were at instrumental background
The Kd values for Tc are significantly lower than that of Pu or Np As a whole the values are
comparable The values for the one-day and four-day equilibrations solutions in the Vault 2 (17 dry wt- slag) and TR545 (90 dry wt- slag) remained constant within reasonable error with just a slight increase from the one-day to four-day equilibration However the Aged Cement (no slag) and TR547 (45 dry wt- slag) showed a noticeable decrease from day one to day four (Figure 45)
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Figure 44 Average solubility of Np under oxidizing conditions Neptunium solubility for various saltstone formulations measured after one-day equilibration (1d) and four-day equilibration (4d) under oxidizing conditions Total Np concentrations in each system were 1 ppb 5 ppb and 10 ppb Samples prepared in triplicate and an average of all samples (9) was used to determine average solubility except as follows TR545-1d is based on 6 samples TR545- 4d on 5 samples TR547-1d on 7 samples and TR547- 4d on 5 samples The error bars represent standard deviation
Figure 45 Technetium Kd values under oxidizing conditions Tc Kd values for various saltstone formulations measured after one-day equilibration (1d) and four-day equilibration (4d) under oxidizing conditions Total Tc concentrations in each system were 1 ppb 5 ppb and 10 ppb as noted above Samples were prepared in triplicate and the error bars represent standard deviation of samples except as follows data sets for Vault 2-1d 1ppb were duplicates and TR547- 4d 10 ppb is based on a single dataset
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Similar to the Tc Kd values the 127I Kd values are much lower than those of Pu and Np The amount of reducing slag present in each of the solids does not appear to have a drastic effect on the 127I Kd values In fact the initial (one day) Aged Cement (0 slag) samples had a Kd almost two orders of magnitude above those with reducing slag The cause of this behavior is not known but it has been shown that iodate IO3
- the oxidized form of iodine sorbs more strongly than iodide I- to charged surfaces (Schwehr et al 2009 Yoshida et al 1992 Fukui et al 1996) It is possible that the slag is reducing the iodine to the I- form converting it to a species that is less likely to sorb to saltstone Additional work would be required to confirm the oxidation state of iodine when associated with saltstone
Figure 46 Iodine Kd Values under Oxidizing Conditions Iodine Kd values for various cementitious formulations measured after one-day equilibration (1d) and four-day equilibration (4d) under oxidizing conditions Total iodine concentrations in the systems were 100ppb 500 ppb and 1000 ppb as noted above Samples were prepared in triplicate and the error bars represent standard deviation of samples except as follows duplicates were used for dataset TR545- 1d 100ppb
42 Radionuclide Sorption to Vial Walls Under Oxidizing Conditions
Figure 47 shows the aqueous fractions found in the no-solids controls It provides a measure of the solubility of each radionuclide as well as examines the fraction of each radionuclide sorbed to the vial walls After one day only 25 of the Pu remained in solution and the concentration decreased even more after four days The loss of Pu from the aqueous phase may be due to sorption of Pu to the vial walls or precipitation of a Pu hydrous oxide solid (discussed with respect to Figure 49 below) Additional experiments would be required to examine the solubility of the Pu in high pH calcite saturated solutions
After one day about 80 of the Np remained in solution However the aqueous concentration in the initially 1-ppb solution was significantly reduced after four days Approximately 60 of the Np remained soluble in the initially 10-ppb solution Once again this drop could be due to sorption to the vial wall The Tc present after one day ranged from about 88 to about 95 and was virtually 100 after four days These values are consistent with internal standards used to monitor Tc detection performance on the ICP-MS Greater than 50 of the I remained in solution after the one-day and four-day equilibrations As shown in Figure 48 the standard deviation between the triplicate I control samples was
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quite large Additional control samples are required to understand the mechanism by which I is being lost from the aqueous phase in these samples
Figure 47 Plutonium Neptunium and Technetium Aqueous Fractions Fraction of Pu Np and Tc remaining in the aqueous phase for the No Solids controls after a one-day equilibration (1d) and four-day equilibration (4d) under oxidizing conditions The total concentration for each radionuclide 10 ppb as noted above Samples were prepared in triplicate and the error bars represent the standard deviation of the samples
Figure 48 Iodine Aqueous Fraction Iodine aqueous fraction for the no-solids controls after a one-day equilibration (1d) and four-day equilibration (4d) under oxidizing conditions The total concentration of iodine was 1000 ppb as noted above Samples were prepared in triplicate and the error bars represent the standard deviation of the samples
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As discussed above the loss of Np and Pu from the no-solids control (Figure 47) could be due to
precipitation of Np and Pu hydrous oxides or sorption to the vial walls To quantify the differences between these possible sinks the vials were washed as described in Section 36 The data in Figure 49 indicate that significant sorption of Np and Pu to the vial walls may occur When combining the mass of Np represented in Figure 47 and Figure 49 there is almost 100 mass recovery of the Np sorbed to the vial wall and the aqueous fraction measured Therefore no precipitation of Np is expected However because 100 recovery was not achieved for Pu a Pu hydrous oxide phase could be precipitating which was washed out of the vial during the cleaning procedure The data in Figure 47 represent the no-solids control samples where there was no solid phase present for Np or Pu to sorb to besides the vial walls However when a cementitious solid phase is present in the sample there will be competition between the vial walls and the cement for sorption of Np and Pu Based on the affinity of metals for metal oxide surfaces as opposed to the polypropylene surface and the much higher surface site density expected for the cementitious samples it is assumed that the cementitious samples will out-compete the vial walls for sorption sites This thesis was tested by taking one of the triplicate samples from each sorption experiment with a solid phase present removing the solid phase from the tubes and leaching any sorbed Np and Pu from the tubes with acid as described in Section 36 Figure 410 and Figure 411 show that although some of the Pu and Np sorbed to the vial walls of the samples this amount accounted for less than 2 in all samples Therefore sorption of Np and Pu to the vial walls does not appear to be a significant factor in experiments where the solid phase is present Note these results do not discount the possibility that Pu hydrous oxide precipitates were forming in both the no-solid control experiments and experiments with cement formulations present Based on the observation of a constant aqueous phase concentration of Pu regardless of the initial Pu concentration the presence of a solubility limiting Pu phase cannot be discounted based on these data Further experiments examining the solubility of Pu in high pH calcite saturated solutions are required
Like Pu Np shows little affinity for the vial walls in the presence of a solid phase In each case tested there was significantly less than 1 of the total Np sorbed to the vial walls This behavior is consistent with the ~100 mass balance on Np achieve in the solid-free controls The majority of Np remained soluble in the solid-free control experiments Therefore it is expected that sorption of Np to the vial walls was the primary reason for the loss of Np from the aqueous phase in the no-solids systems rather than precipitation of a Np solid phase similar to the process discussed for Pu above This assumption is based on the relative solubility of Np(V) as compared with Pu(IV)
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Figure 49 Percent Pu and Np sorbed to vial walls of the no solids controls after the aqueous phases were discarded and the vials were washed Both the 10 ppb and 1 ppb datasets were prepared in triplicate and the error bars show the standard deviation
Figure 410 Percent Pu sorbed to vial walls after the solids and aqueous phases were removed and the vials were washed The graph illustrates one sample from each of the 1 ppb 5 ppb and 10 ppb systems Therefore no error bars are present
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Figure 411 Percent Np sorbed to vial walls after the solids and aqueous phases were removed and the vials were washed The graph illustrates one sample from each of the 1 ppb 5 ppb and 10 ppb systems Therefore no error bars are present
43 Radionuclide Sorption to Cementitious Formulations under Reducing Conditions
Similar to the Pu Kd values under oxidizing conditions Pu Kd values ranged from 104 to gt105 under reducing conditions (Figure 412) Also similar to the results under oxidizing conditions the Kd increases with increasing initial Pu concentration Again this behavior is indicative of the aqueous phase concentration of Pu being controlled by solubility of Pu rather than by sorption In each case the samples appeared to reach steady state within 24 hours This equilibration is evident because the Kd values after one day and four days are very similar Also it appears that the amount of reducing slag does not make a significant difference in the Kd value In fact the TR547 solid consists of 45 reducing grout but produces approximately the same Kd values of the aged cement which does not have any reducing grout Each of these Kd values are higher than the TR545 which is 90 reducing grout These findings are in agreement with those conducted by Allard et al (1984) and Hoglund et al (1985) who reported that concrete containing reducing agents (slag similar to that used in our study) did not have greater Pu Kd values than those that did not contain slag
Similar aqueous concentrations of Pu were observed regardless of the solid phase present Figure 36 shows the average aqueous phase concentrations measured after one day and four days for all solids As stated above triplicate samples were prepared for each solid phase and each initial concentration Therefore each of the reported solubility values in Figure 412 is an average of up to nine measurements of the Pu aqueous concentrations Using the highest reported value with the expected maximum error (00045 ppb for solid Vault 2) the maximum expected aqueous concentration of Pu in the pore water associated with the cementitious formulations will be approximately 2 x 10-11 molL (calculated from Equation 31) This value is on the same order as the solubility of Pu hydrous oxide solid phases (Neck and Kim 2001) A best value would be 10-12 molL
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Figure 412 Pu Kd Values under Reducing Conditions Plutonium Kd values for various cementitious formulations measured after one-day equilibration (1d) and four-day equilibration (4d) under reducing conditions Total plutonium concentrations in each system were 1ppb 5 ppb and 10 ppb Samples prepared in triplicate and error bars represent standard deviation
Figure 413 Average Solubility of Plutonium under Reducing Conditions Plutonium solubility for various cementitious formulations measured after one-day equilibration (1d) and four-day equilibration (4d) under reducing conditions Total plutonium concentrations in each system were 1ppb 5 ppb and 10 ppb as noted Samples prepared in triplicate and an average of all samples (9) was used to determine average solubility The error bars represent standard deviation of samples
The Np Kd values reported in Figure 414 obtained under reducing conditions are very similar to
those obtained under oxidizing conditions In each case the samples appeared to reach steady state within 24 hours This equilibration is evident because the Kd values between the one-day and fourndashday equilibrations are similar As was the case with Pu the amount of slag present in each solid does not
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seem to have a significant effect on the Kd values Again the aged cement with no slag has as high a Kd as the TR545 with 90 reducing slag
Similar aqueous concentrations of Np were observed regardless of the solid phase present Figure 314 shows the average aqueous phase concentrations measured after one day and four days for all solids All Kd values were gt 105 mLg which is considerably larger than those reported by Kaplan and Coates (2007) who reported Np Kd values to 1300 to 1600 mLg This difference can be attributed to two important experimental differences 1) the experiment was designed to permit larger Kd values to be measured (eg solid to liquid ratios and spike concentrations) and more importantly 2) a more sensitive analytical method ICP-MS was used instead of conventional low-energy gamma spectroscopy or liquid scintillation counting (LSC) analysis As stated above triplicate samples were prepared for each solid phase and each initial concentration Therefore each of the reported solubility values in Figure 415 is an average of up to nine measurements Using the highest reported value (to provide the most conservative most soluble values) with the expected maximum error (00045 ppb for solid TR545) the maximum expected aqueous concentration of Np in the pore water associated with the cementitious formulations will be approximately 2 x 10-11 molL A best value taking into consideration the less-than values which are depicted in Figure 414 as running off the top of the plot would be 10-12 molL
Figure 414 Np Kd Values under Reducing Conditions Neptunium Kd values for various cementitious formulations measured after one-day equilibration (1d) and four-day equilibration (4d) under reducing conditions Total Np concentrations in each system were 1 ppb 5 ppb and 10 ppb Samples were prepared in triplicate and the error bars represent standard deviation Kd values limited to gt106 were at instrumental background
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Figure 415 Average Solubility of Neptunium under Reducing Conditions Neptunium solubility for various cementitious formulations measured after one day equilibration (1d) and four day equilibration (4d) under reducing conditions Total plutonium concentrations in each system were 1ppb 5 ppb and 10 ppb Samples prepared in triplicate and an average of all samples (9) was used to determine average solubility The error bars represent standard deviation
A plot of the Tc Kd values for each cementitious formulations under reducing conditions is shown
in Figure 416 (log y-axis) and Figure 417 (reduced scale linear y-axis) The Kd values for each of the initial Tc concentrations are relatively similar This behavior is consistent with the Kd expression However the increasing Kd values from the one-day to four-day day equilibrations for each solid indicate that steady state was not reached within one day and it is unclear whether steady state was reached after four days A possible explanation for this behavior is that Tc(VII) was being reduced to Tc(IV) in these systems due to the reducing conditions As Tc(VII) was reduced the Kd would increase based on the high affinity of Tc(IV) for solid phases This proposed mechanism was observed by Lukens et al (2005) using an SRS saltstone material similar but not identical to TR547 Using synchrotron X-ray absorption fine structure spectroscopy they observed over a 453 month period that Tc(VII) incorporated into SRS saltstone slowly converted to Tc(IV) and that the nearest neighbor was initially predominantly oxygen and eventually became predominantly sulfur (described as a Tc(IV) phase TcSx) Lacking in Lukens et al (2005) is quantification of the solubility of Tc This analysis still needs to be completed along with re-oxidation studies (ie what is the rate that reduced Tc reoxidizes under ambient natural saltstone conditions)
Unlike Np and Pu Tc Kd values changed with the amount of slag included in the formulation Tc Kd values noticeable increase as the amount of slag in the formulation increased TR547 (45 dry-wt- slag) Kd value is visibly higher than the Aged Cement and Vault 2 Kd values while the most reducing TR545 (90 dry wt- slag) Kd value is significantly higher than the others Following a similar trend the reduction capacity that is the total quantity of reductant in the saltstone on a mass basis (units of milli-equivalents of charge per g) of TR547 had slightly greater or equal reduction capacity to that of TR545 (Roberts and Kaplan 2009)
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Figure 416 Tc Kd Values under Reducing Conditions Tc Kd values for various cementitious formulations measured after one-day equilibration (1d) and four-day equilibration (4d) under reducing conditions Total Tc concentrations in each system were 1 ppb 5 ppb and 10 ppb Sample prepared in triplicate and error bars represent standard deviation except as follows TR547-1d 1 ppb is based on a single dataset and datasets Vault 2-1d 5 ppb Vault 2- 4d 1 ppb Aged Cement-1d 5 ppb and Aged Cement-4d 1 ppb are duplicates
Figure 417 Data from Figure 416 replotted on a reduced linear scale for easier viewing Each sample was prepared in triplicate except as follows TR547-1d 1 ppb is based on a single dataset Vault 2-1d 5 ppb Vault 2- 4d 1 ppb Aged Cement-1d 5 ppb and Aged Cement-4d 1 ppb are duplicate datasets
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The calculated Kd values for I sorption to cementitious samples under reducing conditions are shown in Figure 418 Before discussing the data it should be noted that spiked QAQC samples which were analyzed on the ICP-MS along with the samples used to generate the data in Figure 418 were off by an average of 195 with one outlier of approximately 40 This dataset did not include the use of internal standards as discussed in Section 31 above1 Due to a lack of an internal standard the iodine results presented in this report should be considered with a minimum error estimate of 20
The iodine Kd values under reducing conditions are different from those observed under oxidizing conditions Under oxidizing conditions it appears they are at a steady state by day one However under reducing conditions there is a noticeable difference between days one and four indicating steady state was not reached by day one and possibly not by day four Another interesting observation is that the Kd values are decreasing from day one to four A possible reason for this behavior may be due to redox chemistry of iodine in this system If iodine partially or entirely exists in the form as iodate (IO3
-) it is possible it could be reduced to iodide I- within the reducing cementitious system These two iodine species sorb differently iodate sorbing to minerals more strongly than iodide (Denham et al 2009 Schwehr et al 2009 Fukui et al 1996 Yoshida et al 1992) It is hypothesized that the reducing environment of the saltstone is sufficient to reduce iodate ions to the more weakly binding form of iodine iodide
This is one of the few datasets (along with Tc) in this study where there may be a difference between the various solids The degree of iodate reduction would be expected to increase as the slag content increases As mentioned above reduction of iodate to iodide should result in a decrease in sorption Therefore higher Kd values should be observed for solids with less slag such as the Aged Cement (0 dry wt- slag) and Vault 2 (17 dry wt- slag) This is generally the case in Figure 418 where the highest Kd values are reported for the Aged Cement and the lowest values are for solid TR547 However this trend does not hold completely where the saltstone sample containing 90 slag (TR545) has generally equal or higher Kd values than the saltstone containing 45 dry wt- slag (TR547)
1 Clemson University is presently investigating appropriate internal standards for iodine analyses for ICP-MS Of those tested rhenium and molybdenum have shown some promise
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Figure 418 Iodine Kd Values under Reducing Conditions I Kd Values for various cementitious formulations measured after one day equilibration (1d) and four day equilibration (4d) under reducing conditions Total iodine concentrations in each system were 100 ppb 500 ppb and 1000 ppb as noted Sample prepared in triplicate and error bars represent standard deviation of samples except as follows Vault 2-4 d 100 ppb is a single dataset while the datasets for Vault 2-1 d 100 ppb 4 d 1000 ppb TR545-4 d 1000 ppb 100 ppb TR547-4 d 1000 ppb 500 ppb 100 ppb and Aged Cement- 4 d 1000 ppb and 100 ppb are all based on duplicates
44 Radionuclide Sorption to Vial Walls under Reducing Conditions
The aqueous concentrations for Pu Np and Tc in the no solids controls are shown in Figure 419 The results are similar to those presented for experiments performed under oxidizing conditions above The 1 ppb Pu aqueous fraction is approximately three times greater than the 10 ppb fraction at day one This fraction decreases over time and by day four they are approximately equal when taking error into account This behavior is similar to the aqueous fraction under oxidizing conditions The 1 ppb Np aqueous fraction is significantly higher on both day one and day four than the aqueous fraction of the 10 ppb samples However each remained constant from day one to day four The 10 ppb aqueous fraction is twice as low as under oxidizing conditions which suggests either higher sorption to the vial walls or more precipitating out under the reducing conditions Like Pu and Np Tc shows a decrease from day one to day four especially for the 1 ppb samples The decrease in the 10 ppb sample is minimal and the aqueous fraction remains around 09 This value is slightly lower than that under oxidizing conditions
To examine the degree of sorption to the vial walls the tubes were washed again as performed for the experiments under oxidizing conditions above and similar results were found Ninety percent of the 1 ppb Pu sample was sorbed to the vial wall upon completion of the experiment which gives a 100 mass recovery when comparing this value to that found in Figure 419 However this result is not the case with the 10 ppb samples where approximately 75 of the mass remains unaccounted It is noteworthy that approximately 25 of the Pu from the 10 ppb solution sorbed to the vial walls under both oxidizing
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and reducing conditions Np follows the same trend as Pu while less than 005 of the Tc sorbed to the wall
Figure 419 Plutonium Neptunium and Technetium No-Solids Aqueous Fractions under Reducing Conditions Pu Np and Tc aqueous fractions of No Solids controls after a one-day equilibration (1d) and four-day equilibration (4 d) under reducing conditions Total concentration for each radionuclide was 1 ppb and 10 ppb Samples were prepared in triplicate and the error bars represent the standard deviation
Figure 420 Percent of Pu Np and Tc sorbed to the vial walls of the No Solids control samples under reducing conditions Each the 1 ppb and 10 ppb samples were prepared in triplicate and the error bars represent the standard deviations of triplicate samples
Under reducing conditions the fraction of I remaining in the aqueous phase was around 90 with
almost 100 mass recovery of the 100 ppb I after the four-day equilibration These graphs show that
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under reducing conditions there will only be a small fraction of I sorbing to the vial wall or coming out of solution This result is a much better mass recovery than under oxidizing conditions (Figure 48) which had a mass recovery of approximately 65 after four days This result is also consistent with the interpretation that there may be a iodine speciation change between the two redox treatments
Figure 421 Iodine No-Solids Aqueous Fractions under Reducing Conditions I aqueous fractions of No-Solids controls after a one-day equilibration (1d) and four-day equilibration (4d) under reducing conditions The total concentration for each system was 100 ppb and 1000 ppb Samples were prepared in triplicate and the error bars represent the standard deviation
50 Comparison of Radionuclide Sorption under Oxidizing and Reducing Conditions
In the following figures (Figure 51 through Figure 54) the data shown above has been replotted to allow comparison between the oxidizing and reducing conditions for each cementitious formulation General observations based on these data follow Vault 2 Observations (Figure 51)
bull Pu Kds are greater than 104 under both oxidizing and reducing conditions and Pu Kds are slightly lower under reducing conditions This could possibly be due to reduction of Pu(IV) to Pu(III) However no oxidation state analysis was performed in this work
bull Np Kds are generally greater than 104 under both oxidizing and reducing conditions Interestingly Np Kds are higher under reducing conditions by almost an order of magnitude This could possibly be due to reduction of Np(V) to Np(IV) However no oxidation state analysis was performed in this work
bull Regardless of the initial Np or Pu concentration similar aqueous phase concentrations of Np or Pu were observed in all samples This trend indicates that ldquosorptionrdquo of Np and Pu in these systems may be a combination of adsorption absorption and (co)precipitation processes
bull Tc appears to reach a steady state within four days under oxidizing conditions This behavior does not appear to be the case under reducing conditions After four days similar Kd values are reached under both oxidizing and reducing conditions It is unclear
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whether the Kd value of Tc will continue to increase under reducing conditions consistent with reduction of Tc(VII) to Tc(IV) The similarity in Kd values under both oxidizing and reducing conditions is an interesting observation and certainly warrants additional studies
bull I Kd values are similar under both oxidizing and reducing conditions However reducing condition systems may not be at steady state after four days while systems under oxidizing conditions appeared to reach a steady state The difference in rates may be due to reduction of iodate to iodine
bull For all isotopes examined the sorption behavior to each of the solid phases is very similar
TR545 and TR547 Observations (Figure 52 and Figure 53) bull Similar to the discussion above with respect to Vault 2 Pu Np and Tc all appear to reach
a steady state under oxidizing conditions and approach steady state slower under reducing conditions
bull Np and Pu Kd values are greater than 104 for all systems and time steps The aqueous phase concentrations of Np and Pu appear to be better described as a solubility in terms of the aqueous phase concentration of Np and Pu Similar aqueous phase concentrations of both Np and Pu were reached The data indicate that the initial Np and Pu concentration generally does not affect the aqueous phase concentration at an apparent steady state The presence of each solid phase appears to limit the aqueous phase concentration of both Np and Pu on the order of 10-11 molL
bull Tc shows significantly higher Kd values under reducing conditions versus oxidizing conditions
bull For all isotopes examined the sorption behavior to each of the solid phases is very similar
Aged Cement Observations (Figure 54) bull Pu appears to be close to steady state for each solid by day one with similar Kd values
reached on between day one and day four bull Np has a higher Kd under reducing conditions than oxidizing (105 under oxidizing
conditions and gt105 under reducing conditions) bull Neither set of Tc data was at steady state by day one and rates of sorptiondesorption
reactions appear to be different Tc Kds decrease from day one to four under oxidizing conditions but increase under reducing conditions
bull The Kd values for I under oxidizing conditions were considerably higher than those measured for I with any other solid Similar Kd values obtained for the same solids under reducing conditions indicate that the reported Kd values under oxidizing conditions appear to be suspect However analysis of the raw data gives no indication of an experimental artifact As discussed above these observations may be explained based upon the amount of slag contained within the solids which will affect the reducing capacity (ie No reducing slag is in the aged cement which could be reason the reduction of iodate to iodide (speculated in other samples) is not evident)
bull The difference in sorption behavior of iodine to the aged cement between oxidizing and reducing conditions also indicates that the reducing conditions of the solution may affect I redox behavior in addition to any reactivity expected in the solid phases
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Figure 51 Comparison of Tc I Np and Pu sorption to Vault 2 solid under oxidizing and reducing conditions
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Figure 52 Comparison of Tc I Np and Pu sorption to TR 545 solid under oxidizing and reducing conditions
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Figure 53 Comparison of Tc I Np and Pu sorption to TR547 solid under oxidizing and reducing conditions
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Figure 54 Comparison of Tc I Np and Pu sorption to Aged Cement under oxidizing and reducing conditions
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60 Comparison of Radionuclide Sorption and Solubility under Oxidizing and Reducing Conditions
To further summarize the data the following tables provide either the average solubility
(for Np and Pu) or average Kd (for Tc and I) determined under both oxidizing and reducing conditions for each cementitious formulation Each table lists the average value standard deviation and the number of replicate samples used to calculate the reported values
The solubility of Pu in the presence of each solid under oxidizing and reducing conditions is shown in Table 61 (this is taken from experiments equilibrated for four days not one day) Under oxidizing conditions the apparent solubility values associated with the Aged Cement (0 dry wt- slag) Vault 2 (17 dry wt- slag) and TR547 (45 dry wt- slag) are all similar with only a slight increase in solubility as the amount of reducing slag increases There is a significant increase of almost an order of magnitude for the most reducing saltstone TR545 (90 dry wt- slag) However these samples also have a standard deviation on the same order of magnitude as the solubility itself which when taken into account brings the solubility back into the range of the others Under reducing conditions the apparent solubility values are slightly lower than under oxidizing conditions In this set of samples the Vault 2 saltstone with 10 dry wt- reducing slag had the highest apparent solubility but once again when considering the standard deviation the values are similar
Table 61 Comparison of plutonium apparent solubility values under oxidizing and reducing conditions
Table 62 lists the apparent solubility values of Np in the presence of each cementitious
formulation under both oxidizing and reducing conditions Under oxidizing conditions the cementitious formulation does not appear to have a dramatic effect on the solubility The apparent solubility values are similar to those of Pu under similar conditions except the Np standard deviations are much higher The high standard deviations are an analytical artifact since the measured concentrations were close to or at the detection limit of the ICP-MS There does appear to be a slight decrease in Np solubility under reducing conditions However the statistical significance of this decrease was not calculated
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Table 62 Comparison of neptunium apparent solubility values under oxidizing and reducing conditions
Unlike the apparent solubility values of Pu and Np the aqueousatmospheric conditions
and cementitious formulation seem to have an effect on the Tc Kd values (Table 63) Under oxidizing conditions there is not a discernible difference among the different cementitious formulations especially when taking the respective standard deviations into account However when experiments were run under reducing conditions the specific formulation had a noticeable effect The two saltstone samples with the least amount of reducing slag Aged Cement (0 dry-wt- slag) and Vault 2 (17 dry wt- slag) had Kd values which were similar to those observed under oxidizing conditions However the TR547 (45 dry-wt- slag) increased by almost an order of magnitude while the TR545 (90 dry wt- slag) increased by about three orders of magnitude Although the respective standard deviations are large the higher Kd values do appear to be significant
Table 63 Comparison of technetium Kd values under oxidizing and reducing conditions
Unlike Tc I does not seem to be as affected by cementitious formulation and redox status (Table 64) The only treatment (possible outlier) that does not follow this trend is the Aged Cement under oxidizing conditions This Kd value is higher than the others but also has a much higher standard deviation which when accounted for gives a value similar to the others All other treatments had near identical Kd values irrespective of solid phase or redox condition But again the Aged Cement data cannot be discounted at this time given the possibility of the influence that redox may have on iodine speciation and the strong influence I speciation has on sorption to cementitious materials
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Table 64 Comparison of iodine Kd values under oxidizing and reducing conditions
71 Comparison with Previous Data The increased sensitivity of the ICP-MS over conventional low-energy gamma
spectroscopy or liquid scintillation counting (LSC) analysis allowed for much more accurate Kd values and apparent solubility values in this work than were previously obtainable Generally radioanalytical detection methods start with activities on the order of 103 to 104 counts per minute (cpm) and approach background levels of 1 to 5 cpm for strongly sorbing radionuclides Therefore the accuracy of the Kd value will be the difference in analytical sensitivity when the initial aqueous activity decreases by a factor of approximately 5000 (ie the aqueous activity drops from approximately 5000 cpm to the instrument background of 1 cpm following almost complete sorption) As a result the reported Kd values can only be reliably reported up for a Kd of 103 to 104 This constraint is believed to be the difference between the observed Kd values for 237Np of gt 105 observed in this work when compared with the Kd values between 3000 and 4000 reported by Kaplan et al (2008) A similar observation was made for Pu because 242Pu was used for ICP-MS analysis and 238Pu was used in the work of Kaplan et al (2008) This constrint may account for the different Kd value of gt104 reported in Kaplan et al (2008) compared with the value of gt105 observed in this work
In the case of Tc Kaplan et al (2008) reported a Kd of 023 mLg for Vault 2 under oxidizing conditions and 093 mLg under reducing conditions while the above experiment determined the Vault 2 Kd to be 505 mLg under oxidizing conditions and 557 mLg under reducing conditions Unlike the discrepancy in the Kd values for Np Pu and Tc between the above findings and those in Kaplan et al (2008) the reported Kd values for iodine are similar For Vault 2 Kaplan et al (2008) found 125I to have a Kd of 894 mLg under oxidizing conditions and 715 mLg under reducing conditions These values are similar to the Kd values of 766 mLg and 725 mLg observed under oxidizing and reducing conditions respectively in this work These findings appear to confirm the previously accepted Kd values of 0-10 mLg depending on the cementitious formulation
72 Suggested Future Work The above data demonstrate several areas that require further examination The
increasing Tc Kd values over time dataset suggest that steady state had not been achieved It would be beneficial to determine the amount of time required to reach steady state and allow determination of a more accurate Kd value (an assumption of the Kd construct is that it be measured at steady state) Also kinetic studies of both Tc and I are needed to better understand their respective interactions with the different cementitious formulations As for the I additional
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tests should be performed to test the hypothesis that iodine may in part exist as iodate which may initially sorb to the saltstone then undergo reduction to iodine or iodide and then desorbs causing a decrease in Kd
A final area of future work is to examine the possible causes for the similar behavior of each cementitious formulation despite the different slag content This discrepancy is not only observed in the above experiments but also in Kaplan et al (2008) which is illustrated in Table 31 and by recent work in measurements of saltstone reduction capacity (Roberts and Kaplan 2009) The reduction capacity (units in milli-equivalentsg solid) equivalents of the Aged Cement with no slag is 855 plusmn 101 and adding 10 slag gives a reducing equivalent of 2398 plusmn 311 However increasing the slag content to 23 causes the reducing capacity to increase to 8218 plusmn 81 which is almost equivalent to the 8324 plusmn 49 of the 100 slag Understanding the chemistry behind the reducing capacity of each cementitious formulation will help to define what reactions are important for controlling radionuclide release from the saltstone
80 References Allard B L Eliasson S Hoglund and K Andersson 1984 ldquoSorption of Cs I and actinides in
concrete systemsrdquo SKB Technical Report SKBKBS TR-84-15 DKB Stockholm Sweden
Denham M D I Kaplan and C Yeager2009 ldquoGroundwater radioiodine Prevalence biogeochemistry and potential remedial approachesrdquo SRNL-STI-2009-00463 Savannah River National Laboratory Aiken SC
Dixon K L M A Phifer and J R Harbour 2008 ldquoFY09 PACA Maintenance Program Additional Saltstone Property Testingrdquo SRNL-L3100-2009-00019 Rev0 Savannah River National Laboratory Aiken SC
Fukui M Fujikawa Y and Satta N 1996 ldquoFactors affecting interaction of radioiodide and iodate species with soilrdquo Journal of Environmental Radioactivity 31 199-216
Hoglund S L Eliasson B Allard K Andersson and B Torstenfelt 1985 ldquoSorption of some fission products and actinides in concrete systemsrdquo Mat Res Soc Symp Proc 50 683-690
Kaplan D I 2007 Geochemical Data Package for Performance Assessment Calculations Related to the Savannah River Site WSRC-TR-2006-00004 Rev 1 Washington Savannah River Company Aiken SC
Kaplan D I and Coates J 2007 ldquoPartitioning of Dissolved Radionuclides to Concrete under Scenarios Appropriate for Tank Closure Performance Assessmentsrdquo WSRC-STI-2007-00640 Rev 0 Washington Savannah River Company Aiken SC 29808
Kaplan D I Roberts K Coates J Siegfried M Serkiz S 2008 ldquoSaltstone and concrete interactions with radionuclides Sorption (Kd) desorption and reduction capacity measurementsrdquo SRNS-STI-2008-00045 Savannah River National Laboratory Aiken SC 2008
SRNL-STI-2009-00636 Revision 0
50
Neck V and Kim J I 2001 ldquoSolubility and hydrolysis of tetravalent actinidesrdquo Radiochim Acta 89 1
Powell B A Fjeld R A Coates J T Kaplan D I Serkiz S M 2002 ldquoPlutonium Oxidation State Geochemistry in the SRS Subsurface Environmentrdquo WSRC-TR-2003-00035 Westinghouse Savannah River Company US DOE Savannah River Site Aiken SC
Roberts K A and D I Kaplan 2009 Reduction Capacity of Saltstone and Saltstone Componentsrdquo SRNL-STI-2009-00637 Rev0 Savannah River National Laboratory Aiken SC
Schwehr K A Santschi P H D I Kaplan C M Yeager and R Brinkmeyer 2009 ldquoOrgano-iodine formation in soils and aquifer sediments at ambient concentrationsrdquo Environ Sci Technol 437258-7264
Yoshida S Muramatsu Y and Uchida S 1992 ldquoStudies on the sorption of I-(iodide) and IO3-
(iodate) onto andosolsrdquo Water Air and Soil Pollution 63 321-329
SRNL-STI-2009-00636 Revision 0
51
90 Appendix A Data Tables of Radionuclide Sorption to Saltstone under Oxidizing Conditions
The following tables represent data collected for the no solids controls each saltstone and testing of radionuclide sorption to the vial walls The no solids controls tables include the concentration (ppb) of the radionuclide spiked into the sample along with the concentration of the radionuclide (ppb) measured in the aqueous phase after the given equilibration time The pH at the time the sample was taken is also recorded along with the fraction of the radionuclide which stayed in the aqueous phase The tables for the cementitious formulation data include the data above along with the addition of a Kd value The tables of the data for the radionuclides sorbed to the vial walls include the initial concentration (ppb) of the spike the concentration (ppb) of the radionuclide that had sorbed to the vial wall during the experiment and the percentage of the total concentration this represents Important Notes
BDL- Below Detection Limit lt01 denotes no notable sorption occurred
91 Data Tables for No Solid Controls
Table 91 Plutonium no solids control after one day
A 9264165178 402285E‐05 1181 434238E‐06 9980817 B 9352537276 0000110618 1183 118276E‐05 3616813 C 9363541597 705331E‐05 118 753273E‐06 5401186 D 0993110568 BDL 12 NA NA E 0977247222 300794E‐05 1199 307797E‐05 1280331 F 0962441315 BDL 1198 NA NA G 4059128499 BDL 1186 NA NA H 4065161486 705198E‐05 1188 173473E‐05 2380003 I 4116819691 0000110748 1189 269014E‐05 1555864
Table 920 TR545- neptunium after four days
Sample ID
Initial Aq Conc (ppb)
Equil Aq Conc (ppb) pH
Fraction Aq Kd
A 92641652 NA 1188 NA NA B 93525373 00001935 1185 2069E‐05 2067199C 93635416 4119E‐05 1185 44E‐06 9247818D 09931106 BDL 1197 NA NA E 09772472 BDL 12 NA NA F 09624413 00066817 1206 00069424 562421G 40591285 00003289 1196 8103E‐05 5148274H 40651615 00025316 1196 00006228 6625737I 41168197 00001018 1194 2474E‐05 1692126
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58
Table 921 TR545- technetium after one day
Sample ID
Initial Aq Conc (ppb)
Equil Aq Conc (ppb) pH Fraction Aq Kd
A 9655146069 820460082 1181 0849764546 8998984 B 9356176321 7703053505 1183 0823312135 1051242 C 9114122586 7978297395 118 0875377451 7062663 D 1042349157 0853053814 12 0818395456 9099556 E 0983206046 0871198263 1199 0886079033 5196709 F 0905148405 0803451372 1198 0887646013 5098696 G 4950156706 4275082341 1186 0863625658 7213934 H 4889067068 4173762594 1188 0853693053 7687519 I 4854463762 4147024058 1189 0854270268 7771045
A 1048950046 0002141023 1149 0000204111 2112281 B 1039943573 0001770549 1157 0000170254 2460487 C 1084651695 0001127533 1153 0000103953 4014918 D 1088686867 0001201087 1172 0001103244 3564524 E 1119673887 0000783288 1177 0000699568 5709897 F 1045722787 0000914861 1181 000087486 4495324 G 5387981131 0001444832 1169 0000268158 1494715 H 5412748988 0001143483 1169 0000211257 1965749 I 5373948758 00010003 1164 0000186139 2280472
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Table 926 TR547- plutonium after four days
Sample ID
Initial Aq Conc (ppb)
Equil Aq Conc (ppb) pH
Fraction Aq Kd
A 104895 NA 116 NA NA B 10399436 0001828 1165 00001758 2383132C 10846517 00010788 1164 9946E‐05 4196159D 10886869 00009131 1184 00008388 4689778E 11196739 00010624 1189 00009488 4208928F 10457228 00007967 1191 00007619 516258G 53879811 00007915 1173 00001469 2728993H 5412749 00008355 1175 00001544 2690641I 53739488 00006103 1174 00001136 3737892
Table 927 TR547- neptunium after one day
Sample ID
Initial Aq Conc (ppb)
Equil Aq Conc (ppb) pH Fraction Aq Kd
A 9589772032 0000454463 1149 473903E‐05 9116335 B 9293228768 0000260081 1157 27986E‐05 1499475 C 1008725504 0000302018 1153 299405E‐05 1397125 D 0952173007 000019177 1172 0000201403 1954603 E 0992224074 BDL NA NA F 0967815522 402137E‐05 1181 41551E‐05 9474699 G 4068405786 0000222282 1169 546361E‐05 7336986 H 409543171 0000531619 1169 0000129808 3199152 I 4017406611 0000410123 1164 0000102086 4157807
Table 928 TR547- neptunium after four days
Sample ID
Initial Aq Conc (ppb)
Equil Aq Conc (ppb) pH Fraction Aq Kd
A 9589772 NA 116 NA NA B 92932288 00002145 1165 2308E‐05 1818463C 10087255 00001628 1164 1614E‐05 2591215D 0952173 BDL 1184 NA NA E 09922241 BDL NA NA F 09678155 5107E‐05 1191 5277E‐05 7460375G 40684058 00001336 1173 3284E‐05 1220544H 40954317 8151E‐05 1175 199E‐05 2086795I 40174066 00001322 1174 3292E‐05 1289605
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Table 929 TR547- technetium after one day
Sample ID
Initial Aq Conc (ppb)
Equil Aq Conc (ppb) pH Fraction Aq Kd
A 9466799266 8233850788 1149 0869760788 8220086 B 9439556236 817653394 1157 0866198975 8165745 C 9383493063 8086024379 1153 0861728604 8430884 D 1061939876 0919992065 1172 0866331594 6241759 E 0991827343 0836511397 1177 0843404251 7590958 F 0971981155 0839862696 1181 0864073024 6354378 G 4883337077 414858839 1169 0849539633 7903986 H 4691440077 3996173112 1169 0851800949 8038249 I 486993937 4291285586 1164 0881178442 6558707
Table 930 TR547- technetium after four days
Sample ID
Initial Aq Conc (ppb)
Equil Aq Conc (ppb) pH
Fraction Aq Kd
A 94667993 NA 116 NA NA B 94395562 85812109 1165 09090693 5885474C 93834931 84622373 1164 09018217 6279204D 10619399 09580683 1184 09021869 4435663E 09918273 08881507 1189 08954691 4835506F 09719812 09036489 1191 0929698 3138862G 48833371 4490415 1173 09195382 4312104H 46914401 42054182 1175 08964024 5612948I 48699394 43843193 1174 09002821 5536503
Table 931 TR547- iodine after one day
Sample ID
Initial Aq Conc (ppb)
Equil Aq Conc (ppb) pH Fraction Aq Kd
A 9944920441 8813152965 1149 0886196427 738241 B 9956006121 8747156303 1157 0878580848 8007767 C 9822152291 8664470934 1153 0882135674 7988892 D 1002391846 9333490632 1172 0931121963 3368509 E 9918273427 6625075445 1177 0667966607 1551748 F 9918175056 8931364957 1181 0900504872 4773862 G 5166570628 4445386532 1169 0860413387 7961604 H 4847821413 410447427 1169 084666367 8664303 I 4850381381 4266693706 1164 0879661489 6413801
100 Appendix B Data Tables of Radionuclide Sorption to Saltstone Under Reducing Conditions
The following tables represent data collected for the no solids controls each cementitious solid and testing of radionuclide sorption to the vial walls The no solids controls tables include the concentration (ppb) of the radionuclide spiked into the sample along with the concentration of the radionuclide (ppb) measured in the aqueous phase after the given equilibration time The pH at the time the sample was taken is also recorded along with the fraction of the radionuclide which stayed in the aqueous phase The tables for the cementitious solidsrsquo data include the data above along with the addition of a Kd value The tables of the data for the radionuclides sorbed to the vial walls include the initial concentration (ppb) of the spike the concentration (ppb) of the radionuclide that had sorbed to the vial wall during the experiment and the percentage of the total concentration this represents Important Notes
BDL= Below Detection Limit lt01 denotes no notable sorption occurred
101 Data Tables for No-Solid Controls
Table 101 Plutonium no solids control after one day
A 9405892 0007019 111 0000746258 5681206 B 9602498 0003294 1117 0000342992 123554 C 9630619 0002936 1114 0000304893 1396318 D 4945396 0001795 113 0000363011 1171688 E 4964945 0001373 1131 0000276484 1493015 F 4441601 0001516 113 0000341219 1389674 G 1079602 0001109 1142 0001027508 4215519 H 1031512 0000883 1143 0000855983 4820576 I 0939294 0000978 1143 0001040992 4550255
SRNL-STI-2009-00636 Revision 0
70
Table 1011 Vault 2- neptunium after one day
Sample ID Initial Aq Conc (ppb)
Equil Aq Conc (ppb) pH Fraction Aq
A 9425042625 0001709054 1105 0000181331 B 9611386476 0001184125 1110 00001232 C 9579553607 0001155517 1104 0000120623 D 4974000414 0000672325 1125 0000135168 E 4916731623 0000675371 1128 0000137362 F 4373142817 0000570681 1120 0000130497 G 0943366414 0000389738 1129 0000413136 H 1011745587 0000565648 1132 0000559081 I 0865252712 0000379545 1133 0000438653
A 8849444124 0000306309 1150 346133E‐05 1289533 B 8447823057 0000150131 1155 177715E‐05 2711019 C 8590597085 0000199185 1153 231864E‐05 2044057 D 4491250244 517162E‐05 1156 115149E‐05 4020064 E 4391894479 204591E‐05 1158 465838E‐06 9846089 F 4210703646 204376E‐05 1158 485374E‐06 9816203 G 086381524 522216E‐06 1160 604546E‐06 7577764 H 0870501884 BDL 1160 NA NA I 0861953838 BDL 1162 NA NA
SRNL-STI-2009-00636 Revision 0
79
Table 1036 Aged cement- neptunium after four days
Sample ID
Initial Aq Conc (ppb)
Equil Aq Conc (ppb) pH Fraction Aq Kd
A 8849444 0000131 1145 148418E‐05 3007445B 8447823 0000111 1146 131529E‐05 3662996C 8590597 656E‐05 1146 76328E‐06 6209405D 449125 BDL 1155 NA NA E 4391894 BDL 1156 NA NA F 4210704 BDL 1155 NA NA G 0863815 BDL 1165 NA NA H 0870502 BDL 1162 NA NA I 0861954 BDL 1164 NA NA
Table 1037 Aged cement- technetium after one day
Sample ID
Initial Aq Conc (ppb)
Equil Aq Conc (ppb) pH Fraction Aq Kd
A 8426518355 833290075 1150 098889012 0476492 B 8638001423 7823321167 1155 0905686487 4413063 C 9323317745 925927516 1153 0993130923 0294664 D 442651005 4300859603 1156 0971614106 1242837 E 4426849405 4336992073 1158 0979701742 0855315 F 3929483125 3938204338 1158 100221943 lt01 G 0817864386 081693181 1160 0998859743 0049487 H 0878958929 0792412508 1160 0901535306 4510199 I 0772205665 0871436364 1162 1128502941 lt01
Table 1038 Aged cement- technetium after four days
110 Appendix C Dixon et al (2009) FY09 PACA Maintenance Program Additional Saltstone Property Testing SRNL L3100-2009-00019 Rev 0
SRNL-STI-2009-00636 Revision 0
83
SRNL L3100-2009-00019 Rev 0
December 16 2008
Keywords Performance Permeability Modulus
L B Romanowski
Waste Determinations From K L Dixon M A Phifer and J R Harbour
FY09 PACA Maintenance Program Additional Saltstone Property Testing
BACKGROUND
Additional tests have been identified for measurement of important hydraulic and physical properties of saltstone The initial phase of this work [1] was completed last year and the results were detailed in an internal report [2] The proposed testing for FY09 includes measurement of saturated hydraulic conductivity porosity bulk density particle density water retention and Youngrsquos modulus of simulated Saltstone grouts For completeness the bleed volumes and gel times for each mix will also be measured
The testing will be based on a projected salt solution composition for the ARPMCU stream that will be fed to the Saltstone Production Facility over the next few years The scope for FY09 will include testing to determine the impact of (1) admixtures (2) organics (3) wcm ratio (4) aluminate concentration and (5) temperature of curing on the hydraulic properties of saltstone mixes Samples of selected batches prepared as part of this task will be provided to Dan Kaplan for measurement of Kd through leaching tests The eleven mixes that will be batched and tested are detailed in Table 1
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Table 1 The Eleven Mixes That will be Batched and Tested
BFS is Blast Furnace Slag FA is Fly Ash and PC is Portland Cement
TEST DETAILS
Test 1 Control (Mix 1)
A control mix will be based on the baseline mix modified by exclusion of the Class F fly ash Consequently the cementitious materials premix will be a mixture of 90 blast furnace slag and 10 portland cement The degree of reaction will be much greater than with the normal premix and therefore should result in a lower porosity and a lower permeability This bounding test at 060 wcm ratio is expected to yield a hydraulic conductivity at or below the detection limit for the Mactec permeameter measurement system Therefore this test should demonstrate the lowest level of detection of the Mactec system as well as show a resolvable difference between measurements of the control mix and the control mix with the normal premix composition
Test 2 ndashImpact of Admixtures (Mixes 2 and 3)
Recent saltstone batches have required both a set retarder (Daratard 17) and an antifoam agent (Q2) for processing of the saltstone Therefore the baseline mix will be prepared with and without nominal levels of these two admixtures to determine whether these admixtures appreciably affect the hydraulic and physical properties of saltstone at these nominal concentrations
Test 3ndashImpact of Organics (Mixes 2 and 4)
The solvent extraction process is expected to result in some carryover of organics [3]
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85
Consequently a test will be performed on the impact of Caustic Side Solvent Extraction (CSSX) organics at 100 microliters per 1600 gram batch The CSSX solvent consists of 075 M 1-(2233-tetrafluoropropoxy)-3-(4-sec-butylphenoxy)-2-propanol (Cs-7SB) and 0003 M tri-n-octylamine (TOA) in an Isoparreg L diluent Test 4ndashImpact of Combination of Admixtures and Organics (Mixes 2 5 10 and 11)
This test will determine the impact of a combination of admixtures (Test 2) and organics (Test 3) together in the mix vs the baseline case without admixtures and organics
Test 5ndash Impact of wcm Ratio (Mixes 2 6 and 7)
It is well known that decreasing the wcm ratio in a mix will improve permeability in normal portland cement water mixes This test will measure the variation in permeability for the case of the MCU salt solution at three different wcm ratios The initial selection of wcm ratios is 055 060 and 065 However if the mix at an as-batched 065 wcm ratio has significant bleed water and the resulting actual wcm ratio is close to 060 then the three ratios will be adjusted to provide a more evenly spaced set of values However the baseline mix at 060 will be included as one of the three mixes
Test 6 ndash Impact of Aluminate Concentration (Mixes 8 9 and 10)
The DWPF has modified its process flowsheet to include a caustic washing of HLW sludge to remove some of the aluminum from the HLW prior to vitrification The resulting aluminate stream will then be blended with tank 50 material and fed to the SPF This increased aluminate concentration in the salt solution has significant impact on heat of hydration and set times and consequently it is likely that it will also impact permeability Therefore a set of three samples will be made at wcm ratios of 055 060 and 065 (as in Test 3) with a higher level of aluminate (028 M) for testing
Test 7 ndash Impact of Increased Curing Temperature (Mix 11)
In an ongoing task there is evidence that Youngrsquos modulus (a performance indicator) [4] is reduced by increasing the curing temperature of the mix Since the vault temperature increases during curing as a result of the exothermic hydration reactions one of the baseline mixes with a combination of admixtures and organics will be cured at 60
o
C rather than the normal 22
o
C to determine the impact of curing temperature on the permeability
SRNL-STI-2009-00636 Revision 0
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SCHEDULE
The schedule for the task of batching and testing of the samples is provided in Table 2 This schedule is based on the fact that the cementitious materials will be available for the testing as needed
Table 2 Additional Saltstone Hydraulic and Physical Property Tests
Item Schedule Start Work 12108 Test Plan Complete 1509 Preparation of 1st set of Samples Complete 11909 90-Day Cure Period for 1st set of Samples Complete 42009
SRNL-STI-2009-00636 Revision 0
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SRNL-STI-2009-00636 Revision 0
SRNL-STI-2009-00636 Revision 0
DISTRIBUTION Savannah River Site
A B Barnes 999-W Rm 336 H H Burns 999-W Rm 381 B T Butcher 773-43A Rm 212 A D Cozzi 999-W Rm 337 D A Crowley 773-43A Rm 216 M E Denham 773-42A Rm 218 J C Griffin 773-A Rm A-231 J R Harbour 999-W Rm 348 C A Langton 773-43A Rm 219 M H Layton 705-1C Rm 14 D I Kaplan (3 copies) 773-43A Rm 215 S L Marra 773A Rm A-230 A M Murray 773-A Rm 229 K A Roberts 773-43A Rm 225 T C Robinson 705-1C Rm 13 L B Romanowski 705-1C Rm 19 K H Rosenberger 705-1C Rm 16 F M Smith 705-1C Rm 24 RPA File (2 copies) 773-43A Rm 213
Clemson University Environmental Engineering and Earth Sciences 372 Computer Court LG Rich Environmental Laboratory Anderson SC 29625
Table 31 Characteristics of saltstone formulations used in this work Kaplan et al (2008) 19
Table 32 Detection limits for each isotope based on representative calibration curves generated in PlasmaLab software associated with the ICP-MS 20
Table 33 Experimental Matrix of Sorption Experiments under Aerobic Conditions 22
Table 61 Comparison of plutonium apparent solubility values under oxidizing and reducing conditions 46
Table 62 Comparison of neptunium apparent solubility values under oxidizing and reducing conditions 47
Table 63 Comparison of technetium Kd values under oxidizing and reducing conditions 47
Table 64 Comparison of iodine Kd values under oxidizing and reducing conditions 48
Table 91 Plutonium no solids control after one day 51
Table 92 Plutonium no solids control after four days 51
Table 93 Neptunium no solids control after one day 52
Table 94 Neptunium no solids control after four days 52
Table 95 Technetium no solids control after one day 52
Table 96 Technetium no solids control after four days 53
Table 97 Iodine no solids control after one day 53
Table 98 Iodine no solids control after four days 53
Table 99 Vault 2- plutonium after one day 54
Table 910 Vault 2- plutonium after four days 54
Table 911 Vault 2- neptunium after one day 54
Table 912 Vault 2- neptunium after four days 55
Table 913 Vault 2- technetium after one day 55
Table 914 Vault 2- technetium after four days 55
Table 915 Vault 2- iodine after one day 56
Table 916 Vault 2- iodine after four days 56
Table 917 TR545- plutonium after one day 56
Table 918 TR545- plutonium after four days 57
SRNL-STI-2009-00636 Revision 0
viii
Table 919 TR545- neptunium after one day 57
Table 920 TR545- neptunium after four days 57
Table 921 TR545- technetium after one day 58
Table 922 TR545- technetium after four days 58
Table 923 TR545- iodine after one day 58
Table 924 TR545- iodine after four days 59
Table 925 TR547- plutonium after one day 59
Table 926 TR547- plutonium after four days 60
Table 927 TR547- neptunium after one day 60
Table 928 TR547- neptunium after four days 60
Table 929 TR547- technetium after one day 61
Table 930 TR547- technetium after four days 61
Table 931 TR547- iodine after one day 61
Table 932 TR547- iodine after four days 62
Table 933 Aged cement- plutonium after one day 62
Table 934 Aged cement- plutonium after four days 63
Table 935 Aged cement- neptunium after one day 63
Table 936 Aged cement- neptunium after four days 63
Table 937 Aged cement- technetium after one day 64
Table 938 Aged cement- technetium after four days 64
Table 939 Aged cement- iodine after one day 64
Table 940 Aged cement- iodine after four days 65
Table 941 Plutonium sorbed to vial wall in no solids control 65
Table 942 Neptunium sorbed to vial wall in no solids control 65
Table 101 Plutonium no solids control after one day 66
Table 102 Plutonium no solids control after four days 67
Table 103 Neptunium no solids control after one day 67
Table 104 Neptunium no solids control after four days 67
Table 105 Technetium no solids control after one day 67
SRNL-STI-2009-00636 Revision 0
ix
Table 106 Technetium no solids control after four days 68
Table 107 Iodine no solids control after one day 68
Table 108 Iodine no solids control after four days 68
Table 109 Vault 2- plutonium after one day 69
Table 1010 Vault 2- plutonium after four days 69
Table 1011 Vault 2- neptunium after one day 70
Table 1012 Vault 2- neptunium after four days 70
Table 1013 Vault 2- technetium after one day 70
Table 1014 Vault 2- technetium after four days 71
Table 1015 Vault 2- iodine after one day 71
Table 1016 Vault 2- iodine after four days 71
Table 1017 TR545- plutonium after one day 72
Table 1018 TR545- plutonium after four days 72
Table 1019 TR545- neptunium after one day 73
Table 1020 TR545- neptunium after four days 73
Table 1021 TR545- technetium after one day 73
Table 1022 TR545- technetium after four days 74
Table 1023 TR545- iodine after one day 74
Table 1024 TR545- iodine after four days 74
Table 1025 TR547- plutonium after one day 75
Table 1026 TR547- plutonium after four days 75
Table 1027 TR547- neptunium after one day 76
Table 1028 TR547- neptunium after four days 76
Table 1029 TR547- technetium after one day 76
Table 1030 TR547- technetium after four days 77
Table 1031 TR547- iodine after one day 77
Table 1032 TR547- iodine after four days 77
Table 1033 Aged cement- plutonium after one day 78
Table 1034 Aged cement- plutonium after four days 78
SRNL-STI-2009-00636 Revision 0
x
Table 1035 Aged cement- neptunium after one day 78
Table 1036 Aged cement- neptunium after four days 79
Table 1037 Aged cement- technetium after one day 79
Table 1038 Aged cement- technetium after four days 79
Table 1039 Aged cement- iodine after one day 80
Table 1040 Aged cement- iodine after four days 80
Table 1041 Plutonium sorbed to vial wall in no solids control 80
Table 1042 Neptunium sorbed to vial wall in no solids control 81
Table 1043 Technetium sorbed to vial wall in no solids control 81
SRNL-STI-2009-00636 Revision 0
xi
LIST OF FIGURES
Figure 31 Screen capture of a typical 242Pu calibration curve using Thermo PlasmaLab software to control the data collection and analysis R2=0999872 Intercept Conc (Detection Limit) = 0000044 ppb 16
Figure 32 Screen capture of a typical 237Np calibration curve using Thermo PlasmaLab software to control the data collection and analysis R2=0999981 Intercept Conc (Detection Limit) = 0000026 ppb 17
Figure 33 Screen capture of a typical 99Tc calibration curve using Thermo PlasmaLab software to control the data collection and analysis R2=0999984 Intercept Conc (Detection Limit) = 0000013 ppb 18
Figure 34 Screen capture of a typical 127I calibration curve using Thermo PlasmaLab software to control the data collection and analysis R2=0999991 Intercept Conc (Detection Limit) = 024 ppb 19
Figure 41 Plutonium Kd Values under Oxidizing Conditions Plutonium Kd values for various saltstone formulations measured after one-day equilibration (1d) and four-day equilibration (4d under oxidizing conditions Total plutonium concentrations in each system were 1 ppb 5 ppb and 10 ppb Sample prepared in triplicate and error bars represent standard deviation of samples except as follows value for dataset TR547-4d 10 ppb is reported based on duplicate samples 25
Figure 42 Plutonium solubility for various saltstone formulations measured after one-day equilibration (1d) and four-day equilibration (4d) under oxidizing conditions Total plutonium concentrations in each system were 1 ppb 5 ppb and 10 ppb as noted Samples prepared in triplicate and an average of all samples (9) was used to determine average solubility The error bars represent standard deviation of samples 25
Figure 43 Neptunium Kd values under oxidizing conditions Neptunium Kd values for various saltstone formulations measured after one-day equilibration (1d) and four-day equilibration (4d) under oxidizing conditions Total plutonium concentrations in each system were 1 ppb 5 ppb and 10 ppb as noted Samples prepared in triplicate and error bars represent standard deviation of samples except as follows value for datasets TR545-1d 1ppb TR545-4d 1 ppb TR547 4d 1 ppb TR545-4d 10 ppb TR547-1d 1ppb TR547-4d 10 ppb are reported based on a single sample and for dataset TR545-1d 5ppb is reported based on duplicate samples Kd values limited to gt106 were at instrumental background 26
Figure 44 Average solubility of Np under oxidizing conditions Neptunium solubility for various saltstone formulations measured after one-day equilibration (1d) and four-day equilibration (4d) under oxidizing conditions Total Np concentrations in each system were 1 ppb 5 ppb and 10 ppb Samples prepared in triplicate and an average of all samples (9) was used to determine average solubility except as follows TR545-1d is based on 6 samples TR545- 4d on 5 samples TR547-1d on 7 samples and TR547- 4d on 5 samples The error bars represent standard deviation 27
Figure 45 Technetium Kd values under oxidizing conditions Tc Kd values for various saltstone formulations measured after one-day equilibration (1d) and four-day equilibration (4d) under oxidizing conditions Total Tc concentrations in each system were 1 ppb 5 ppb and 10 ppb as noted above Samples were prepared in triplicate and the error bars represent standard deviation
SRNL-STI-2009-00636 Revision 0
xii
of samples except as follows data sets for Vault 2-1d 1ppb were duplicates and TR547- 4d 10 ppb is based on a single dataset 27
Figure 46 Iodine Kd Values under Oxidizing Conditions Iodine Kd values for various cementitious formulations measured after one-day equilibration (1d) and four-day equilibration (4d) under oxidizing conditions Total iodine concentrations in the systems were 100ppb 500 ppb and 1000 ppb as noted above Samples were prepared in triplicate and the error bars represent standard deviation of samples except as follows duplicates were used for dataset TR545- 1d 100ppb 28
Figure 47 Plutonium Neptunium and Technetium Aqueous Fractions Fraction of Pu Np and Tc remaining in the aqueous phase for the No Solids controls after a one-day equilibration (1d) and four-day equilibration (4d) under oxidizing conditions The total concentration for each radionuclide 10 ppb as noted above Samples were prepared in triplicate and the error bars represent the standard deviation of the samples 29
Figure 48 Iodine Aqueous Fraction Iodine aqueous fraction for the no-solids controls after a one-day equilibration (1d) and four-day equilibration (4d) under oxidizing conditions The total concentration of iodine was 1000 ppb as noted above Samples were prepared in triplicate and the error bars represent the standard deviation of the samples 29
Figure 49 Percent Pu and Np sorbed to vial walls of the no solids controls after the aqueous phases were discarded and the vials were washed Both the 10 ppb (blueleft) and 1 ppb (redright)) datasets were prepared in triplicate and the error bars show the standard deviation 31
Figure 410 Percent Pu sorbed to vial walls after the solids and aqueous phases were removed and the vials were washed The graph illustrates one sample from each of the 1 ppb (redleft) 5 ppb (greenmiddle) and 10 ppb (blueright) systems Therefore no error bars are present 31
Figure 411 Percent Np sorbed to vial walls after the solids and aqueous phases were removed and the vials were washed The graph illustrates one sample from each of the 1 ppb (redleft) 5 ppb (greenmiddle) and 10 ppb (blueright) systems Therefore no error bars are present 32
Figure 412 Pu Kd Values under Reducing Conditions Plutonium Kd values for various cementitious formulations measured after one-day equilibration (1d) and four-day equilibration (4d) under reducing conditions Total plutonium concentrations in each system were 1ppb 5 ppb and 10 ppb Samples prepared in triplicate and error bars represent standard deviation 33
Figure 413 Average Solubility of Plutonium under Reducing Conditions Plutonium solubility for various cementitious formulations measured after one-day equilibration (1d) and four-day equilibration (4d) under reducing conditions Total plutonium concentrations in each system were 1ppb 5 ppb and 10 ppb as noted Samples prepared in triplicate and an average of all samples (9) was used to determine average solubility The error bars represent standard deviation of samples 33
Figure 414 Np Kd Values under Reducing Conditions Neptunium Kd values for various cementitious formulations measured after one-day equilibration (1d) and four-day equilibration (4d) under reducing conditions Total Np concentrations in each system were 1 ppb 5 ppb and 10 ppb Samples were prepared in triplicate and the error bars represent standard deviation Kd values limited to gt106 were at instrumental background 34
Figure 415 Average Solubility of Neptunium under Reducing Conditions Neptunium solubility for various cementitious formulations measured after one day equilibration (1d) and four day
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xiii
equilibration (4d) under reducing conditions Total plutonium concentrations in each system were 1ppb 5 ppb and 10 ppb Samples prepared in triplicate and an average of all samples (9) was used to determine average solubility The error bars represent standard deviation 35
Figure 416 Tc Kd Values under Reducing Conditions Tc Kd values for various cementitious formulations measured after one-day equilibration (1d) and four-day equilibration (4d) under reducing conditions Total Tc concentrations in each system were 1 ppb 5 ppb and 10 ppb Sample prepared in triplicate and error bars represent standard deviation except as follows TR547-1d 1 ppb is based on a single dataset and datasets Vault 2-1d 5 ppb Vault 2- 4d 1 ppb Aged Cement-1d 5 ppb and Aged Cement-4d 1 ppb are duplicates 36
Figure 417 Data from Figure 416 replotted on a reduced linear scale for easier viewing Each sample was prepared in triplicate except as follows TR547-1d 1 ppb is based on a single dataset Vault 2-1d 5 ppb Vault 2- 4d 1 ppb Aged Cement-1d 5 ppb and Aged Cement-4d 1 ppb are duplicate datasets 36
Figure 418 Iodine Kd Values under Reducing Conditions I Kd Values for various cementitious formulations measured after one day equilibration (1d) and four day equilibration (4d) under reducing conditions Total iodine concentrations in each system were 100 ppb 500 ppb and 1000 ppb as noted Sample prepared in triplicate and error bars represent standard deviation of samples except as follows Vault 2-4 d 100 ppb is a single dataset while the datasets for Vault 2-1 d 100 ppb 4 d 1000 ppb TR545-4 d 1000 ppb 100 ppb TR547-4 d 1000 ppb 500 ppb 100 ppb and Aged Cement- 4 d 1000 ppb and 100 ppb are all based on duplicates 38
Figure 419 Plutonium Neptunium and Technetium No-Solids Aqueous Fractions under Reducing Conditions Pu Np and Tc aqueous fractions of No Solids controls after a one-day equilibration (1d) and four-day equilibration (4 d) under reducing conditions Total concentration for each radionuclide was 1 ppb and 10 ppb Samples were prepared in triplicate and the error bars represent the standard deviation 39
Figure 420 Percent of Pu Np and Tc sorbed to the vial walls of the No Solids control samples under reducing conditions Each the 1 ppb and 10 ppb samples were prepared in triplicate and the error bars represent the standard deviations of triplicate samples 39
Figure 421 Iodine No-Solids Aqueous Fractions under Reducing Conditions I aqueous fractions of No-Solids controls after a one-day equilibration (1d) and four-day equilibration (4d) under reducing conditions The total concentration for each system was 100 ppb and 1000 ppb Samples were prepared in triplicate and the error bars represent the standard deviation 40
Figure 51 Comparison of Tc I Np and Pu sorption to Vault 2 solid under oxidizing and reducing conditions 42
Figure 52 Comparison of Tc I Np and Pu sorption to TR 545 solid under oxidizing and reducing conditions 43
Figure 53 Comparison of Tc I Np and Pu sorption to TR547 solid under oxidizing and reducing conditions 44
Figure 54 Comparison of Tc I Np and Pu sorption to Aged Cement under oxidizing and reducing conditions 45
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xiv
LIST OF ABBREVIATIONS
DDI water Distilled deionized water ICP-MS Inductively coupled plasma ndash mass spectrometer
Kd Distribution coefficient LSC liquid scintillation counting NOM Natural organic matter PA Performance Assessment ppb parts per billion ppq parts per quadrillion QAQC Quality AssuranceQuality Control SA Special Analyses SRNL Savannah River National Laboratory SRS Savannah River Site
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10 Introduction Performance Assessments (PA) are risk calculations designed to determine (1) the maximum
amount of radioactivity that can be safely buried in a subsurface facility and (2) the potential human risk associated with disposing of radioactive waste in a subsurface facility Special Analyses (SAs) are similar to PAs except that they are designed to address specific issues related to PAs such as a new discovery since the PA was issued Commonly parameters describing the extent that a radionuclide interacts with solids at the source vadose zone and aquifer influence the extent of calculated human risk The two parameters that the SRS use to represent radionuclidesolid interactions are Kd and apparent solubility values together these parameters are referred to as sorption values Sorption values vary with radionuclides groundwater chemistry and the type of solid phase (and for cementitious materials by the age of the material during the calculation) In this work Kd and apparent solubility values are reported for 99Tc 127I 237Np and 242Pu sorption to various cementitious formulations
20 Objectives
The objectives of this work were to 1 Determine the influence of cementitious formulation on technetium (Tc) iodine (I) neptunium
(Np) and plutonium (Pu) sorption under oxidizing conditions The specific formulations that were evaluated included 1) an aged cement recovered from a 30-year old outdoor concrete pad on the SRS 2) Vault 2 concrete 3) TR545 saltstone and 4) TR547 saltstone (additional details are presented in Section 30 Materials and Methods)
2 Measure Tc I Np and Pu sorption to the cementitious formulations under reducing conditions
30 Materials and Methods
31 Preparation of ICP-MS Standards Stock Solutions and Working Solutions
311 242Pu
A National Institute of Standards and Technology Standard Reference Material (NIST SRM 434H) was used to prepare a stock 242Pu solution by dilution in 2 Aristar Optima HNO3 All volume additions were monitored gravimetrically This working solution was then used to make a set of 001 005 1 2 5 10 parts per billion (ppb) standards by dilution using 2 HNO3 Again all volume additions were monitored gravimetrically These standards were used to calibrate the Thermo Scientific X Series 2 inductively coupled plasma ndash mass spectrometer (ICP-MS) for quantification of 242Pu A representative calibration curve for 242Pu is shown in Figure 31 The instrument performance was monitored using 209Bi 232Th and 238U as internal standards The recovery of each sample during analysis was corrected based on the internal standard recovery The internal standard recoveries remained within standard quality assurancequality control QAQC protocols for the instrument (between 80 and 120)
A 242Pu stock solution was prepared by dissolving 1mg of Pu(NO3)4 obtained as a Certified Reference Material from New Brunswick Laboratory (CRM 130) This CRM is gt999 242Pu by atom percent The CRM was dissolved in 20mL of 8M HNO3 (Aristar Optima Grade) Because no chemicals or heat have been introduced to manipulate the Pu oxidation state it can be assumed that Pu(IV) is the predominant oxidation state in this stock solution A working solution to be used in spiking 242Pu experiments was prepared by diluting 25 mL of the CRM stock solution with 100 mL 10 M Aristar Optima HNO3 The concentration of 242Pu in this stock solution was determined using ICP-MS calibrated using the NIST SRM standards The concentration of Pu in this stock solution was 1065 ppb The total Pu
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concentration was also determined using liquid scintillation counting using the isotopic ratios reported for CRM 130 These compared favorably with the ICP-MS results but are reported here as a rigorous standardization because the isotopic ratios of CRM 130 have not yet been certified
Figure 31 Screen capture of a typical 242Pu calibration curve using Thermo PlasmaLab software to control the data collection and analysis R2=0999872 Intercept Conc (Detection Limit) = 0000044 ppb
312 237Np
A National Institute of Standards and Technology Standard Reference Material (NIST SRM 4341) was used to prepare a stock 237Np solution by dilution in 2 Aristar Optima HNO3 All volume additions were monitored gravimetrically This working solution was then used to make a set of 001 005 1 2 5 10 ppb standards by dilution using 2 HNO3 Again all volume additions were monitored gravimetrically These standards were used to calibrate the Thermo Scientific X Series 2 ICP-MS for quantification of 237Np A representative calibration curve for 237Np is shown in Figure 32 The instrument performance was monitored using 209Bi 232Th and 238U as internal standards The recovery of each sample during analysis was corrected based on the internal standard recovery The internal standard recoveries remained within standard QAQC protocols for the instrument (between 80 and 120)
A compiled 237Np stock solution from the Environmental Engineering and Earth Science (EEampES) inventory (primarily purchased from Isotope Products Valencia CA) was evaporated to dryness then the residue was brought up in approximately 5mL 80 M HNO3 Then 10 M hydroxylamine hydrochloride (NH2OHHCl EMD Chemicals ACS grade) and water were added to achieve a 3M HNO303M NH2OHHCl solution This solution was purified by extraction chromatography using Eichrom TEVA resin packed in a Bio-Rad poly-prep column The 3M HNO303 M NH2OHHCl neptunium solution was loaded on a 2 mL column and washed with 3 column volumes of 3 M HNO3 The Np(IV) was eluted with 002 M HCl + 02 M HF The effluent was evaporated to dryness then redissolved in 10 M HNO3 Additional 10 M HNO3 was added to maintain a approximately 10 mL then the solution was evaporated to incipient dryness and redissolved in a 50 mL of 10 M HNO3 An aliquot of the stock solution was evaporated to dryness on a stainless steel planchet and counted on the EGampG Ortec Alpha Spectrometer (Octete PC Detectors) No other alpha energies besides 237Np were observed The approximate concentration was determined using liquid scintillation counting and little 233Pa was observed The fuming in HNO3 as performed at the end of the purification procedure will drive Np to the soluble pentavalent state This is the stable oxidation state of Np under the experimental conditions Therefore experiments performed here can be assumed to be initially Np(V) The exact Np
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concentration in this solution was determined using ICP-MS calibrated with a NIST standard as discussed in section 312 below
A 237Np working solution (Working Solution 1) was created by pipetting an aliquot of the 237Np stock solution into a 100 mL Nalgene Teflon bottle and diluting with 2 BDH Aristar Ultra HNO3 to give a working solution concentration of 820 ppb All volumes were monitored gravimetrically Analysis on the ICP-MS calibrated against NIST Standards as described below gave a concentration of 820 ppb in Working Solution 1
Figure 32 Screen capture of a typical 237Np calibration curve using Thermo PlasmaLab software to control the data collection and analysis R2=0999981 Intercept Conc (Detection Limit) = 0000026 ppb
313 99Tc
A 99Tc working solution was prepared by diluting a stock solution of 99Tc (from the EEampES inventory purchased from Isotope Products Valencia CA) in distilled-deionized water (DDI Resistivity gt18 MΩcm) The oxidation state of Tc was not measured However based on the aqueous concentration in the DDI water solution Tc(VII) is the expected oxidation state The reduced Tc(IV) oxidation state would not be soluble under these conditions The expected concentration of 950 ppb based on the dilution was verified using liquid scintillation counting The 99Tc working solution was used to make 001 005 1 2 5 and 10 ppb standards by dilution using 2 HNO3 These standards were used to calibrate the Thermo Scientific X Series 2 ICP-MS for quantification of 99Tc A screen shot of a representative calibration curve is shown in Figure 33 The instrument performance was monitored by interpolating between 89Y and 115In internal standards The recovery of each sample during analysis was corrected based on the internal standard recovery The internal standard recoveries remained within standard QAQC protocols for the instrument (between 80 and 120)
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Figure 33 Screen capture of a typical 99Tc calibration curve using Thermo PlasmaLab software to control the data collection and analysis R2=0999984 Intercept Conc (Detection Limit) = 0000013 ppb
314 127I
A 100 microgmL iodate (IO3-) stock solution from High Purity Standards (Charleston SC) was used
to make 1 5 10 50 and 100 ppb standards by dilution using the ldquotraprdquo solution (discussed in Section 32 below) These standards were used to calibrate the Thermo Scientific X Series 2 ICP-MS for quantification of 127I A screen shot of a representative calibration curve is shown in Figure 34 The use of a reducing basic trap solution for iodine analysis limits the number of available internal standards that can be used to monitor ICP-MS instrument performance during iodine analysis Experiments are underway to identify acceptable internal standards However the data presented in this work did not use any internal standards prior to rigorous testing and analysis of representative standards As with the analyses for all isotopes (Tc I Np and Pu) spiked QAQC samples were frequently analyzed throughout the analysis as a check on instrument performance While these values cannot be used to correct individual samples in the same manner that the internal standards can they can be used to ensure accurate measurements of each isotope In almost all cases QAQC standards were within 10 of the expected value Because the average internal standard recovery ranges between 80 and 120 for the ICP-MS the iodine QAQC standard appears to be acceptable However a significant amount of ongoing work is testing various internal standards to improve the accuracy of iodine analysis using ICP-MS In one experiment (discussed in detail below) the QAQC standards deviated by an average value of 195 This will be specifically discussed below
Because experiments were performed with 127I concentrations up to 1000 ppb the 100 microgmL (ppm) stock iodate solution from High Purity Standards was used as the working solution
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Figure 34 Screen capture of a typical 127I calibration curve using Thermo PlasmaLab software to control the data collection and analysis R2=0999991 Intercept Conc (Detection Limit) = 024 ppb
315 Cementitious Materials Selected for Experiments There were four cementitious materials selected for this sorption study The first referred to as Aged Cement is a 30 year old sample that does not contain any reducing slag The aggregate from the Vault 2 cement had its aggregate removed prior to conducted tests in an effort to make subsamples more uniform This was necessary because some of the aggregate were larger than the 05 g subsamples used in individual sorption tests The Vault 2 cementitious material contained 17 dry wt- reducing slag on a dry weight basis before the water was added to the mix (Table 31) The TR547 and TR545 saltstone formulations contain 45 dry wt- and 90 dry wt- reducing slag respectively
Table 31 Characteristics of saltstone formulations used in this work Kaplan et al (2008)
Sample Percent Reducing Slag (dry wt-) (c)
Percent Portland Cement
(dry wt-) (c)
Percent Fly Ash
(dry wt-) (c)
Percent Aggregatesand ( dry wt-) (c)
Reducing Equivalents
(microeqg)
Aged Cement 0 10 45 45 855 plusmn 101(a)
Vault 2 Cement 17 10 45 0 178(b)
TR547 45 10 45 0 607(b) TR545 90 10 0 0 681(b) Blast furnace slag 100 0 0 0 819(b) (a) Kaplan et al (2008) (b) Roberts and Kaplan (2009) (c) All percentages of saltstone formulations are reported on a dry weight percentage basis that is the weight of the ingredients before water was added (d) Based on Table 8 in Dixon et al (2008 SRNL-STI-2008-00421) which shows the following quantity (lbscu yd) for saltstone Vault 2 Mix 1 concrete formulation 201 cement (1271 wt-) 268 slag (1695 wt-) 447 silica fume (283 wt-) 1563 fly ash (989 wt-) 911 fine sand (5762 wt-) The large aggregate was removed before the sorption tests were conducted The large aggregate accounted for 75 wt- of the original field sample not the sample used in these test before water was added to the mix TR547 is referred to as the Baseline by Dixon et al (2008) and is described in more detail in Appendix C (Mix 2) by Dixon et al (2008) (Control-BFSPC) and 1 (Baseline)
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TR545 saltstone contains 90 reducing slag and it is Mix 1 in Dixon et al (2008) and is described as
ldquoA control mix will be based on the baseline mix modified by exclusion of the Class F fly ash Consequently the cementitious materials premix will be a mixture of 90 blast furnace slag and 10 Portland cement The degree of reaction will be much greater than with the normal premix and therefore should result in a lower porosity and a lower permeability This bounding test at 060 wcm ratio is expected to yield a hydraulic conductivity at or below the detection limit for the Mactec permeameter measurement system Therefore this test should demonstrate the lowest level of detection of the Mactec system as well as show a resolvable difference between measurements of the control mix and the control mix with the normal premix compositionrdquo
32 ICP-MS Detection Limits
The PlasmaLab software platform determines a detection limit for each isotope based upon the intercept concentration A new calibration curve was generated for each experimental run and curves were very similar Using representative calibrations curves the detection limits for each isotope were as listed in Table 32 Note the higher detection limit for 127I is primarily due to the higher background count rate observed on the instrument This is believed to be due to the minimum purity levels of chemicals required for the iodine ldquotraprdquo solution as discussed in Section 33 below Therefore experiments were run with initial iodate concentrations higher than Tc Np and Pu to maintain analytical sensitivity
Table 32 Detection limits for each isotope based on representative calibration curves generated in PlasmaLab software associated with the ICP-MS
33 Experimental Methods
The experimental methods used in this work followed closely those previously described for experiments examining radionuclide sorption to saltstone (Kaplan et al 2007 Kaplan et al 2008) Brief descriptions of each method are provided below
Preparation of Calcite Solution Using a hotstirring plate 10 L of distilled-deionized (DDI)
water was heated to 3-100C above room temperature Then 001 g CaCO3 (EM Science ACS grade) was added to the solution and the resulting suspension was mixed for 24 hours at the elevated temperature The solution was then vacuum filtered through a 045-microm filter to ensure no solid CaCO3 remained in solution
Preparation of 2 HNO3 Analysis of Tc Np and Pu on the ICP-MS required dilution in 2
HNO3 This was prepared by adding 28 mL of Aristar Optima HNO3 from a clean graduated cylinder (designated to 2 HNO3) into a 1 L volumetric flask (designated to 2 HNO3) partially filled with DDI water and then further diluted to volume
Preparation of Trap Solution for Iodine Analysis Analysis of I required the use of a reducing
basic solution that was capable of reducing iodate to iodine and holding the iodine in solution This minimized the loss of I during sample analysis A 1 L trap solution was prepared by weighing out 00500 g NaHSO3 (Fisher Scientific ACS Grade) on a calibrated Sartorous LA 230S scale and adding it to a 1L volumetric flask Then 40 mL of 25 ww tetramethylammonium hydroxide (Alfa Aesar electronic grade) and 10 mL CFA-C solution (Spectrasol Inc) were added to the volumetric flask via a calibrated 1000-5000 microL Eppendorf Research pipette The solution was then diluted to volume with DDI water
34 Experimental Protocol for Sorption Experiments under Aerobic Conditions
Falcon BlueMax 15mL polypropylene vials were labeled and weighed to within 0001 g on a calibrated Sartorious LA 230S scale The scale was then zeroed and 025 +- 001 g of a given solid were added to each tube and the weight was recorded to within 0001g
For each of the four solids three sets of triplicate samples were prepared The three sets of samples were used to allow for experiments to be run with varying concentrations of each isotope Target initial concentrations for 99Tc 237Np and 242Pu samples were 1 ppb 5 ppb and 10 ppb Target initial concentrations for the 127I samples were 100 ppb 500 ppb and 1000 ppb A set of no solids controls at initial concentrations of 1 ppb and 10 ppb for 99Tc 237Np and 242Pu and initial concentrations of 100 ppb and 1000 ppb 127I were also prepared by adding the calcite solution to pre-weighed pre-labeled centrifuge tubes as discussed above
The solids were equilibrated with the calcite solution before spiking with the radionuclides This was done by adding 10 plusmn 01 mL of calcite solution to each tube and recording the mass The samples were then placed on a Thermo Scientific shaker overnight After 24 hours the solutions were allowed to settle for 1 hour The pH was then measured and the samples were then centrifuged for 15 minutes at 8000 rpm to further separate the solids The aqueous phase was then decanted and 10 plusmn 01 mL of calcite solution was added to each tube The weight of the tube (labeled tube + solid + calcite solution) was measured to within 0001g During this washing process the pH was monitored and held steady throughout the process The pH ranged from 11-12 depending on the particular saltstone used During the experiments the exact pH for all samples at all equilibration times was measured and is reported in Appendix A and B
The resulting suspensions were then spiked with 127I 237Np 242Pu and 99Tc It is important to note that all four isotopes were added to the same vial Use of the ICP-MS to determine the concentration of each isotope allows for a single solution to contain all analytes of concern This allowed for a greater variability in the sample set and increased replicates as opposed to running individual sorption tests for each isotope For the systems with initial 99Tc 237Np and 242Pu concentrations of 10 ppb and initial 127I concentration of 100 ppb a 100 microL aliquot of each radionuclide working solution was added to the first three tubes for each solid The addition was made with the tube resting on a tared analytical balance so that the exact mass of each radionuclide solution added was recorded and the solution was gently swirled before the next radionuclide was added The 5 ppb 237Np 242Pu and 99Tc and 500 ppb 127I samples were prepared in the same manner but adding 50 microL of the respective spike solutions The final three tubes with initial 237Np 242Pu and 99Tc concentrations of 1 ppb and 100 ppb 127I were prepared by using 10 microL of the spike solutions for all four solids as well as a set of solid-free controls (No-Solids Controls) For clarity this experimental matrix is shown in Table 33 below
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Table 33 Experimental Matrix of Sorption Experiments under Aerobic Conditions
After spiking the radionuclides a precalculated amount of 10M NaOH was added to each sample
to counter the acidic radionuclide spike solutions and the pH of one of the triplicate samples was measured to ensure the proper pH range was reached The samples were then placed on and end-over-end shaker to mix at approximately 8 rpm After 24 hours the samples were removed from the shaker and the pH of each sample was measured using an Orion Ross semi-micro glass electrode calibrated against pH 4 7 and 10 buffers (Thermo) The samples were then shaken and a transfer pipette was used to transfer 35 mL of a homogenous suspension to a 5mL syringe The solution was then passed through a 100 nm nylon syringe filter The first 025-050 mL of filtrate was discarded and the remaining filtrate was collected in a clean polyethylene vial Then 10 mL of the filtrate was removed and diluted in 90 mL 2 HNO3 The mass of each phase was determined and recorded gravimetrically Then 10 mL of the remaining filtrate was transferred to a clean Falcon BlueMax 15mL vial and diluted with 90 mL of trap solution for 127I analysis Again the volume of each phase was monitored gravimetrically After the 24 hour sampling event the samples were put back on the shaker to mix for three additional days On day four the above sampling procedure was repeated
The 237Np 242Pu and 99Tc samples can be run on the Thermo Scientific ICP-MS using the standard setup and procedure which included a standard flow glass nebulizer and bulb spray chamber However for the 127I analysis the ICP-MS must be reconfigured to accommodate the basic reducing trap solution This is to alleviate problems with iodine signal stability over time frequently observed in ICP-MS analysis The reconfigured instrument uses an Elemental Science Microflow PFA-100 Teflon nebulizer with a flow rate of 100microLmin along with a sapphire torch and a Teflon spray chamber This configuration must be run with a low pump speed to prevent back pressure on the system Two 30 minute stability tests were performed using a 50 ppb iodate solution Each experiment consisted of 40 separate measurements After each experiment was completed the uncorrected mass counts were examined and found to stay steady over the sampling period The relative standard deviation ( RSD) over all samples for each experiment was 1866 and 1460 respectively This shows that there was no significant ldquomemoryrdquo or loss of the iodine signal over time and that the reconfigured instrument has a stable iodine signal over time However as will be discussed below some difficulty has been encountered in finding an adequate internal standard for iodine analysis
35 Experimental Protocol for Sorption Experiments under Anerobic Conditions In order to examine the effects of reducing conditions of sorption of each isotope to the various cementitious samples a series of sorption experiments were performed in an anaerobic glovebox under a 2 H2(g) 98 N2(g) atmosphere Based on the measured pH and EH of these systems as discussed below these systems were at the point of reducing water Therefore they are expected to represent a lower end of the possible range for reducing conditions expected in the porewater available within cementitious materials
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Preparation of Calcite for Reducing Conditions Approximately 35 L of DDI water was boiled for 45 minutes Argon was slowly bubbled through the water as it cooled Once it cooled to below 500C approximately 3 g of calcite was added This solution mixed overnight under a continuous Ar flow After 12 hours the solution was moved into an oxygen free glove bag for filtration as described in 3231 After filtration the calcite solution was moved into the glove box
Preparation of Working Solutions under Reducing Conditions The calcite and solid solutions
were prepared in the glove box using the previously mentioned procedure used under aerobic conditions The radionuclide working solutions were transferred to the glovebox and stirred open to the reducing atmosphere for at least three days The concentration of each isotope in the working solutions was measured to determine any change in the concentration due to evaporation while the solutions were equilibrating
The preparation and spiking of samples for sorption experiments was performed exactly as described for the oxidizing conditions except all sample handling was performed in the glovebox After the 1 day and 4 day equilibration the samples were filtered within the glovebox then transferred outside for dilution and ICP-MS analysis similar to the description provided about for the oxidizing conditions For these experiments only 4 mL of either 2 HNO3 or trap solution were used to dilute the filtrate instead of the 90 mL used above for experiments performed under oxidizing conditions
36 Examination of Sorption to Vial Walls for Solids and No Solids Controls
As will be discussed below the solid-free controls samples indicated significant loss of Np and Pu Once the one and four days samples were collected and run on the ICP-MS it was necessary to determine the degree each radionuclide was sorbing to the vial walls The remaining suspensions and controls were emptied into a waste container Then 5 mL of the calcite solution was added to each vial using a calibrated pipette The vials were sonicated for approximately one minute and then emptied into the waste container Another 5 mL of calcite solution was added for the second wash and then discarded into the waste container This procedure was expected to remove any soluble Pu from the system or Pu associated with colloidal particles After each vial was washed 10 mL of 2 HNO3 was added using a calibrated pipette The acid solution is expected to remove any Tc Np or Pu associated with the vial walls This procedure has been shown to complete mass balances of Pu in similar sorption experiments using Pu (Powell et al 2002) This process was performed for both the solid suspension and the no solids controls The samples were then run on the ICP-MS to determine the concentration of 99Tc 237Np and 242Pu sorbed to the vial walls
37 Data Analysis The solubilities of 242Pu and 237Np were calculated by using the formula
nuclide
nuclide
nuclideMSICP
sol Mg
gCC
)(10 6
microminus
minus
= (Equation 31)
Csol = observed nuclide solubility (molnuclidekgsolution) CICP-MS = aqueous concentration of nuclide from ICP-MS measurement (ppb micrognuclidekgsolution) Mnuclide = molecular mass of nuclide (gnuclidemolnuclide)
In order to determine the Kd values one first needs to determine the concentration on the solid by using
SRNL-STI-2009-00636 Revision 0
24
solid
calcitespikeaqspikecalcite
spikestock
solid m
mmCmmmC
C)(
)()(
+⎥⎥⎦
⎤
⎢⎢⎣
⎡minus
+
lowast
= (Equation 32)
Csolid = calculated solid phase concentration of the nuclide (ppb) Cstock = concentration of the nuclide stock solution (ppb) mspike = mass of nuclide spiked into the saltstone suspension (g) mcalcite = total mass of calcite solution used in the saltstone suspension (g) Caq = aqueous concentration of nuclide from ICP-MS measurement (ppb) msolid = mass of the saltstone used in the suspension (g)
The Kd can be calculated using the equation
aq
solidd C
CK = (Equation 33)
Kd = solid-water partitioning coefficient (gsolutiongsolid assuming density of 10 gmL traditional
unit of mLsolutiongsolid can be obtained) This Kd Equation (33) is numerically equivalent to the traditional Kd equation proposed in ASTM D-4646 which has been used in previous saltstone experiments (Kaplan et al 2007 Kaplan et al 2008)
40 Results and Discussion
41 Radionuclide Sorption to Cementitious Formulations under Oxidizing Conditions
Figure 41 shows Pu Kd values ranging from 104 to gt105 mLg Generally for each solid the Kd increases with increasing initial Pu concentrations typical behavior of systems where the aqueous concentrations of the radionuclides are solubility controlled This is not expected because the Kd expression indicates that the Kd value should remain constant with increasing total Pu concentrations It was noted that aqueous phase concentration of Pu remained relatively constant in all samples (see discussion below regarding Pu solubility) Therefore the sorption capacity of each solid phase for Pu has not been overcome For each of these solid phases it appears the solutions had reached equilibrium before the first samples were taken at 24 hours In each case the Kd values for the one day and four day are similar A trend between the solid phases is not discernible The aged cement with no reducing slag was expected to have the lowest Kd values but in actuality it has the highest Kd Also there is no correlation with the concentration of reducing slag The Vault 2 samples with 17 dry wt- reducing slag has a Kd similar to that of the TR547 (45 dry wt- slag) while the saltstone with the most slag TR545 (90 dry wt- slag) has the lowest Kd value Others have observed that Pu Kd values of cementitious materials are similar in the absence and presence of slag (Allard et al 1984 Hoaglund et al 1985)
It was observed that similar aqueous concentrations of Pu were observed regardless of the solid phase present Figure 42 shows the average aqueous phase concentrations measured after one day and four days for all solids As stated above triplicate samples were prepared for each solid phase and each initial concentration Therefore each of the reported solubility values in Figure 42 is an average of nine measurements Using the highest reported value with the expected maximum error (0018 ppb for solid TR545) the maximum expected aqueous concentration of Pu in the pore water associated with the
SRNL-STI-2009-00636 Revision 0
25
saltstone formulations will be approximately 7 x 10-11 molL as calculated using Equation 31 This is on the same order as the solubility of Pu hydrous oxide solid phases (Neck and Kim 2001)
Figure 41 Plutonium Kd Values under Oxidizing Conditions Plutonium Kd values for various saltstone formulations measured after one-day equilibration (1d) and four-day equilibration (4d under oxidizing conditions Total plutonium concentrations in each system were 1 ppb 5 ppb and 10 ppb Sample prepared in triplicate and error bars represent standard deviation of samples except as follows value for dataset TR547-4d 10 ppb is reported based on duplicate samples
Figure 42 Plutonium solubility for various saltstone formulations measured after one-day equilibration (1d) and four-day equilibration (4d) under oxidizing conditions Total plutonium concentrations in each system were 1 ppb 5 ppb and 10 ppb as noted Samples prepared in triplicate and an average of all samples (9) was used to determine average solubility The error bars represent standard deviation of samples
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Overall the Kd values for Np range from 105 to gt106 with only a few outliers The most significant outlier is the 1 ppb solution in the TR545 sample after the four-day equilibration It drops two orders of magnitude while the 5 and 10 ppb solutions remain constant However this result is most likely an analytical artifact from working at the detection limits of the ICP-MS In the one-day equilibration samples only one of the triplicates S-2-E had detectable Np while in the four-day equilibration samples only S-2-F had detectable amounts present The graph also shows that with the exception of the 5 ppb sample in the aged cement Np sorption to TR545 (90 dry-wt- slag) and TR547 (45 dry wt- slag) have Kd values approximately one order of magnitude over the aged cement (no slag) and Vault 2 (17 dry wt- slag) samples
It was observed that similar aqueous concentrations of Np were observed regardless of the solid phase present Figure 44 shows the average aqueous phase concentrations measured after one day and four-day equilibrations for all solids As stated above triplicate samples were prepared for each solid phase and each initial concentration Therefore each of the reported solubility values in Figure 44 is an average of nine measurements of Np concentration unless stated otherwise Using the highest reported value with the expected maximum error (00026 ppb for solid TR545) the maximum expected aqueous concentration of Pu in the pore water associated with the saltstone formulations will be approximately 2 x 10-11 molL
Figure 43 Neptunium Kd values under oxidizing conditions Neptunium Kd values for various saltstone formulations measured after one-day equilibration (1d) and four-day equilibration (4d) under oxidizing conditions Total plutonium concentrations in each system were 1 ppb 5 ppb and 10 ppb as noted Samples prepared in triplicate and error bars represent standard deviation of samples except as follows value for datasets TR545-1d 1ppb TR545-4d 1 ppb TR547 4d 1 ppb TR545-4d 10 ppb TR547-1d 1ppb TR547-4d 10 ppb are reported based on a single sample and for dataset TR545-1d 5ppb is reported based on duplicate samples Kd values limited to gt106 were at instrumental background
The Kd values for Tc are significantly lower than that of Pu or Np As a whole the values are
comparable The values for the one-day and four-day equilibrations solutions in the Vault 2 (17 dry wt- slag) and TR545 (90 dry wt- slag) remained constant within reasonable error with just a slight increase from the one-day to four-day equilibration However the Aged Cement (no slag) and TR547 (45 dry wt- slag) showed a noticeable decrease from day one to day four (Figure 45)
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Figure 44 Average solubility of Np under oxidizing conditions Neptunium solubility for various saltstone formulations measured after one-day equilibration (1d) and four-day equilibration (4d) under oxidizing conditions Total Np concentrations in each system were 1 ppb 5 ppb and 10 ppb Samples prepared in triplicate and an average of all samples (9) was used to determine average solubility except as follows TR545-1d is based on 6 samples TR545- 4d on 5 samples TR547-1d on 7 samples and TR547- 4d on 5 samples The error bars represent standard deviation
Figure 45 Technetium Kd values under oxidizing conditions Tc Kd values for various saltstone formulations measured after one-day equilibration (1d) and four-day equilibration (4d) under oxidizing conditions Total Tc concentrations in each system were 1 ppb 5 ppb and 10 ppb as noted above Samples were prepared in triplicate and the error bars represent standard deviation of samples except as follows data sets for Vault 2-1d 1ppb were duplicates and TR547- 4d 10 ppb is based on a single dataset
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Similar to the Tc Kd values the 127I Kd values are much lower than those of Pu and Np The amount of reducing slag present in each of the solids does not appear to have a drastic effect on the 127I Kd values In fact the initial (one day) Aged Cement (0 slag) samples had a Kd almost two orders of magnitude above those with reducing slag The cause of this behavior is not known but it has been shown that iodate IO3
- the oxidized form of iodine sorbs more strongly than iodide I- to charged surfaces (Schwehr et al 2009 Yoshida et al 1992 Fukui et al 1996) It is possible that the slag is reducing the iodine to the I- form converting it to a species that is less likely to sorb to saltstone Additional work would be required to confirm the oxidation state of iodine when associated with saltstone
Figure 46 Iodine Kd Values under Oxidizing Conditions Iodine Kd values for various cementitious formulations measured after one-day equilibration (1d) and four-day equilibration (4d) under oxidizing conditions Total iodine concentrations in the systems were 100ppb 500 ppb and 1000 ppb as noted above Samples were prepared in triplicate and the error bars represent standard deviation of samples except as follows duplicates were used for dataset TR545- 1d 100ppb
42 Radionuclide Sorption to Vial Walls Under Oxidizing Conditions
Figure 47 shows the aqueous fractions found in the no-solids controls It provides a measure of the solubility of each radionuclide as well as examines the fraction of each radionuclide sorbed to the vial walls After one day only 25 of the Pu remained in solution and the concentration decreased even more after four days The loss of Pu from the aqueous phase may be due to sorption of Pu to the vial walls or precipitation of a Pu hydrous oxide solid (discussed with respect to Figure 49 below) Additional experiments would be required to examine the solubility of the Pu in high pH calcite saturated solutions
After one day about 80 of the Np remained in solution However the aqueous concentration in the initially 1-ppb solution was significantly reduced after four days Approximately 60 of the Np remained soluble in the initially 10-ppb solution Once again this drop could be due to sorption to the vial wall The Tc present after one day ranged from about 88 to about 95 and was virtually 100 after four days These values are consistent with internal standards used to monitor Tc detection performance on the ICP-MS Greater than 50 of the I remained in solution after the one-day and four-day equilibrations As shown in Figure 48 the standard deviation between the triplicate I control samples was
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quite large Additional control samples are required to understand the mechanism by which I is being lost from the aqueous phase in these samples
Figure 47 Plutonium Neptunium and Technetium Aqueous Fractions Fraction of Pu Np and Tc remaining in the aqueous phase for the No Solids controls after a one-day equilibration (1d) and four-day equilibration (4d) under oxidizing conditions The total concentration for each radionuclide 10 ppb as noted above Samples were prepared in triplicate and the error bars represent the standard deviation of the samples
Figure 48 Iodine Aqueous Fraction Iodine aqueous fraction for the no-solids controls after a one-day equilibration (1d) and four-day equilibration (4d) under oxidizing conditions The total concentration of iodine was 1000 ppb as noted above Samples were prepared in triplicate and the error bars represent the standard deviation of the samples
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As discussed above the loss of Np and Pu from the no-solids control (Figure 47) could be due to
precipitation of Np and Pu hydrous oxides or sorption to the vial walls To quantify the differences between these possible sinks the vials were washed as described in Section 36 The data in Figure 49 indicate that significant sorption of Np and Pu to the vial walls may occur When combining the mass of Np represented in Figure 47 and Figure 49 there is almost 100 mass recovery of the Np sorbed to the vial wall and the aqueous fraction measured Therefore no precipitation of Np is expected However because 100 recovery was not achieved for Pu a Pu hydrous oxide phase could be precipitating which was washed out of the vial during the cleaning procedure The data in Figure 47 represent the no-solids control samples where there was no solid phase present for Np or Pu to sorb to besides the vial walls However when a cementitious solid phase is present in the sample there will be competition between the vial walls and the cement for sorption of Np and Pu Based on the affinity of metals for metal oxide surfaces as opposed to the polypropylene surface and the much higher surface site density expected for the cementitious samples it is assumed that the cementitious samples will out-compete the vial walls for sorption sites This thesis was tested by taking one of the triplicate samples from each sorption experiment with a solid phase present removing the solid phase from the tubes and leaching any sorbed Np and Pu from the tubes with acid as described in Section 36 Figure 410 and Figure 411 show that although some of the Pu and Np sorbed to the vial walls of the samples this amount accounted for less than 2 in all samples Therefore sorption of Np and Pu to the vial walls does not appear to be a significant factor in experiments where the solid phase is present Note these results do not discount the possibility that Pu hydrous oxide precipitates were forming in both the no-solid control experiments and experiments with cement formulations present Based on the observation of a constant aqueous phase concentration of Pu regardless of the initial Pu concentration the presence of a solubility limiting Pu phase cannot be discounted based on these data Further experiments examining the solubility of Pu in high pH calcite saturated solutions are required
Like Pu Np shows little affinity for the vial walls in the presence of a solid phase In each case tested there was significantly less than 1 of the total Np sorbed to the vial walls This behavior is consistent with the ~100 mass balance on Np achieve in the solid-free controls The majority of Np remained soluble in the solid-free control experiments Therefore it is expected that sorption of Np to the vial walls was the primary reason for the loss of Np from the aqueous phase in the no-solids systems rather than precipitation of a Np solid phase similar to the process discussed for Pu above This assumption is based on the relative solubility of Np(V) as compared with Pu(IV)
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Figure 49 Percent Pu and Np sorbed to vial walls of the no solids controls after the aqueous phases were discarded and the vials were washed Both the 10 ppb and 1 ppb datasets were prepared in triplicate and the error bars show the standard deviation
Figure 410 Percent Pu sorbed to vial walls after the solids and aqueous phases were removed and the vials were washed The graph illustrates one sample from each of the 1 ppb 5 ppb and 10 ppb systems Therefore no error bars are present
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Figure 411 Percent Np sorbed to vial walls after the solids and aqueous phases were removed and the vials were washed The graph illustrates one sample from each of the 1 ppb 5 ppb and 10 ppb systems Therefore no error bars are present
43 Radionuclide Sorption to Cementitious Formulations under Reducing Conditions
Similar to the Pu Kd values under oxidizing conditions Pu Kd values ranged from 104 to gt105 under reducing conditions (Figure 412) Also similar to the results under oxidizing conditions the Kd increases with increasing initial Pu concentration Again this behavior is indicative of the aqueous phase concentration of Pu being controlled by solubility of Pu rather than by sorption In each case the samples appeared to reach steady state within 24 hours This equilibration is evident because the Kd values after one day and four days are very similar Also it appears that the amount of reducing slag does not make a significant difference in the Kd value In fact the TR547 solid consists of 45 reducing grout but produces approximately the same Kd values of the aged cement which does not have any reducing grout Each of these Kd values are higher than the TR545 which is 90 reducing grout These findings are in agreement with those conducted by Allard et al (1984) and Hoglund et al (1985) who reported that concrete containing reducing agents (slag similar to that used in our study) did not have greater Pu Kd values than those that did not contain slag
Similar aqueous concentrations of Pu were observed regardless of the solid phase present Figure 36 shows the average aqueous phase concentrations measured after one day and four days for all solids As stated above triplicate samples were prepared for each solid phase and each initial concentration Therefore each of the reported solubility values in Figure 412 is an average of up to nine measurements of the Pu aqueous concentrations Using the highest reported value with the expected maximum error (00045 ppb for solid Vault 2) the maximum expected aqueous concentration of Pu in the pore water associated with the cementitious formulations will be approximately 2 x 10-11 molL (calculated from Equation 31) This value is on the same order as the solubility of Pu hydrous oxide solid phases (Neck and Kim 2001) A best value would be 10-12 molL
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Figure 412 Pu Kd Values under Reducing Conditions Plutonium Kd values for various cementitious formulations measured after one-day equilibration (1d) and four-day equilibration (4d) under reducing conditions Total plutonium concentrations in each system were 1ppb 5 ppb and 10 ppb Samples prepared in triplicate and error bars represent standard deviation
Figure 413 Average Solubility of Plutonium under Reducing Conditions Plutonium solubility for various cementitious formulations measured after one-day equilibration (1d) and four-day equilibration (4d) under reducing conditions Total plutonium concentrations in each system were 1ppb 5 ppb and 10 ppb as noted Samples prepared in triplicate and an average of all samples (9) was used to determine average solubility The error bars represent standard deviation of samples
The Np Kd values reported in Figure 414 obtained under reducing conditions are very similar to
those obtained under oxidizing conditions In each case the samples appeared to reach steady state within 24 hours This equilibration is evident because the Kd values between the one-day and fourndashday equilibrations are similar As was the case with Pu the amount of slag present in each solid does not
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seem to have a significant effect on the Kd values Again the aged cement with no slag has as high a Kd as the TR545 with 90 reducing slag
Similar aqueous concentrations of Np were observed regardless of the solid phase present Figure 314 shows the average aqueous phase concentrations measured after one day and four days for all solids All Kd values were gt 105 mLg which is considerably larger than those reported by Kaplan and Coates (2007) who reported Np Kd values to 1300 to 1600 mLg This difference can be attributed to two important experimental differences 1) the experiment was designed to permit larger Kd values to be measured (eg solid to liquid ratios and spike concentrations) and more importantly 2) a more sensitive analytical method ICP-MS was used instead of conventional low-energy gamma spectroscopy or liquid scintillation counting (LSC) analysis As stated above triplicate samples were prepared for each solid phase and each initial concentration Therefore each of the reported solubility values in Figure 415 is an average of up to nine measurements Using the highest reported value (to provide the most conservative most soluble values) with the expected maximum error (00045 ppb for solid TR545) the maximum expected aqueous concentration of Np in the pore water associated with the cementitious formulations will be approximately 2 x 10-11 molL A best value taking into consideration the less-than values which are depicted in Figure 414 as running off the top of the plot would be 10-12 molL
Figure 414 Np Kd Values under Reducing Conditions Neptunium Kd values for various cementitious formulations measured after one-day equilibration (1d) and four-day equilibration (4d) under reducing conditions Total Np concentrations in each system were 1 ppb 5 ppb and 10 ppb Samples were prepared in triplicate and the error bars represent standard deviation Kd values limited to gt106 were at instrumental background
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Figure 415 Average Solubility of Neptunium under Reducing Conditions Neptunium solubility for various cementitious formulations measured after one day equilibration (1d) and four day equilibration (4d) under reducing conditions Total plutonium concentrations in each system were 1ppb 5 ppb and 10 ppb Samples prepared in triplicate and an average of all samples (9) was used to determine average solubility The error bars represent standard deviation
A plot of the Tc Kd values for each cementitious formulations under reducing conditions is shown
in Figure 416 (log y-axis) and Figure 417 (reduced scale linear y-axis) The Kd values for each of the initial Tc concentrations are relatively similar This behavior is consistent with the Kd expression However the increasing Kd values from the one-day to four-day day equilibrations for each solid indicate that steady state was not reached within one day and it is unclear whether steady state was reached after four days A possible explanation for this behavior is that Tc(VII) was being reduced to Tc(IV) in these systems due to the reducing conditions As Tc(VII) was reduced the Kd would increase based on the high affinity of Tc(IV) for solid phases This proposed mechanism was observed by Lukens et al (2005) using an SRS saltstone material similar but not identical to TR547 Using synchrotron X-ray absorption fine structure spectroscopy they observed over a 453 month period that Tc(VII) incorporated into SRS saltstone slowly converted to Tc(IV) and that the nearest neighbor was initially predominantly oxygen and eventually became predominantly sulfur (described as a Tc(IV) phase TcSx) Lacking in Lukens et al (2005) is quantification of the solubility of Tc This analysis still needs to be completed along with re-oxidation studies (ie what is the rate that reduced Tc reoxidizes under ambient natural saltstone conditions)
Unlike Np and Pu Tc Kd values changed with the amount of slag included in the formulation Tc Kd values noticeable increase as the amount of slag in the formulation increased TR547 (45 dry-wt- slag) Kd value is visibly higher than the Aged Cement and Vault 2 Kd values while the most reducing TR545 (90 dry wt- slag) Kd value is significantly higher than the others Following a similar trend the reduction capacity that is the total quantity of reductant in the saltstone on a mass basis (units of milli-equivalents of charge per g) of TR547 had slightly greater or equal reduction capacity to that of TR545 (Roberts and Kaplan 2009)
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Figure 416 Tc Kd Values under Reducing Conditions Tc Kd values for various cementitious formulations measured after one-day equilibration (1d) and four-day equilibration (4d) under reducing conditions Total Tc concentrations in each system were 1 ppb 5 ppb and 10 ppb Sample prepared in triplicate and error bars represent standard deviation except as follows TR547-1d 1 ppb is based on a single dataset and datasets Vault 2-1d 5 ppb Vault 2- 4d 1 ppb Aged Cement-1d 5 ppb and Aged Cement-4d 1 ppb are duplicates
Figure 417 Data from Figure 416 replotted on a reduced linear scale for easier viewing Each sample was prepared in triplicate except as follows TR547-1d 1 ppb is based on a single dataset Vault 2-1d 5 ppb Vault 2- 4d 1 ppb Aged Cement-1d 5 ppb and Aged Cement-4d 1 ppb are duplicate datasets
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The calculated Kd values for I sorption to cementitious samples under reducing conditions are shown in Figure 418 Before discussing the data it should be noted that spiked QAQC samples which were analyzed on the ICP-MS along with the samples used to generate the data in Figure 418 were off by an average of 195 with one outlier of approximately 40 This dataset did not include the use of internal standards as discussed in Section 31 above1 Due to a lack of an internal standard the iodine results presented in this report should be considered with a minimum error estimate of 20
The iodine Kd values under reducing conditions are different from those observed under oxidizing conditions Under oxidizing conditions it appears they are at a steady state by day one However under reducing conditions there is a noticeable difference between days one and four indicating steady state was not reached by day one and possibly not by day four Another interesting observation is that the Kd values are decreasing from day one to four A possible reason for this behavior may be due to redox chemistry of iodine in this system If iodine partially or entirely exists in the form as iodate (IO3
-) it is possible it could be reduced to iodide I- within the reducing cementitious system These two iodine species sorb differently iodate sorbing to minerals more strongly than iodide (Denham et al 2009 Schwehr et al 2009 Fukui et al 1996 Yoshida et al 1992) It is hypothesized that the reducing environment of the saltstone is sufficient to reduce iodate ions to the more weakly binding form of iodine iodide
This is one of the few datasets (along with Tc) in this study where there may be a difference between the various solids The degree of iodate reduction would be expected to increase as the slag content increases As mentioned above reduction of iodate to iodide should result in a decrease in sorption Therefore higher Kd values should be observed for solids with less slag such as the Aged Cement (0 dry wt- slag) and Vault 2 (17 dry wt- slag) This is generally the case in Figure 418 where the highest Kd values are reported for the Aged Cement and the lowest values are for solid TR547 However this trend does not hold completely where the saltstone sample containing 90 slag (TR545) has generally equal or higher Kd values than the saltstone containing 45 dry wt- slag (TR547)
1 Clemson University is presently investigating appropriate internal standards for iodine analyses for ICP-MS Of those tested rhenium and molybdenum have shown some promise
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Figure 418 Iodine Kd Values under Reducing Conditions I Kd Values for various cementitious formulations measured after one day equilibration (1d) and four day equilibration (4d) under reducing conditions Total iodine concentrations in each system were 100 ppb 500 ppb and 1000 ppb as noted Sample prepared in triplicate and error bars represent standard deviation of samples except as follows Vault 2-4 d 100 ppb is a single dataset while the datasets for Vault 2-1 d 100 ppb 4 d 1000 ppb TR545-4 d 1000 ppb 100 ppb TR547-4 d 1000 ppb 500 ppb 100 ppb and Aged Cement- 4 d 1000 ppb and 100 ppb are all based on duplicates
44 Radionuclide Sorption to Vial Walls under Reducing Conditions
The aqueous concentrations for Pu Np and Tc in the no solids controls are shown in Figure 419 The results are similar to those presented for experiments performed under oxidizing conditions above The 1 ppb Pu aqueous fraction is approximately three times greater than the 10 ppb fraction at day one This fraction decreases over time and by day four they are approximately equal when taking error into account This behavior is similar to the aqueous fraction under oxidizing conditions The 1 ppb Np aqueous fraction is significantly higher on both day one and day four than the aqueous fraction of the 10 ppb samples However each remained constant from day one to day four The 10 ppb aqueous fraction is twice as low as under oxidizing conditions which suggests either higher sorption to the vial walls or more precipitating out under the reducing conditions Like Pu and Np Tc shows a decrease from day one to day four especially for the 1 ppb samples The decrease in the 10 ppb sample is minimal and the aqueous fraction remains around 09 This value is slightly lower than that under oxidizing conditions
To examine the degree of sorption to the vial walls the tubes were washed again as performed for the experiments under oxidizing conditions above and similar results were found Ninety percent of the 1 ppb Pu sample was sorbed to the vial wall upon completion of the experiment which gives a 100 mass recovery when comparing this value to that found in Figure 419 However this result is not the case with the 10 ppb samples where approximately 75 of the mass remains unaccounted It is noteworthy that approximately 25 of the Pu from the 10 ppb solution sorbed to the vial walls under both oxidizing
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and reducing conditions Np follows the same trend as Pu while less than 005 of the Tc sorbed to the wall
Figure 419 Plutonium Neptunium and Technetium No-Solids Aqueous Fractions under Reducing Conditions Pu Np and Tc aqueous fractions of No Solids controls after a one-day equilibration (1d) and four-day equilibration (4 d) under reducing conditions Total concentration for each radionuclide was 1 ppb and 10 ppb Samples were prepared in triplicate and the error bars represent the standard deviation
Figure 420 Percent of Pu Np and Tc sorbed to the vial walls of the No Solids control samples under reducing conditions Each the 1 ppb and 10 ppb samples were prepared in triplicate and the error bars represent the standard deviations of triplicate samples
Under reducing conditions the fraction of I remaining in the aqueous phase was around 90 with
almost 100 mass recovery of the 100 ppb I after the four-day equilibration These graphs show that
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under reducing conditions there will only be a small fraction of I sorbing to the vial wall or coming out of solution This result is a much better mass recovery than under oxidizing conditions (Figure 48) which had a mass recovery of approximately 65 after four days This result is also consistent with the interpretation that there may be a iodine speciation change between the two redox treatments
Figure 421 Iodine No-Solids Aqueous Fractions under Reducing Conditions I aqueous fractions of No-Solids controls after a one-day equilibration (1d) and four-day equilibration (4d) under reducing conditions The total concentration for each system was 100 ppb and 1000 ppb Samples were prepared in triplicate and the error bars represent the standard deviation
50 Comparison of Radionuclide Sorption under Oxidizing and Reducing Conditions
In the following figures (Figure 51 through Figure 54) the data shown above has been replotted to allow comparison between the oxidizing and reducing conditions for each cementitious formulation General observations based on these data follow Vault 2 Observations (Figure 51)
bull Pu Kds are greater than 104 under both oxidizing and reducing conditions and Pu Kds are slightly lower under reducing conditions This could possibly be due to reduction of Pu(IV) to Pu(III) However no oxidation state analysis was performed in this work
bull Np Kds are generally greater than 104 under both oxidizing and reducing conditions Interestingly Np Kds are higher under reducing conditions by almost an order of magnitude This could possibly be due to reduction of Np(V) to Np(IV) However no oxidation state analysis was performed in this work
bull Regardless of the initial Np or Pu concentration similar aqueous phase concentrations of Np or Pu were observed in all samples This trend indicates that ldquosorptionrdquo of Np and Pu in these systems may be a combination of adsorption absorption and (co)precipitation processes
bull Tc appears to reach a steady state within four days under oxidizing conditions This behavior does not appear to be the case under reducing conditions After four days similar Kd values are reached under both oxidizing and reducing conditions It is unclear
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whether the Kd value of Tc will continue to increase under reducing conditions consistent with reduction of Tc(VII) to Tc(IV) The similarity in Kd values under both oxidizing and reducing conditions is an interesting observation and certainly warrants additional studies
bull I Kd values are similar under both oxidizing and reducing conditions However reducing condition systems may not be at steady state after four days while systems under oxidizing conditions appeared to reach a steady state The difference in rates may be due to reduction of iodate to iodine
bull For all isotopes examined the sorption behavior to each of the solid phases is very similar
TR545 and TR547 Observations (Figure 52 and Figure 53) bull Similar to the discussion above with respect to Vault 2 Pu Np and Tc all appear to reach
a steady state under oxidizing conditions and approach steady state slower under reducing conditions
bull Np and Pu Kd values are greater than 104 for all systems and time steps The aqueous phase concentrations of Np and Pu appear to be better described as a solubility in terms of the aqueous phase concentration of Np and Pu Similar aqueous phase concentrations of both Np and Pu were reached The data indicate that the initial Np and Pu concentration generally does not affect the aqueous phase concentration at an apparent steady state The presence of each solid phase appears to limit the aqueous phase concentration of both Np and Pu on the order of 10-11 molL
bull Tc shows significantly higher Kd values under reducing conditions versus oxidizing conditions
bull For all isotopes examined the sorption behavior to each of the solid phases is very similar
Aged Cement Observations (Figure 54) bull Pu appears to be close to steady state for each solid by day one with similar Kd values
reached on between day one and day four bull Np has a higher Kd under reducing conditions than oxidizing (105 under oxidizing
conditions and gt105 under reducing conditions) bull Neither set of Tc data was at steady state by day one and rates of sorptiondesorption
reactions appear to be different Tc Kds decrease from day one to four under oxidizing conditions but increase under reducing conditions
bull The Kd values for I under oxidizing conditions were considerably higher than those measured for I with any other solid Similar Kd values obtained for the same solids under reducing conditions indicate that the reported Kd values under oxidizing conditions appear to be suspect However analysis of the raw data gives no indication of an experimental artifact As discussed above these observations may be explained based upon the amount of slag contained within the solids which will affect the reducing capacity (ie No reducing slag is in the aged cement which could be reason the reduction of iodate to iodide (speculated in other samples) is not evident)
bull The difference in sorption behavior of iodine to the aged cement between oxidizing and reducing conditions also indicates that the reducing conditions of the solution may affect I redox behavior in addition to any reactivity expected in the solid phases
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Figure 51 Comparison of Tc I Np and Pu sorption to Vault 2 solid under oxidizing and reducing conditions
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Figure 52 Comparison of Tc I Np and Pu sorption to TR 545 solid under oxidizing and reducing conditions
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Figure 53 Comparison of Tc I Np and Pu sorption to TR547 solid under oxidizing and reducing conditions
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Figure 54 Comparison of Tc I Np and Pu sorption to Aged Cement under oxidizing and reducing conditions
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60 Comparison of Radionuclide Sorption and Solubility under Oxidizing and Reducing Conditions
To further summarize the data the following tables provide either the average solubility
(for Np and Pu) or average Kd (for Tc and I) determined under both oxidizing and reducing conditions for each cementitious formulation Each table lists the average value standard deviation and the number of replicate samples used to calculate the reported values
The solubility of Pu in the presence of each solid under oxidizing and reducing conditions is shown in Table 61 (this is taken from experiments equilibrated for four days not one day) Under oxidizing conditions the apparent solubility values associated with the Aged Cement (0 dry wt- slag) Vault 2 (17 dry wt- slag) and TR547 (45 dry wt- slag) are all similar with only a slight increase in solubility as the amount of reducing slag increases There is a significant increase of almost an order of magnitude for the most reducing saltstone TR545 (90 dry wt- slag) However these samples also have a standard deviation on the same order of magnitude as the solubility itself which when taken into account brings the solubility back into the range of the others Under reducing conditions the apparent solubility values are slightly lower than under oxidizing conditions In this set of samples the Vault 2 saltstone with 10 dry wt- reducing slag had the highest apparent solubility but once again when considering the standard deviation the values are similar
Table 61 Comparison of plutonium apparent solubility values under oxidizing and reducing conditions
Table 62 lists the apparent solubility values of Np in the presence of each cementitious
formulation under both oxidizing and reducing conditions Under oxidizing conditions the cementitious formulation does not appear to have a dramatic effect on the solubility The apparent solubility values are similar to those of Pu under similar conditions except the Np standard deviations are much higher The high standard deviations are an analytical artifact since the measured concentrations were close to or at the detection limit of the ICP-MS There does appear to be a slight decrease in Np solubility under reducing conditions However the statistical significance of this decrease was not calculated
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Table 62 Comparison of neptunium apparent solubility values under oxidizing and reducing conditions
Unlike the apparent solubility values of Pu and Np the aqueousatmospheric conditions
and cementitious formulation seem to have an effect on the Tc Kd values (Table 63) Under oxidizing conditions there is not a discernible difference among the different cementitious formulations especially when taking the respective standard deviations into account However when experiments were run under reducing conditions the specific formulation had a noticeable effect The two saltstone samples with the least amount of reducing slag Aged Cement (0 dry-wt- slag) and Vault 2 (17 dry wt- slag) had Kd values which were similar to those observed under oxidizing conditions However the TR547 (45 dry-wt- slag) increased by almost an order of magnitude while the TR545 (90 dry wt- slag) increased by about three orders of magnitude Although the respective standard deviations are large the higher Kd values do appear to be significant
Table 63 Comparison of technetium Kd values under oxidizing and reducing conditions
Unlike Tc I does not seem to be as affected by cementitious formulation and redox status (Table 64) The only treatment (possible outlier) that does not follow this trend is the Aged Cement under oxidizing conditions This Kd value is higher than the others but also has a much higher standard deviation which when accounted for gives a value similar to the others All other treatments had near identical Kd values irrespective of solid phase or redox condition But again the Aged Cement data cannot be discounted at this time given the possibility of the influence that redox may have on iodine speciation and the strong influence I speciation has on sorption to cementitious materials
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Table 64 Comparison of iodine Kd values under oxidizing and reducing conditions
71 Comparison with Previous Data The increased sensitivity of the ICP-MS over conventional low-energy gamma
spectroscopy or liquid scintillation counting (LSC) analysis allowed for much more accurate Kd values and apparent solubility values in this work than were previously obtainable Generally radioanalytical detection methods start with activities on the order of 103 to 104 counts per minute (cpm) and approach background levels of 1 to 5 cpm for strongly sorbing radionuclides Therefore the accuracy of the Kd value will be the difference in analytical sensitivity when the initial aqueous activity decreases by a factor of approximately 5000 (ie the aqueous activity drops from approximately 5000 cpm to the instrument background of 1 cpm following almost complete sorption) As a result the reported Kd values can only be reliably reported up for a Kd of 103 to 104 This constraint is believed to be the difference between the observed Kd values for 237Np of gt 105 observed in this work when compared with the Kd values between 3000 and 4000 reported by Kaplan et al (2008) A similar observation was made for Pu because 242Pu was used for ICP-MS analysis and 238Pu was used in the work of Kaplan et al (2008) This constrint may account for the different Kd value of gt104 reported in Kaplan et al (2008) compared with the value of gt105 observed in this work
In the case of Tc Kaplan et al (2008) reported a Kd of 023 mLg for Vault 2 under oxidizing conditions and 093 mLg under reducing conditions while the above experiment determined the Vault 2 Kd to be 505 mLg under oxidizing conditions and 557 mLg under reducing conditions Unlike the discrepancy in the Kd values for Np Pu and Tc between the above findings and those in Kaplan et al (2008) the reported Kd values for iodine are similar For Vault 2 Kaplan et al (2008) found 125I to have a Kd of 894 mLg under oxidizing conditions and 715 mLg under reducing conditions These values are similar to the Kd values of 766 mLg and 725 mLg observed under oxidizing and reducing conditions respectively in this work These findings appear to confirm the previously accepted Kd values of 0-10 mLg depending on the cementitious formulation
72 Suggested Future Work The above data demonstrate several areas that require further examination The
increasing Tc Kd values over time dataset suggest that steady state had not been achieved It would be beneficial to determine the amount of time required to reach steady state and allow determination of a more accurate Kd value (an assumption of the Kd construct is that it be measured at steady state) Also kinetic studies of both Tc and I are needed to better understand their respective interactions with the different cementitious formulations As for the I additional
SRNL-STI-2009-00636 Revision 0
49
tests should be performed to test the hypothesis that iodine may in part exist as iodate which may initially sorb to the saltstone then undergo reduction to iodine or iodide and then desorbs causing a decrease in Kd
A final area of future work is to examine the possible causes for the similar behavior of each cementitious formulation despite the different slag content This discrepancy is not only observed in the above experiments but also in Kaplan et al (2008) which is illustrated in Table 31 and by recent work in measurements of saltstone reduction capacity (Roberts and Kaplan 2009) The reduction capacity (units in milli-equivalentsg solid) equivalents of the Aged Cement with no slag is 855 plusmn 101 and adding 10 slag gives a reducing equivalent of 2398 plusmn 311 However increasing the slag content to 23 causes the reducing capacity to increase to 8218 plusmn 81 which is almost equivalent to the 8324 plusmn 49 of the 100 slag Understanding the chemistry behind the reducing capacity of each cementitious formulation will help to define what reactions are important for controlling radionuclide release from the saltstone
80 References Allard B L Eliasson S Hoglund and K Andersson 1984 ldquoSorption of Cs I and actinides in
concrete systemsrdquo SKB Technical Report SKBKBS TR-84-15 DKB Stockholm Sweden
Denham M D I Kaplan and C Yeager2009 ldquoGroundwater radioiodine Prevalence biogeochemistry and potential remedial approachesrdquo SRNL-STI-2009-00463 Savannah River National Laboratory Aiken SC
Dixon K L M A Phifer and J R Harbour 2008 ldquoFY09 PACA Maintenance Program Additional Saltstone Property Testingrdquo SRNL-L3100-2009-00019 Rev0 Savannah River National Laboratory Aiken SC
Fukui M Fujikawa Y and Satta N 1996 ldquoFactors affecting interaction of radioiodide and iodate species with soilrdquo Journal of Environmental Radioactivity 31 199-216
Hoglund S L Eliasson B Allard K Andersson and B Torstenfelt 1985 ldquoSorption of some fission products and actinides in concrete systemsrdquo Mat Res Soc Symp Proc 50 683-690
Kaplan D I 2007 Geochemical Data Package for Performance Assessment Calculations Related to the Savannah River Site WSRC-TR-2006-00004 Rev 1 Washington Savannah River Company Aiken SC
Kaplan D I and Coates J 2007 ldquoPartitioning of Dissolved Radionuclides to Concrete under Scenarios Appropriate for Tank Closure Performance Assessmentsrdquo WSRC-STI-2007-00640 Rev 0 Washington Savannah River Company Aiken SC 29808
Kaplan D I Roberts K Coates J Siegfried M Serkiz S 2008 ldquoSaltstone and concrete interactions with radionuclides Sorption (Kd) desorption and reduction capacity measurementsrdquo SRNS-STI-2008-00045 Savannah River National Laboratory Aiken SC 2008
SRNL-STI-2009-00636 Revision 0
50
Neck V and Kim J I 2001 ldquoSolubility and hydrolysis of tetravalent actinidesrdquo Radiochim Acta 89 1
Powell B A Fjeld R A Coates J T Kaplan D I Serkiz S M 2002 ldquoPlutonium Oxidation State Geochemistry in the SRS Subsurface Environmentrdquo WSRC-TR-2003-00035 Westinghouse Savannah River Company US DOE Savannah River Site Aiken SC
Roberts K A and D I Kaplan 2009 Reduction Capacity of Saltstone and Saltstone Componentsrdquo SRNL-STI-2009-00637 Rev0 Savannah River National Laboratory Aiken SC
Schwehr K A Santschi P H D I Kaplan C M Yeager and R Brinkmeyer 2009 ldquoOrgano-iodine formation in soils and aquifer sediments at ambient concentrationsrdquo Environ Sci Technol 437258-7264
Yoshida S Muramatsu Y and Uchida S 1992 ldquoStudies on the sorption of I-(iodide) and IO3-
(iodate) onto andosolsrdquo Water Air and Soil Pollution 63 321-329
SRNL-STI-2009-00636 Revision 0
51
90 Appendix A Data Tables of Radionuclide Sorption to Saltstone under Oxidizing Conditions
The following tables represent data collected for the no solids controls each saltstone and testing of radionuclide sorption to the vial walls The no solids controls tables include the concentration (ppb) of the radionuclide spiked into the sample along with the concentration of the radionuclide (ppb) measured in the aqueous phase after the given equilibration time The pH at the time the sample was taken is also recorded along with the fraction of the radionuclide which stayed in the aqueous phase The tables for the cementitious formulation data include the data above along with the addition of a Kd value The tables of the data for the radionuclides sorbed to the vial walls include the initial concentration (ppb) of the spike the concentration (ppb) of the radionuclide that had sorbed to the vial wall during the experiment and the percentage of the total concentration this represents Important Notes
BDL- Below Detection Limit lt01 denotes no notable sorption occurred
91 Data Tables for No Solid Controls
Table 91 Plutonium no solids control after one day
A 9264165178 402285E‐05 1181 434238E‐06 9980817 B 9352537276 0000110618 1183 118276E‐05 3616813 C 9363541597 705331E‐05 118 753273E‐06 5401186 D 0993110568 BDL 12 NA NA E 0977247222 300794E‐05 1199 307797E‐05 1280331 F 0962441315 BDL 1198 NA NA G 4059128499 BDL 1186 NA NA H 4065161486 705198E‐05 1188 173473E‐05 2380003 I 4116819691 0000110748 1189 269014E‐05 1555864
Table 920 TR545- neptunium after four days
Sample ID
Initial Aq Conc (ppb)
Equil Aq Conc (ppb) pH
Fraction Aq Kd
A 92641652 NA 1188 NA NA B 93525373 00001935 1185 2069E‐05 2067199C 93635416 4119E‐05 1185 44E‐06 9247818D 09931106 BDL 1197 NA NA E 09772472 BDL 12 NA NA F 09624413 00066817 1206 00069424 562421G 40591285 00003289 1196 8103E‐05 5148274H 40651615 00025316 1196 00006228 6625737I 41168197 00001018 1194 2474E‐05 1692126
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Table 921 TR545- technetium after one day
Sample ID
Initial Aq Conc (ppb)
Equil Aq Conc (ppb) pH Fraction Aq Kd
A 9655146069 820460082 1181 0849764546 8998984 B 9356176321 7703053505 1183 0823312135 1051242 C 9114122586 7978297395 118 0875377451 7062663 D 1042349157 0853053814 12 0818395456 9099556 E 0983206046 0871198263 1199 0886079033 5196709 F 0905148405 0803451372 1198 0887646013 5098696 G 4950156706 4275082341 1186 0863625658 7213934 H 4889067068 4173762594 1188 0853693053 7687519 I 4854463762 4147024058 1189 0854270268 7771045
A 1048950046 0002141023 1149 0000204111 2112281 B 1039943573 0001770549 1157 0000170254 2460487 C 1084651695 0001127533 1153 0000103953 4014918 D 1088686867 0001201087 1172 0001103244 3564524 E 1119673887 0000783288 1177 0000699568 5709897 F 1045722787 0000914861 1181 000087486 4495324 G 5387981131 0001444832 1169 0000268158 1494715 H 5412748988 0001143483 1169 0000211257 1965749 I 5373948758 00010003 1164 0000186139 2280472
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Table 926 TR547- plutonium after four days
Sample ID
Initial Aq Conc (ppb)
Equil Aq Conc (ppb) pH
Fraction Aq Kd
A 104895 NA 116 NA NA B 10399436 0001828 1165 00001758 2383132C 10846517 00010788 1164 9946E‐05 4196159D 10886869 00009131 1184 00008388 4689778E 11196739 00010624 1189 00009488 4208928F 10457228 00007967 1191 00007619 516258G 53879811 00007915 1173 00001469 2728993H 5412749 00008355 1175 00001544 2690641I 53739488 00006103 1174 00001136 3737892
Table 927 TR547- neptunium after one day
Sample ID
Initial Aq Conc (ppb)
Equil Aq Conc (ppb) pH Fraction Aq Kd
A 9589772032 0000454463 1149 473903E‐05 9116335 B 9293228768 0000260081 1157 27986E‐05 1499475 C 1008725504 0000302018 1153 299405E‐05 1397125 D 0952173007 000019177 1172 0000201403 1954603 E 0992224074 BDL NA NA F 0967815522 402137E‐05 1181 41551E‐05 9474699 G 4068405786 0000222282 1169 546361E‐05 7336986 H 409543171 0000531619 1169 0000129808 3199152 I 4017406611 0000410123 1164 0000102086 4157807
Table 928 TR547- neptunium after four days
Sample ID
Initial Aq Conc (ppb)
Equil Aq Conc (ppb) pH Fraction Aq Kd
A 9589772 NA 116 NA NA B 92932288 00002145 1165 2308E‐05 1818463C 10087255 00001628 1164 1614E‐05 2591215D 0952173 BDL 1184 NA NA E 09922241 BDL NA NA F 09678155 5107E‐05 1191 5277E‐05 7460375G 40684058 00001336 1173 3284E‐05 1220544H 40954317 8151E‐05 1175 199E‐05 2086795I 40174066 00001322 1174 3292E‐05 1289605
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Table 929 TR547- technetium after one day
Sample ID
Initial Aq Conc (ppb)
Equil Aq Conc (ppb) pH Fraction Aq Kd
A 9466799266 8233850788 1149 0869760788 8220086 B 9439556236 817653394 1157 0866198975 8165745 C 9383493063 8086024379 1153 0861728604 8430884 D 1061939876 0919992065 1172 0866331594 6241759 E 0991827343 0836511397 1177 0843404251 7590958 F 0971981155 0839862696 1181 0864073024 6354378 G 4883337077 414858839 1169 0849539633 7903986 H 4691440077 3996173112 1169 0851800949 8038249 I 486993937 4291285586 1164 0881178442 6558707
Table 930 TR547- technetium after four days
Sample ID
Initial Aq Conc (ppb)
Equil Aq Conc (ppb) pH
Fraction Aq Kd
A 94667993 NA 116 NA NA B 94395562 85812109 1165 09090693 5885474C 93834931 84622373 1164 09018217 6279204D 10619399 09580683 1184 09021869 4435663E 09918273 08881507 1189 08954691 4835506F 09719812 09036489 1191 0929698 3138862G 48833371 4490415 1173 09195382 4312104H 46914401 42054182 1175 08964024 5612948I 48699394 43843193 1174 09002821 5536503
Table 931 TR547- iodine after one day
Sample ID
Initial Aq Conc (ppb)
Equil Aq Conc (ppb) pH Fraction Aq Kd
A 9944920441 8813152965 1149 0886196427 738241 B 9956006121 8747156303 1157 0878580848 8007767 C 9822152291 8664470934 1153 0882135674 7988892 D 1002391846 9333490632 1172 0931121963 3368509 E 9918273427 6625075445 1177 0667966607 1551748 F 9918175056 8931364957 1181 0900504872 4773862 G 5166570628 4445386532 1169 0860413387 7961604 H 4847821413 410447427 1169 084666367 8664303 I 4850381381 4266693706 1164 0879661489 6413801
100 Appendix B Data Tables of Radionuclide Sorption to Saltstone Under Reducing Conditions
The following tables represent data collected for the no solids controls each cementitious solid and testing of radionuclide sorption to the vial walls The no solids controls tables include the concentration (ppb) of the radionuclide spiked into the sample along with the concentration of the radionuclide (ppb) measured in the aqueous phase after the given equilibration time The pH at the time the sample was taken is also recorded along with the fraction of the radionuclide which stayed in the aqueous phase The tables for the cementitious solidsrsquo data include the data above along with the addition of a Kd value The tables of the data for the radionuclides sorbed to the vial walls include the initial concentration (ppb) of the spike the concentration (ppb) of the radionuclide that had sorbed to the vial wall during the experiment and the percentage of the total concentration this represents Important Notes
BDL= Below Detection Limit lt01 denotes no notable sorption occurred
101 Data Tables for No-Solid Controls
Table 101 Plutonium no solids control after one day
A 9405892 0007019 111 0000746258 5681206 B 9602498 0003294 1117 0000342992 123554 C 9630619 0002936 1114 0000304893 1396318 D 4945396 0001795 113 0000363011 1171688 E 4964945 0001373 1131 0000276484 1493015 F 4441601 0001516 113 0000341219 1389674 G 1079602 0001109 1142 0001027508 4215519 H 1031512 0000883 1143 0000855983 4820576 I 0939294 0000978 1143 0001040992 4550255
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Table 1011 Vault 2- neptunium after one day
Sample ID Initial Aq Conc (ppb)
Equil Aq Conc (ppb) pH Fraction Aq
A 9425042625 0001709054 1105 0000181331 B 9611386476 0001184125 1110 00001232 C 9579553607 0001155517 1104 0000120623 D 4974000414 0000672325 1125 0000135168 E 4916731623 0000675371 1128 0000137362 F 4373142817 0000570681 1120 0000130497 G 0943366414 0000389738 1129 0000413136 H 1011745587 0000565648 1132 0000559081 I 0865252712 0000379545 1133 0000438653
A 8849444124 0000306309 1150 346133E‐05 1289533 B 8447823057 0000150131 1155 177715E‐05 2711019 C 8590597085 0000199185 1153 231864E‐05 2044057 D 4491250244 517162E‐05 1156 115149E‐05 4020064 E 4391894479 204591E‐05 1158 465838E‐06 9846089 F 4210703646 204376E‐05 1158 485374E‐06 9816203 G 086381524 522216E‐06 1160 604546E‐06 7577764 H 0870501884 BDL 1160 NA NA I 0861953838 BDL 1162 NA NA
SRNL-STI-2009-00636 Revision 0
79
Table 1036 Aged cement- neptunium after four days
Sample ID
Initial Aq Conc (ppb)
Equil Aq Conc (ppb) pH Fraction Aq Kd
A 8849444 0000131 1145 148418E‐05 3007445B 8447823 0000111 1146 131529E‐05 3662996C 8590597 656E‐05 1146 76328E‐06 6209405D 449125 BDL 1155 NA NA E 4391894 BDL 1156 NA NA F 4210704 BDL 1155 NA NA G 0863815 BDL 1165 NA NA H 0870502 BDL 1162 NA NA I 0861954 BDL 1164 NA NA
Table 1037 Aged cement- technetium after one day
Sample ID
Initial Aq Conc (ppb)
Equil Aq Conc (ppb) pH Fraction Aq Kd
A 8426518355 833290075 1150 098889012 0476492 B 8638001423 7823321167 1155 0905686487 4413063 C 9323317745 925927516 1153 0993130923 0294664 D 442651005 4300859603 1156 0971614106 1242837 E 4426849405 4336992073 1158 0979701742 0855315 F 3929483125 3938204338 1158 100221943 lt01 G 0817864386 081693181 1160 0998859743 0049487 H 0878958929 0792412508 1160 0901535306 4510199 I 0772205665 0871436364 1162 1128502941 lt01
Table 1038 Aged cement- technetium after four days
110 Appendix C Dixon et al (2009) FY09 PACA Maintenance Program Additional Saltstone Property Testing SRNL L3100-2009-00019 Rev 0
SRNL-STI-2009-00636 Revision 0
83
SRNL L3100-2009-00019 Rev 0
December 16 2008
Keywords Performance Permeability Modulus
L B Romanowski
Waste Determinations From K L Dixon M A Phifer and J R Harbour
FY09 PACA Maintenance Program Additional Saltstone Property Testing
BACKGROUND
Additional tests have been identified for measurement of important hydraulic and physical properties of saltstone The initial phase of this work [1] was completed last year and the results were detailed in an internal report [2] The proposed testing for FY09 includes measurement of saturated hydraulic conductivity porosity bulk density particle density water retention and Youngrsquos modulus of simulated Saltstone grouts For completeness the bleed volumes and gel times for each mix will also be measured
The testing will be based on a projected salt solution composition for the ARPMCU stream that will be fed to the Saltstone Production Facility over the next few years The scope for FY09 will include testing to determine the impact of (1) admixtures (2) organics (3) wcm ratio (4) aluminate concentration and (5) temperature of curing on the hydraulic properties of saltstone mixes Samples of selected batches prepared as part of this task will be provided to Dan Kaplan for measurement of Kd through leaching tests The eleven mixes that will be batched and tested are detailed in Table 1
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Table 1 The Eleven Mixes That will be Batched and Tested
BFS is Blast Furnace Slag FA is Fly Ash and PC is Portland Cement
TEST DETAILS
Test 1 Control (Mix 1)
A control mix will be based on the baseline mix modified by exclusion of the Class F fly ash Consequently the cementitious materials premix will be a mixture of 90 blast furnace slag and 10 portland cement The degree of reaction will be much greater than with the normal premix and therefore should result in a lower porosity and a lower permeability This bounding test at 060 wcm ratio is expected to yield a hydraulic conductivity at or below the detection limit for the Mactec permeameter measurement system Therefore this test should demonstrate the lowest level of detection of the Mactec system as well as show a resolvable difference between measurements of the control mix and the control mix with the normal premix composition
Test 2 ndashImpact of Admixtures (Mixes 2 and 3)
Recent saltstone batches have required both a set retarder (Daratard 17) and an antifoam agent (Q2) for processing of the saltstone Therefore the baseline mix will be prepared with and without nominal levels of these two admixtures to determine whether these admixtures appreciably affect the hydraulic and physical properties of saltstone at these nominal concentrations
Test 3ndashImpact of Organics (Mixes 2 and 4)
The solvent extraction process is expected to result in some carryover of organics [3]
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Consequently a test will be performed on the impact of Caustic Side Solvent Extraction (CSSX) organics at 100 microliters per 1600 gram batch The CSSX solvent consists of 075 M 1-(2233-tetrafluoropropoxy)-3-(4-sec-butylphenoxy)-2-propanol (Cs-7SB) and 0003 M tri-n-octylamine (TOA) in an Isoparreg L diluent Test 4ndashImpact of Combination of Admixtures and Organics (Mixes 2 5 10 and 11)
This test will determine the impact of a combination of admixtures (Test 2) and organics (Test 3) together in the mix vs the baseline case without admixtures and organics
Test 5ndash Impact of wcm Ratio (Mixes 2 6 and 7)
It is well known that decreasing the wcm ratio in a mix will improve permeability in normal portland cement water mixes This test will measure the variation in permeability for the case of the MCU salt solution at three different wcm ratios The initial selection of wcm ratios is 055 060 and 065 However if the mix at an as-batched 065 wcm ratio has significant bleed water and the resulting actual wcm ratio is close to 060 then the three ratios will be adjusted to provide a more evenly spaced set of values However the baseline mix at 060 will be included as one of the three mixes
Test 6 ndash Impact of Aluminate Concentration (Mixes 8 9 and 10)
The DWPF has modified its process flowsheet to include a caustic washing of HLW sludge to remove some of the aluminum from the HLW prior to vitrification The resulting aluminate stream will then be blended with tank 50 material and fed to the SPF This increased aluminate concentration in the salt solution has significant impact on heat of hydration and set times and consequently it is likely that it will also impact permeability Therefore a set of three samples will be made at wcm ratios of 055 060 and 065 (as in Test 3) with a higher level of aluminate (028 M) for testing
Test 7 ndash Impact of Increased Curing Temperature (Mix 11)
In an ongoing task there is evidence that Youngrsquos modulus (a performance indicator) [4] is reduced by increasing the curing temperature of the mix Since the vault temperature increases during curing as a result of the exothermic hydration reactions one of the baseline mixes with a combination of admixtures and organics will be cured at 60
o
C rather than the normal 22
o
C to determine the impact of curing temperature on the permeability
SRNL-STI-2009-00636 Revision 0
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SCHEDULE
The schedule for the task of batching and testing of the samples is provided in Table 2 This schedule is based on the fact that the cementitious materials will be available for the testing as needed
Table 2 Additional Saltstone Hydraulic and Physical Property Tests
Item Schedule Start Work 12108 Test Plan Complete 1509 Preparation of 1st set of Samples Complete 11909 90-Day Cure Period for 1st set of Samples Complete 42009
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SRNL-STI-2009-00636 Revision 0
SRNL-STI-2009-00636 Revision 0
DISTRIBUTION Savannah River Site
A B Barnes 999-W Rm 336 H H Burns 999-W Rm 381 B T Butcher 773-43A Rm 212 A D Cozzi 999-W Rm 337 D A Crowley 773-43A Rm 216 M E Denham 773-42A Rm 218 J C Griffin 773-A Rm A-231 J R Harbour 999-W Rm 348 C A Langton 773-43A Rm 219 M H Layton 705-1C Rm 14 D I Kaplan (3 copies) 773-43A Rm 215 S L Marra 773A Rm A-230 A M Murray 773-A Rm 229 K A Roberts 773-43A Rm 225 T C Robinson 705-1C Rm 13 L B Romanowski 705-1C Rm 19 K H Rosenberger 705-1C Rm 16 F M Smith 705-1C Rm 24 RPA File (2 copies) 773-43A Rm 213
Clemson University Environmental Engineering and Earth Sciences 372 Computer Court LG Rich Environmental Laboratory Anderson SC 29625
Table 934 Aged cement- plutonium after four days 63
Table 935 Aged cement- neptunium after one day 63
Table 936 Aged cement- neptunium after four days 63
Table 937 Aged cement- technetium after one day 64
Table 938 Aged cement- technetium after four days 64
Table 939 Aged cement- iodine after one day 64
Table 940 Aged cement- iodine after four days 65
Table 941 Plutonium sorbed to vial wall in no solids control 65
Table 942 Neptunium sorbed to vial wall in no solids control 65
Table 101 Plutonium no solids control after one day 66
Table 102 Plutonium no solids control after four days 67
Table 103 Neptunium no solids control after one day 67
Table 104 Neptunium no solids control after four days 67
Table 105 Technetium no solids control after one day 67
SRNL-STI-2009-00636 Revision 0
ix
Table 106 Technetium no solids control after four days 68
Table 107 Iodine no solids control after one day 68
Table 108 Iodine no solids control after four days 68
Table 109 Vault 2- plutonium after one day 69
Table 1010 Vault 2- plutonium after four days 69
Table 1011 Vault 2- neptunium after one day 70
Table 1012 Vault 2- neptunium after four days 70
Table 1013 Vault 2- technetium after one day 70
Table 1014 Vault 2- technetium after four days 71
Table 1015 Vault 2- iodine after one day 71
Table 1016 Vault 2- iodine after four days 71
Table 1017 TR545- plutonium after one day 72
Table 1018 TR545- plutonium after four days 72
Table 1019 TR545- neptunium after one day 73
Table 1020 TR545- neptunium after four days 73
Table 1021 TR545- technetium after one day 73
Table 1022 TR545- technetium after four days 74
Table 1023 TR545- iodine after one day 74
Table 1024 TR545- iodine after four days 74
Table 1025 TR547- plutonium after one day 75
Table 1026 TR547- plutonium after four days 75
Table 1027 TR547- neptunium after one day 76
Table 1028 TR547- neptunium after four days 76
Table 1029 TR547- technetium after one day 76
Table 1030 TR547- technetium after four days 77
Table 1031 TR547- iodine after one day 77
Table 1032 TR547- iodine after four days 77
Table 1033 Aged cement- plutonium after one day 78
Table 1034 Aged cement- plutonium after four days 78
SRNL-STI-2009-00636 Revision 0
x
Table 1035 Aged cement- neptunium after one day 78
Table 1036 Aged cement- neptunium after four days 79
Table 1037 Aged cement- technetium after one day 79
Table 1038 Aged cement- technetium after four days 79
Table 1039 Aged cement- iodine after one day 80
Table 1040 Aged cement- iodine after four days 80
Table 1041 Plutonium sorbed to vial wall in no solids control 80
Table 1042 Neptunium sorbed to vial wall in no solids control 81
Table 1043 Technetium sorbed to vial wall in no solids control 81
SRNL-STI-2009-00636 Revision 0
xi
LIST OF FIGURES
Figure 31 Screen capture of a typical 242Pu calibration curve using Thermo PlasmaLab software to control the data collection and analysis R2=0999872 Intercept Conc (Detection Limit) = 0000044 ppb 16
Figure 32 Screen capture of a typical 237Np calibration curve using Thermo PlasmaLab software to control the data collection and analysis R2=0999981 Intercept Conc (Detection Limit) = 0000026 ppb 17
Figure 33 Screen capture of a typical 99Tc calibration curve using Thermo PlasmaLab software to control the data collection and analysis R2=0999984 Intercept Conc (Detection Limit) = 0000013 ppb 18
Figure 34 Screen capture of a typical 127I calibration curve using Thermo PlasmaLab software to control the data collection and analysis R2=0999991 Intercept Conc (Detection Limit) = 024 ppb 19
Figure 41 Plutonium Kd Values under Oxidizing Conditions Plutonium Kd values for various saltstone formulations measured after one-day equilibration (1d) and four-day equilibration (4d under oxidizing conditions Total plutonium concentrations in each system were 1 ppb 5 ppb and 10 ppb Sample prepared in triplicate and error bars represent standard deviation of samples except as follows value for dataset TR547-4d 10 ppb is reported based on duplicate samples 25
Figure 42 Plutonium solubility for various saltstone formulations measured after one-day equilibration (1d) and four-day equilibration (4d) under oxidizing conditions Total plutonium concentrations in each system were 1 ppb 5 ppb and 10 ppb as noted Samples prepared in triplicate and an average of all samples (9) was used to determine average solubility The error bars represent standard deviation of samples 25
Figure 43 Neptunium Kd values under oxidizing conditions Neptunium Kd values for various saltstone formulations measured after one-day equilibration (1d) and four-day equilibration (4d) under oxidizing conditions Total plutonium concentrations in each system were 1 ppb 5 ppb and 10 ppb as noted Samples prepared in triplicate and error bars represent standard deviation of samples except as follows value for datasets TR545-1d 1ppb TR545-4d 1 ppb TR547 4d 1 ppb TR545-4d 10 ppb TR547-1d 1ppb TR547-4d 10 ppb are reported based on a single sample and for dataset TR545-1d 5ppb is reported based on duplicate samples Kd values limited to gt106 were at instrumental background 26
Figure 44 Average solubility of Np under oxidizing conditions Neptunium solubility for various saltstone formulations measured after one-day equilibration (1d) and four-day equilibration (4d) under oxidizing conditions Total Np concentrations in each system were 1 ppb 5 ppb and 10 ppb Samples prepared in triplicate and an average of all samples (9) was used to determine average solubility except as follows TR545-1d is based on 6 samples TR545- 4d on 5 samples TR547-1d on 7 samples and TR547- 4d on 5 samples The error bars represent standard deviation 27
Figure 45 Technetium Kd values under oxidizing conditions Tc Kd values for various saltstone formulations measured after one-day equilibration (1d) and four-day equilibration (4d) under oxidizing conditions Total Tc concentrations in each system were 1 ppb 5 ppb and 10 ppb as noted above Samples were prepared in triplicate and the error bars represent standard deviation
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xii
of samples except as follows data sets for Vault 2-1d 1ppb were duplicates and TR547- 4d 10 ppb is based on a single dataset 27
Figure 46 Iodine Kd Values under Oxidizing Conditions Iodine Kd values for various cementitious formulations measured after one-day equilibration (1d) and four-day equilibration (4d) under oxidizing conditions Total iodine concentrations in the systems were 100ppb 500 ppb and 1000 ppb as noted above Samples were prepared in triplicate and the error bars represent standard deviation of samples except as follows duplicates were used for dataset TR545- 1d 100ppb 28
Figure 47 Plutonium Neptunium and Technetium Aqueous Fractions Fraction of Pu Np and Tc remaining in the aqueous phase for the No Solids controls after a one-day equilibration (1d) and four-day equilibration (4d) under oxidizing conditions The total concentration for each radionuclide 10 ppb as noted above Samples were prepared in triplicate and the error bars represent the standard deviation of the samples 29
Figure 48 Iodine Aqueous Fraction Iodine aqueous fraction for the no-solids controls after a one-day equilibration (1d) and four-day equilibration (4d) under oxidizing conditions The total concentration of iodine was 1000 ppb as noted above Samples were prepared in triplicate and the error bars represent the standard deviation of the samples 29
Figure 49 Percent Pu and Np sorbed to vial walls of the no solids controls after the aqueous phases were discarded and the vials were washed Both the 10 ppb (blueleft) and 1 ppb (redright)) datasets were prepared in triplicate and the error bars show the standard deviation 31
Figure 410 Percent Pu sorbed to vial walls after the solids and aqueous phases were removed and the vials were washed The graph illustrates one sample from each of the 1 ppb (redleft) 5 ppb (greenmiddle) and 10 ppb (blueright) systems Therefore no error bars are present 31
Figure 411 Percent Np sorbed to vial walls after the solids and aqueous phases were removed and the vials were washed The graph illustrates one sample from each of the 1 ppb (redleft) 5 ppb (greenmiddle) and 10 ppb (blueright) systems Therefore no error bars are present 32
Figure 412 Pu Kd Values under Reducing Conditions Plutonium Kd values for various cementitious formulations measured after one-day equilibration (1d) and four-day equilibration (4d) under reducing conditions Total plutonium concentrations in each system were 1ppb 5 ppb and 10 ppb Samples prepared in triplicate and error bars represent standard deviation 33
Figure 413 Average Solubility of Plutonium under Reducing Conditions Plutonium solubility for various cementitious formulations measured after one-day equilibration (1d) and four-day equilibration (4d) under reducing conditions Total plutonium concentrations in each system were 1ppb 5 ppb and 10 ppb as noted Samples prepared in triplicate and an average of all samples (9) was used to determine average solubility The error bars represent standard deviation of samples 33
Figure 414 Np Kd Values under Reducing Conditions Neptunium Kd values for various cementitious formulations measured after one-day equilibration (1d) and four-day equilibration (4d) under reducing conditions Total Np concentrations in each system were 1 ppb 5 ppb and 10 ppb Samples were prepared in triplicate and the error bars represent standard deviation Kd values limited to gt106 were at instrumental background 34
Figure 415 Average Solubility of Neptunium under Reducing Conditions Neptunium solubility for various cementitious formulations measured after one day equilibration (1d) and four day
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xiii
equilibration (4d) under reducing conditions Total plutonium concentrations in each system were 1ppb 5 ppb and 10 ppb Samples prepared in triplicate and an average of all samples (9) was used to determine average solubility The error bars represent standard deviation 35
Figure 416 Tc Kd Values under Reducing Conditions Tc Kd values for various cementitious formulations measured after one-day equilibration (1d) and four-day equilibration (4d) under reducing conditions Total Tc concentrations in each system were 1 ppb 5 ppb and 10 ppb Sample prepared in triplicate and error bars represent standard deviation except as follows TR547-1d 1 ppb is based on a single dataset and datasets Vault 2-1d 5 ppb Vault 2- 4d 1 ppb Aged Cement-1d 5 ppb and Aged Cement-4d 1 ppb are duplicates 36
Figure 417 Data from Figure 416 replotted on a reduced linear scale for easier viewing Each sample was prepared in triplicate except as follows TR547-1d 1 ppb is based on a single dataset Vault 2-1d 5 ppb Vault 2- 4d 1 ppb Aged Cement-1d 5 ppb and Aged Cement-4d 1 ppb are duplicate datasets 36
Figure 418 Iodine Kd Values under Reducing Conditions I Kd Values for various cementitious formulations measured after one day equilibration (1d) and four day equilibration (4d) under reducing conditions Total iodine concentrations in each system were 100 ppb 500 ppb and 1000 ppb as noted Sample prepared in triplicate and error bars represent standard deviation of samples except as follows Vault 2-4 d 100 ppb is a single dataset while the datasets for Vault 2-1 d 100 ppb 4 d 1000 ppb TR545-4 d 1000 ppb 100 ppb TR547-4 d 1000 ppb 500 ppb 100 ppb and Aged Cement- 4 d 1000 ppb and 100 ppb are all based on duplicates 38
Figure 419 Plutonium Neptunium and Technetium No-Solids Aqueous Fractions under Reducing Conditions Pu Np and Tc aqueous fractions of No Solids controls after a one-day equilibration (1d) and four-day equilibration (4 d) under reducing conditions Total concentration for each radionuclide was 1 ppb and 10 ppb Samples were prepared in triplicate and the error bars represent the standard deviation 39
Figure 420 Percent of Pu Np and Tc sorbed to the vial walls of the No Solids control samples under reducing conditions Each the 1 ppb and 10 ppb samples were prepared in triplicate and the error bars represent the standard deviations of triplicate samples 39
Figure 421 Iodine No-Solids Aqueous Fractions under Reducing Conditions I aqueous fractions of No-Solids controls after a one-day equilibration (1d) and four-day equilibration (4d) under reducing conditions The total concentration for each system was 100 ppb and 1000 ppb Samples were prepared in triplicate and the error bars represent the standard deviation 40
Figure 51 Comparison of Tc I Np and Pu sorption to Vault 2 solid under oxidizing and reducing conditions 42
Figure 52 Comparison of Tc I Np and Pu sorption to TR 545 solid under oxidizing and reducing conditions 43
Figure 53 Comparison of Tc I Np and Pu sorption to TR547 solid under oxidizing and reducing conditions 44
Figure 54 Comparison of Tc I Np and Pu sorption to Aged Cement under oxidizing and reducing conditions 45
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xiv
LIST OF ABBREVIATIONS
DDI water Distilled deionized water ICP-MS Inductively coupled plasma ndash mass spectrometer
Kd Distribution coefficient LSC liquid scintillation counting NOM Natural organic matter PA Performance Assessment ppb parts per billion ppq parts per quadrillion QAQC Quality AssuranceQuality Control SA Special Analyses SRNL Savannah River National Laboratory SRS Savannah River Site
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10 Introduction Performance Assessments (PA) are risk calculations designed to determine (1) the maximum
amount of radioactivity that can be safely buried in a subsurface facility and (2) the potential human risk associated with disposing of radioactive waste in a subsurface facility Special Analyses (SAs) are similar to PAs except that they are designed to address specific issues related to PAs such as a new discovery since the PA was issued Commonly parameters describing the extent that a radionuclide interacts with solids at the source vadose zone and aquifer influence the extent of calculated human risk The two parameters that the SRS use to represent radionuclidesolid interactions are Kd and apparent solubility values together these parameters are referred to as sorption values Sorption values vary with radionuclides groundwater chemistry and the type of solid phase (and for cementitious materials by the age of the material during the calculation) In this work Kd and apparent solubility values are reported for 99Tc 127I 237Np and 242Pu sorption to various cementitious formulations
20 Objectives
The objectives of this work were to 1 Determine the influence of cementitious formulation on technetium (Tc) iodine (I) neptunium
(Np) and plutonium (Pu) sorption under oxidizing conditions The specific formulations that were evaluated included 1) an aged cement recovered from a 30-year old outdoor concrete pad on the SRS 2) Vault 2 concrete 3) TR545 saltstone and 4) TR547 saltstone (additional details are presented in Section 30 Materials and Methods)
2 Measure Tc I Np and Pu sorption to the cementitious formulations under reducing conditions
30 Materials and Methods
31 Preparation of ICP-MS Standards Stock Solutions and Working Solutions
311 242Pu
A National Institute of Standards and Technology Standard Reference Material (NIST SRM 434H) was used to prepare a stock 242Pu solution by dilution in 2 Aristar Optima HNO3 All volume additions were monitored gravimetrically This working solution was then used to make a set of 001 005 1 2 5 10 parts per billion (ppb) standards by dilution using 2 HNO3 Again all volume additions were monitored gravimetrically These standards were used to calibrate the Thermo Scientific X Series 2 inductively coupled plasma ndash mass spectrometer (ICP-MS) for quantification of 242Pu A representative calibration curve for 242Pu is shown in Figure 31 The instrument performance was monitored using 209Bi 232Th and 238U as internal standards The recovery of each sample during analysis was corrected based on the internal standard recovery The internal standard recoveries remained within standard quality assurancequality control QAQC protocols for the instrument (between 80 and 120)
A 242Pu stock solution was prepared by dissolving 1mg of Pu(NO3)4 obtained as a Certified Reference Material from New Brunswick Laboratory (CRM 130) This CRM is gt999 242Pu by atom percent The CRM was dissolved in 20mL of 8M HNO3 (Aristar Optima Grade) Because no chemicals or heat have been introduced to manipulate the Pu oxidation state it can be assumed that Pu(IV) is the predominant oxidation state in this stock solution A working solution to be used in spiking 242Pu experiments was prepared by diluting 25 mL of the CRM stock solution with 100 mL 10 M Aristar Optima HNO3 The concentration of 242Pu in this stock solution was determined using ICP-MS calibrated using the NIST SRM standards The concentration of Pu in this stock solution was 1065 ppb The total Pu
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concentration was also determined using liquid scintillation counting using the isotopic ratios reported for CRM 130 These compared favorably with the ICP-MS results but are reported here as a rigorous standardization because the isotopic ratios of CRM 130 have not yet been certified
Figure 31 Screen capture of a typical 242Pu calibration curve using Thermo PlasmaLab software to control the data collection and analysis R2=0999872 Intercept Conc (Detection Limit) = 0000044 ppb
312 237Np
A National Institute of Standards and Technology Standard Reference Material (NIST SRM 4341) was used to prepare a stock 237Np solution by dilution in 2 Aristar Optima HNO3 All volume additions were monitored gravimetrically This working solution was then used to make a set of 001 005 1 2 5 10 ppb standards by dilution using 2 HNO3 Again all volume additions were monitored gravimetrically These standards were used to calibrate the Thermo Scientific X Series 2 ICP-MS for quantification of 237Np A representative calibration curve for 237Np is shown in Figure 32 The instrument performance was monitored using 209Bi 232Th and 238U as internal standards The recovery of each sample during analysis was corrected based on the internal standard recovery The internal standard recoveries remained within standard QAQC protocols for the instrument (between 80 and 120)
A compiled 237Np stock solution from the Environmental Engineering and Earth Science (EEampES) inventory (primarily purchased from Isotope Products Valencia CA) was evaporated to dryness then the residue was brought up in approximately 5mL 80 M HNO3 Then 10 M hydroxylamine hydrochloride (NH2OHHCl EMD Chemicals ACS grade) and water were added to achieve a 3M HNO303M NH2OHHCl solution This solution was purified by extraction chromatography using Eichrom TEVA resin packed in a Bio-Rad poly-prep column The 3M HNO303 M NH2OHHCl neptunium solution was loaded on a 2 mL column and washed with 3 column volumes of 3 M HNO3 The Np(IV) was eluted with 002 M HCl + 02 M HF The effluent was evaporated to dryness then redissolved in 10 M HNO3 Additional 10 M HNO3 was added to maintain a approximately 10 mL then the solution was evaporated to incipient dryness and redissolved in a 50 mL of 10 M HNO3 An aliquot of the stock solution was evaporated to dryness on a stainless steel planchet and counted on the EGampG Ortec Alpha Spectrometer (Octete PC Detectors) No other alpha energies besides 237Np were observed The approximate concentration was determined using liquid scintillation counting and little 233Pa was observed The fuming in HNO3 as performed at the end of the purification procedure will drive Np to the soluble pentavalent state This is the stable oxidation state of Np under the experimental conditions Therefore experiments performed here can be assumed to be initially Np(V) The exact Np
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concentration in this solution was determined using ICP-MS calibrated with a NIST standard as discussed in section 312 below
A 237Np working solution (Working Solution 1) was created by pipetting an aliquot of the 237Np stock solution into a 100 mL Nalgene Teflon bottle and diluting with 2 BDH Aristar Ultra HNO3 to give a working solution concentration of 820 ppb All volumes were monitored gravimetrically Analysis on the ICP-MS calibrated against NIST Standards as described below gave a concentration of 820 ppb in Working Solution 1
Figure 32 Screen capture of a typical 237Np calibration curve using Thermo PlasmaLab software to control the data collection and analysis R2=0999981 Intercept Conc (Detection Limit) = 0000026 ppb
313 99Tc
A 99Tc working solution was prepared by diluting a stock solution of 99Tc (from the EEampES inventory purchased from Isotope Products Valencia CA) in distilled-deionized water (DDI Resistivity gt18 MΩcm) The oxidation state of Tc was not measured However based on the aqueous concentration in the DDI water solution Tc(VII) is the expected oxidation state The reduced Tc(IV) oxidation state would not be soluble under these conditions The expected concentration of 950 ppb based on the dilution was verified using liquid scintillation counting The 99Tc working solution was used to make 001 005 1 2 5 and 10 ppb standards by dilution using 2 HNO3 These standards were used to calibrate the Thermo Scientific X Series 2 ICP-MS for quantification of 99Tc A screen shot of a representative calibration curve is shown in Figure 33 The instrument performance was monitored by interpolating between 89Y and 115In internal standards The recovery of each sample during analysis was corrected based on the internal standard recovery The internal standard recoveries remained within standard QAQC protocols for the instrument (between 80 and 120)
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Figure 33 Screen capture of a typical 99Tc calibration curve using Thermo PlasmaLab software to control the data collection and analysis R2=0999984 Intercept Conc (Detection Limit) = 0000013 ppb
314 127I
A 100 microgmL iodate (IO3-) stock solution from High Purity Standards (Charleston SC) was used
to make 1 5 10 50 and 100 ppb standards by dilution using the ldquotraprdquo solution (discussed in Section 32 below) These standards were used to calibrate the Thermo Scientific X Series 2 ICP-MS for quantification of 127I A screen shot of a representative calibration curve is shown in Figure 34 The use of a reducing basic trap solution for iodine analysis limits the number of available internal standards that can be used to monitor ICP-MS instrument performance during iodine analysis Experiments are underway to identify acceptable internal standards However the data presented in this work did not use any internal standards prior to rigorous testing and analysis of representative standards As with the analyses for all isotopes (Tc I Np and Pu) spiked QAQC samples were frequently analyzed throughout the analysis as a check on instrument performance While these values cannot be used to correct individual samples in the same manner that the internal standards can they can be used to ensure accurate measurements of each isotope In almost all cases QAQC standards were within 10 of the expected value Because the average internal standard recovery ranges between 80 and 120 for the ICP-MS the iodine QAQC standard appears to be acceptable However a significant amount of ongoing work is testing various internal standards to improve the accuracy of iodine analysis using ICP-MS In one experiment (discussed in detail below) the QAQC standards deviated by an average value of 195 This will be specifically discussed below
Because experiments were performed with 127I concentrations up to 1000 ppb the 100 microgmL (ppm) stock iodate solution from High Purity Standards was used as the working solution
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Figure 34 Screen capture of a typical 127I calibration curve using Thermo PlasmaLab software to control the data collection and analysis R2=0999991 Intercept Conc (Detection Limit) = 024 ppb
315 Cementitious Materials Selected for Experiments There were four cementitious materials selected for this sorption study The first referred to as Aged Cement is a 30 year old sample that does not contain any reducing slag The aggregate from the Vault 2 cement had its aggregate removed prior to conducted tests in an effort to make subsamples more uniform This was necessary because some of the aggregate were larger than the 05 g subsamples used in individual sorption tests The Vault 2 cementitious material contained 17 dry wt- reducing slag on a dry weight basis before the water was added to the mix (Table 31) The TR547 and TR545 saltstone formulations contain 45 dry wt- and 90 dry wt- reducing slag respectively
Table 31 Characteristics of saltstone formulations used in this work Kaplan et al (2008)
Sample Percent Reducing Slag (dry wt-) (c)
Percent Portland Cement
(dry wt-) (c)
Percent Fly Ash
(dry wt-) (c)
Percent Aggregatesand ( dry wt-) (c)
Reducing Equivalents
(microeqg)
Aged Cement 0 10 45 45 855 plusmn 101(a)
Vault 2 Cement 17 10 45 0 178(b)
TR547 45 10 45 0 607(b) TR545 90 10 0 0 681(b) Blast furnace slag 100 0 0 0 819(b) (a) Kaplan et al (2008) (b) Roberts and Kaplan (2009) (c) All percentages of saltstone formulations are reported on a dry weight percentage basis that is the weight of the ingredients before water was added (d) Based on Table 8 in Dixon et al (2008 SRNL-STI-2008-00421) which shows the following quantity (lbscu yd) for saltstone Vault 2 Mix 1 concrete formulation 201 cement (1271 wt-) 268 slag (1695 wt-) 447 silica fume (283 wt-) 1563 fly ash (989 wt-) 911 fine sand (5762 wt-) The large aggregate was removed before the sorption tests were conducted The large aggregate accounted for 75 wt- of the original field sample not the sample used in these test before water was added to the mix TR547 is referred to as the Baseline by Dixon et al (2008) and is described in more detail in Appendix C (Mix 2) by Dixon et al (2008) (Control-BFSPC) and 1 (Baseline)
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TR545 saltstone contains 90 reducing slag and it is Mix 1 in Dixon et al (2008) and is described as
ldquoA control mix will be based on the baseline mix modified by exclusion of the Class F fly ash Consequently the cementitious materials premix will be a mixture of 90 blast furnace slag and 10 Portland cement The degree of reaction will be much greater than with the normal premix and therefore should result in a lower porosity and a lower permeability This bounding test at 060 wcm ratio is expected to yield a hydraulic conductivity at or below the detection limit for the Mactec permeameter measurement system Therefore this test should demonstrate the lowest level of detection of the Mactec system as well as show a resolvable difference between measurements of the control mix and the control mix with the normal premix compositionrdquo
32 ICP-MS Detection Limits
The PlasmaLab software platform determines a detection limit for each isotope based upon the intercept concentration A new calibration curve was generated for each experimental run and curves were very similar Using representative calibrations curves the detection limits for each isotope were as listed in Table 32 Note the higher detection limit for 127I is primarily due to the higher background count rate observed on the instrument This is believed to be due to the minimum purity levels of chemicals required for the iodine ldquotraprdquo solution as discussed in Section 33 below Therefore experiments were run with initial iodate concentrations higher than Tc Np and Pu to maintain analytical sensitivity
Table 32 Detection limits for each isotope based on representative calibration curves generated in PlasmaLab software associated with the ICP-MS
33 Experimental Methods
The experimental methods used in this work followed closely those previously described for experiments examining radionuclide sorption to saltstone (Kaplan et al 2007 Kaplan et al 2008) Brief descriptions of each method are provided below
Preparation of Calcite Solution Using a hotstirring plate 10 L of distilled-deionized (DDI)
water was heated to 3-100C above room temperature Then 001 g CaCO3 (EM Science ACS grade) was added to the solution and the resulting suspension was mixed for 24 hours at the elevated temperature The solution was then vacuum filtered through a 045-microm filter to ensure no solid CaCO3 remained in solution
Preparation of 2 HNO3 Analysis of Tc Np and Pu on the ICP-MS required dilution in 2
HNO3 This was prepared by adding 28 mL of Aristar Optima HNO3 from a clean graduated cylinder (designated to 2 HNO3) into a 1 L volumetric flask (designated to 2 HNO3) partially filled with DDI water and then further diluted to volume
Preparation of Trap Solution for Iodine Analysis Analysis of I required the use of a reducing
basic solution that was capable of reducing iodate to iodine and holding the iodine in solution This minimized the loss of I during sample analysis A 1 L trap solution was prepared by weighing out 00500 g NaHSO3 (Fisher Scientific ACS Grade) on a calibrated Sartorous LA 230S scale and adding it to a 1L volumetric flask Then 40 mL of 25 ww tetramethylammonium hydroxide (Alfa Aesar electronic grade) and 10 mL CFA-C solution (Spectrasol Inc) were added to the volumetric flask via a calibrated 1000-5000 microL Eppendorf Research pipette The solution was then diluted to volume with DDI water
34 Experimental Protocol for Sorption Experiments under Aerobic Conditions
Falcon BlueMax 15mL polypropylene vials were labeled and weighed to within 0001 g on a calibrated Sartorious LA 230S scale The scale was then zeroed and 025 +- 001 g of a given solid were added to each tube and the weight was recorded to within 0001g
For each of the four solids three sets of triplicate samples were prepared The three sets of samples were used to allow for experiments to be run with varying concentrations of each isotope Target initial concentrations for 99Tc 237Np and 242Pu samples were 1 ppb 5 ppb and 10 ppb Target initial concentrations for the 127I samples were 100 ppb 500 ppb and 1000 ppb A set of no solids controls at initial concentrations of 1 ppb and 10 ppb for 99Tc 237Np and 242Pu and initial concentrations of 100 ppb and 1000 ppb 127I were also prepared by adding the calcite solution to pre-weighed pre-labeled centrifuge tubes as discussed above
The solids were equilibrated with the calcite solution before spiking with the radionuclides This was done by adding 10 plusmn 01 mL of calcite solution to each tube and recording the mass The samples were then placed on a Thermo Scientific shaker overnight After 24 hours the solutions were allowed to settle for 1 hour The pH was then measured and the samples were then centrifuged for 15 minutes at 8000 rpm to further separate the solids The aqueous phase was then decanted and 10 plusmn 01 mL of calcite solution was added to each tube The weight of the tube (labeled tube + solid + calcite solution) was measured to within 0001g During this washing process the pH was monitored and held steady throughout the process The pH ranged from 11-12 depending on the particular saltstone used During the experiments the exact pH for all samples at all equilibration times was measured and is reported in Appendix A and B
The resulting suspensions were then spiked with 127I 237Np 242Pu and 99Tc It is important to note that all four isotopes were added to the same vial Use of the ICP-MS to determine the concentration of each isotope allows for a single solution to contain all analytes of concern This allowed for a greater variability in the sample set and increased replicates as opposed to running individual sorption tests for each isotope For the systems with initial 99Tc 237Np and 242Pu concentrations of 10 ppb and initial 127I concentration of 100 ppb a 100 microL aliquot of each radionuclide working solution was added to the first three tubes for each solid The addition was made with the tube resting on a tared analytical balance so that the exact mass of each radionuclide solution added was recorded and the solution was gently swirled before the next radionuclide was added The 5 ppb 237Np 242Pu and 99Tc and 500 ppb 127I samples were prepared in the same manner but adding 50 microL of the respective spike solutions The final three tubes with initial 237Np 242Pu and 99Tc concentrations of 1 ppb and 100 ppb 127I were prepared by using 10 microL of the spike solutions for all four solids as well as a set of solid-free controls (No-Solids Controls) For clarity this experimental matrix is shown in Table 33 below
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Table 33 Experimental Matrix of Sorption Experiments under Aerobic Conditions
After spiking the radionuclides a precalculated amount of 10M NaOH was added to each sample
to counter the acidic radionuclide spike solutions and the pH of one of the triplicate samples was measured to ensure the proper pH range was reached The samples were then placed on and end-over-end shaker to mix at approximately 8 rpm After 24 hours the samples were removed from the shaker and the pH of each sample was measured using an Orion Ross semi-micro glass electrode calibrated against pH 4 7 and 10 buffers (Thermo) The samples were then shaken and a transfer pipette was used to transfer 35 mL of a homogenous suspension to a 5mL syringe The solution was then passed through a 100 nm nylon syringe filter The first 025-050 mL of filtrate was discarded and the remaining filtrate was collected in a clean polyethylene vial Then 10 mL of the filtrate was removed and diluted in 90 mL 2 HNO3 The mass of each phase was determined and recorded gravimetrically Then 10 mL of the remaining filtrate was transferred to a clean Falcon BlueMax 15mL vial and diluted with 90 mL of trap solution for 127I analysis Again the volume of each phase was monitored gravimetrically After the 24 hour sampling event the samples were put back on the shaker to mix for three additional days On day four the above sampling procedure was repeated
The 237Np 242Pu and 99Tc samples can be run on the Thermo Scientific ICP-MS using the standard setup and procedure which included a standard flow glass nebulizer and bulb spray chamber However for the 127I analysis the ICP-MS must be reconfigured to accommodate the basic reducing trap solution This is to alleviate problems with iodine signal stability over time frequently observed in ICP-MS analysis The reconfigured instrument uses an Elemental Science Microflow PFA-100 Teflon nebulizer with a flow rate of 100microLmin along with a sapphire torch and a Teflon spray chamber This configuration must be run with a low pump speed to prevent back pressure on the system Two 30 minute stability tests were performed using a 50 ppb iodate solution Each experiment consisted of 40 separate measurements After each experiment was completed the uncorrected mass counts were examined and found to stay steady over the sampling period The relative standard deviation ( RSD) over all samples for each experiment was 1866 and 1460 respectively This shows that there was no significant ldquomemoryrdquo or loss of the iodine signal over time and that the reconfigured instrument has a stable iodine signal over time However as will be discussed below some difficulty has been encountered in finding an adequate internal standard for iodine analysis
35 Experimental Protocol for Sorption Experiments under Anerobic Conditions In order to examine the effects of reducing conditions of sorption of each isotope to the various cementitious samples a series of sorption experiments were performed in an anaerobic glovebox under a 2 H2(g) 98 N2(g) atmosphere Based on the measured pH and EH of these systems as discussed below these systems were at the point of reducing water Therefore they are expected to represent a lower end of the possible range for reducing conditions expected in the porewater available within cementitious materials
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Preparation of Calcite for Reducing Conditions Approximately 35 L of DDI water was boiled for 45 minutes Argon was slowly bubbled through the water as it cooled Once it cooled to below 500C approximately 3 g of calcite was added This solution mixed overnight under a continuous Ar flow After 12 hours the solution was moved into an oxygen free glove bag for filtration as described in 3231 After filtration the calcite solution was moved into the glove box
Preparation of Working Solutions under Reducing Conditions The calcite and solid solutions
were prepared in the glove box using the previously mentioned procedure used under aerobic conditions The radionuclide working solutions were transferred to the glovebox and stirred open to the reducing atmosphere for at least three days The concentration of each isotope in the working solutions was measured to determine any change in the concentration due to evaporation while the solutions were equilibrating
The preparation and spiking of samples for sorption experiments was performed exactly as described for the oxidizing conditions except all sample handling was performed in the glovebox After the 1 day and 4 day equilibration the samples were filtered within the glovebox then transferred outside for dilution and ICP-MS analysis similar to the description provided about for the oxidizing conditions For these experiments only 4 mL of either 2 HNO3 or trap solution were used to dilute the filtrate instead of the 90 mL used above for experiments performed under oxidizing conditions
36 Examination of Sorption to Vial Walls for Solids and No Solids Controls
As will be discussed below the solid-free controls samples indicated significant loss of Np and Pu Once the one and four days samples were collected and run on the ICP-MS it was necessary to determine the degree each radionuclide was sorbing to the vial walls The remaining suspensions and controls were emptied into a waste container Then 5 mL of the calcite solution was added to each vial using a calibrated pipette The vials were sonicated for approximately one minute and then emptied into the waste container Another 5 mL of calcite solution was added for the second wash and then discarded into the waste container This procedure was expected to remove any soluble Pu from the system or Pu associated with colloidal particles After each vial was washed 10 mL of 2 HNO3 was added using a calibrated pipette The acid solution is expected to remove any Tc Np or Pu associated with the vial walls This procedure has been shown to complete mass balances of Pu in similar sorption experiments using Pu (Powell et al 2002) This process was performed for both the solid suspension and the no solids controls The samples were then run on the ICP-MS to determine the concentration of 99Tc 237Np and 242Pu sorbed to the vial walls
37 Data Analysis The solubilities of 242Pu and 237Np were calculated by using the formula
nuclide
nuclide
nuclideMSICP
sol Mg
gCC
)(10 6
microminus
minus
= (Equation 31)
Csol = observed nuclide solubility (molnuclidekgsolution) CICP-MS = aqueous concentration of nuclide from ICP-MS measurement (ppb micrognuclidekgsolution) Mnuclide = molecular mass of nuclide (gnuclidemolnuclide)
In order to determine the Kd values one first needs to determine the concentration on the solid by using
SRNL-STI-2009-00636 Revision 0
24
solid
calcitespikeaqspikecalcite
spikestock
solid m
mmCmmmC
C)(
)()(
+⎥⎥⎦
⎤
⎢⎢⎣
⎡minus
+
lowast
= (Equation 32)
Csolid = calculated solid phase concentration of the nuclide (ppb) Cstock = concentration of the nuclide stock solution (ppb) mspike = mass of nuclide spiked into the saltstone suspension (g) mcalcite = total mass of calcite solution used in the saltstone suspension (g) Caq = aqueous concentration of nuclide from ICP-MS measurement (ppb) msolid = mass of the saltstone used in the suspension (g)
The Kd can be calculated using the equation
aq
solidd C
CK = (Equation 33)
Kd = solid-water partitioning coefficient (gsolutiongsolid assuming density of 10 gmL traditional
unit of mLsolutiongsolid can be obtained) This Kd Equation (33) is numerically equivalent to the traditional Kd equation proposed in ASTM D-4646 which has been used in previous saltstone experiments (Kaplan et al 2007 Kaplan et al 2008)
40 Results and Discussion
41 Radionuclide Sorption to Cementitious Formulations under Oxidizing Conditions
Figure 41 shows Pu Kd values ranging from 104 to gt105 mLg Generally for each solid the Kd increases with increasing initial Pu concentrations typical behavior of systems where the aqueous concentrations of the radionuclides are solubility controlled This is not expected because the Kd expression indicates that the Kd value should remain constant with increasing total Pu concentrations It was noted that aqueous phase concentration of Pu remained relatively constant in all samples (see discussion below regarding Pu solubility) Therefore the sorption capacity of each solid phase for Pu has not been overcome For each of these solid phases it appears the solutions had reached equilibrium before the first samples were taken at 24 hours In each case the Kd values for the one day and four day are similar A trend between the solid phases is not discernible The aged cement with no reducing slag was expected to have the lowest Kd values but in actuality it has the highest Kd Also there is no correlation with the concentration of reducing slag The Vault 2 samples with 17 dry wt- reducing slag has a Kd similar to that of the TR547 (45 dry wt- slag) while the saltstone with the most slag TR545 (90 dry wt- slag) has the lowest Kd value Others have observed that Pu Kd values of cementitious materials are similar in the absence and presence of slag (Allard et al 1984 Hoaglund et al 1985)
It was observed that similar aqueous concentrations of Pu were observed regardless of the solid phase present Figure 42 shows the average aqueous phase concentrations measured after one day and four days for all solids As stated above triplicate samples were prepared for each solid phase and each initial concentration Therefore each of the reported solubility values in Figure 42 is an average of nine measurements Using the highest reported value with the expected maximum error (0018 ppb for solid TR545) the maximum expected aqueous concentration of Pu in the pore water associated with the
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saltstone formulations will be approximately 7 x 10-11 molL as calculated using Equation 31 This is on the same order as the solubility of Pu hydrous oxide solid phases (Neck and Kim 2001)
Figure 41 Plutonium Kd Values under Oxidizing Conditions Plutonium Kd values for various saltstone formulations measured after one-day equilibration (1d) and four-day equilibration (4d under oxidizing conditions Total plutonium concentrations in each system were 1 ppb 5 ppb and 10 ppb Sample prepared in triplicate and error bars represent standard deviation of samples except as follows value for dataset TR547-4d 10 ppb is reported based on duplicate samples
Figure 42 Plutonium solubility for various saltstone formulations measured after one-day equilibration (1d) and four-day equilibration (4d) under oxidizing conditions Total plutonium concentrations in each system were 1 ppb 5 ppb and 10 ppb as noted Samples prepared in triplicate and an average of all samples (9) was used to determine average solubility The error bars represent standard deviation of samples
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Overall the Kd values for Np range from 105 to gt106 with only a few outliers The most significant outlier is the 1 ppb solution in the TR545 sample after the four-day equilibration It drops two orders of magnitude while the 5 and 10 ppb solutions remain constant However this result is most likely an analytical artifact from working at the detection limits of the ICP-MS In the one-day equilibration samples only one of the triplicates S-2-E had detectable Np while in the four-day equilibration samples only S-2-F had detectable amounts present The graph also shows that with the exception of the 5 ppb sample in the aged cement Np sorption to TR545 (90 dry-wt- slag) and TR547 (45 dry wt- slag) have Kd values approximately one order of magnitude over the aged cement (no slag) and Vault 2 (17 dry wt- slag) samples
It was observed that similar aqueous concentrations of Np were observed regardless of the solid phase present Figure 44 shows the average aqueous phase concentrations measured after one day and four-day equilibrations for all solids As stated above triplicate samples were prepared for each solid phase and each initial concentration Therefore each of the reported solubility values in Figure 44 is an average of nine measurements of Np concentration unless stated otherwise Using the highest reported value with the expected maximum error (00026 ppb for solid TR545) the maximum expected aqueous concentration of Pu in the pore water associated with the saltstone formulations will be approximately 2 x 10-11 molL
Figure 43 Neptunium Kd values under oxidizing conditions Neptunium Kd values for various saltstone formulations measured after one-day equilibration (1d) and four-day equilibration (4d) under oxidizing conditions Total plutonium concentrations in each system were 1 ppb 5 ppb and 10 ppb as noted Samples prepared in triplicate and error bars represent standard deviation of samples except as follows value for datasets TR545-1d 1ppb TR545-4d 1 ppb TR547 4d 1 ppb TR545-4d 10 ppb TR547-1d 1ppb TR547-4d 10 ppb are reported based on a single sample and for dataset TR545-1d 5ppb is reported based on duplicate samples Kd values limited to gt106 were at instrumental background
The Kd values for Tc are significantly lower than that of Pu or Np As a whole the values are
comparable The values for the one-day and four-day equilibrations solutions in the Vault 2 (17 dry wt- slag) and TR545 (90 dry wt- slag) remained constant within reasonable error with just a slight increase from the one-day to four-day equilibration However the Aged Cement (no slag) and TR547 (45 dry wt- slag) showed a noticeable decrease from day one to day four (Figure 45)
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Figure 44 Average solubility of Np under oxidizing conditions Neptunium solubility for various saltstone formulations measured after one-day equilibration (1d) and four-day equilibration (4d) under oxidizing conditions Total Np concentrations in each system were 1 ppb 5 ppb and 10 ppb Samples prepared in triplicate and an average of all samples (9) was used to determine average solubility except as follows TR545-1d is based on 6 samples TR545- 4d on 5 samples TR547-1d on 7 samples and TR547- 4d on 5 samples The error bars represent standard deviation
Figure 45 Technetium Kd values under oxidizing conditions Tc Kd values for various saltstone formulations measured after one-day equilibration (1d) and four-day equilibration (4d) under oxidizing conditions Total Tc concentrations in each system were 1 ppb 5 ppb and 10 ppb as noted above Samples were prepared in triplicate and the error bars represent standard deviation of samples except as follows data sets for Vault 2-1d 1ppb were duplicates and TR547- 4d 10 ppb is based on a single dataset
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Similar to the Tc Kd values the 127I Kd values are much lower than those of Pu and Np The amount of reducing slag present in each of the solids does not appear to have a drastic effect on the 127I Kd values In fact the initial (one day) Aged Cement (0 slag) samples had a Kd almost two orders of magnitude above those with reducing slag The cause of this behavior is not known but it has been shown that iodate IO3
- the oxidized form of iodine sorbs more strongly than iodide I- to charged surfaces (Schwehr et al 2009 Yoshida et al 1992 Fukui et al 1996) It is possible that the slag is reducing the iodine to the I- form converting it to a species that is less likely to sorb to saltstone Additional work would be required to confirm the oxidation state of iodine when associated with saltstone
Figure 46 Iodine Kd Values under Oxidizing Conditions Iodine Kd values for various cementitious formulations measured after one-day equilibration (1d) and four-day equilibration (4d) under oxidizing conditions Total iodine concentrations in the systems were 100ppb 500 ppb and 1000 ppb as noted above Samples were prepared in triplicate and the error bars represent standard deviation of samples except as follows duplicates were used for dataset TR545- 1d 100ppb
42 Radionuclide Sorption to Vial Walls Under Oxidizing Conditions
Figure 47 shows the aqueous fractions found in the no-solids controls It provides a measure of the solubility of each radionuclide as well as examines the fraction of each radionuclide sorbed to the vial walls After one day only 25 of the Pu remained in solution and the concentration decreased even more after four days The loss of Pu from the aqueous phase may be due to sorption of Pu to the vial walls or precipitation of a Pu hydrous oxide solid (discussed with respect to Figure 49 below) Additional experiments would be required to examine the solubility of the Pu in high pH calcite saturated solutions
After one day about 80 of the Np remained in solution However the aqueous concentration in the initially 1-ppb solution was significantly reduced after four days Approximately 60 of the Np remained soluble in the initially 10-ppb solution Once again this drop could be due to sorption to the vial wall The Tc present after one day ranged from about 88 to about 95 and was virtually 100 after four days These values are consistent with internal standards used to monitor Tc detection performance on the ICP-MS Greater than 50 of the I remained in solution after the one-day and four-day equilibrations As shown in Figure 48 the standard deviation between the triplicate I control samples was
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quite large Additional control samples are required to understand the mechanism by which I is being lost from the aqueous phase in these samples
Figure 47 Plutonium Neptunium and Technetium Aqueous Fractions Fraction of Pu Np and Tc remaining in the aqueous phase for the No Solids controls after a one-day equilibration (1d) and four-day equilibration (4d) under oxidizing conditions The total concentration for each radionuclide 10 ppb as noted above Samples were prepared in triplicate and the error bars represent the standard deviation of the samples
Figure 48 Iodine Aqueous Fraction Iodine aqueous fraction for the no-solids controls after a one-day equilibration (1d) and four-day equilibration (4d) under oxidizing conditions The total concentration of iodine was 1000 ppb as noted above Samples were prepared in triplicate and the error bars represent the standard deviation of the samples
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As discussed above the loss of Np and Pu from the no-solids control (Figure 47) could be due to
precipitation of Np and Pu hydrous oxides or sorption to the vial walls To quantify the differences between these possible sinks the vials were washed as described in Section 36 The data in Figure 49 indicate that significant sorption of Np and Pu to the vial walls may occur When combining the mass of Np represented in Figure 47 and Figure 49 there is almost 100 mass recovery of the Np sorbed to the vial wall and the aqueous fraction measured Therefore no precipitation of Np is expected However because 100 recovery was not achieved for Pu a Pu hydrous oxide phase could be precipitating which was washed out of the vial during the cleaning procedure The data in Figure 47 represent the no-solids control samples where there was no solid phase present for Np or Pu to sorb to besides the vial walls However when a cementitious solid phase is present in the sample there will be competition between the vial walls and the cement for sorption of Np and Pu Based on the affinity of metals for metal oxide surfaces as opposed to the polypropylene surface and the much higher surface site density expected for the cementitious samples it is assumed that the cementitious samples will out-compete the vial walls for sorption sites This thesis was tested by taking one of the triplicate samples from each sorption experiment with a solid phase present removing the solid phase from the tubes and leaching any sorbed Np and Pu from the tubes with acid as described in Section 36 Figure 410 and Figure 411 show that although some of the Pu and Np sorbed to the vial walls of the samples this amount accounted for less than 2 in all samples Therefore sorption of Np and Pu to the vial walls does not appear to be a significant factor in experiments where the solid phase is present Note these results do not discount the possibility that Pu hydrous oxide precipitates were forming in both the no-solid control experiments and experiments with cement formulations present Based on the observation of a constant aqueous phase concentration of Pu regardless of the initial Pu concentration the presence of a solubility limiting Pu phase cannot be discounted based on these data Further experiments examining the solubility of Pu in high pH calcite saturated solutions are required
Like Pu Np shows little affinity for the vial walls in the presence of a solid phase In each case tested there was significantly less than 1 of the total Np sorbed to the vial walls This behavior is consistent with the ~100 mass balance on Np achieve in the solid-free controls The majority of Np remained soluble in the solid-free control experiments Therefore it is expected that sorption of Np to the vial walls was the primary reason for the loss of Np from the aqueous phase in the no-solids systems rather than precipitation of a Np solid phase similar to the process discussed for Pu above This assumption is based on the relative solubility of Np(V) as compared with Pu(IV)
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Figure 49 Percent Pu and Np sorbed to vial walls of the no solids controls after the aqueous phases were discarded and the vials were washed Both the 10 ppb and 1 ppb datasets were prepared in triplicate and the error bars show the standard deviation
Figure 410 Percent Pu sorbed to vial walls after the solids and aqueous phases were removed and the vials were washed The graph illustrates one sample from each of the 1 ppb 5 ppb and 10 ppb systems Therefore no error bars are present
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Figure 411 Percent Np sorbed to vial walls after the solids and aqueous phases were removed and the vials were washed The graph illustrates one sample from each of the 1 ppb 5 ppb and 10 ppb systems Therefore no error bars are present
43 Radionuclide Sorption to Cementitious Formulations under Reducing Conditions
Similar to the Pu Kd values under oxidizing conditions Pu Kd values ranged from 104 to gt105 under reducing conditions (Figure 412) Also similar to the results under oxidizing conditions the Kd increases with increasing initial Pu concentration Again this behavior is indicative of the aqueous phase concentration of Pu being controlled by solubility of Pu rather than by sorption In each case the samples appeared to reach steady state within 24 hours This equilibration is evident because the Kd values after one day and four days are very similar Also it appears that the amount of reducing slag does not make a significant difference in the Kd value In fact the TR547 solid consists of 45 reducing grout but produces approximately the same Kd values of the aged cement which does not have any reducing grout Each of these Kd values are higher than the TR545 which is 90 reducing grout These findings are in agreement with those conducted by Allard et al (1984) and Hoglund et al (1985) who reported that concrete containing reducing agents (slag similar to that used in our study) did not have greater Pu Kd values than those that did not contain slag
Similar aqueous concentrations of Pu were observed regardless of the solid phase present Figure 36 shows the average aqueous phase concentrations measured after one day and four days for all solids As stated above triplicate samples were prepared for each solid phase and each initial concentration Therefore each of the reported solubility values in Figure 412 is an average of up to nine measurements of the Pu aqueous concentrations Using the highest reported value with the expected maximum error (00045 ppb for solid Vault 2) the maximum expected aqueous concentration of Pu in the pore water associated with the cementitious formulations will be approximately 2 x 10-11 molL (calculated from Equation 31) This value is on the same order as the solubility of Pu hydrous oxide solid phases (Neck and Kim 2001) A best value would be 10-12 molL
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Figure 412 Pu Kd Values under Reducing Conditions Plutonium Kd values for various cementitious formulations measured after one-day equilibration (1d) and four-day equilibration (4d) under reducing conditions Total plutonium concentrations in each system were 1ppb 5 ppb and 10 ppb Samples prepared in triplicate and error bars represent standard deviation
Figure 413 Average Solubility of Plutonium under Reducing Conditions Plutonium solubility for various cementitious formulations measured after one-day equilibration (1d) and four-day equilibration (4d) under reducing conditions Total plutonium concentrations in each system were 1ppb 5 ppb and 10 ppb as noted Samples prepared in triplicate and an average of all samples (9) was used to determine average solubility The error bars represent standard deviation of samples
The Np Kd values reported in Figure 414 obtained under reducing conditions are very similar to
those obtained under oxidizing conditions In each case the samples appeared to reach steady state within 24 hours This equilibration is evident because the Kd values between the one-day and fourndashday equilibrations are similar As was the case with Pu the amount of slag present in each solid does not
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seem to have a significant effect on the Kd values Again the aged cement with no slag has as high a Kd as the TR545 with 90 reducing slag
Similar aqueous concentrations of Np were observed regardless of the solid phase present Figure 314 shows the average aqueous phase concentrations measured after one day and four days for all solids All Kd values were gt 105 mLg which is considerably larger than those reported by Kaplan and Coates (2007) who reported Np Kd values to 1300 to 1600 mLg This difference can be attributed to two important experimental differences 1) the experiment was designed to permit larger Kd values to be measured (eg solid to liquid ratios and spike concentrations) and more importantly 2) a more sensitive analytical method ICP-MS was used instead of conventional low-energy gamma spectroscopy or liquid scintillation counting (LSC) analysis As stated above triplicate samples were prepared for each solid phase and each initial concentration Therefore each of the reported solubility values in Figure 415 is an average of up to nine measurements Using the highest reported value (to provide the most conservative most soluble values) with the expected maximum error (00045 ppb for solid TR545) the maximum expected aqueous concentration of Np in the pore water associated with the cementitious formulations will be approximately 2 x 10-11 molL A best value taking into consideration the less-than values which are depicted in Figure 414 as running off the top of the plot would be 10-12 molL
Figure 414 Np Kd Values under Reducing Conditions Neptunium Kd values for various cementitious formulations measured after one-day equilibration (1d) and four-day equilibration (4d) under reducing conditions Total Np concentrations in each system were 1 ppb 5 ppb and 10 ppb Samples were prepared in triplicate and the error bars represent standard deviation Kd values limited to gt106 were at instrumental background
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Figure 415 Average Solubility of Neptunium under Reducing Conditions Neptunium solubility for various cementitious formulations measured after one day equilibration (1d) and four day equilibration (4d) under reducing conditions Total plutonium concentrations in each system were 1ppb 5 ppb and 10 ppb Samples prepared in triplicate and an average of all samples (9) was used to determine average solubility The error bars represent standard deviation
A plot of the Tc Kd values for each cementitious formulations under reducing conditions is shown
in Figure 416 (log y-axis) and Figure 417 (reduced scale linear y-axis) The Kd values for each of the initial Tc concentrations are relatively similar This behavior is consistent with the Kd expression However the increasing Kd values from the one-day to four-day day equilibrations for each solid indicate that steady state was not reached within one day and it is unclear whether steady state was reached after four days A possible explanation for this behavior is that Tc(VII) was being reduced to Tc(IV) in these systems due to the reducing conditions As Tc(VII) was reduced the Kd would increase based on the high affinity of Tc(IV) for solid phases This proposed mechanism was observed by Lukens et al (2005) using an SRS saltstone material similar but not identical to TR547 Using synchrotron X-ray absorption fine structure spectroscopy they observed over a 453 month period that Tc(VII) incorporated into SRS saltstone slowly converted to Tc(IV) and that the nearest neighbor was initially predominantly oxygen and eventually became predominantly sulfur (described as a Tc(IV) phase TcSx) Lacking in Lukens et al (2005) is quantification of the solubility of Tc This analysis still needs to be completed along with re-oxidation studies (ie what is the rate that reduced Tc reoxidizes under ambient natural saltstone conditions)
Unlike Np and Pu Tc Kd values changed with the amount of slag included in the formulation Tc Kd values noticeable increase as the amount of slag in the formulation increased TR547 (45 dry-wt- slag) Kd value is visibly higher than the Aged Cement and Vault 2 Kd values while the most reducing TR545 (90 dry wt- slag) Kd value is significantly higher than the others Following a similar trend the reduction capacity that is the total quantity of reductant in the saltstone on a mass basis (units of milli-equivalents of charge per g) of TR547 had slightly greater or equal reduction capacity to that of TR545 (Roberts and Kaplan 2009)
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Figure 416 Tc Kd Values under Reducing Conditions Tc Kd values for various cementitious formulations measured after one-day equilibration (1d) and four-day equilibration (4d) under reducing conditions Total Tc concentrations in each system were 1 ppb 5 ppb and 10 ppb Sample prepared in triplicate and error bars represent standard deviation except as follows TR547-1d 1 ppb is based on a single dataset and datasets Vault 2-1d 5 ppb Vault 2- 4d 1 ppb Aged Cement-1d 5 ppb and Aged Cement-4d 1 ppb are duplicates
Figure 417 Data from Figure 416 replotted on a reduced linear scale for easier viewing Each sample was prepared in triplicate except as follows TR547-1d 1 ppb is based on a single dataset Vault 2-1d 5 ppb Vault 2- 4d 1 ppb Aged Cement-1d 5 ppb and Aged Cement-4d 1 ppb are duplicate datasets
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The calculated Kd values for I sorption to cementitious samples under reducing conditions are shown in Figure 418 Before discussing the data it should be noted that spiked QAQC samples which were analyzed on the ICP-MS along with the samples used to generate the data in Figure 418 were off by an average of 195 with one outlier of approximately 40 This dataset did not include the use of internal standards as discussed in Section 31 above1 Due to a lack of an internal standard the iodine results presented in this report should be considered with a minimum error estimate of 20
The iodine Kd values under reducing conditions are different from those observed under oxidizing conditions Under oxidizing conditions it appears they are at a steady state by day one However under reducing conditions there is a noticeable difference between days one and four indicating steady state was not reached by day one and possibly not by day four Another interesting observation is that the Kd values are decreasing from day one to four A possible reason for this behavior may be due to redox chemistry of iodine in this system If iodine partially or entirely exists in the form as iodate (IO3
-) it is possible it could be reduced to iodide I- within the reducing cementitious system These two iodine species sorb differently iodate sorbing to minerals more strongly than iodide (Denham et al 2009 Schwehr et al 2009 Fukui et al 1996 Yoshida et al 1992) It is hypothesized that the reducing environment of the saltstone is sufficient to reduce iodate ions to the more weakly binding form of iodine iodide
This is one of the few datasets (along with Tc) in this study where there may be a difference between the various solids The degree of iodate reduction would be expected to increase as the slag content increases As mentioned above reduction of iodate to iodide should result in a decrease in sorption Therefore higher Kd values should be observed for solids with less slag such as the Aged Cement (0 dry wt- slag) and Vault 2 (17 dry wt- slag) This is generally the case in Figure 418 where the highest Kd values are reported for the Aged Cement and the lowest values are for solid TR547 However this trend does not hold completely where the saltstone sample containing 90 slag (TR545) has generally equal or higher Kd values than the saltstone containing 45 dry wt- slag (TR547)
1 Clemson University is presently investigating appropriate internal standards for iodine analyses for ICP-MS Of those tested rhenium and molybdenum have shown some promise
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Figure 418 Iodine Kd Values under Reducing Conditions I Kd Values for various cementitious formulations measured after one day equilibration (1d) and four day equilibration (4d) under reducing conditions Total iodine concentrations in each system were 100 ppb 500 ppb and 1000 ppb as noted Sample prepared in triplicate and error bars represent standard deviation of samples except as follows Vault 2-4 d 100 ppb is a single dataset while the datasets for Vault 2-1 d 100 ppb 4 d 1000 ppb TR545-4 d 1000 ppb 100 ppb TR547-4 d 1000 ppb 500 ppb 100 ppb and Aged Cement- 4 d 1000 ppb and 100 ppb are all based on duplicates
44 Radionuclide Sorption to Vial Walls under Reducing Conditions
The aqueous concentrations for Pu Np and Tc in the no solids controls are shown in Figure 419 The results are similar to those presented for experiments performed under oxidizing conditions above The 1 ppb Pu aqueous fraction is approximately three times greater than the 10 ppb fraction at day one This fraction decreases over time and by day four they are approximately equal when taking error into account This behavior is similar to the aqueous fraction under oxidizing conditions The 1 ppb Np aqueous fraction is significantly higher on both day one and day four than the aqueous fraction of the 10 ppb samples However each remained constant from day one to day four The 10 ppb aqueous fraction is twice as low as under oxidizing conditions which suggests either higher sorption to the vial walls or more precipitating out under the reducing conditions Like Pu and Np Tc shows a decrease from day one to day four especially for the 1 ppb samples The decrease in the 10 ppb sample is minimal and the aqueous fraction remains around 09 This value is slightly lower than that under oxidizing conditions
To examine the degree of sorption to the vial walls the tubes were washed again as performed for the experiments under oxidizing conditions above and similar results were found Ninety percent of the 1 ppb Pu sample was sorbed to the vial wall upon completion of the experiment which gives a 100 mass recovery when comparing this value to that found in Figure 419 However this result is not the case with the 10 ppb samples where approximately 75 of the mass remains unaccounted It is noteworthy that approximately 25 of the Pu from the 10 ppb solution sorbed to the vial walls under both oxidizing
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and reducing conditions Np follows the same trend as Pu while less than 005 of the Tc sorbed to the wall
Figure 419 Plutonium Neptunium and Technetium No-Solids Aqueous Fractions under Reducing Conditions Pu Np and Tc aqueous fractions of No Solids controls after a one-day equilibration (1d) and four-day equilibration (4 d) under reducing conditions Total concentration for each radionuclide was 1 ppb and 10 ppb Samples were prepared in triplicate and the error bars represent the standard deviation
Figure 420 Percent of Pu Np and Tc sorbed to the vial walls of the No Solids control samples under reducing conditions Each the 1 ppb and 10 ppb samples were prepared in triplicate and the error bars represent the standard deviations of triplicate samples
Under reducing conditions the fraction of I remaining in the aqueous phase was around 90 with
almost 100 mass recovery of the 100 ppb I after the four-day equilibration These graphs show that
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under reducing conditions there will only be a small fraction of I sorbing to the vial wall or coming out of solution This result is a much better mass recovery than under oxidizing conditions (Figure 48) which had a mass recovery of approximately 65 after four days This result is also consistent with the interpretation that there may be a iodine speciation change between the two redox treatments
Figure 421 Iodine No-Solids Aqueous Fractions under Reducing Conditions I aqueous fractions of No-Solids controls after a one-day equilibration (1d) and four-day equilibration (4d) under reducing conditions The total concentration for each system was 100 ppb and 1000 ppb Samples were prepared in triplicate and the error bars represent the standard deviation
50 Comparison of Radionuclide Sorption under Oxidizing and Reducing Conditions
In the following figures (Figure 51 through Figure 54) the data shown above has been replotted to allow comparison between the oxidizing and reducing conditions for each cementitious formulation General observations based on these data follow Vault 2 Observations (Figure 51)
bull Pu Kds are greater than 104 under both oxidizing and reducing conditions and Pu Kds are slightly lower under reducing conditions This could possibly be due to reduction of Pu(IV) to Pu(III) However no oxidation state analysis was performed in this work
bull Np Kds are generally greater than 104 under both oxidizing and reducing conditions Interestingly Np Kds are higher under reducing conditions by almost an order of magnitude This could possibly be due to reduction of Np(V) to Np(IV) However no oxidation state analysis was performed in this work
bull Regardless of the initial Np or Pu concentration similar aqueous phase concentrations of Np or Pu were observed in all samples This trend indicates that ldquosorptionrdquo of Np and Pu in these systems may be a combination of adsorption absorption and (co)precipitation processes
bull Tc appears to reach a steady state within four days under oxidizing conditions This behavior does not appear to be the case under reducing conditions After four days similar Kd values are reached under both oxidizing and reducing conditions It is unclear
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whether the Kd value of Tc will continue to increase under reducing conditions consistent with reduction of Tc(VII) to Tc(IV) The similarity in Kd values under both oxidizing and reducing conditions is an interesting observation and certainly warrants additional studies
bull I Kd values are similar under both oxidizing and reducing conditions However reducing condition systems may not be at steady state after four days while systems under oxidizing conditions appeared to reach a steady state The difference in rates may be due to reduction of iodate to iodine
bull For all isotopes examined the sorption behavior to each of the solid phases is very similar
TR545 and TR547 Observations (Figure 52 and Figure 53) bull Similar to the discussion above with respect to Vault 2 Pu Np and Tc all appear to reach
a steady state under oxidizing conditions and approach steady state slower under reducing conditions
bull Np and Pu Kd values are greater than 104 for all systems and time steps The aqueous phase concentrations of Np and Pu appear to be better described as a solubility in terms of the aqueous phase concentration of Np and Pu Similar aqueous phase concentrations of both Np and Pu were reached The data indicate that the initial Np and Pu concentration generally does not affect the aqueous phase concentration at an apparent steady state The presence of each solid phase appears to limit the aqueous phase concentration of both Np and Pu on the order of 10-11 molL
bull Tc shows significantly higher Kd values under reducing conditions versus oxidizing conditions
bull For all isotopes examined the sorption behavior to each of the solid phases is very similar
Aged Cement Observations (Figure 54) bull Pu appears to be close to steady state for each solid by day one with similar Kd values
reached on between day one and day four bull Np has a higher Kd under reducing conditions than oxidizing (105 under oxidizing
conditions and gt105 under reducing conditions) bull Neither set of Tc data was at steady state by day one and rates of sorptiondesorption
reactions appear to be different Tc Kds decrease from day one to four under oxidizing conditions but increase under reducing conditions
bull The Kd values for I under oxidizing conditions were considerably higher than those measured for I with any other solid Similar Kd values obtained for the same solids under reducing conditions indicate that the reported Kd values under oxidizing conditions appear to be suspect However analysis of the raw data gives no indication of an experimental artifact As discussed above these observations may be explained based upon the amount of slag contained within the solids which will affect the reducing capacity (ie No reducing slag is in the aged cement which could be reason the reduction of iodate to iodide (speculated in other samples) is not evident)
bull The difference in sorption behavior of iodine to the aged cement between oxidizing and reducing conditions also indicates that the reducing conditions of the solution may affect I redox behavior in addition to any reactivity expected in the solid phases
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Figure 51 Comparison of Tc I Np and Pu sorption to Vault 2 solid under oxidizing and reducing conditions
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Figure 52 Comparison of Tc I Np and Pu sorption to TR 545 solid under oxidizing and reducing conditions
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Figure 53 Comparison of Tc I Np and Pu sorption to TR547 solid under oxidizing and reducing conditions
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Figure 54 Comparison of Tc I Np and Pu sorption to Aged Cement under oxidizing and reducing conditions
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60 Comparison of Radionuclide Sorption and Solubility under Oxidizing and Reducing Conditions
To further summarize the data the following tables provide either the average solubility
(for Np and Pu) or average Kd (for Tc and I) determined under both oxidizing and reducing conditions for each cementitious formulation Each table lists the average value standard deviation and the number of replicate samples used to calculate the reported values
The solubility of Pu in the presence of each solid under oxidizing and reducing conditions is shown in Table 61 (this is taken from experiments equilibrated for four days not one day) Under oxidizing conditions the apparent solubility values associated with the Aged Cement (0 dry wt- slag) Vault 2 (17 dry wt- slag) and TR547 (45 dry wt- slag) are all similar with only a slight increase in solubility as the amount of reducing slag increases There is a significant increase of almost an order of magnitude for the most reducing saltstone TR545 (90 dry wt- slag) However these samples also have a standard deviation on the same order of magnitude as the solubility itself which when taken into account brings the solubility back into the range of the others Under reducing conditions the apparent solubility values are slightly lower than under oxidizing conditions In this set of samples the Vault 2 saltstone with 10 dry wt- reducing slag had the highest apparent solubility but once again when considering the standard deviation the values are similar
Table 61 Comparison of plutonium apparent solubility values under oxidizing and reducing conditions
Table 62 lists the apparent solubility values of Np in the presence of each cementitious
formulation under both oxidizing and reducing conditions Under oxidizing conditions the cementitious formulation does not appear to have a dramatic effect on the solubility The apparent solubility values are similar to those of Pu under similar conditions except the Np standard deviations are much higher The high standard deviations are an analytical artifact since the measured concentrations were close to or at the detection limit of the ICP-MS There does appear to be a slight decrease in Np solubility under reducing conditions However the statistical significance of this decrease was not calculated
SRNL-STI-2009-00636 Revision 0
47
Table 62 Comparison of neptunium apparent solubility values under oxidizing and reducing conditions
Unlike the apparent solubility values of Pu and Np the aqueousatmospheric conditions
and cementitious formulation seem to have an effect on the Tc Kd values (Table 63) Under oxidizing conditions there is not a discernible difference among the different cementitious formulations especially when taking the respective standard deviations into account However when experiments were run under reducing conditions the specific formulation had a noticeable effect The two saltstone samples with the least amount of reducing slag Aged Cement (0 dry-wt- slag) and Vault 2 (17 dry wt- slag) had Kd values which were similar to those observed under oxidizing conditions However the TR547 (45 dry-wt- slag) increased by almost an order of magnitude while the TR545 (90 dry wt- slag) increased by about three orders of magnitude Although the respective standard deviations are large the higher Kd values do appear to be significant
Table 63 Comparison of technetium Kd values under oxidizing and reducing conditions
Unlike Tc I does not seem to be as affected by cementitious formulation and redox status (Table 64) The only treatment (possible outlier) that does not follow this trend is the Aged Cement under oxidizing conditions This Kd value is higher than the others but also has a much higher standard deviation which when accounted for gives a value similar to the others All other treatments had near identical Kd values irrespective of solid phase or redox condition But again the Aged Cement data cannot be discounted at this time given the possibility of the influence that redox may have on iodine speciation and the strong influence I speciation has on sorption to cementitious materials
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Table 64 Comparison of iodine Kd values under oxidizing and reducing conditions
71 Comparison with Previous Data The increased sensitivity of the ICP-MS over conventional low-energy gamma
spectroscopy or liquid scintillation counting (LSC) analysis allowed for much more accurate Kd values and apparent solubility values in this work than were previously obtainable Generally radioanalytical detection methods start with activities on the order of 103 to 104 counts per minute (cpm) and approach background levels of 1 to 5 cpm for strongly sorbing radionuclides Therefore the accuracy of the Kd value will be the difference in analytical sensitivity when the initial aqueous activity decreases by a factor of approximately 5000 (ie the aqueous activity drops from approximately 5000 cpm to the instrument background of 1 cpm following almost complete sorption) As a result the reported Kd values can only be reliably reported up for a Kd of 103 to 104 This constraint is believed to be the difference between the observed Kd values for 237Np of gt 105 observed in this work when compared with the Kd values between 3000 and 4000 reported by Kaplan et al (2008) A similar observation was made for Pu because 242Pu was used for ICP-MS analysis and 238Pu was used in the work of Kaplan et al (2008) This constrint may account for the different Kd value of gt104 reported in Kaplan et al (2008) compared with the value of gt105 observed in this work
In the case of Tc Kaplan et al (2008) reported a Kd of 023 mLg for Vault 2 under oxidizing conditions and 093 mLg under reducing conditions while the above experiment determined the Vault 2 Kd to be 505 mLg under oxidizing conditions and 557 mLg under reducing conditions Unlike the discrepancy in the Kd values for Np Pu and Tc between the above findings and those in Kaplan et al (2008) the reported Kd values for iodine are similar For Vault 2 Kaplan et al (2008) found 125I to have a Kd of 894 mLg under oxidizing conditions and 715 mLg under reducing conditions These values are similar to the Kd values of 766 mLg and 725 mLg observed under oxidizing and reducing conditions respectively in this work These findings appear to confirm the previously accepted Kd values of 0-10 mLg depending on the cementitious formulation
72 Suggested Future Work The above data demonstrate several areas that require further examination The
increasing Tc Kd values over time dataset suggest that steady state had not been achieved It would be beneficial to determine the amount of time required to reach steady state and allow determination of a more accurate Kd value (an assumption of the Kd construct is that it be measured at steady state) Also kinetic studies of both Tc and I are needed to better understand their respective interactions with the different cementitious formulations As for the I additional
SRNL-STI-2009-00636 Revision 0
49
tests should be performed to test the hypothesis that iodine may in part exist as iodate which may initially sorb to the saltstone then undergo reduction to iodine or iodide and then desorbs causing a decrease in Kd
A final area of future work is to examine the possible causes for the similar behavior of each cementitious formulation despite the different slag content This discrepancy is not only observed in the above experiments but also in Kaplan et al (2008) which is illustrated in Table 31 and by recent work in measurements of saltstone reduction capacity (Roberts and Kaplan 2009) The reduction capacity (units in milli-equivalentsg solid) equivalents of the Aged Cement with no slag is 855 plusmn 101 and adding 10 slag gives a reducing equivalent of 2398 plusmn 311 However increasing the slag content to 23 causes the reducing capacity to increase to 8218 plusmn 81 which is almost equivalent to the 8324 plusmn 49 of the 100 slag Understanding the chemistry behind the reducing capacity of each cementitious formulation will help to define what reactions are important for controlling radionuclide release from the saltstone
80 References Allard B L Eliasson S Hoglund and K Andersson 1984 ldquoSorption of Cs I and actinides in
concrete systemsrdquo SKB Technical Report SKBKBS TR-84-15 DKB Stockholm Sweden
Denham M D I Kaplan and C Yeager2009 ldquoGroundwater radioiodine Prevalence biogeochemistry and potential remedial approachesrdquo SRNL-STI-2009-00463 Savannah River National Laboratory Aiken SC
Dixon K L M A Phifer and J R Harbour 2008 ldquoFY09 PACA Maintenance Program Additional Saltstone Property Testingrdquo SRNL-L3100-2009-00019 Rev0 Savannah River National Laboratory Aiken SC
Fukui M Fujikawa Y and Satta N 1996 ldquoFactors affecting interaction of radioiodide and iodate species with soilrdquo Journal of Environmental Radioactivity 31 199-216
Hoglund S L Eliasson B Allard K Andersson and B Torstenfelt 1985 ldquoSorption of some fission products and actinides in concrete systemsrdquo Mat Res Soc Symp Proc 50 683-690
Kaplan D I 2007 Geochemical Data Package for Performance Assessment Calculations Related to the Savannah River Site WSRC-TR-2006-00004 Rev 1 Washington Savannah River Company Aiken SC
Kaplan D I and Coates J 2007 ldquoPartitioning of Dissolved Radionuclides to Concrete under Scenarios Appropriate for Tank Closure Performance Assessmentsrdquo WSRC-STI-2007-00640 Rev 0 Washington Savannah River Company Aiken SC 29808
Kaplan D I Roberts K Coates J Siegfried M Serkiz S 2008 ldquoSaltstone and concrete interactions with radionuclides Sorption (Kd) desorption and reduction capacity measurementsrdquo SRNS-STI-2008-00045 Savannah River National Laboratory Aiken SC 2008
SRNL-STI-2009-00636 Revision 0
50
Neck V and Kim J I 2001 ldquoSolubility and hydrolysis of tetravalent actinidesrdquo Radiochim Acta 89 1
Powell B A Fjeld R A Coates J T Kaplan D I Serkiz S M 2002 ldquoPlutonium Oxidation State Geochemistry in the SRS Subsurface Environmentrdquo WSRC-TR-2003-00035 Westinghouse Savannah River Company US DOE Savannah River Site Aiken SC
Roberts K A and D I Kaplan 2009 Reduction Capacity of Saltstone and Saltstone Componentsrdquo SRNL-STI-2009-00637 Rev0 Savannah River National Laboratory Aiken SC
Schwehr K A Santschi P H D I Kaplan C M Yeager and R Brinkmeyer 2009 ldquoOrgano-iodine formation in soils and aquifer sediments at ambient concentrationsrdquo Environ Sci Technol 437258-7264
Yoshida S Muramatsu Y and Uchida S 1992 ldquoStudies on the sorption of I-(iodide) and IO3-
(iodate) onto andosolsrdquo Water Air and Soil Pollution 63 321-329
SRNL-STI-2009-00636 Revision 0
51
90 Appendix A Data Tables of Radionuclide Sorption to Saltstone under Oxidizing Conditions
The following tables represent data collected for the no solids controls each saltstone and testing of radionuclide sorption to the vial walls The no solids controls tables include the concentration (ppb) of the radionuclide spiked into the sample along with the concentration of the radionuclide (ppb) measured in the aqueous phase after the given equilibration time The pH at the time the sample was taken is also recorded along with the fraction of the radionuclide which stayed in the aqueous phase The tables for the cementitious formulation data include the data above along with the addition of a Kd value The tables of the data for the radionuclides sorbed to the vial walls include the initial concentration (ppb) of the spike the concentration (ppb) of the radionuclide that had sorbed to the vial wall during the experiment and the percentage of the total concentration this represents Important Notes
BDL- Below Detection Limit lt01 denotes no notable sorption occurred
91 Data Tables for No Solid Controls
Table 91 Plutonium no solids control after one day
A 9264165178 402285E‐05 1181 434238E‐06 9980817 B 9352537276 0000110618 1183 118276E‐05 3616813 C 9363541597 705331E‐05 118 753273E‐06 5401186 D 0993110568 BDL 12 NA NA E 0977247222 300794E‐05 1199 307797E‐05 1280331 F 0962441315 BDL 1198 NA NA G 4059128499 BDL 1186 NA NA H 4065161486 705198E‐05 1188 173473E‐05 2380003 I 4116819691 0000110748 1189 269014E‐05 1555864
Table 920 TR545- neptunium after four days
Sample ID
Initial Aq Conc (ppb)
Equil Aq Conc (ppb) pH
Fraction Aq Kd
A 92641652 NA 1188 NA NA B 93525373 00001935 1185 2069E‐05 2067199C 93635416 4119E‐05 1185 44E‐06 9247818D 09931106 BDL 1197 NA NA E 09772472 BDL 12 NA NA F 09624413 00066817 1206 00069424 562421G 40591285 00003289 1196 8103E‐05 5148274H 40651615 00025316 1196 00006228 6625737I 41168197 00001018 1194 2474E‐05 1692126
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58
Table 921 TR545- technetium after one day
Sample ID
Initial Aq Conc (ppb)
Equil Aq Conc (ppb) pH Fraction Aq Kd
A 9655146069 820460082 1181 0849764546 8998984 B 9356176321 7703053505 1183 0823312135 1051242 C 9114122586 7978297395 118 0875377451 7062663 D 1042349157 0853053814 12 0818395456 9099556 E 0983206046 0871198263 1199 0886079033 5196709 F 0905148405 0803451372 1198 0887646013 5098696 G 4950156706 4275082341 1186 0863625658 7213934 H 4889067068 4173762594 1188 0853693053 7687519 I 4854463762 4147024058 1189 0854270268 7771045
A 1048950046 0002141023 1149 0000204111 2112281 B 1039943573 0001770549 1157 0000170254 2460487 C 1084651695 0001127533 1153 0000103953 4014918 D 1088686867 0001201087 1172 0001103244 3564524 E 1119673887 0000783288 1177 0000699568 5709897 F 1045722787 0000914861 1181 000087486 4495324 G 5387981131 0001444832 1169 0000268158 1494715 H 5412748988 0001143483 1169 0000211257 1965749 I 5373948758 00010003 1164 0000186139 2280472
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Table 926 TR547- plutonium after four days
Sample ID
Initial Aq Conc (ppb)
Equil Aq Conc (ppb) pH
Fraction Aq Kd
A 104895 NA 116 NA NA B 10399436 0001828 1165 00001758 2383132C 10846517 00010788 1164 9946E‐05 4196159D 10886869 00009131 1184 00008388 4689778E 11196739 00010624 1189 00009488 4208928F 10457228 00007967 1191 00007619 516258G 53879811 00007915 1173 00001469 2728993H 5412749 00008355 1175 00001544 2690641I 53739488 00006103 1174 00001136 3737892
Table 927 TR547- neptunium after one day
Sample ID
Initial Aq Conc (ppb)
Equil Aq Conc (ppb) pH Fraction Aq Kd
A 9589772032 0000454463 1149 473903E‐05 9116335 B 9293228768 0000260081 1157 27986E‐05 1499475 C 1008725504 0000302018 1153 299405E‐05 1397125 D 0952173007 000019177 1172 0000201403 1954603 E 0992224074 BDL NA NA F 0967815522 402137E‐05 1181 41551E‐05 9474699 G 4068405786 0000222282 1169 546361E‐05 7336986 H 409543171 0000531619 1169 0000129808 3199152 I 4017406611 0000410123 1164 0000102086 4157807
Table 928 TR547- neptunium after four days
Sample ID
Initial Aq Conc (ppb)
Equil Aq Conc (ppb) pH Fraction Aq Kd
A 9589772 NA 116 NA NA B 92932288 00002145 1165 2308E‐05 1818463C 10087255 00001628 1164 1614E‐05 2591215D 0952173 BDL 1184 NA NA E 09922241 BDL NA NA F 09678155 5107E‐05 1191 5277E‐05 7460375G 40684058 00001336 1173 3284E‐05 1220544H 40954317 8151E‐05 1175 199E‐05 2086795I 40174066 00001322 1174 3292E‐05 1289605
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Table 929 TR547- technetium after one day
Sample ID
Initial Aq Conc (ppb)
Equil Aq Conc (ppb) pH Fraction Aq Kd
A 9466799266 8233850788 1149 0869760788 8220086 B 9439556236 817653394 1157 0866198975 8165745 C 9383493063 8086024379 1153 0861728604 8430884 D 1061939876 0919992065 1172 0866331594 6241759 E 0991827343 0836511397 1177 0843404251 7590958 F 0971981155 0839862696 1181 0864073024 6354378 G 4883337077 414858839 1169 0849539633 7903986 H 4691440077 3996173112 1169 0851800949 8038249 I 486993937 4291285586 1164 0881178442 6558707
Table 930 TR547- technetium after four days
Sample ID
Initial Aq Conc (ppb)
Equil Aq Conc (ppb) pH
Fraction Aq Kd
A 94667993 NA 116 NA NA B 94395562 85812109 1165 09090693 5885474C 93834931 84622373 1164 09018217 6279204D 10619399 09580683 1184 09021869 4435663E 09918273 08881507 1189 08954691 4835506F 09719812 09036489 1191 0929698 3138862G 48833371 4490415 1173 09195382 4312104H 46914401 42054182 1175 08964024 5612948I 48699394 43843193 1174 09002821 5536503
Table 931 TR547- iodine after one day
Sample ID
Initial Aq Conc (ppb)
Equil Aq Conc (ppb) pH Fraction Aq Kd
A 9944920441 8813152965 1149 0886196427 738241 B 9956006121 8747156303 1157 0878580848 8007767 C 9822152291 8664470934 1153 0882135674 7988892 D 1002391846 9333490632 1172 0931121963 3368509 E 9918273427 6625075445 1177 0667966607 1551748 F 9918175056 8931364957 1181 0900504872 4773862 G 5166570628 4445386532 1169 0860413387 7961604 H 4847821413 410447427 1169 084666367 8664303 I 4850381381 4266693706 1164 0879661489 6413801
100 Appendix B Data Tables of Radionuclide Sorption to Saltstone Under Reducing Conditions
The following tables represent data collected for the no solids controls each cementitious solid and testing of radionuclide sorption to the vial walls The no solids controls tables include the concentration (ppb) of the radionuclide spiked into the sample along with the concentration of the radionuclide (ppb) measured in the aqueous phase after the given equilibration time The pH at the time the sample was taken is also recorded along with the fraction of the radionuclide which stayed in the aqueous phase The tables for the cementitious solidsrsquo data include the data above along with the addition of a Kd value The tables of the data for the radionuclides sorbed to the vial walls include the initial concentration (ppb) of the spike the concentration (ppb) of the radionuclide that had sorbed to the vial wall during the experiment and the percentage of the total concentration this represents Important Notes
BDL= Below Detection Limit lt01 denotes no notable sorption occurred
101 Data Tables for No-Solid Controls
Table 101 Plutonium no solids control after one day
A 9405892 0007019 111 0000746258 5681206 B 9602498 0003294 1117 0000342992 123554 C 9630619 0002936 1114 0000304893 1396318 D 4945396 0001795 113 0000363011 1171688 E 4964945 0001373 1131 0000276484 1493015 F 4441601 0001516 113 0000341219 1389674 G 1079602 0001109 1142 0001027508 4215519 H 1031512 0000883 1143 0000855983 4820576 I 0939294 0000978 1143 0001040992 4550255
SRNL-STI-2009-00636 Revision 0
70
Table 1011 Vault 2- neptunium after one day
Sample ID Initial Aq Conc (ppb)
Equil Aq Conc (ppb) pH Fraction Aq
A 9425042625 0001709054 1105 0000181331 B 9611386476 0001184125 1110 00001232 C 9579553607 0001155517 1104 0000120623 D 4974000414 0000672325 1125 0000135168 E 4916731623 0000675371 1128 0000137362 F 4373142817 0000570681 1120 0000130497 G 0943366414 0000389738 1129 0000413136 H 1011745587 0000565648 1132 0000559081 I 0865252712 0000379545 1133 0000438653
A 8849444124 0000306309 1150 346133E‐05 1289533 B 8447823057 0000150131 1155 177715E‐05 2711019 C 8590597085 0000199185 1153 231864E‐05 2044057 D 4491250244 517162E‐05 1156 115149E‐05 4020064 E 4391894479 204591E‐05 1158 465838E‐06 9846089 F 4210703646 204376E‐05 1158 485374E‐06 9816203 G 086381524 522216E‐06 1160 604546E‐06 7577764 H 0870501884 BDL 1160 NA NA I 0861953838 BDL 1162 NA NA
SRNL-STI-2009-00636 Revision 0
79
Table 1036 Aged cement- neptunium after four days
Sample ID
Initial Aq Conc (ppb)
Equil Aq Conc (ppb) pH Fraction Aq Kd
A 8849444 0000131 1145 148418E‐05 3007445B 8447823 0000111 1146 131529E‐05 3662996C 8590597 656E‐05 1146 76328E‐06 6209405D 449125 BDL 1155 NA NA E 4391894 BDL 1156 NA NA F 4210704 BDL 1155 NA NA G 0863815 BDL 1165 NA NA H 0870502 BDL 1162 NA NA I 0861954 BDL 1164 NA NA
Table 1037 Aged cement- technetium after one day
Sample ID
Initial Aq Conc (ppb)
Equil Aq Conc (ppb) pH Fraction Aq Kd
A 8426518355 833290075 1150 098889012 0476492 B 8638001423 7823321167 1155 0905686487 4413063 C 9323317745 925927516 1153 0993130923 0294664 D 442651005 4300859603 1156 0971614106 1242837 E 4426849405 4336992073 1158 0979701742 0855315 F 3929483125 3938204338 1158 100221943 lt01 G 0817864386 081693181 1160 0998859743 0049487 H 0878958929 0792412508 1160 0901535306 4510199 I 0772205665 0871436364 1162 1128502941 lt01
Table 1038 Aged cement- technetium after four days
110 Appendix C Dixon et al (2009) FY09 PACA Maintenance Program Additional Saltstone Property Testing SRNL L3100-2009-00019 Rev 0
SRNL-STI-2009-00636 Revision 0
83
SRNL L3100-2009-00019 Rev 0
December 16 2008
Keywords Performance Permeability Modulus
L B Romanowski
Waste Determinations From K L Dixon M A Phifer and J R Harbour
FY09 PACA Maintenance Program Additional Saltstone Property Testing
BACKGROUND
Additional tests have been identified for measurement of important hydraulic and physical properties of saltstone The initial phase of this work [1] was completed last year and the results were detailed in an internal report [2] The proposed testing for FY09 includes measurement of saturated hydraulic conductivity porosity bulk density particle density water retention and Youngrsquos modulus of simulated Saltstone grouts For completeness the bleed volumes and gel times for each mix will also be measured
The testing will be based on a projected salt solution composition for the ARPMCU stream that will be fed to the Saltstone Production Facility over the next few years The scope for FY09 will include testing to determine the impact of (1) admixtures (2) organics (3) wcm ratio (4) aluminate concentration and (5) temperature of curing on the hydraulic properties of saltstone mixes Samples of selected batches prepared as part of this task will be provided to Dan Kaplan for measurement of Kd through leaching tests The eleven mixes that will be batched and tested are detailed in Table 1
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84
Table 1 The Eleven Mixes That will be Batched and Tested
BFS is Blast Furnace Slag FA is Fly Ash and PC is Portland Cement
TEST DETAILS
Test 1 Control (Mix 1)
A control mix will be based on the baseline mix modified by exclusion of the Class F fly ash Consequently the cementitious materials premix will be a mixture of 90 blast furnace slag and 10 portland cement The degree of reaction will be much greater than with the normal premix and therefore should result in a lower porosity and a lower permeability This bounding test at 060 wcm ratio is expected to yield a hydraulic conductivity at or below the detection limit for the Mactec permeameter measurement system Therefore this test should demonstrate the lowest level of detection of the Mactec system as well as show a resolvable difference between measurements of the control mix and the control mix with the normal premix composition
Test 2 ndashImpact of Admixtures (Mixes 2 and 3)
Recent saltstone batches have required both a set retarder (Daratard 17) and an antifoam agent (Q2) for processing of the saltstone Therefore the baseline mix will be prepared with and without nominal levels of these two admixtures to determine whether these admixtures appreciably affect the hydraulic and physical properties of saltstone at these nominal concentrations
Test 3ndashImpact of Organics (Mixes 2 and 4)
The solvent extraction process is expected to result in some carryover of organics [3]
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85
Consequently a test will be performed on the impact of Caustic Side Solvent Extraction (CSSX) organics at 100 microliters per 1600 gram batch The CSSX solvent consists of 075 M 1-(2233-tetrafluoropropoxy)-3-(4-sec-butylphenoxy)-2-propanol (Cs-7SB) and 0003 M tri-n-octylamine (TOA) in an Isoparreg L diluent Test 4ndashImpact of Combination of Admixtures and Organics (Mixes 2 5 10 and 11)
This test will determine the impact of a combination of admixtures (Test 2) and organics (Test 3) together in the mix vs the baseline case without admixtures and organics
Test 5ndash Impact of wcm Ratio (Mixes 2 6 and 7)
It is well known that decreasing the wcm ratio in a mix will improve permeability in normal portland cement water mixes This test will measure the variation in permeability for the case of the MCU salt solution at three different wcm ratios The initial selection of wcm ratios is 055 060 and 065 However if the mix at an as-batched 065 wcm ratio has significant bleed water and the resulting actual wcm ratio is close to 060 then the three ratios will be adjusted to provide a more evenly spaced set of values However the baseline mix at 060 will be included as one of the three mixes
Test 6 ndash Impact of Aluminate Concentration (Mixes 8 9 and 10)
The DWPF has modified its process flowsheet to include a caustic washing of HLW sludge to remove some of the aluminum from the HLW prior to vitrification The resulting aluminate stream will then be blended with tank 50 material and fed to the SPF This increased aluminate concentration in the salt solution has significant impact on heat of hydration and set times and consequently it is likely that it will also impact permeability Therefore a set of three samples will be made at wcm ratios of 055 060 and 065 (as in Test 3) with a higher level of aluminate (028 M) for testing
Test 7 ndash Impact of Increased Curing Temperature (Mix 11)
In an ongoing task there is evidence that Youngrsquos modulus (a performance indicator) [4] is reduced by increasing the curing temperature of the mix Since the vault temperature increases during curing as a result of the exothermic hydration reactions one of the baseline mixes with a combination of admixtures and organics will be cured at 60
o
C rather than the normal 22
o
C to determine the impact of curing temperature on the permeability
SRNL-STI-2009-00636 Revision 0
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SCHEDULE
The schedule for the task of batching and testing of the samples is provided in Table 2 This schedule is based on the fact that the cementitious materials will be available for the testing as needed
Table 2 Additional Saltstone Hydraulic and Physical Property Tests
Item Schedule Start Work 12108 Test Plan Complete 1509 Preparation of 1st set of Samples Complete 11909 90-Day Cure Period for 1st set of Samples Complete 42009
SRNL-STI-2009-00636 Revision 0
87
SRNL-STI-2009-00636 Revision 0
SRNL-STI-2009-00636 Revision 0
DISTRIBUTION Savannah River Site
A B Barnes 999-W Rm 336 H H Burns 999-W Rm 381 B T Butcher 773-43A Rm 212 A D Cozzi 999-W Rm 337 D A Crowley 773-43A Rm 216 M E Denham 773-42A Rm 218 J C Griffin 773-A Rm A-231 J R Harbour 999-W Rm 348 C A Langton 773-43A Rm 219 M H Layton 705-1C Rm 14 D I Kaplan (3 copies) 773-43A Rm 215 S L Marra 773A Rm A-230 A M Murray 773-A Rm 229 K A Roberts 773-43A Rm 225 T C Robinson 705-1C Rm 13 L B Romanowski 705-1C Rm 19 K H Rosenberger 705-1C Rm 16 F M Smith 705-1C Rm 24 RPA File (2 copies) 773-43A Rm 213
Clemson University Environmental Engineering and Earth Sciences 372 Computer Court LG Rich Environmental Laboratory Anderson SC 29625
Table 106 Technetium no solids control after four days 68
Table 107 Iodine no solids control after one day 68
Table 108 Iodine no solids control after four days 68
Table 109 Vault 2- plutonium after one day 69
Table 1010 Vault 2- plutonium after four days 69
Table 1011 Vault 2- neptunium after one day 70
Table 1012 Vault 2- neptunium after four days 70
Table 1013 Vault 2- technetium after one day 70
Table 1014 Vault 2- technetium after four days 71
Table 1015 Vault 2- iodine after one day 71
Table 1016 Vault 2- iodine after four days 71
Table 1017 TR545- plutonium after one day 72
Table 1018 TR545- plutonium after four days 72
Table 1019 TR545- neptunium after one day 73
Table 1020 TR545- neptunium after four days 73
Table 1021 TR545- technetium after one day 73
Table 1022 TR545- technetium after four days 74
Table 1023 TR545- iodine after one day 74
Table 1024 TR545- iodine after four days 74
Table 1025 TR547- plutonium after one day 75
Table 1026 TR547- plutonium after four days 75
Table 1027 TR547- neptunium after one day 76
Table 1028 TR547- neptunium after four days 76
Table 1029 TR547- technetium after one day 76
Table 1030 TR547- technetium after four days 77
Table 1031 TR547- iodine after one day 77
Table 1032 TR547- iodine after four days 77
Table 1033 Aged cement- plutonium after one day 78
Table 1034 Aged cement- plutonium after four days 78
SRNL-STI-2009-00636 Revision 0
x
Table 1035 Aged cement- neptunium after one day 78
Table 1036 Aged cement- neptunium after four days 79
Table 1037 Aged cement- technetium after one day 79
Table 1038 Aged cement- technetium after four days 79
Table 1039 Aged cement- iodine after one day 80
Table 1040 Aged cement- iodine after four days 80
Table 1041 Plutonium sorbed to vial wall in no solids control 80
Table 1042 Neptunium sorbed to vial wall in no solids control 81
Table 1043 Technetium sorbed to vial wall in no solids control 81
SRNL-STI-2009-00636 Revision 0
xi
LIST OF FIGURES
Figure 31 Screen capture of a typical 242Pu calibration curve using Thermo PlasmaLab software to control the data collection and analysis R2=0999872 Intercept Conc (Detection Limit) = 0000044 ppb 16
Figure 32 Screen capture of a typical 237Np calibration curve using Thermo PlasmaLab software to control the data collection and analysis R2=0999981 Intercept Conc (Detection Limit) = 0000026 ppb 17
Figure 33 Screen capture of a typical 99Tc calibration curve using Thermo PlasmaLab software to control the data collection and analysis R2=0999984 Intercept Conc (Detection Limit) = 0000013 ppb 18
Figure 34 Screen capture of a typical 127I calibration curve using Thermo PlasmaLab software to control the data collection and analysis R2=0999991 Intercept Conc (Detection Limit) = 024 ppb 19
Figure 41 Plutonium Kd Values under Oxidizing Conditions Plutonium Kd values for various saltstone formulations measured after one-day equilibration (1d) and four-day equilibration (4d under oxidizing conditions Total plutonium concentrations in each system were 1 ppb 5 ppb and 10 ppb Sample prepared in triplicate and error bars represent standard deviation of samples except as follows value for dataset TR547-4d 10 ppb is reported based on duplicate samples 25
Figure 42 Plutonium solubility for various saltstone formulations measured after one-day equilibration (1d) and four-day equilibration (4d) under oxidizing conditions Total plutonium concentrations in each system were 1 ppb 5 ppb and 10 ppb as noted Samples prepared in triplicate and an average of all samples (9) was used to determine average solubility The error bars represent standard deviation of samples 25
Figure 43 Neptunium Kd values under oxidizing conditions Neptunium Kd values for various saltstone formulations measured after one-day equilibration (1d) and four-day equilibration (4d) under oxidizing conditions Total plutonium concentrations in each system were 1 ppb 5 ppb and 10 ppb as noted Samples prepared in triplicate and error bars represent standard deviation of samples except as follows value for datasets TR545-1d 1ppb TR545-4d 1 ppb TR547 4d 1 ppb TR545-4d 10 ppb TR547-1d 1ppb TR547-4d 10 ppb are reported based on a single sample and for dataset TR545-1d 5ppb is reported based on duplicate samples Kd values limited to gt106 were at instrumental background 26
Figure 44 Average solubility of Np under oxidizing conditions Neptunium solubility for various saltstone formulations measured after one-day equilibration (1d) and four-day equilibration (4d) under oxidizing conditions Total Np concentrations in each system were 1 ppb 5 ppb and 10 ppb Samples prepared in triplicate and an average of all samples (9) was used to determine average solubility except as follows TR545-1d is based on 6 samples TR545- 4d on 5 samples TR547-1d on 7 samples and TR547- 4d on 5 samples The error bars represent standard deviation 27
Figure 45 Technetium Kd values under oxidizing conditions Tc Kd values for various saltstone formulations measured after one-day equilibration (1d) and four-day equilibration (4d) under oxidizing conditions Total Tc concentrations in each system were 1 ppb 5 ppb and 10 ppb as noted above Samples were prepared in triplicate and the error bars represent standard deviation
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xii
of samples except as follows data sets for Vault 2-1d 1ppb were duplicates and TR547- 4d 10 ppb is based on a single dataset 27
Figure 46 Iodine Kd Values under Oxidizing Conditions Iodine Kd values for various cementitious formulations measured after one-day equilibration (1d) and four-day equilibration (4d) under oxidizing conditions Total iodine concentrations in the systems were 100ppb 500 ppb and 1000 ppb as noted above Samples were prepared in triplicate and the error bars represent standard deviation of samples except as follows duplicates were used for dataset TR545- 1d 100ppb 28
Figure 47 Plutonium Neptunium and Technetium Aqueous Fractions Fraction of Pu Np and Tc remaining in the aqueous phase for the No Solids controls after a one-day equilibration (1d) and four-day equilibration (4d) under oxidizing conditions The total concentration for each radionuclide 10 ppb as noted above Samples were prepared in triplicate and the error bars represent the standard deviation of the samples 29
Figure 48 Iodine Aqueous Fraction Iodine aqueous fraction for the no-solids controls after a one-day equilibration (1d) and four-day equilibration (4d) under oxidizing conditions The total concentration of iodine was 1000 ppb as noted above Samples were prepared in triplicate and the error bars represent the standard deviation of the samples 29
Figure 49 Percent Pu and Np sorbed to vial walls of the no solids controls after the aqueous phases were discarded and the vials were washed Both the 10 ppb (blueleft) and 1 ppb (redright)) datasets were prepared in triplicate and the error bars show the standard deviation 31
Figure 410 Percent Pu sorbed to vial walls after the solids and aqueous phases were removed and the vials were washed The graph illustrates one sample from each of the 1 ppb (redleft) 5 ppb (greenmiddle) and 10 ppb (blueright) systems Therefore no error bars are present 31
Figure 411 Percent Np sorbed to vial walls after the solids and aqueous phases were removed and the vials were washed The graph illustrates one sample from each of the 1 ppb (redleft) 5 ppb (greenmiddle) and 10 ppb (blueright) systems Therefore no error bars are present 32
Figure 412 Pu Kd Values under Reducing Conditions Plutonium Kd values for various cementitious formulations measured after one-day equilibration (1d) and four-day equilibration (4d) under reducing conditions Total plutonium concentrations in each system were 1ppb 5 ppb and 10 ppb Samples prepared in triplicate and error bars represent standard deviation 33
Figure 413 Average Solubility of Plutonium under Reducing Conditions Plutonium solubility for various cementitious formulations measured after one-day equilibration (1d) and four-day equilibration (4d) under reducing conditions Total plutonium concentrations in each system were 1ppb 5 ppb and 10 ppb as noted Samples prepared in triplicate and an average of all samples (9) was used to determine average solubility The error bars represent standard deviation of samples 33
Figure 414 Np Kd Values under Reducing Conditions Neptunium Kd values for various cementitious formulations measured after one-day equilibration (1d) and four-day equilibration (4d) under reducing conditions Total Np concentrations in each system were 1 ppb 5 ppb and 10 ppb Samples were prepared in triplicate and the error bars represent standard deviation Kd values limited to gt106 were at instrumental background 34
Figure 415 Average Solubility of Neptunium under Reducing Conditions Neptunium solubility for various cementitious formulations measured after one day equilibration (1d) and four day
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xiii
equilibration (4d) under reducing conditions Total plutonium concentrations in each system were 1ppb 5 ppb and 10 ppb Samples prepared in triplicate and an average of all samples (9) was used to determine average solubility The error bars represent standard deviation 35
Figure 416 Tc Kd Values under Reducing Conditions Tc Kd values for various cementitious formulations measured after one-day equilibration (1d) and four-day equilibration (4d) under reducing conditions Total Tc concentrations in each system were 1 ppb 5 ppb and 10 ppb Sample prepared in triplicate and error bars represent standard deviation except as follows TR547-1d 1 ppb is based on a single dataset and datasets Vault 2-1d 5 ppb Vault 2- 4d 1 ppb Aged Cement-1d 5 ppb and Aged Cement-4d 1 ppb are duplicates 36
Figure 417 Data from Figure 416 replotted on a reduced linear scale for easier viewing Each sample was prepared in triplicate except as follows TR547-1d 1 ppb is based on a single dataset Vault 2-1d 5 ppb Vault 2- 4d 1 ppb Aged Cement-1d 5 ppb and Aged Cement-4d 1 ppb are duplicate datasets 36
Figure 418 Iodine Kd Values under Reducing Conditions I Kd Values for various cementitious formulations measured after one day equilibration (1d) and four day equilibration (4d) under reducing conditions Total iodine concentrations in each system were 100 ppb 500 ppb and 1000 ppb as noted Sample prepared in triplicate and error bars represent standard deviation of samples except as follows Vault 2-4 d 100 ppb is a single dataset while the datasets for Vault 2-1 d 100 ppb 4 d 1000 ppb TR545-4 d 1000 ppb 100 ppb TR547-4 d 1000 ppb 500 ppb 100 ppb and Aged Cement- 4 d 1000 ppb and 100 ppb are all based on duplicates 38
Figure 419 Plutonium Neptunium and Technetium No-Solids Aqueous Fractions under Reducing Conditions Pu Np and Tc aqueous fractions of No Solids controls after a one-day equilibration (1d) and four-day equilibration (4 d) under reducing conditions Total concentration for each radionuclide was 1 ppb and 10 ppb Samples were prepared in triplicate and the error bars represent the standard deviation 39
Figure 420 Percent of Pu Np and Tc sorbed to the vial walls of the No Solids control samples under reducing conditions Each the 1 ppb and 10 ppb samples were prepared in triplicate and the error bars represent the standard deviations of triplicate samples 39
Figure 421 Iodine No-Solids Aqueous Fractions under Reducing Conditions I aqueous fractions of No-Solids controls after a one-day equilibration (1d) and four-day equilibration (4d) under reducing conditions The total concentration for each system was 100 ppb and 1000 ppb Samples were prepared in triplicate and the error bars represent the standard deviation 40
Figure 51 Comparison of Tc I Np and Pu sorption to Vault 2 solid under oxidizing and reducing conditions 42
Figure 52 Comparison of Tc I Np and Pu sorption to TR 545 solid under oxidizing and reducing conditions 43
Figure 53 Comparison of Tc I Np and Pu sorption to TR547 solid under oxidizing and reducing conditions 44
Figure 54 Comparison of Tc I Np and Pu sorption to Aged Cement under oxidizing and reducing conditions 45
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xiv
LIST OF ABBREVIATIONS
DDI water Distilled deionized water ICP-MS Inductively coupled plasma ndash mass spectrometer
Kd Distribution coefficient LSC liquid scintillation counting NOM Natural organic matter PA Performance Assessment ppb parts per billion ppq parts per quadrillion QAQC Quality AssuranceQuality Control SA Special Analyses SRNL Savannah River National Laboratory SRS Savannah River Site
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10 Introduction Performance Assessments (PA) are risk calculations designed to determine (1) the maximum
amount of radioactivity that can be safely buried in a subsurface facility and (2) the potential human risk associated with disposing of radioactive waste in a subsurface facility Special Analyses (SAs) are similar to PAs except that they are designed to address specific issues related to PAs such as a new discovery since the PA was issued Commonly parameters describing the extent that a radionuclide interacts with solids at the source vadose zone and aquifer influence the extent of calculated human risk The two parameters that the SRS use to represent radionuclidesolid interactions are Kd and apparent solubility values together these parameters are referred to as sorption values Sorption values vary with radionuclides groundwater chemistry and the type of solid phase (and for cementitious materials by the age of the material during the calculation) In this work Kd and apparent solubility values are reported for 99Tc 127I 237Np and 242Pu sorption to various cementitious formulations
20 Objectives
The objectives of this work were to 1 Determine the influence of cementitious formulation on technetium (Tc) iodine (I) neptunium
(Np) and plutonium (Pu) sorption under oxidizing conditions The specific formulations that were evaluated included 1) an aged cement recovered from a 30-year old outdoor concrete pad on the SRS 2) Vault 2 concrete 3) TR545 saltstone and 4) TR547 saltstone (additional details are presented in Section 30 Materials and Methods)
2 Measure Tc I Np and Pu sorption to the cementitious formulations under reducing conditions
30 Materials and Methods
31 Preparation of ICP-MS Standards Stock Solutions and Working Solutions
311 242Pu
A National Institute of Standards and Technology Standard Reference Material (NIST SRM 434H) was used to prepare a stock 242Pu solution by dilution in 2 Aristar Optima HNO3 All volume additions were monitored gravimetrically This working solution was then used to make a set of 001 005 1 2 5 10 parts per billion (ppb) standards by dilution using 2 HNO3 Again all volume additions were monitored gravimetrically These standards were used to calibrate the Thermo Scientific X Series 2 inductively coupled plasma ndash mass spectrometer (ICP-MS) for quantification of 242Pu A representative calibration curve for 242Pu is shown in Figure 31 The instrument performance was monitored using 209Bi 232Th and 238U as internal standards The recovery of each sample during analysis was corrected based on the internal standard recovery The internal standard recoveries remained within standard quality assurancequality control QAQC protocols for the instrument (between 80 and 120)
A 242Pu stock solution was prepared by dissolving 1mg of Pu(NO3)4 obtained as a Certified Reference Material from New Brunswick Laboratory (CRM 130) This CRM is gt999 242Pu by atom percent The CRM was dissolved in 20mL of 8M HNO3 (Aristar Optima Grade) Because no chemicals or heat have been introduced to manipulate the Pu oxidation state it can be assumed that Pu(IV) is the predominant oxidation state in this stock solution A working solution to be used in spiking 242Pu experiments was prepared by diluting 25 mL of the CRM stock solution with 100 mL 10 M Aristar Optima HNO3 The concentration of 242Pu in this stock solution was determined using ICP-MS calibrated using the NIST SRM standards The concentration of Pu in this stock solution was 1065 ppb The total Pu
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concentration was also determined using liquid scintillation counting using the isotopic ratios reported for CRM 130 These compared favorably with the ICP-MS results but are reported here as a rigorous standardization because the isotopic ratios of CRM 130 have not yet been certified
Figure 31 Screen capture of a typical 242Pu calibration curve using Thermo PlasmaLab software to control the data collection and analysis R2=0999872 Intercept Conc (Detection Limit) = 0000044 ppb
312 237Np
A National Institute of Standards and Technology Standard Reference Material (NIST SRM 4341) was used to prepare a stock 237Np solution by dilution in 2 Aristar Optima HNO3 All volume additions were monitored gravimetrically This working solution was then used to make a set of 001 005 1 2 5 10 ppb standards by dilution using 2 HNO3 Again all volume additions were monitored gravimetrically These standards were used to calibrate the Thermo Scientific X Series 2 ICP-MS for quantification of 237Np A representative calibration curve for 237Np is shown in Figure 32 The instrument performance was monitored using 209Bi 232Th and 238U as internal standards The recovery of each sample during analysis was corrected based on the internal standard recovery The internal standard recoveries remained within standard QAQC protocols for the instrument (between 80 and 120)
A compiled 237Np stock solution from the Environmental Engineering and Earth Science (EEampES) inventory (primarily purchased from Isotope Products Valencia CA) was evaporated to dryness then the residue was brought up in approximately 5mL 80 M HNO3 Then 10 M hydroxylamine hydrochloride (NH2OHHCl EMD Chemicals ACS grade) and water were added to achieve a 3M HNO303M NH2OHHCl solution This solution was purified by extraction chromatography using Eichrom TEVA resin packed in a Bio-Rad poly-prep column The 3M HNO303 M NH2OHHCl neptunium solution was loaded on a 2 mL column and washed with 3 column volumes of 3 M HNO3 The Np(IV) was eluted with 002 M HCl + 02 M HF The effluent was evaporated to dryness then redissolved in 10 M HNO3 Additional 10 M HNO3 was added to maintain a approximately 10 mL then the solution was evaporated to incipient dryness and redissolved in a 50 mL of 10 M HNO3 An aliquot of the stock solution was evaporated to dryness on a stainless steel planchet and counted on the EGampG Ortec Alpha Spectrometer (Octete PC Detectors) No other alpha energies besides 237Np were observed The approximate concentration was determined using liquid scintillation counting and little 233Pa was observed The fuming in HNO3 as performed at the end of the purification procedure will drive Np to the soluble pentavalent state This is the stable oxidation state of Np under the experimental conditions Therefore experiments performed here can be assumed to be initially Np(V) The exact Np
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concentration in this solution was determined using ICP-MS calibrated with a NIST standard as discussed in section 312 below
A 237Np working solution (Working Solution 1) was created by pipetting an aliquot of the 237Np stock solution into a 100 mL Nalgene Teflon bottle and diluting with 2 BDH Aristar Ultra HNO3 to give a working solution concentration of 820 ppb All volumes were monitored gravimetrically Analysis on the ICP-MS calibrated against NIST Standards as described below gave a concentration of 820 ppb in Working Solution 1
Figure 32 Screen capture of a typical 237Np calibration curve using Thermo PlasmaLab software to control the data collection and analysis R2=0999981 Intercept Conc (Detection Limit) = 0000026 ppb
313 99Tc
A 99Tc working solution was prepared by diluting a stock solution of 99Tc (from the EEampES inventory purchased from Isotope Products Valencia CA) in distilled-deionized water (DDI Resistivity gt18 MΩcm) The oxidation state of Tc was not measured However based on the aqueous concentration in the DDI water solution Tc(VII) is the expected oxidation state The reduced Tc(IV) oxidation state would not be soluble under these conditions The expected concentration of 950 ppb based on the dilution was verified using liquid scintillation counting The 99Tc working solution was used to make 001 005 1 2 5 and 10 ppb standards by dilution using 2 HNO3 These standards were used to calibrate the Thermo Scientific X Series 2 ICP-MS for quantification of 99Tc A screen shot of a representative calibration curve is shown in Figure 33 The instrument performance was monitored by interpolating between 89Y and 115In internal standards The recovery of each sample during analysis was corrected based on the internal standard recovery The internal standard recoveries remained within standard QAQC protocols for the instrument (between 80 and 120)
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Figure 33 Screen capture of a typical 99Tc calibration curve using Thermo PlasmaLab software to control the data collection and analysis R2=0999984 Intercept Conc (Detection Limit) = 0000013 ppb
314 127I
A 100 microgmL iodate (IO3-) stock solution from High Purity Standards (Charleston SC) was used
to make 1 5 10 50 and 100 ppb standards by dilution using the ldquotraprdquo solution (discussed in Section 32 below) These standards were used to calibrate the Thermo Scientific X Series 2 ICP-MS for quantification of 127I A screen shot of a representative calibration curve is shown in Figure 34 The use of a reducing basic trap solution for iodine analysis limits the number of available internal standards that can be used to monitor ICP-MS instrument performance during iodine analysis Experiments are underway to identify acceptable internal standards However the data presented in this work did not use any internal standards prior to rigorous testing and analysis of representative standards As with the analyses for all isotopes (Tc I Np and Pu) spiked QAQC samples were frequently analyzed throughout the analysis as a check on instrument performance While these values cannot be used to correct individual samples in the same manner that the internal standards can they can be used to ensure accurate measurements of each isotope In almost all cases QAQC standards were within 10 of the expected value Because the average internal standard recovery ranges between 80 and 120 for the ICP-MS the iodine QAQC standard appears to be acceptable However a significant amount of ongoing work is testing various internal standards to improve the accuracy of iodine analysis using ICP-MS In one experiment (discussed in detail below) the QAQC standards deviated by an average value of 195 This will be specifically discussed below
Because experiments were performed with 127I concentrations up to 1000 ppb the 100 microgmL (ppm) stock iodate solution from High Purity Standards was used as the working solution
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Figure 34 Screen capture of a typical 127I calibration curve using Thermo PlasmaLab software to control the data collection and analysis R2=0999991 Intercept Conc (Detection Limit) = 024 ppb
315 Cementitious Materials Selected for Experiments There were four cementitious materials selected for this sorption study The first referred to as Aged Cement is a 30 year old sample that does not contain any reducing slag The aggregate from the Vault 2 cement had its aggregate removed prior to conducted tests in an effort to make subsamples more uniform This was necessary because some of the aggregate were larger than the 05 g subsamples used in individual sorption tests The Vault 2 cementitious material contained 17 dry wt- reducing slag on a dry weight basis before the water was added to the mix (Table 31) The TR547 and TR545 saltstone formulations contain 45 dry wt- and 90 dry wt- reducing slag respectively
Table 31 Characteristics of saltstone formulations used in this work Kaplan et al (2008)
Sample Percent Reducing Slag (dry wt-) (c)
Percent Portland Cement
(dry wt-) (c)
Percent Fly Ash
(dry wt-) (c)
Percent Aggregatesand ( dry wt-) (c)
Reducing Equivalents
(microeqg)
Aged Cement 0 10 45 45 855 plusmn 101(a)
Vault 2 Cement 17 10 45 0 178(b)
TR547 45 10 45 0 607(b) TR545 90 10 0 0 681(b) Blast furnace slag 100 0 0 0 819(b) (a) Kaplan et al (2008) (b) Roberts and Kaplan (2009) (c) All percentages of saltstone formulations are reported on a dry weight percentage basis that is the weight of the ingredients before water was added (d) Based on Table 8 in Dixon et al (2008 SRNL-STI-2008-00421) which shows the following quantity (lbscu yd) for saltstone Vault 2 Mix 1 concrete formulation 201 cement (1271 wt-) 268 slag (1695 wt-) 447 silica fume (283 wt-) 1563 fly ash (989 wt-) 911 fine sand (5762 wt-) The large aggregate was removed before the sorption tests were conducted The large aggregate accounted for 75 wt- of the original field sample not the sample used in these test before water was added to the mix TR547 is referred to as the Baseline by Dixon et al (2008) and is described in more detail in Appendix C (Mix 2) by Dixon et al (2008) (Control-BFSPC) and 1 (Baseline)
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TR545 saltstone contains 90 reducing slag and it is Mix 1 in Dixon et al (2008) and is described as
ldquoA control mix will be based on the baseline mix modified by exclusion of the Class F fly ash Consequently the cementitious materials premix will be a mixture of 90 blast furnace slag and 10 Portland cement The degree of reaction will be much greater than with the normal premix and therefore should result in a lower porosity and a lower permeability This bounding test at 060 wcm ratio is expected to yield a hydraulic conductivity at or below the detection limit for the Mactec permeameter measurement system Therefore this test should demonstrate the lowest level of detection of the Mactec system as well as show a resolvable difference between measurements of the control mix and the control mix with the normal premix compositionrdquo
32 ICP-MS Detection Limits
The PlasmaLab software platform determines a detection limit for each isotope based upon the intercept concentration A new calibration curve was generated for each experimental run and curves were very similar Using representative calibrations curves the detection limits for each isotope were as listed in Table 32 Note the higher detection limit for 127I is primarily due to the higher background count rate observed on the instrument This is believed to be due to the minimum purity levels of chemicals required for the iodine ldquotraprdquo solution as discussed in Section 33 below Therefore experiments were run with initial iodate concentrations higher than Tc Np and Pu to maintain analytical sensitivity
Table 32 Detection limits for each isotope based on representative calibration curves generated in PlasmaLab software associated with the ICP-MS
33 Experimental Methods
The experimental methods used in this work followed closely those previously described for experiments examining radionuclide sorption to saltstone (Kaplan et al 2007 Kaplan et al 2008) Brief descriptions of each method are provided below
Preparation of Calcite Solution Using a hotstirring plate 10 L of distilled-deionized (DDI)
water was heated to 3-100C above room temperature Then 001 g CaCO3 (EM Science ACS grade) was added to the solution and the resulting suspension was mixed for 24 hours at the elevated temperature The solution was then vacuum filtered through a 045-microm filter to ensure no solid CaCO3 remained in solution
Preparation of 2 HNO3 Analysis of Tc Np and Pu on the ICP-MS required dilution in 2
HNO3 This was prepared by adding 28 mL of Aristar Optima HNO3 from a clean graduated cylinder (designated to 2 HNO3) into a 1 L volumetric flask (designated to 2 HNO3) partially filled with DDI water and then further diluted to volume
Preparation of Trap Solution for Iodine Analysis Analysis of I required the use of a reducing
basic solution that was capable of reducing iodate to iodine and holding the iodine in solution This minimized the loss of I during sample analysis A 1 L trap solution was prepared by weighing out 00500 g NaHSO3 (Fisher Scientific ACS Grade) on a calibrated Sartorous LA 230S scale and adding it to a 1L volumetric flask Then 40 mL of 25 ww tetramethylammonium hydroxide (Alfa Aesar electronic grade) and 10 mL CFA-C solution (Spectrasol Inc) were added to the volumetric flask via a calibrated 1000-5000 microL Eppendorf Research pipette The solution was then diluted to volume with DDI water
34 Experimental Protocol for Sorption Experiments under Aerobic Conditions
Falcon BlueMax 15mL polypropylene vials were labeled and weighed to within 0001 g on a calibrated Sartorious LA 230S scale The scale was then zeroed and 025 +- 001 g of a given solid were added to each tube and the weight was recorded to within 0001g
For each of the four solids three sets of triplicate samples were prepared The three sets of samples were used to allow for experiments to be run with varying concentrations of each isotope Target initial concentrations for 99Tc 237Np and 242Pu samples were 1 ppb 5 ppb and 10 ppb Target initial concentrations for the 127I samples were 100 ppb 500 ppb and 1000 ppb A set of no solids controls at initial concentrations of 1 ppb and 10 ppb for 99Tc 237Np and 242Pu and initial concentrations of 100 ppb and 1000 ppb 127I were also prepared by adding the calcite solution to pre-weighed pre-labeled centrifuge tubes as discussed above
The solids were equilibrated with the calcite solution before spiking with the radionuclides This was done by adding 10 plusmn 01 mL of calcite solution to each tube and recording the mass The samples were then placed on a Thermo Scientific shaker overnight After 24 hours the solutions were allowed to settle for 1 hour The pH was then measured and the samples were then centrifuged for 15 minutes at 8000 rpm to further separate the solids The aqueous phase was then decanted and 10 plusmn 01 mL of calcite solution was added to each tube The weight of the tube (labeled tube + solid + calcite solution) was measured to within 0001g During this washing process the pH was monitored and held steady throughout the process The pH ranged from 11-12 depending on the particular saltstone used During the experiments the exact pH for all samples at all equilibration times was measured and is reported in Appendix A and B
The resulting suspensions were then spiked with 127I 237Np 242Pu and 99Tc It is important to note that all four isotopes were added to the same vial Use of the ICP-MS to determine the concentration of each isotope allows for a single solution to contain all analytes of concern This allowed for a greater variability in the sample set and increased replicates as opposed to running individual sorption tests for each isotope For the systems with initial 99Tc 237Np and 242Pu concentrations of 10 ppb and initial 127I concentration of 100 ppb a 100 microL aliquot of each radionuclide working solution was added to the first three tubes for each solid The addition was made with the tube resting on a tared analytical balance so that the exact mass of each radionuclide solution added was recorded and the solution was gently swirled before the next radionuclide was added The 5 ppb 237Np 242Pu and 99Tc and 500 ppb 127I samples were prepared in the same manner but adding 50 microL of the respective spike solutions The final three tubes with initial 237Np 242Pu and 99Tc concentrations of 1 ppb and 100 ppb 127I were prepared by using 10 microL of the spike solutions for all four solids as well as a set of solid-free controls (No-Solids Controls) For clarity this experimental matrix is shown in Table 33 below
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Table 33 Experimental Matrix of Sorption Experiments under Aerobic Conditions
After spiking the radionuclides a precalculated amount of 10M NaOH was added to each sample
to counter the acidic radionuclide spike solutions and the pH of one of the triplicate samples was measured to ensure the proper pH range was reached The samples were then placed on and end-over-end shaker to mix at approximately 8 rpm After 24 hours the samples were removed from the shaker and the pH of each sample was measured using an Orion Ross semi-micro glass electrode calibrated against pH 4 7 and 10 buffers (Thermo) The samples were then shaken and a transfer pipette was used to transfer 35 mL of a homogenous suspension to a 5mL syringe The solution was then passed through a 100 nm nylon syringe filter The first 025-050 mL of filtrate was discarded and the remaining filtrate was collected in a clean polyethylene vial Then 10 mL of the filtrate was removed and diluted in 90 mL 2 HNO3 The mass of each phase was determined and recorded gravimetrically Then 10 mL of the remaining filtrate was transferred to a clean Falcon BlueMax 15mL vial and diluted with 90 mL of trap solution for 127I analysis Again the volume of each phase was monitored gravimetrically After the 24 hour sampling event the samples were put back on the shaker to mix for three additional days On day four the above sampling procedure was repeated
The 237Np 242Pu and 99Tc samples can be run on the Thermo Scientific ICP-MS using the standard setup and procedure which included a standard flow glass nebulizer and bulb spray chamber However for the 127I analysis the ICP-MS must be reconfigured to accommodate the basic reducing trap solution This is to alleviate problems with iodine signal stability over time frequently observed in ICP-MS analysis The reconfigured instrument uses an Elemental Science Microflow PFA-100 Teflon nebulizer with a flow rate of 100microLmin along with a sapphire torch and a Teflon spray chamber This configuration must be run with a low pump speed to prevent back pressure on the system Two 30 minute stability tests were performed using a 50 ppb iodate solution Each experiment consisted of 40 separate measurements After each experiment was completed the uncorrected mass counts were examined and found to stay steady over the sampling period The relative standard deviation ( RSD) over all samples for each experiment was 1866 and 1460 respectively This shows that there was no significant ldquomemoryrdquo or loss of the iodine signal over time and that the reconfigured instrument has a stable iodine signal over time However as will be discussed below some difficulty has been encountered in finding an adequate internal standard for iodine analysis
35 Experimental Protocol for Sorption Experiments under Anerobic Conditions In order to examine the effects of reducing conditions of sorption of each isotope to the various cementitious samples a series of sorption experiments were performed in an anaerobic glovebox under a 2 H2(g) 98 N2(g) atmosphere Based on the measured pH and EH of these systems as discussed below these systems were at the point of reducing water Therefore they are expected to represent a lower end of the possible range for reducing conditions expected in the porewater available within cementitious materials
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Preparation of Calcite for Reducing Conditions Approximately 35 L of DDI water was boiled for 45 minutes Argon was slowly bubbled through the water as it cooled Once it cooled to below 500C approximately 3 g of calcite was added This solution mixed overnight under a continuous Ar flow After 12 hours the solution was moved into an oxygen free glove bag for filtration as described in 3231 After filtration the calcite solution was moved into the glove box
Preparation of Working Solutions under Reducing Conditions The calcite and solid solutions
were prepared in the glove box using the previously mentioned procedure used under aerobic conditions The radionuclide working solutions were transferred to the glovebox and stirred open to the reducing atmosphere for at least three days The concentration of each isotope in the working solutions was measured to determine any change in the concentration due to evaporation while the solutions were equilibrating
The preparation and spiking of samples for sorption experiments was performed exactly as described for the oxidizing conditions except all sample handling was performed in the glovebox After the 1 day and 4 day equilibration the samples were filtered within the glovebox then transferred outside for dilution and ICP-MS analysis similar to the description provided about for the oxidizing conditions For these experiments only 4 mL of either 2 HNO3 or trap solution were used to dilute the filtrate instead of the 90 mL used above for experiments performed under oxidizing conditions
36 Examination of Sorption to Vial Walls for Solids and No Solids Controls
As will be discussed below the solid-free controls samples indicated significant loss of Np and Pu Once the one and four days samples were collected and run on the ICP-MS it was necessary to determine the degree each radionuclide was sorbing to the vial walls The remaining suspensions and controls were emptied into a waste container Then 5 mL of the calcite solution was added to each vial using a calibrated pipette The vials were sonicated for approximately one minute and then emptied into the waste container Another 5 mL of calcite solution was added for the second wash and then discarded into the waste container This procedure was expected to remove any soluble Pu from the system or Pu associated with colloidal particles After each vial was washed 10 mL of 2 HNO3 was added using a calibrated pipette The acid solution is expected to remove any Tc Np or Pu associated with the vial walls This procedure has been shown to complete mass balances of Pu in similar sorption experiments using Pu (Powell et al 2002) This process was performed for both the solid suspension and the no solids controls The samples were then run on the ICP-MS to determine the concentration of 99Tc 237Np and 242Pu sorbed to the vial walls
37 Data Analysis The solubilities of 242Pu and 237Np were calculated by using the formula
nuclide
nuclide
nuclideMSICP
sol Mg
gCC
)(10 6
microminus
minus
= (Equation 31)
Csol = observed nuclide solubility (molnuclidekgsolution) CICP-MS = aqueous concentration of nuclide from ICP-MS measurement (ppb micrognuclidekgsolution) Mnuclide = molecular mass of nuclide (gnuclidemolnuclide)
In order to determine the Kd values one first needs to determine the concentration on the solid by using
SRNL-STI-2009-00636 Revision 0
24
solid
calcitespikeaqspikecalcite
spikestock
solid m
mmCmmmC
C)(
)()(
+⎥⎥⎦
⎤
⎢⎢⎣
⎡minus
+
lowast
= (Equation 32)
Csolid = calculated solid phase concentration of the nuclide (ppb) Cstock = concentration of the nuclide stock solution (ppb) mspike = mass of nuclide spiked into the saltstone suspension (g) mcalcite = total mass of calcite solution used in the saltstone suspension (g) Caq = aqueous concentration of nuclide from ICP-MS measurement (ppb) msolid = mass of the saltstone used in the suspension (g)
The Kd can be calculated using the equation
aq
solidd C
CK = (Equation 33)
Kd = solid-water partitioning coefficient (gsolutiongsolid assuming density of 10 gmL traditional
unit of mLsolutiongsolid can be obtained) This Kd Equation (33) is numerically equivalent to the traditional Kd equation proposed in ASTM D-4646 which has been used in previous saltstone experiments (Kaplan et al 2007 Kaplan et al 2008)
40 Results and Discussion
41 Radionuclide Sorption to Cementitious Formulations under Oxidizing Conditions
Figure 41 shows Pu Kd values ranging from 104 to gt105 mLg Generally for each solid the Kd increases with increasing initial Pu concentrations typical behavior of systems where the aqueous concentrations of the radionuclides are solubility controlled This is not expected because the Kd expression indicates that the Kd value should remain constant with increasing total Pu concentrations It was noted that aqueous phase concentration of Pu remained relatively constant in all samples (see discussion below regarding Pu solubility) Therefore the sorption capacity of each solid phase for Pu has not been overcome For each of these solid phases it appears the solutions had reached equilibrium before the first samples were taken at 24 hours In each case the Kd values for the one day and four day are similar A trend between the solid phases is not discernible The aged cement with no reducing slag was expected to have the lowest Kd values but in actuality it has the highest Kd Also there is no correlation with the concentration of reducing slag The Vault 2 samples with 17 dry wt- reducing slag has a Kd similar to that of the TR547 (45 dry wt- slag) while the saltstone with the most slag TR545 (90 dry wt- slag) has the lowest Kd value Others have observed that Pu Kd values of cementitious materials are similar in the absence and presence of slag (Allard et al 1984 Hoaglund et al 1985)
It was observed that similar aqueous concentrations of Pu were observed regardless of the solid phase present Figure 42 shows the average aqueous phase concentrations measured after one day and four days for all solids As stated above triplicate samples were prepared for each solid phase and each initial concentration Therefore each of the reported solubility values in Figure 42 is an average of nine measurements Using the highest reported value with the expected maximum error (0018 ppb for solid TR545) the maximum expected aqueous concentration of Pu in the pore water associated with the
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saltstone formulations will be approximately 7 x 10-11 molL as calculated using Equation 31 This is on the same order as the solubility of Pu hydrous oxide solid phases (Neck and Kim 2001)
Figure 41 Plutonium Kd Values under Oxidizing Conditions Plutonium Kd values for various saltstone formulations measured after one-day equilibration (1d) and four-day equilibration (4d under oxidizing conditions Total plutonium concentrations in each system were 1 ppb 5 ppb and 10 ppb Sample prepared in triplicate and error bars represent standard deviation of samples except as follows value for dataset TR547-4d 10 ppb is reported based on duplicate samples
Figure 42 Plutonium solubility for various saltstone formulations measured after one-day equilibration (1d) and four-day equilibration (4d) under oxidizing conditions Total plutonium concentrations in each system were 1 ppb 5 ppb and 10 ppb as noted Samples prepared in triplicate and an average of all samples (9) was used to determine average solubility The error bars represent standard deviation of samples
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Overall the Kd values for Np range from 105 to gt106 with only a few outliers The most significant outlier is the 1 ppb solution in the TR545 sample after the four-day equilibration It drops two orders of magnitude while the 5 and 10 ppb solutions remain constant However this result is most likely an analytical artifact from working at the detection limits of the ICP-MS In the one-day equilibration samples only one of the triplicates S-2-E had detectable Np while in the four-day equilibration samples only S-2-F had detectable amounts present The graph also shows that with the exception of the 5 ppb sample in the aged cement Np sorption to TR545 (90 dry-wt- slag) and TR547 (45 dry wt- slag) have Kd values approximately one order of magnitude over the aged cement (no slag) and Vault 2 (17 dry wt- slag) samples
It was observed that similar aqueous concentrations of Np were observed regardless of the solid phase present Figure 44 shows the average aqueous phase concentrations measured after one day and four-day equilibrations for all solids As stated above triplicate samples were prepared for each solid phase and each initial concentration Therefore each of the reported solubility values in Figure 44 is an average of nine measurements of Np concentration unless stated otherwise Using the highest reported value with the expected maximum error (00026 ppb for solid TR545) the maximum expected aqueous concentration of Pu in the pore water associated with the saltstone formulations will be approximately 2 x 10-11 molL
Figure 43 Neptunium Kd values under oxidizing conditions Neptunium Kd values for various saltstone formulations measured after one-day equilibration (1d) and four-day equilibration (4d) under oxidizing conditions Total plutonium concentrations in each system were 1 ppb 5 ppb and 10 ppb as noted Samples prepared in triplicate and error bars represent standard deviation of samples except as follows value for datasets TR545-1d 1ppb TR545-4d 1 ppb TR547 4d 1 ppb TR545-4d 10 ppb TR547-1d 1ppb TR547-4d 10 ppb are reported based on a single sample and for dataset TR545-1d 5ppb is reported based on duplicate samples Kd values limited to gt106 were at instrumental background
The Kd values for Tc are significantly lower than that of Pu or Np As a whole the values are
comparable The values for the one-day and four-day equilibrations solutions in the Vault 2 (17 dry wt- slag) and TR545 (90 dry wt- slag) remained constant within reasonable error with just a slight increase from the one-day to four-day equilibration However the Aged Cement (no slag) and TR547 (45 dry wt- slag) showed a noticeable decrease from day one to day four (Figure 45)
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Figure 44 Average solubility of Np under oxidizing conditions Neptunium solubility for various saltstone formulations measured after one-day equilibration (1d) and four-day equilibration (4d) under oxidizing conditions Total Np concentrations in each system were 1 ppb 5 ppb and 10 ppb Samples prepared in triplicate and an average of all samples (9) was used to determine average solubility except as follows TR545-1d is based on 6 samples TR545- 4d on 5 samples TR547-1d on 7 samples and TR547- 4d on 5 samples The error bars represent standard deviation
Figure 45 Technetium Kd values under oxidizing conditions Tc Kd values for various saltstone formulations measured after one-day equilibration (1d) and four-day equilibration (4d) under oxidizing conditions Total Tc concentrations in each system were 1 ppb 5 ppb and 10 ppb as noted above Samples were prepared in triplicate and the error bars represent standard deviation of samples except as follows data sets for Vault 2-1d 1ppb were duplicates and TR547- 4d 10 ppb is based on a single dataset
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Similar to the Tc Kd values the 127I Kd values are much lower than those of Pu and Np The amount of reducing slag present in each of the solids does not appear to have a drastic effect on the 127I Kd values In fact the initial (one day) Aged Cement (0 slag) samples had a Kd almost two orders of magnitude above those with reducing slag The cause of this behavior is not known but it has been shown that iodate IO3
- the oxidized form of iodine sorbs more strongly than iodide I- to charged surfaces (Schwehr et al 2009 Yoshida et al 1992 Fukui et al 1996) It is possible that the slag is reducing the iodine to the I- form converting it to a species that is less likely to sorb to saltstone Additional work would be required to confirm the oxidation state of iodine when associated with saltstone
Figure 46 Iodine Kd Values under Oxidizing Conditions Iodine Kd values for various cementitious formulations measured after one-day equilibration (1d) and four-day equilibration (4d) under oxidizing conditions Total iodine concentrations in the systems were 100ppb 500 ppb and 1000 ppb as noted above Samples were prepared in triplicate and the error bars represent standard deviation of samples except as follows duplicates were used for dataset TR545- 1d 100ppb
42 Radionuclide Sorption to Vial Walls Under Oxidizing Conditions
Figure 47 shows the aqueous fractions found in the no-solids controls It provides a measure of the solubility of each radionuclide as well as examines the fraction of each radionuclide sorbed to the vial walls After one day only 25 of the Pu remained in solution and the concentration decreased even more after four days The loss of Pu from the aqueous phase may be due to sorption of Pu to the vial walls or precipitation of a Pu hydrous oxide solid (discussed with respect to Figure 49 below) Additional experiments would be required to examine the solubility of the Pu in high pH calcite saturated solutions
After one day about 80 of the Np remained in solution However the aqueous concentration in the initially 1-ppb solution was significantly reduced after four days Approximately 60 of the Np remained soluble in the initially 10-ppb solution Once again this drop could be due to sorption to the vial wall The Tc present after one day ranged from about 88 to about 95 and was virtually 100 after four days These values are consistent with internal standards used to monitor Tc detection performance on the ICP-MS Greater than 50 of the I remained in solution after the one-day and four-day equilibrations As shown in Figure 48 the standard deviation between the triplicate I control samples was
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quite large Additional control samples are required to understand the mechanism by which I is being lost from the aqueous phase in these samples
Figure 47 Plutonium Neptunium and Technetium Aqueous Fractions Fraction of Pu Np and Tc remaining in the aqueous phase for the No Solids controls after a one-day equilibration (1d) and four-day equilibration (4d) under oxidizing conditions The total concentration for each radionuclide 10 ppb as noted above Samples were prepared in triplicate and the error bars represent the standard deviation of the samples
Figure 48 Iodine Aqueous Fraction Iodine aqueous fraction for the no-solids controls after a one-day equilibration (1d) and four-day equilibration (4d) under oxidizing conditions The total concentration of iodine was 1000 ppb as noted above Samples were prepared in triplicate and the error bars represent the standard deviation of the samples
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As discussed above the loss of Np and Pu from the no-solids control (Figure 47) could be due to
precipitation of Np and Pu hydrous oxides or sorption to the vial walls To quantify the differences between these possible sinks the vials were washed as described in Section 36 The data in Figure 49 indicate that significant sorption of Np and Pu to the vial walls may occur When combining the mass of Np represented in Figure 47 and Figure 49 there is almost 100 mass recovery of the Np sorbed to the vial wall and the aqueous fraction measured Therefore no precipitation of Np is expected However because 100 recovery was not achieved for Pu a Pu hydrous oxide phase could be precipitating which was washed out of the vial during the cleaning procedure The data in Figure 47 represent the no-solids control samples where there was no solid phase present for Np or Pu to sorb to besides the vial walls However when a cementitious solid phase is present in the sample there will be competition between the vial walls and the cement for sorption of Np and Pu Based on the affinity of metals for metal oxide surfaces as opposed to the polypropylene surface and the much higher surface site density expected for the cementitious samples it is assumed that the cementitious samples will out-compete the vial walls for sorption sites This thesis was tested by taking one of the triplicate samples from each sorption experiment with a solid phase present removing the solid phase from the tubes and leaching any sorbed Np and Pu from the tubes with acid as described in Section 36 Figure 410 and Figure 411 show that although some of the Pu and Np sorbed to the vial walls of the samples this amount accounted for less than 2 in all samples Therefore sorption of Np and Pu to the vial walls does not appear to be a significant factor in experiments where the solid phase is present Note these results do not discount the possibility that Pu hydrous oxide precipitates were forming in both the no-solid control experiments and experiments with cement formulations present Based on the observation of a constant aqueous phase concentration of Pu regardless of the initial Pu concentration the presence of a solubility limiting Pu phase cannot be discounted based on these data Further experiments examining the solubility of Pu in high pH calcite saturated solutions are required
Like Pu Np shows little affinity for the vial walls in the presence of a solid phase In each case tested there was significantly less than 1 of the total Np sorbed to the vial walls This behavior is consistent with the ~100 mass balance on Np achieve in the solid-free controls The majority of Np remained soluble in the solid-free control experiments Therefore it is expected that sorption of Np to the vial walls was the primary reason for the loss of Np from the aqueous phase in the no-solids systems rather than precipitation of a Np solid phase similar to the process discussed for Pu above This assumption is based on the relative solubility of Np(V) as compared with Pu(IV)
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Figure 49 Percent Pu and Np sorbed to vial walls of the no solids controls after the aqueous phases were discarded and the vials were washed Both the 10 ppb and 1 ppb datasets were prepared in triplicate and the error bars show the standard deviation
Figure 410 Percent Pu sorbed to vial walls after the solids and aqueous phases were removed and the vials were washed The graph illustrates one sample from each of the 1 ppb 5 ppb and 10 ppb systems Therefore no error bars are present
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Figure 411 Percent Np sorbed to vial walls after the solids and aqueous phases were removed and the vials were washed The graph illustrates one sample from each of the 1 ppb 5 ppb and 10 ppb systems Therefore no error bars are present
43 Radionuclide Sorption to Cementitious Formulations under Reducing Conditions
Similar to the Pu Kd values under oxidizing conditions Pu Kd values ranged from 104 to gt105 under reducing conditions (Figure 412) Also similar to the results under oxidizing conditions the Kd increases with increasing initial Pu concentration Again this behavior is indicative of the aqueous phase concentration of Pu being controlled by solubility of Pu rather than by sorption In each case the samples appeared to reach steady state within 24 hours This equilibration is evident because the Kd values after one day and four days are very similar Also it appears that the amount of reducing slag does not make a significant difference in the Kd value In fact the TR547 solid consists of 45 reducing grout but produces approximately the same Kd values of the aged cement which does not have any reducing grout Each of these Kd values are higher than the TR545 which is 90 reducing grout These findings are in agreement with those conducted by Allard et al (1984) and Hoglund et al (1985) who reported that concrete containing reducing agents (slag similar to that used in our study) did not have greater Pu Kd values than those that did not contain slag
Similar aqueous concentrations of Pu were observed regardless of the solid phase present Figure 36 shows the average aqueous phase concentrations measured after one day and four days for all solids As stated above triplicate samples were prepared for each solid phase and each initial concentration Therefore each of the reported solubility values in Figure 412 is an average of up to nine measurements of the Pu aqueous concentrations Using the highest reported value with the expected maximum error (00045 ppb for solid Vault 2) the maximum expected aqueous concentration of Pu in the pore water associated with the cementitious formulations will be approximately 2 x 10-11 molL (calculated from Equation 31) This value is on the same order as the solubility of Pu hydrous oxide solid phases (Neck and Kim 2001) A best value would be 10-12 molL
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Figure 412 Pu Kd Values under Reducing Conditions Plutonium Kd values for various cementitious formulations measured after one-day equilibration (1d) and four-day equilibration (4d) under reducing conditions Total plutonium concentrations in each system were 1ppb 5 ppb and 10 ppb Samples prepared in triplicate and error bars represent standard deviation
Figure 413 Average Solubility of Plutonium under Reducing Conditions Plutonium solubility for various cementitious formulations measured after one-day equilibration (1d) and four-day equilibration (4d) under reducing conditions Total plutonium concentrations in each system were 1ppb 5 ppb and 10 ppb as noted Samples prepared in triplicate and an average of all samples (9) was used to determine average solubility The error bars represent standard deviation of samples
The Np Kd values reported in Figure 414 obtained under reducing conditions are very similar to
those obtained under oxidizing conditions In each case the samples appeared to reach steady state within 24 hours This equilibration is evident because the Kd values between the one-day and fourndashday equilibrations are similar As was the case with Pu the amount of slag present in each solid does not
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seem to have a significant effect on the Kd values Again the aged cement with no slag has as high a Kd as the TR545 with 90 reducing slag
Similar aqueous concentrations of Np were observed regardless of the solid phase present Figure 314 shows the average aqueous phase concentrations measured after one day and four days for all solids All Kd values were gt 105 mLg which is considerably larger than those reported by Kaplan and Coates (2007) who reported Np Kd values to 1300 to 1600 mLg This difference can be attributed to two important experimental differences 1) the experiment was designed to permit larger Kd values to be measured (eg solid to liquid ratios and spike concentrations) and more importantly 2) a more sensitive analytical method ICP-MS was used instead of conventional low-energy gamma spectroscopy or liquid scintillation counting (LSC) analysis As stated above triplicate samples were prepared for each solid phase and each initial concentration Therefore each of the reported solubility values in Figure 415 is an average of up to nine measurements Using the highest reported value (to provide the most conservative most soluble values) with the expected maximum error (00045 ppb for solid TR545) the maximum expected aqueous concentration of Np in the pore water associated with the cementitious formulations will be approximately 2 x 10-11 molL A best value taking into consideration the less-than values which are depicted in Figure 414 as running off the top of the plot would be 10-12 molL
Figure 414 Np Kd Values under Reducing Conditions Neptunium Kd values for various cementitious formulations measured after one-day equilibration (1d) and four-day equilibration (4d) under reducing conditions Total Np concentrations in each system were 1 ppb 5 ppb and 10 ppb Samples were prepared in triplicate and the error bars represent standard deviation Kd values limited to gt106 were at instrumental background
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Figure 415 Average Solubility of Neptunium under Reducing Conditions Neptunium solubility for various cementitious formulations measured after one day equilibration (1d) and four day equilibration (4d) under reducing conditions Total plutonium concentrations in each system were 1ppb 5 ppb and 10 ppb Samples prepared in triplicate and an average of all samples (9) was used to determine average solubility The error bars represent standard deviation
A plot of the Tc Kd values for each cementitious formulations under reducing conditions is shown
in Figure 416 (log y-axis) and Figure 417 (reduced scale linear y-axis) The Kd values for each of the initial Tc concentrations are relatively similar This behavior is consistent with the Kd expression However the increasing Kd values from the one-day to four-day day equilibrations for each solid indicate that steady state was not reached within one day and it is unclear whether steady state was reached after four days A possible explanation for this behavior is that Tc(VII) was being reduced to Tc(IV) in these systems due to the reducing conditions As Tc(VII) was reduced the Kd would increase based on the high affinity of Tc(IV) for solid phases This proposed mechanism was observed by Lukens et al (2005) using an SRS saltstone material similar but not identical to TR547 Using synchrotron X-ray absorption fine structure spectroscopy they observed over a 453 month period that Tc(VII) incorporated into SRS saltstone slowly converted to Tc(IV) and that the nearest neighbor was initially predominantly oxygen and eventually became predominantly sulfur (described as a Tc(IV) phase TcSx) Lacking in Lukens et al (2005) is quantification of the solubility of Tc This analysis still needs to be completed along with re-oxidation studies (ie what is the rate that reduced Tc reoxidizes under ambient natural saltstone conditions)
Unlike Np and Pu Tc Kd values changed with the amount of slag included in the formulation Tc Kd values noticeable increase as the amount of slag in the formulation increased TR547 (45 dry-wt- slag) Kd value is visibly higher than the Aged Cement and Vault 2 Kd values while the most reducing TR545 (90 dry wt- slag) Kd value is significantly higher than the others Following a similar trend the reduction capacity that is the total quantity of reductant in the saltstone on a mass basis (units of milli-equivalents of charge per g) of TR547 had slightly greater or equal reduction capacity to that of TR545 (Roberts and Kaplan 2009)
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Figure 416 Tc Kd Values under Reducing Conditions Tc Kd values for various cementitious formulations measured after one-day equilibration (1d) and four-day equilibration (4d) under reducing conditions Total Tc concentrations in each system were 1 ppb 5 ppb and 10 ppb Sample prepared in triplicate and error bars represent standard deviation except as follows TR547-1d 1 ppb is based on a single dataset and datasets Vault 2-1d 5 ppb Vault 2- 4d 1 ppb Aged Cement-1d 5 ppb and Aged Cement-4d 1 ppb are duplicates
Figure 417 Data from Figure 416 replotted on a reduced linear scale for easier viewing Each sample was prepared in triplicate except as follows TR547-1d 1 ppb is based on a single dataset Vault 2-1d 5 ppb Vault 2- 4d 1 ppb Aged Cement-1d 5 ppb and Aged Cement-4d 1 ppb are duplicate datasets
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The calculated Kd values for I sorption to cementitious samples under reducing conditions are shown in Figure 418 Before discussing the data it should be noted that spiked QAQC samples which were analyzed on the ICP-MS along with the samples used to generate the data in Figure 418 were off by an average of 195 with one outlier of approximately 40 This dataset did not include the use of internal standards as discussed in Section 31 above1 Due to a lack of an internal standard the iodine results presented in this report should be considered with a minimum error estimate of 20
The iodine Kd values under reducing conditions are different from those observed under oxidizing conditions Under oxidizing conditions it appears they are at a steady state by day one However under reducing conditions there is a noticeable difference between days one and four indicating steady state was not reached by day one and possibly not by day four Another interesting observation is that the Kd values are decreasing from day one to four A possible reason for this behavior may be due to redox chemistry of iodine in this system If iodine partially or entirely exists in the form as iodate (IO3
-) it is possible it could be reduced to iodide I- within the reducing cementitious system These two iodine species sorb differently iodate sorbing to minerals more strongly than iodide (Denham et al 2009 Schwehr et al 2009 Fukui et al 1996 Yoshida et al 1992) It is hypothesized that the reducing environment of the saltstone is sufficient to reduce iodate ions to the more weakly binding form of iodine iodide
This is one of the few datasets (along with Tc) in this study where there may be a difference between the various solids The degree of iodate reduction would be expected to increase as the slag content increases As mentioned above reduction of iodate to iodide should result in a decrease in sorption Therefore higher Kd values should be observed for solids with less slag such as the Aged Cement (0 dry wt- slag) and Vault 2 (17 dry wt- slag) This is generally the case in Figure 418 where the highest Kd values are reported for the Aged Cement and the lowest values are for solid TR547 However this trend does not hold completely where the saltstone sample containing 90 slag (TR545) has generally equal or higher Kd values than the saltstone containing 45 dry wt- slag (TR547)
1 Clemson University is presently investigating appropriate internal standards for iodine analyses for ICP-MS Of those tested rhenium and molybdenum have shown some promise
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Figure 418 Iodine Kd Values under Reducing Conditions I Kd Values for various cementitious formulations measured after one day equilibration (1d) and four day equilibration (4d) under reducing conditions Total iodine concentrations in each system were 100 ppb 500 ppb and 1000 ppb as noted Sample prepared in triplicate and error bars represent standard deviation of samples except as follows Vault 2-4 d 100 ppb is a single dataset while the datasets for Vault 2-1 d 100 ppb 4 d 1000 ppb TR545-4 d 1000 ppb 100 ppb TR547-4 d 1000 ppb 500 ppb 100 ppb and Aged Cement- 4 d 1000 ppb and 100 ppb are all based on duplicates
44 Radionuclide Sorption to Vial Walls under Reducing Conditions
The aqueous concentrations for Pu Np and Tc in the no solids controls are shown in Figure 419 The results are similar to those presented for experiments performed under oxidizing conditions above The 1 ppb Pu aqueous fraction is approximately three times greater than the 10 ppb fraction at day one This fraction decreases over time and by day four they are approximately equal when taking error into account This behavior is similar to the aqueous fraction under oxidizing conditions The 1 ppb Np aqueous fraction is significantly higher on both day one and day four than the aqueous fraction of the 10 ppb samples However each remained constant from day one to day four The 10 ppb aqueous fraction is twice as low as under oxidizing conditions which suggests either higher sorption to the vial walls or more precipitating out under the reducing conditions Like Pu and Np Tc shows a decrease from day one to day four especially for the 1 ppb samples The decrease in the 10 ppb sample is minimal and the aqueous fraction remains around 09 This value is slightly lower than that under oxidizing conditions
To examine the degree of sorption to the vial walls the tubes were washed again as performed for the experiments under oxidizing conditions above and similar results were found Ninety percent of the 1 ppb Pu sample was sorbed to the vial wall upon completion of the experiment which gives a 100 mass recovery when comparing this value to that found in Figure 419 However this result is not the case with the 10 ppb samples where approximately 75 of the mass remains unaccounted It is noteworthy that approximately 25 of the Pu from the 10 ppb solution sorbed to the vial walls under both oxidizing
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and reducing conditions Np follows the same trend as Pu while less than 005 of the Tc sorbed to the wall
Figure 419 Plutonium Neptunium and Technetium No-Solids Aqueous Fractions under Reducing Conditions Pu Np and Tc aqueous fractions of No Solids controls after a one-day equilibration (1d) and four-day equilibration (4 d) under reducing conditions Total concentration for each radionuclide was 1 ppb and 10 ppb Samples were prepared in triplicate and the error bars represent the standard deviation
Figure 420 Percent of Pu Np and Tc sorbed to the vial walls of the No Solids control samples under reducing conditions Each the 1 ppb and 10 ppb samples were prepared in triplicate and the error bars represent the standard deviations of triplicate samples
Under reducing conditions the fraction of I remaining in the aqueous phase was around 90 with
almost 100 mass recovery of the 100 ppb I after the four-day equilibration These graphs show that
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under reducing conditions there will only be a small fraction of I sorbing to the vial wall or coming out of solution This result is a much better mass recovery than under oxidizing conditions (Figure 48) which had a mass recovery of approximately 65 after four days This result is also consistent with the interpretation that there may be a iodine speciation change between the two redox treatments
Figure 421 Iodine No-Solids Aqueous Fractions under Reducing Conditions I aqueous fractions of No-Solids controls after a one-day equilibration (1d) and four-day equilibration (4d) under reducing conditions The total concentration for each system was 100 ppb and 1000 ppb Samples were prepared in triplicate and the error bars represent the standard deviation
50 Comparison of Radionuclide Sorption under Oxidizing and Reducing Conditions
In the following figures (Figure 51 through Figure 54) the data shown above has been replotted to allow comparison between the oxidizing and reducing conditions for each cementitious formulation General observations based on these data follow Vault 2 Observations (Figure 51)
bull Pu Kds are greater than 104 under both oxidizing and reducing conditions and Pu Kds are slightly lower under reducing conditions This could possibly be due to reduction of Pu(IV) to Pu(III) However no oxidation state analysis was performed in this work
bull Np Kds are generally greater than 104 under both oxidizing and reducing conditions Interestingly Np Kds are higher under reducing conditions by almost an order of magnitude This could possibly be due to reduction of Np(V) to Np(IV) However no oxidation state analysis was performed in this work
bull Regardless of the initial Np or Pu concentration similar aqueous phase concentrations of Np or Pu were observed in all samples This trend indicates that ldquosorptionrdquo of Np and Pu in these systems may be a combination of adsorption absorption and (co)precipitation processes
bull Tc appears to reach a steady state within four days under oxidizing conditions This behavior does not appear to be the case under reducing conditions After four days similar Kd values are reached under both oxidizing and reducing conditions It is unclear
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whether the Kd value of Tc will continue to increase under reducing conditions consistent with reduction of Tc(VII) to Tc(IV) The similarity in Kd values under both oxidizing and reducing conditions is an interesting observation and certainly warrants additional studies
bull I Kd values are similar under both oxidizing and reducing conditions However reducing condition systems may not be at steady state after four days while systems under oxidizing conditions appeared to reach a steady state The difference in rates may be due to reduction of iodate to iodine
bull For all isotopes examined the sorption behavior to each of the solid phases is very similar
TR545 and TR547 Observations (Figure 52 and Figure 53) bull Similar to the discussion above with respect to Vault 2 Pu Np and Tc all appear to reach
a steady state under oxidizing conditions and approach steady state slower under reducing conditions
bull Np and Pu Kd values are greater than 104 for all systems and time steps The aqueous phase concentrations of Np and Pu appear to be better described as a solubility in terms of the aqueous phase concentration of Np and Pu Similar aqueous phase concentrations of both Np and Pu were reached The data indicate that the initial Np and Pu concentration generally does not affect the aqueous phase concentration at an apparent steady state The presence of each solid phase appears to limit the aqueous phase concentration of both Np and Pu on the order of 10-11 molL
bull Tc shows significantly higher Kd values under reducing conditions versus oxidizing conditions
bull For all isotopes examined the sorption behavior to each of the solid phases is very similar
Aged Cement Observations (Figure 54) bull Pu appears to be close to steady state for each solid by day one with similar Kd values
reached on between day one and day four bull Np has a higher Kd under reducing conditions than oxidizing (105 under oxidizing
conditions and gt105 under reducing conditions) bull Neither set of Tc data was at steady state by day one and rates of sorptiondesorption
reactions appear to be different Tc Kds decrease from day one to four under oxidizing conditions but increase under reducing conditions
bull The Kd values for I under oxidizing conditions were considerably higher than those measured for I with any other solid Similar Kd values obtained for the same solids under reducing conditions indicate that the reported Kd values under oxidizing conditions appear to be suspect However analysis of the raw data gives no indication of an experimental artifact As discussed above these observations may be explained based upon the amount of slag contained within the solids which will affect the reducing capacity (ie No reducing slag is in the aged cement which could be reason the reduction of iodate to iodide (speculated in other samples) is not evident)
bull The difference in sorption behavior of iodine to the aged cement between oxidizing and reducing conditions also indicates that the reducing conditions of the solution may affect I redox behavior in addition to any reactivity expected in the solid phases
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Figure 51 Comparison of Tc I Np and Pu sorption to Vault 2 solid under oxidizing and reducing conditions
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Figure 52 Comparison of Tc I Np and Pu sorption to TR 545 solid under oxidizing and reducing conditions
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Figure 53 Comparison of Tc I Np and Pu sorption to TR547 solid under oxidizing and reducing conditions
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Figure 54 Comparison of Tc I Np and Pu sorption to Aged Cement under oxidizing and reducing conditions
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60 Comparison of Radionuclide Sorption and Solubility under Oxidizing and Reducing Conditions
To further summarize the data the following tables provide either the average solubility
(for Np and Pu) or average Kd (for Tc and I) determined under both oxidizing and reducing conditions for each cementitious formulation Each table lists the average value standard deviation and the number of replicate samples used to calculate the reported values
The solubility of Pu in the presence of each solid under oxidizing and reducing conditions is shown in Table 61 (this is taken from experiments equilibrated for four days not one day) Under oxidizing conditions the apparent solubility values associated with the Aged Cement (0 dry wt- slag) Vault 2 (17 dry wt- slag) and TR547 (45 dry wt- slag) are all similar with only a slight increase in solubility as the amount of reducing slag increases There is a significant increase of almost an order of magnitude for the most reducing saltstone TR545 (90 dry wt- slag) However these samples also have a standard deviation on the same order of magnitude as the solubility itself which when taken into account brings the solubility back into the range of the others Under reducing conditions the apparent solubility values are slightly lower than under oxidizing conditions In this set of samples the Vault 2 saltstone with 10 dry wt- reducing slag had the highest apparent solubility but once again when considering the standard deviation the values are similar
Table 61 Comparison of plutonium apparent solubility values under oxidizing and reducing conditions
Table 62 lists the apparent solubility values of Np in the presence of each cementitious
formulation under both oxidizing and reducing conditions Under oxidizing conditions the cementitious formulation does not appear to have a dramatic effect on the solubility The apparent solubility values are similar to those of Pu under similar conditions except the Np standard deviations are much higher The high standard deviations are an analytical artifact since the measured concentrations were close to or at the detection limit of the ICP-MS There does appear to be a slight decrease in Np solubility under reducing conditions However the statistical significance of this decrease was not calculated
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47
Table 62 Comparison of neptunium apparent solubility values under oxidizing and reducing conditions
Unlike the apparent solubility values of Pu and Np the aqueousatmospheric conditions
and cementitious formulation seem to have an effect on the Tc Kd values (Table 63) Under oxidizing conditions there is not a discernible difference among the different cementitious formulations especially when taking the respective standard deviations into account However when experiments were run under reducing conditions the specific formulation had a noticeable effect The two saltstone samples with the least amount of reducing slag Aged Cement (0 dry-wt- slag) and Vault 2 (17 dry wt- slag) had Kd values which were similar to those observed under oxidizing conditions However the TR547 (45 dry-wt- slag) increased by almost an order of magnitude while the TR545 (90 dry wt- slag) increased by about three orders of magnitude Although the respective standard deviations are large the higher Kd values do appear to be significant
Table 63 Comparison of technetium Kd values under oxidizing and reducing conditions
Unlike Tc I does not seem to be as affected by cementitious formulation and redox status (Table 64) The only treatment (possible outlier) that does not follow this trend is the Aged Cement under oxidizing conditions This Kd value is higher than the others but also has a much higher standard deviation which when accounted for gives a value similar to the others All other treatments had near identical Kd values irrespective of solid phase or redox condition But again the Aged Cement data cannot be discounted at this time given the possibility of the influence that redox may have on iodine speciation and the strong influence I speciation has on sorption to cementitious materials
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Table 64 Comparison of iodine Kd values under oxidizing and reducing conditions
71 Comparison with Previous Data The increased sensitivity of the ICP-MS over conventional low-energy gamma
spectroscopy or liquid scintillation counting (LSC) analysis allowed for much more accurate Kd values and apparent solubility values in this work than were previously obtainable Generally radioanalytical detection methods start with activities on the order of 103 to 104 counts per minute (cpm) and approach background levels of 1 to 5 cpm for strongly sorbing radionuclides Therefore the accuracy of the Kd value will be the difference in analytical sensitivity when the initial aqueous activity decreases by a factor of approximately 5000 (ie the aqueous activity drops from approximately 5000 cpm to the instrument background of 1 cpm following almost complete sorption) As a result the reported Kd values can only be reliably reported up for a Kd of 103 to 104 This constraint is believed to be the difference between the observed Kd values for 237Np of gt 105 observed in this work when compared with the Kd values between 3000 and 4000 reported by Kaplan et al (2008) A similar observation was made for Pu because 242Pu was used for ICP-MS analysis and 238Pu was used in the work of Kaplan et al (2008) This constrint may account for the different Kd value of gt104 reported in Kaplan et al (2008) compared with the value of gt105 observed in this work
In the case of Tc Kaplan et al (2008) reported a Kd of 023 mLg for Vault 2 under oxidizing conditions and 093 mLg under reducing conditions while the above experiment determined the Vault 2 Kd to be 505 mLg under oxidizing conditions and 557 mLg under reducing conditions Unlike the discrepancy in the Kd values for Np Pu and Tc between the above findings and those in Kaplan et al (2008) the reported Kd values for iodine are similar For Vault 2 Kaplan et al (2008) found 125I to have a Kd of 894 mLg under oxidizing conditions and 715 mLg under reducing conditions These values are similar to the Kd values of 766 mLg and 725 mLg observed under oxidizing and reducing conditions respectively in this work These findings appear to confirm the previously accepted Kd values of 0-10 mLg depending on the cementitious formulation
72 Suggested Future Work The above data demonstrate several areas that require further examination The
increasing Tc Kd values over time dataset suggest that steady state had not been achieved It would be beneficial to determine the amount of time required to reach steady state and allow determination of a more accurate Kd value (an assumption of the Kd construct is that it be measured at steady state) Also kinetic studies of both Tc and I are needed to better understand their respective interactions with the different cementitious formulations As for the I additional
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49
tests should be performed to test the hypothesis that iodine may in part exist as iodate which may initially sorb to the saltstone then undergo reduction to iodine or iodide and then desorbs causing a decrease in Kd
A final area of future work is to examine the possible causes for the similar behavior of each cementitious formulation despite the different slag content This discrepancy is not only observed in the above experiments but also in Kaplan et al (2008) which is illustrated in Table 31 and by recent work in measurements of saltstone reduction capacity (Roberts and Kaplan 2009) The reduction capacity (units in milli-equivalentsg solid) equivalents of the Aged Cement with no slag is 855 plusmn 101 and adding 10 slag gives a reducing equivalent of 2398 plusmn 311 However increasing the slag content to 23 causes the reducing capacity to increase to 8218 plusmn 81 which is almost equivalent to the 8324 plusmn 49 of the 100 slag Understanding the chemistry behind the reducing capacity of each cementitious formulation will help to define what reactions are important for controlling radionuclide release from the saltstone
80 References Allard B L Eliasson S Hoglund and K Andersson 1984 ldquoSorption of Cs I and actinides in
concrete systemsrdquo SKB Technical Report SKBKBS TR-84-15 DKB Stockholm Sweden
Denham M D I Kaplan and C Yeager2009 ldquoGroundwater radioiodine Prevalence biogeochemistry and potential remedial approachesrdquo SRNL-STI-2009-00463 Savannah River National Laboratory Aiken SC
Dixon K L M A Phifer and J R Harbour 2008 ldquoFY09 PACA Maintenance Program Additional Saltstone Property Testingrdquo SRNL-L3100-2009-00019 Rev0 Savannah River National Laboratory Aiken SC
Fukui M Fujikawa Y and Satta N 1996 ldquoFactors affecting interaction of radioiodide and iodate species with soilrdquo Journal of Environmental Radioactivity 31 199-216
Hoglund S L Eliasson B Allard K Andersson and B Torstenfelt 1985 ldquoSorption of some fission products and actinides in concrete systemsrdquo Mat Res Soc Symp Proc 50 683-690
Kaplan D I 2007 Geochemical Data Package for Performance Assessment Calculations Related to the Savannah River Site WSRC-TR-2006-00004 Rev 1 Washington Savannah River Company Aiken SC
Kaplan D I and Coates J 2007 ldquoPartitioning of Dissolved Radionuclides to Concrete under Scenarios Appropriate for Tank Closure Performance Assessmentsrdquo WSRC-STI-2007-00640 Rev 0 Washington Savannah River Company Aiken SC 29808
Kaplan D I Roberts K Coates J Siegfried M Serkiz S 2008 ldquoSaltstone and concrete interactions with radionuclides Sorption (Kd) desorption and reduction capacity measurementsrdquo SRNS-STI-2008-00045 Savannah River National Laboratory Aiken SC 2008
SRNL-STI-2009-00636 Revision 0
50
Neck V and Kim J I 2001 ldquoSolubility and hydrolysis of tetravalent actinidesrdquo Radiochim Acta 89 1
Powell B A Fjeld R A Coates J T Kaplan D I Serkiz S M 2002 ldquoPlutonium Oxidation State Geochemistry in the SRS Subsurface Environmentrdquo WSRC-TR-2003-00035 Westinghouse Savannah River Company US DOE Savannah River Site Aiken SC
Roberts K A and D I Kaplan 2009 Reduction Capacity of Saltstone and Saltstone Componentsrdquo SRNL-STI-2009-00637 Rev0 Savannah River National Laboratory Aiken SC
Schwehr K A Santschi P H D I Kaplan C M Yeager and R Brinkmeyer 2009 ldquoOrgano-iodine formation in soils and aquifer sediments at ambient concentrationsrdquo Environ Sci Technol 437258-7264
Yoshida S Muramatsu Y and Uchida S 1992 ldquoStudies on the sorption of I-(iodide) and IO3-
(iodate) onto andosolsrdquo Water Air and Soil Pollution 63 321-329
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51
90 Appendix A Data Tables of Radionuclide Sorption to Saltstone under Oxidizing Conditions
The following tables represent data collected for the no solids controls each saltstone and testing of radionuclide sorption to the vial walls The no solids controls tables include the concentration (ppb) of the radionuclide spiked into the sample along with the concentration of the radionuclide (ppb) measured in the aqueous phase after the given equilibration time The pH at the time the sample was taken is also recorded along with the fraction of the radionuclide which stayed in the aqueous phase The tables for the cementitious formulation data include the data above along with the addition of a Kd value The tables of the data for the radionuclides sorbed to the vial walls include the initial concentration (ppb) of the spike the concentration (ppb) of the radionuclide that had sorbed to the vial wall during the experiment and the percentage of the total concentration this represents Important Notes
BDL- Below Detection Limit lt01 denotes no notable sorption occurred
91 Data Tables for No Solid Controls
Table 91 Plutonium no solids control after one day
A 9264165178 402285E‐05 1181 434238E‐06 9980817 B 9352537276 0000110618 1183 118276E‐05 3616813 C 9363541597 705331E‐05 118 753273E‐06 5401186 D 0993110568 BDL 12 NA NA E 0977247222 300794E‐05 1199 307797E‐05 1280331 F 0962441315 BDL 1198 NA NA G 4059128499 BDL 1186 NA NA H 4065161486 705198E‐05 1188 173473E‐05 2380003 I 4116819691 0000110748 1189 269014E‐05 1555864
Table 920 TR545- neptunium after four days
Sample ID
Initial Aq Conc (ppb)
Equil Aq Conc (ppb) pH
Fraction Aq Kd
A 92641652 NA 1188 NA NA B 93525373 00001935 1185 2069E‐05 2067199C 93635416 4119E‐05 1185 44E‐06 9247818D 09931106 BDL 1197 NA NA E 09772472 BDL 12 NA NA F 09624413 00066817 1206 00069424 562421G 40591285 00003289 1196 8103E‐05 5148274H 40651615 00025316 1196 00006228 6625737I 41168197 00001018 1194 2474E‐05 1692126
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Table 921 TR545- technetium after one day
Sample ID
Initial Aq Conc (ppb)
Equil Aq Conc (ppb) pH Fraction Aq Kd
A 9655146069 820460082 1181 0849764546 8998984 B 9356176321 7703053505 1183 0823312135 1051242 C 9114122586 7978297395 118 0875377451 7062663 D 1042349157 0853053814 12 0818395456 9099556 E 0983206046 0871198263 1199 0886079033 5196709 F 0905148405 0803451372 1198 0887646013 5098696 G 4950156706 4275082341 1186 0863625658 7213934 H 4889067068 4173762594 1188 0853693053 7687519 I 4854463762 4147024058 1189 0854270268 7771045
A 1048950046 0002141023 1149 0000204111 2112281 B 1039943573 0001770549 1157 0000170254 2460487 C 1084651695 0001127533 1153 0000103953 4014918 D 1088686867 0001201087 1172 0001103244 3564524 E 1119673887 0000783288 1177 0000699568 5709897 F 1045722787 0000914861 1181 000087486 4495324 G 5387981131 0001444832 1169 0000268158 1494715 H 5412748988 0001143483 1169 0000211257 1965749 I 5373948758 00010003 1164 0000186139 2280472
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Table 926 TR547- plutonium after four days
Sample ID
Initial Aq Conc (ppb)
Equil Aq Conc (ppb) pH
Fraction Aq Kd
A 104895 NA 116 NA NA B 10399436 0001828 1165 00001758 2383132C 10846517 00010788 1164 9946E‐05 4196159D 10886869 00009131 1184 00008388 4689778E 11196739 00010624 1189 00009488 4208928F 10457228 00007967 1191 00007619 516258G 53879811 00007915 1173 00001469 2728993H 5412749 00008355 1175 00001544 2690641I 53739488 00006103 1174 00001136 3737892
Table 927 TR547- neptunium after one day
Sample ID
Initial Aq Conc (ppb)
Equil Aq Conc (ppb) pH Fraction Aq Kd
A 9589772032 0000454463 1149 473903E‐05 9116335 B 9293228768 0000260081 1157 27986E‐05 1499475 C 1008725504 0000302018 1153 299405E‐05 1397125 D 0952173007 000019177 1172 0000201403 1954603 E 0992224074 BDL NA NA F 0967815522 402137E‐05 1181 41551E‐05 9474699 G 4068405786 0000222282 1169 546361E‐05 7336986 H 409543171 0000531619 1169 0000129808 3199152 I 4017406611 0000410123 1164 0000102086 4157807
Table 928 TR547- neptunium after four days
Sample ID
Initial Aq Conc (ppb)
Equil Aq Conc (ppb) pH Fraction Aq Kd
A 9589772 NA 116 NA NA B 92932288 00002145 1165 2308E‐05 1818463C 10087255 00001628 1164 1614E‐05 2591215D 0952173 BDL 1184 NA NA E 09922241 BDL NA NA F 09678155 5107E‐05 1191 5277E‐05 7460375G 40684058 00001336 1173 3284E‐05 1220544H 40954317 8151E‐05 1175 199E‐05 2086795I 40174066 00001322 1174 3292E‐05 1289605
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Table 929 TR547- technetium after one day
Sample ID
Initial Aq Conc (ppb)
Equil Aq Conc (ppb) pH Fraction Aq Kd
A 9466799266 8233850788 1149 0869760788 8220086 B 9439556236 817653394 1157 0866198975 8165745 C 9383493063 8086024379 1153 0861728604 8430884 D 1061939876 0919992065 1172 0866331594 6241759 E 0991827343 0836511397 1177 0843404251 7590958 F 0971981155 0839862696 1181 0864073024 6354378 G 4883337077 414858839 1169 0849539633 7903986 H 4691440077 3996173112 1169 0851800949 8038249 I 486993937 4291285586 1164 0881178442 6558707
Table 930 TR547- technetium after four days
Sample ID
Initial Aq Conc (ppb)
Equil Aq Conc (ppb) pH
Fraction Aq Kd
A 94667993 NA 116 NA NA B 94395562 85812109 1165 09090693 5885474C 93834931 84622373 1164 09018217 6279204D 10619399 09580683 1184 09021869 4435663E 09918273 08881507 1189 08954691 4835506F 09719812 09036489 1191 0929698 3138862G 48833371 4490415 1173 09195382 4312104H 46914401 42054182 1175 08964024 5612948I 48699394 43843193 1174 09002821 5536503
Table 931 TR547- iodine after one day
Sample ID
Initial Aq Conc (ppb)
Equil Aq Conc (ppb) pH Fraction Aq Kd
A 9944920441 8813152965 1149 0886196427 738241 B 9956006121 8747156303 1157 0878580848 8007767 C 9822152291 8664470934 1153 0882135674 7988892 D 1002391846 9333490632 1172 0931121963 3368509 E 9918273427 6625075445 1177 0667966607 1551748 F 9918175056 8931364957 1181 0900504872 4773862 G 5166570628 4445386532 1169 0860413387 7961604 H 4847821413 410447427 1169 084666367 8664303 I 4850381381 4266693706 1164 0879661489 6413801
100 Appendix B Data Tables of Radionuclide Sorption to Saltstone Under Reducing Conditions
The following tables represent data collected for the no solids controls each cementitious solid and testing of radionuclide sorption to the vial walls The no solids controls tables include the concentration (ppb) of the radionuclide spiked into the sample along with the concentration of the radionuclide (ppb) measured in the aqueous phase after the given equilibration time The pH at the time the sample was taken is also recorded along with the fraction of the radionuclide which stayed in the aqueous phase The tables for the cementitious solidsrsquo data include the data above along with the addition of a Kd value The tables of the data for the radionuclides sorbed to the vial walls include the initial concentration (ppb) of the spike the concentration (ppb) of the radionuclide that had sorbed to the vial wall during the experiment and the percentage of the total concentration this represents Important Notes
BDL= Below Detection Limit lt01 denotes no notable sorption occurred
101 Data Tables for No-Solid Controls
Table 101 Plutonium no solids control after one day
A 9405892 0007019 111 0000746258 5681206 B 9602498 0003294 1117 0000342992 123554 C 9630619 0002936 1114 0000304893 1396318 D 4945396 0001795 113 0000363011 1171688 E 4964945 0001373 1131 0000276484 1493015 F 4441601 0001516 113 0000341219 1389674 G 1079602 0001109 1142 0001027508 4215519 H 1031512 0000883 1143 0000855983 4820576 I 0939294 0000978 1143 0001040992 4550255
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Table 1011 Vault 2- neptunium after one day
Sample ID Initial Aq Conc (ppb)
Equil Aq Conc (ppb) pH Fraction Aq
A 9425042625 0001709054 1105 0000181331 B 9611386476 0001184125 1110 00001232 C 9579553607 0001155517 1104 0000120623 D 4974000414 0000672325 1125 0000135168 E 4916731623 0000675371 1128 0000137362 F 4373142817 0000570681 1120 0000130497 G 0943366414 0000389738 1129 0000413136 H 1011745587 0000565648 1132 0000559081 I 0865252712 0000379545 1133 0000438653
A 8849444124 0000306309 1150 346133E‐05 1289533 B 8447823057 0000150131 1155 177715E‐05 2711019 C 8590597085 0000199185 1153 231864E‐05 2044057 D 4491250244 517162E‐05 1156 115149E‐05 4020064 E 4391894479 204591E‐05 1158 465838E‐06 9846089 F 4210703646 204376E‐05 1158 485374E‐06 9816203 G 086381524 522216E‐06 1160 604546E‐06 7577764 H 0870501884 BDL 1160 NA NA I 0861953838 BDL 1162 NA NA
SRNL-STI-2009-00636 Revision 0
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Table 1036 Aged cement- neptunium after four days
Sample ID
Initial Aq Conc (ppb)
Equil Aq Conc (ppb) pH Fraction Aq Kd
A 8849444 0000131 1145 148418E‐05 3007445B 8447823 0000111 1146 131529E‐05 3662996C 8590597 656E‐05 1146 76328E‐06 6209405D 449125 BDL 1155 NA NA E 4391894 BDL 1156 NA NA F 4210704 BDL 1155 NA NA G 0863815 BDL 1165 NA NA H 0870502 BDL 1162 NA NA I 0861954 BDL 1164 NA NA
Table 1037 Aged cement- technetium after one day
Sample ID
Initial Aq Conc (ppb)
Equil Aq Conc (ppb) pH Fraction Aq Kd
A 8426518355 833290075 1150 098889012 0476492 B 8638001423 7823321167 1155 0905686487 4413063 C 9323317745 925927516 1153 0993130923 0294664 D 442651005 4300859603 1156 0971614106 1242837 E 4426849405 4336992073 1158 0979701742 0855315 F 3929483125 3938204338 1158 100221943 lt01 G 0817864386 081693181 1160 0998859743 0049487 H 0878958929 0792412508 1160 0901535306 4510199 I 0772205665 0871436364 1162 1128502941 lt01
Table 1038 Aged cement- technetium after four days
110 Appendix C Dixon et al (2009) FY09 PACA Maintenance Program Additional Saltstone Property Testing SRNL L3100-2009-00019 Rev 0
SRNL-STI-2009-00636 Revision 0
83
SRNL L3100-2009-00019 Rev 0
December 16 2008
Keywords Performance Permeability Modulus
L B Romanowski
Waste Determinations From K L Dixon M A Phifer and J R Harbour
FY09 PACA Maintenance Program Additional Saltstone Property Testing
BACKGROUND
Additional tests have been identified for measurement of important hydraulic and physical properties of saltstone The initial phase of this work [1] was completed last year and the results were detailed in an internal report [2] The proposed testing for FY09 includes measurement of saturated hydraulic conductivity porosity bulk density particle density water retention and Youngrsquos modulus of simulated Saltstone grouts For completeness the bleed volumes and gel times for each mix will also be measured
The testing will be based on a projected salt solution composition for the ARPMCU stream that will be fed to the Saltstone Production Facility over the next few years The scope for FY09 will include testing to determine the impact of (1) admixtures (2) organics (3) wcm ratio (4) aluminate concentration and (5) temperature of curing on the hydraulic properties of saltstone mixes Samples of selected batches prepared as part of this task will be provided to Dan Kaplan for measurement of Kd through leaching tests The eleven mixes that will be batched and tested are detailed in Table 1
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Table 1 The Eleven Mixes That will be Batched and Tested
BFS is Blast Furnace Slag FA is Fly Ash and PC is Portland Cement
TEST DETAILS
Test 1 Control (Mix 1)
A control mix will be based on the baseline mix modified by exclusion of the Class F fly ash Consequently the cementitious materials premix will be a mixture of 90 blast furnace slag and 10 portland cement The degree of reaction will be much greater than with the normal premix and therefore should result in a lower porosity and a lower permeability This bounding test at 060 wcm ratio is expected to yield a hydraulic conductivity at or below the detection limit for the Mactec permeameter measurement system Therefore this test should demonstrate the lowest level of detection of the Mactec system as well as show a resolvable difference between measurements of the control mix and the control mix with the normal premix composition
Test 2 ndashImpact of Admixtures (Mixes 2 and 3)
Recent saltstone batches have required both a set retarder (Daratard 17) and an antifoam agent (Q2) for processing of the saltstone Therefore the baseline mix will be prepared with and without nominal levels of these two admixtures to determine whether these admixtures appreciably affect the hydraulic and physical properties of saltstone at these nominal concentrations
Test 3ndashImpact of Organics (Mixes 2 and 4)
The solvent extraction process is expected to result in some carryover of organics [3]
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85
Consequently a test will be performed on the impact of Caustic Side Solvent Extraction (CSSX) organics at 100 microliters per 1600 gram batch The CSSX solvent consists of 075 M 1-(2233-tetrafluoropropoxy)-3-(4-sec-butylphenoxy)-2-propanol (Cs-7SB) and 0003 M tri-n-octylamine (TOA) in an Isoparreg L diluent Test 4ndashImpact of Combination of Admixtures and Organics (Mixes 2 5 10 and 11)
This test will determine the impact of a combination of admixtures (Test 2) and organics (Test 3) together in the mix vs the baseline case without admixtures and organics
Test 5ndash Impact of wcm Ratio (Mixes 2 6 and 7)
It is well known that decreasing the wcm ratio in a mix will improve permeability in normal portland cement water mixes This test will measure the variation in permeability for the case of the MCU salt solution at three different wcm ratios The initial selection of wcm ratios is 055 060 and 065 However if the mix at an as-batched 065 wcm ratio has significant bleed water and the resulting actual wcm ratio is close to 060 then the three ratios will be adjusted to provide a more evenly spaced set of values However the baseline mix at 060 will be included as one of the three mixes
Test 6 ndash Impact of Aluminate Concentration (Mixes 8 9 and 10)
The DWPF has modified its process flowsheet to include a caustic washing of HLW sludge to remove some of the aluminum from the HLW prior to vitrification The resulting aluminate stream will then be blended with tank 50 material and fed to the SPF This increased aluminate concentration in the salt solution has significant impact on heat of hydration and set times and consequently it is likely that it will also impact permeability Therefore a set of three samples will be made at wcm ratios of 055 060 and 065 (as in Test 3) with a higher level of aluminate (028 M) for testing
Test 7 ndash Impact of Increased Curing Temperature (Mix 11)
In an ongoing task there is evidence that Youngrsquos modulus (a performance indicator) [4] is reduced by increasing the curing temperature of the mix Since the vault temperature increases during curing as a result of the exothermic hydration reactions one of the baseline mixes with a combination of admixtures and organics will be cured at 60
o
C rather than the normal 22
o
C to determine the impact of curing temperature on the permeability
SRNL-STI-2009-00636 Revision 0
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SCHEDULE
The schedule for the task of batching and testing of the samples is provided in Table 2 This schedule is based on the fact that the cementitious materials will be available for the testing as needed
Table 2 Additional Saltstone Hydraulic and Physical Property Tests
Item Schedule Start Work 12108 Test Plan Complete 1509 Preparation of 1st set of Samples Complete 11909 90-Day Cure Period for 1st set of Samples Complete 42009
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87
SRNL-STI-2009-00636 Revision 0
SRNL-STI-2009-00636 Revision 0
DISTRIBUTION Savannah River Site
A B Barnes 999-W Rm 336 H H Burns 999-W Rm 381 B T Butcher 773-43A Rm 212 A D Cozzi 999-W Rm 337 D A Crowley 773-43A Rm 216 M E Denham 773-42A Rm 218 J C Griffin 773-A Rm A-231 J R Harbour 999-W Rm 348 C A Langton 773-43A Rm 219 M H Layton 705-1C Rm 14 D I Kaplan (3 copies) 773-43A Rm 215 S L Marra 773A Rm A-230 A M Murray 773-A Rm 229 K A Roberts 773-43A Rm 225 T C Robinson 705-1C Rm 13 L B Romanowski 705-1C Rm 19 K H Rosenberger 705-1C Rm 16 F M Smith 705-1C Rm 24 RPA File (2 copies) 773-43A Rm 213
Clemson University Environmental Engineering and Earth Sciences 372 Computer Court LG Rich Environmental Laboratory Anderson SC 29625
Table 1035 Aged cement- neptunium after one day 78
Table 1036 Aged cement- neptunium after four days 79
Table 1037 Aged cement- technetium after one day 79
Table 1038 Aged cement- technetium after four days 79
Table 1039 Aged cement- iodine after one day 80
Table 1040 Aged cement- iodine after four days 80
Table 1041 Plutonium sorbed to vial wall in no solids control 80
Table 1042 Neptunium sorbed to vial wall in no solids control 81
Table 1043 Technetium sorbed to vial wall in no solids control 81
SRNL-STI-2009-00636 Revision 0
xi
LIST OF FIGURES
Figure 31 Screen capture of a typical 242Pu calibration curve using Thermo PlasmaLab software to control the data collection and analysis R2=0999872 Intercept Conc (Detection Limit) = 0000044 ppb 16
Figure 32 Screen capture of a typical 237Np calibration curve using Thermo PlasmaLab software to control the data collection and analysis R2=0999981 Intercept Conc (Detection Limit) = 0000026 ppb 17
Figure 33 Screen capture of a typical 99Tc calibration curve using Thermo PlasmaLab software to control the data collection and analysis R2=0999984 Intercept Conc (Detection Limit) = 0000013 ppb 18
Figure 34 Screen capture of a typical 127I calibration curve using Thermo PlasmaLab software to control the data collection and analysis R2=0999991 Intercept Conc (Detection Limit) = 024 ppb 19
Figure 41 Plutonium Kd Values under Oxidizing Conditions Plutonium Kd values for various saltstone formulations measured after one-day equilibration (1d) and four-day equilibration (4d under oxidizing conditions Total plutonium concentrations in each system were 1 ppb 5 ppb and 10 ppb Sample prepared in triplicate and error bars represent standard deviation of samples except as follows value for dataset TR547-4d 10 ppb is reported based on duplicate samples 25
Figure 42 Plutonium solubility for various saltstone formulations measured after one-day equilibration (1d) and four-day equilibration (4d) under oxidizing conditions Total plutonium concentrations in each system were 1 ppb 5 ppb and 10 ppb as noted Samples prepared in triplicate and an average of all samples (9) was used to determine average solubility The error bars represent standard deviation of samples 25
Figure 43 Neptunium Kd values under oxidizing conditions Neptunium Kd values for various saltstone formulations measured after one-day equilibration (1d) and four-day equilibration (4d) under oxidizing conditions Total plutonium concentrations in each system were 1 ppb 5 ppb and 10 ppb as noted Samples prepared in triplicate and error bars represent standard deviation of samples except as follows value for datasets TR545-1d 1ppb TR545-4d 1 ppb TR547 4d 1 ppb TR545-4d 10 ppb TR547-1d 1ppb TR547-4d 10 ppb are reported based on a single sample and for dataset TR545-1d 5ppb is reported based on duplicate samples Kd values limited to gt106 were at instrumental background 26
Figure 44 Average solubility of Np under oxidizing conditions Neptunium solubility for various saltstone formulations measured after one-day equilibration (1d) and four-day equilibration (4d) under oxidizing conditions Total Np concentrations in each system were 1 ppb 5 ppb and 10 ppb Samples prepared in triplicate and an average of all samples (9) was used to determine average solubility except as follows TR545-1d is based on 6 samples TR545- 4d on 5 samples TR547-1d on 7 samples and TR547- 4d on 5 samples The error bars represent standard deviation 27
Figure 45 Technetium Kd values under oxidizing conditions Tc Kd values for various saltstone formulations measured after one-day equilibration (1d) and four-day equilibration (4d) under oxidizing conditions Total Tc concentrations in each system were 1 ppb 5 ppb and 10 ppb as noted above Samples were prepared in triplicate and the error bars represent standard deviation
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xii
of samples except as follows data sets for Vault 2-1d 1ppb were duplicates and TR547- 4d 10 ppb is based on a single dataset 27
Figure 46 Iodine Kd Values under Oxidizing Conditions Iodine Kd values for various cementitious formulations measured after one-day equilibration (1d) and four-day equilibration (4d) under oxidizing conditions Total iodine concentrations in the systems were 100ppb 500 ppb and 1000 ppb as noted above Samples were prepared in triplicate and the error bars represent standard deviation of samples except as follows duplicates were used for dataset TR545- 1d 100ppb 28
Figure 47 Plutonium Neptunium and Technetium Aqueous Fractions Fraction of Pu Np and Tc remaining in the aqueous phase for the No Solids controls after a one-day equilibration (1d) and four-day equilibration (4d) under oxidizing conditions The total concentration for each radionuclide 10 ppb as noted above Samples were prepared in triplicate and the error bars represent the standard deviation of the samples 29
Figure 48 Iodine Aqueous Fraction Iodine aqueous fraction for the no-solids controls after a one-day equilibration (1d) and four-day equilibration (4d) under oxidizing conditions The total concentration of iodine was 1000 ppb as noted above Samples were prepared in triplicate and the error bars represent the standard deviation of the samples 29
Figure 49 Percent Pu and Np sorbed to vial walls of the no solids controls after the aqueous phases were discarded and the vials were washed Both the 10 ppb (blueleft) and 1 ppb (redright)) datasets were prepared in triplicate and the error bars show the standard deviation 31
Figure 410 Percent Pu sorbed to vial walls after the solids and aqueous phases were removed and the vials were washed The graph illustrates one sample from each of the 1 ppb (redleft) 5 ppb (greenmiddle) and 10 ppb (blueright) systems Therefore no error bars are present 31
Figure 411 Percent Np sorbed to vial walls after the solids and aqueous phases were removed and the vials were washed The graph illustrates one sample from each of the 1 ppb (redleft) 5 ppb (greenmiddle) and 10 ppb (blueright) systems Therefore no error bars are present 32
Figure 412 Pu Kd Values under Reducing Conditions Plutonium Kd values for various cementitious formulations measured after one-day equilibration (1d) and four-day equilibration (4d) under reducing conditions Total plutonium concentrations in each system were 1ppb 5 ppb and 10 ppb Samples prepared in triplicate and error bars represent standard deviation 33
Figure 413 Average Solubility of Plutonium under Reducing Conditions Plutonium solubility for various cementitious formulations measured after one-day equilibration (1d) and four-day equilibration (4d) under reducing conditions Total plutonium concentrations in each system were 1ppb 5 ppb and 10 ppb as noted Samples prepared in triplicate and an average of all samples (9) was used to determine average solubility The error bars represent standard deviation of samples 33
Figure 414 Np Kd Values under Reducing Conditions Neptunium Kd values for various cementitious formulations measured after one-day equilibration (1d) and four-day equilibration (4d) under reducing conditions Total Np concentrations in each system were 1 ppb 5 ppb and 10 ppb Samples were prepared in triplicate and the error bars represent standard deviation Kd values limited to gt106 were at instrumental background 34
Figure 415 Average Solubility of Neptunium under Reducing Conditions Neptunium solubility for various cementitious formulations measured after one day equilibration (1d) and four day
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xiii
equilibration (4d) under reducing conditions Total plutonium concentrations in each system were 1ppb 5 ppb and 10 ppb Samples prepared in triplicate and an average of all samples (9) was used to determine average solubility The error bars represent standard deviation 35
Figure 416 Tc Kd Values under Reducing Conditions Tc Kd values for various cementitious formulations measured after one-day equilibration (1d) and four-day equilibration (4d) under reducing conditions Total Tc concentrations in each system were 1 ppb 5 ppb and 10 ppb Sample prepared in triplicate and error bars represent standard deviation except as follows TR547-1d 1 ppb is based on a single dataset and datasets Vault 2-1d 5 ppb Vault 2- 4d 1 ppb Aged Cement-1d 5 ppb and Aged Cement-4d 1 ppb are duplicates 36
Figure 417 Data from Figure 416 replotted on a reduced linear scale for easier viewing Each sample was prepared in triplicate except as follows TR547-1d 1 ppb is based on a single dataset Vault 2-1d 5 ppb Vault 2- 4d 1 ppb Aged Cement-1d 5 ppb and Aged Cement-4d 1 ppb are duplicate datasets 36
Figure 418 Iodine Kd Values under Reducing Conditions I Kd Values for various cementitious formulations measured after one day equilibration (1d) and four day equilibration (4d) under reducing conditions Total iodine concentrations in each system were 100 ppb 500 ppb and 1000 ppb as noted Sample prepared in triplicate and error bars represent standard deviation of samples except as follows Vault 2-4 d 100 ppb is a single dataset while the datasets for Vault 2-1 d 100 ppb 4 d 1000 ppb TR545-4 d 1000 ppb 100 ppb TR547-4 d 1000 ppb 500 ppb 100 ppb and Aged Cement- 4 d 1000 ppb and 100 ppb are all based on duplicates 38
Figure 419 Plutonium Neptunium and Technetium No-Solids Aqueous Fractions under Reducing Conditions Pu Np and Tc aqueous fractions of No Solids controls after a one-day equilibration (1d) and four-day equilibration (4 d) under reducing conditions Total concentration for each radionuclide was 1 ppb and 10 ppb Samples were prepared in triplicate and the error bars represent the standard deviation 39
Figure 420 Percent of Pu Np and Tc sorbed to the vial walls of the No Solids control samples under reducing conditions Each the 1 ppb and 10 ppb samples were prepared in triplicate and the error bars represent the standard deviations of triplicate samples 39
Figure 421 Iodine No-Solids Aqueous Fractions under Reducing Conditions I aqueous fractions of No-Solids controls after a one-day equilibration (1d) and four-day equilibration (4d) under reducing conditions The total concentration for each system was 100 ppb and 1000 ppb Samples were prepared in triplicate and the error bars represent the standard deviation 40
Figure 51 Comparison of Tc I Np and Pu sorption to Vault 2 solid under oxidizing and reducing conditions 42
Figure 52 Comparison of Tc I Np and Pu sorption to TR 545 solid under oxidizing and reducing conditions 43
Figure 53 Comparison of Tc I Np and Pu sorption to TR547 solid under oxidizing and reducing conditions 44
Figure 54 Comparison of Tc I Np and Pu sorption to Aged Cement under oxidizing and reducing conditions 45
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LIST OF ABBREVIATIONS
DDI water Distilled deionized water ICP-MS Inductively coupled plasma ndash mass spectrometer
Kd Distribution coefficient LSC liquid scintillation counting NOM Natural organic matter PA Performance Assessment ppb parts per billion ppq parts per quadrillion QAQC Quality AssuranceQuality Control SA Special Analyses SRNL Savannah River National Laboratory SRS Savannah River Site
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10 Introduction Performance Assessments (PA) are risk calculations designed to determine (1) the maximum
amount of radioactivity that can be safely buried in a subsurface facility and (2) the potential human risk associated with disposing of radioactive waste in a subsurface facility Special Analyses (SAs) are similar to PAs except that they are designed to address specific issues related to PAs such as a new discovery since the PA was issued Commonly parameters describing the extent that a radionuclide interacts with solids at the source vadose zone and aquifer influence the extent of calculated human risk The two parameters that the SRS use to represent radionuclidesolid interactions are Kd and apparent solubility values together these parameters are referred to as sorption values Sorption values vary with radionuclides groundwater chemistry and the type of solid phase (and for cementitious materials by the age of the material during the calculation) In this work Kd and apparent solubility values are reported for 99Tc 127I 237Np and 242Pu sorption to various cementitious formulations
20 Objectives
The objectives of this work were to 1 Determine the influence of cementitious formulation on technetium (Tc) iodine (I) neptunium
(Np) and plutonium (Pu) sorption under oxidizing conditions The specific formulations that were evaluated included 1) an aged cement recovered from a 30-year old outdoor concrete pad on the SRS 2) Vault 2 concrete 3) TR545 saltstone and 4) TR547 saltstone (additional details are presented in Section 30 Materials and Methods)
2 Measure Tc I Np and Pu sorption to the cementitious formulations under reducing conditions
30 Materials and Methods
31 Preparation of ICP-MS Standards Stock Solutions and Working Solutions
311 242Pu
A National Institute of Standards and Technology Standard Reference Material (NIST SRM 434H) was used to prepare a stock 242Pu solution by dilution in 2 Aristar Optima HNO3 All volume additions were monitored gravimetrically This working solution was then used to make a set of 001 005 1 2 5 10 parts per billion (ppb) standards by dilution using 2 HNO3 Again all volume additions were monitored gravimetrically These standards were used to calibrate the Thermo Scientific X Series 2 inductively coupled plasma ndash mass spectrometer (ICP-MS) for quantification of 242Pu A representative calibration curve for 242Pu is shown in Figure 31 The instrument performance was monitored using 209Bi 232Th and 238U as internal standards The recovery of each sample during analysis was corrected based on the internal standard recovery The internal standard recoveries remained within standard quality assurancequality control QAQC protocols for the instrument (between 80 and 120)
A 242Pu stock solution was prepared by dissolving 1mg of Pu(NO3)4 obtained as a Certified Reference Material from New Brunswick Laboratory (CRM 130) This CRM is gt999 242Pu by atom percent The CRM was dissolved in 20mL of 8M HNO3 (Aristar Optima Grade) Because no chemicals or heat have been introduced to manipulate the Pu oxidation state it can be assumed that Pu(IV) is the predominant oxidation state in this stock solution A working solution to be used in spiking 242Pu experiments was prepared by diluting 25 mL of the CRM stock solution with 100 mL 10 M Aristar Optima HNO3 The concentration of 242Pu in this stock solution was determined using ICP-MS calibrated using the NIST SRM standards The concentration of Pu in this stock solution was 1065 ppb The total Pu
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concentration was also determined using liquid scintillation counting using the isotopic ratios reported for CRM 130 These compared favorably with the ICP-MS results but are reported here as a rigorous standardization because the isotopic ratios of CRM 130 have not yet been certified
Figure 31 Screen capture of a typical 242Pu calibration curve using Thermo PlasmaLab software to control the data collection and analysis R2=0999872 Intercept Conc (Detection Limit) = 0000044 ppb
312 237Np
A National Institute of Standards and Technology Standard Reference Material (NIST SRM 4341) was used to prepare a stock 237Np solution by dilution in 2 Aristar Optima HNO3 All volume additions were monitored gravimetrically This working solution was then used to make a set of 001 005 1 2 5 10 ppb standards by dilution using 2 HNO3 Again all volume additions were monitored gravimetrically These standards were used to calibrate the Thermo Scientific X Series 2 ICP-MS for quantification of 237Np A representative calibration curve for 237Np is shown in Figure 32 The instrument performance was monitored using 209Bi 232Th and 238U as internal standards The recovery of each sample during analysis was corrected based on the internal standard recovery The internal standard recoveries remained within standard QAQC protocols for the instrument (between 80 and 120)
A compiled 237Np stock solution from the Environmental Engineering and Earth Science (EEampES) inventory (primarily purchased from Isotope Products Valencia CA) was evaporated to dryness then the residue was brought up in approximately 5mL 80 M HNO3 Then 10 M hydroxylamine hydrochloride (NH2OHHCl EMD Chemicals ACS grade) and water were added to achieve a 3M HNO303M NH2OHHCl solution This solution was purified by extraction chromatography using Eichrom TEVA resin packed in a Bio-Rad poly-prep column The 3M HNO303 M NH2OHHCl neptunium solution was loaded on a 2 mL column and washed with 3 column volumes of 3 M HNO3 The Np(IV) was eluted with 002 M HCl + 02 M HF The effluent was evaporated to dryness then redissolved in 10 M HNO3 Additional 10 M HNO3 was added to maintain a approximately 10 mL then the solution was evaporated to incipient dryness and redissolved in a 50 mL of 10 M HNO3 An aliquot of the stock solution was evaporated to dryness on a stainless steel planchet and counted on the EGampG Ortec Alpha Spectrometer (Octete PC Detectors) No other alpha energies besides 237Np were observed The approximate concentration was determined using liquid scintillation counting and little 233Pa was observed The fuming in HNO3 as performed at the end of the purification procedure will drive Np to the soluble pentavalent state This is the stable oxidation state of Np under the experimental conditions Therefore experiments performed here can be assumed to be initially Np(V) The exact Np
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concentration in this solution was determined using ICP-MS calibrated with a NIST standard as discussed in section 312 below
A 237Np working solution (Working Solution 1) was created by pipetting an aliquot of the 237Np stock solution into a 100 mL Nalgene Teflon bottle and diluting with 2 BDH Aristar Ultra HNO3 to give a working solution concentration of 820 ppb All volumes were monitored gravimetrically Analysis on the ICP-MS calibrated against NIST Standards as described below gave a concentration of 820 ppb in Working Solution 1
Figure 32 Screen capture of a typical 237Np calibration curve using Thermo PlasmaLab software to control the data collection and analysis R2=0999981 Intercept Conc (Detection Limit) = 0000026 ppb
313 99Tc
A 99Tc working solution was prepared by diluting a stock solution of 99Tc (from the EEampES inventory purchased from Isotope Products Valencia CA) in distilled-deionized water (DDI Resistivity gt18 MΩcm) The oxidation state of Tc was not measured However based on the aqueous concentration in the DDI water solution Tc(VII) is the expected oxidation state The reduced Tc(IV) oxidation state would not be soluble under these conditions The expected concentration of 950 ppb based on the dilution was verified using liquid scintillation counting The 99Tc working solution was used to make 001 005 1 2 5 and 10 ppb standards by dilution using 2 HNO3 These standards were used to calibrate the Thermo Scientific X Series 2 ICP-MS for quantification of 99Tc A screen shot of a representative calibration curve is shown in Figure 33 The instrument performance was monitored by interpolating between 89Y and 115In internal standards The recovery of each sample during analysis was corrected based on the internal standard recovery The internal standard recoveries remained within standard QAQC protocols for the instrument (between 80 and 120)
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Figure 33 Screen capture of a typical 99Tc calibration curve using Thermo PlasmaLab software to control the data collection and analysis R2=0999984 Intercept Conc (Detection Limit) = 0000013 ppb
314 127I
A 100 microgmL iodate (IO3-) stock solution from High Purity Standards (Charleston SC) was used
to make 1 5 10 50 and 100 ppb standards by dilution using the ldquotraprdquo solution (discussed in Section 32 below) These standards were used to calibrate the Thermo Scientific X Series 2 ICP-MS for quantification of 127I A screen shot of a representative calibration curve is shown in Figure 34 The use of a reducing basic trap solution for iodine analysis limits the number of available internal standards that can be used to monitor ICP-MS instrument performance during iodine analysis Experiments are underway to identify acceptable internal standards However the data presented in this work did not use any internal standards prior to rigorous testing and analysis of representative standards As with the analyses for all isotopes (Tc I Np and Pu) spiked QAQC samples were frequently analyzed throughout the analysis as a check on instrument performance While these values cannot be used to correct individual samples in the same manner that the internal standards can they can be used to ensure accurate measurements of each isotope In almost all cases QAQC standards were within 10 of the expected value Because the average internal standard recovery ranges between 80 and 120 for the ICP-MS the iodine QAQC standard appears to be acceptable However a significant amount of ongoing work is testing various internal standards to improve the accuracy of iodine analysis using ICP-MS In one experiment (discussed in detail below) the QAQC standards deviated by an average value of 195 This will be specifically discussed below
Because experiments were performed with 127I concentrations up to 1000 ppb the 100 microgmL (ppm) stock iodate solution from High Purity Standards was used as the working solution
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Figure 34 Screen capture of a typical 127I calibration curve using Thermo PlasmaLab software to control the data collection and analysis R2=0999991 Intercept Conc (Detection Limit) = 024 ppb
315 Cementitious Materials Selected for Experiments There were four cementitious materials selected for this sorption study The first referred to as Aged Cement is a 30 year old sample that does not contain any reducing slag The aggregate from the Vault 2 cement had its aggregate removed prior to conducted tests in an effort to make subsamples more uniform This was necessary because some of the aggregate were larger than the 05 g subsamples used in individual sorption tests The Vault 2 cementitious material contained 17 dry wt- reducing slag on a dry weight basis before the water was added to the mix (Table 31) The TR547 and TR545 saltstone formulations contain 45 dry wt- and 90 dry wt- reducing slag respectively
Table 31 Characteristics of saltstone formulations used in this work Kaplan et al (2008)
Sample Percent Reducing Slag (dry wt-) (c)
Percent Portland Cement
(dry wt-) (c)
Percent Fly Ash
(dry wt-) (c)
Percent Aggregatesand ( dry wt-) (c)
Reducing Equivalents
(microeqg)
Aged Cement 0 10 45 45 855 plusmn 101(a)
Vault 2 Cement 17 10 45 0 178(b)
TR547 45 10 45 0 607(b) TR545 90 10 0 0 681(b) Blast furnace slag 100 0 0 0 819(b) (a) Kaplan et al (2008) (b) Roberts and Kaplan (2009) (c) All percentages of saltstone formulations are reported on a dry weight percentage basis that is the weight of the ingredients before water was added (d) Based on Table 8 in Dixon et al (2008 SRNL-STI-2008-00421) which shows the following quantity (lbscu yd) for saltstone Vault 2 Mix 1 concrete formulation 201 cement (1271 wt-) 268 slag (1695 wt-) 447 silica fume (283 wt-) 1563 fly ash (989 wt-) 911 fine sand (5762 wt-) The large aggregate was removed before the sorption tests were conducted The large aggregate accounted for 75 wt- of the original field sample not the sample used in these test before water was added to the mix TR547 is referred to as the Baseline by Dixon et al (2008) and is described in more detail in Appendix C (Mix 2) by Dixon et al (2008) (Control-BFSPC) and 1 (Baseline)
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TR545 saltstone contains 90 reducing slag and it is Mix 1 in Dixon et al (2008) and is described as
ldquoA control mix will be based on the baseline mix modified by exclusion of the Class F fly ash Consequently the cementitious materials premix will be a mixture of 90 blast furnace slag and 10 Portland cement The degree of reaction will be much greater than with the normal premix and therefore should result in a lower porosity and a lower permeability This bounding test at 060 wcm ratio is expected to yield a hydraulic conductivity at or below the detection limit for the Mactec permeameter measurement system Therefore this test should demonstrate the lowest level of detection of the Mactec system as well as show a resolvable difference between measurements of the control mix and the control mix with the normal premix compositionrdquo
32 ICP-MS Detection Limits
The PlasmaLab software platform determines a detection limit for each isotope based upon the intercept concentration A new calibration curve was generated for each experimental run and curves were very similar Using representative calibrations curves the detection limits for each isotope were as listed in Table 32 Note the higher detection limit for 127I is primarily due to the higher background count rate observed on the instrument This is believed to be due to the minimum purity levels of chemicals required for the iodine ldquotraprdquo solution as discussed in Section 33 below Therefore experiments were run with initial iodate concentrations higher than Tc Np and Pu to maintain analytical sensitivity
Table 32 Detection limits for each isotope based on representative calibration curves generated in PlasmaLab software associated with the ICP-MS
33 Experimental Methods
The experimental methods used in this work followed closely those previously described for experiments examining radionuclide sorption to saltstone (Kaplan et al 2007 Kaplan et al 2008) Brief descriptions of each method are provided below
Preparation of Calcite Solution Using a hotstirring plate 10 L of distilled-deionized (DDI)
water was heated to 3-100C above room temperature Then 001 g CaCO3 (EM Science ACS grade) was added to the solution and the resulting suspension was mixed for 24 hours at the elevated temperature The solution was then vacuum filtered through a 045-microm filter to ensure no solid CaCO3 remained in solution
Preparation of 2 HNO3 Analysis of Tc Np and Pu on the ICP-MS required dilution in 2
HNO3 This was prepared by adding 28 mL of Aristar Optima HNO3 from a clean graduated cylinder (designated to 2 HNO3) into a 1 L volumetric flask (designated to 2 HNO3) partially filled with DDI water and then further diluted to volume
Preparation of Trap Solution for Iodine Analysis Analysis of I required the use of a reducing
basic solution that was capable of reducing iodate to iodine and holding the iodine in solution This minimized the loss of I during sample analysis A 1 L trap solution was prepared by weighing out 00500 g NaHSO3 (Fisher Scientific ACS Grade) on a calibrated Sartorous LA 230S scale and adding it to a 1L volumetric flask Then 40 mL of 25 ww tetramethylammonium hydroxide (Alfa Aesar electronic grade) and 10 mL CFA-C solution (Spectrasol Inc) were added to the volumetric flask via a calibrated 1000-5000 microL Eppendorf Research pipette The solution was then diluted to volume with DDI water
34 Experimental Protocol for Sorption Experiments under Aerobic Conditions
Falcon BlueMax 15mL polypropylene vials were labeled and weighed to within 0001 g on a calibrated Sartorious LA 230S scale The scale was then zeroed and 025 +- 001 g of a given solid were added to each tube and the weight was recorded to within 0001g
For each of the four solids three sets of triplicate samples were prepared The three sets of samples were used to allow for experiments to be run with varying concentrations of each isotope Target initial concentrations for 99Tc 237Np and 242Pu samples were 1 ppb 5 ppb and 10 ppb Target initial concentrations for the 127I samples were 100 ppb 500 ppb and 1000 ppb A set of no solids controls at initial concentrations of 1 ppb and 10 ppb for 99Tc 237Np and 242Pu and initial concentrations of 100 ppb and 1000 ppb 127I were also prepared by adding the calcite solution to pre-weighed pre-labeled centrifuge tubes as discussed above
The solids were equilibrated with the calcite solution before spiking with the radionuclides This was done by adding 10 plusmn 01 mL of calcite solution to each tube and recording the mass The samples were then placed on a Thermo Scientific shaker overnight After 24 hours the solutions were allowed to settle for 1 hour The pH was then measured and the samples were then centrifuged for 15 minutes at 8000 rpm to further separate the solids The aqueous phase was then decanted and 10 plusmn 01 mL of calcite solution was added to each tube The weight of the tube (labeled tube + solid + calcite solution) was measured to within 0001g During this washing process the pH was monitored and held steady throughout the process The pH ranged from 11-12 depending on the particular saltstone used During the experiments the exact pH for all samples at all equilibration times was measured and is reported in Appendix A and B
The resulting suspensions were then spiked with 127I 237Np 242Pu and 99Tc It is important to note that all four isotopes were added to the same vial Use of the ICP-MS to determine the concentration of each isotope allows for a single solution to contain all analytes of concern This allowed for a greater variability in the sample set and increased replicates as opposed to running individual sorption tests for each isotope For the systems with initial 99Tc 237Np and 242Pu concentrations of 10 ppb and initial 127I concentration of 100 ppb a 100 microL aliquot of each radionuclide working solution was added to the first three tubes for each solid The addition was made with the tube resting on a tared analytical balance so that the exact mass of each radionuclide solution added was recorded and the solution was gently swirled before the next radionuclide was added The 5 ppb 237Np 242Pu and 99Tc and 500 ppb 127I samples were prepared in the same manner but adding 50 microL of the respective spike solutions The final three tubes with initial 237Np 242Pu and 99Tc concentrations of 1 ppb and 100 ppb 127I were prepared by using 10 microL of the spike solutions for all four solids as well as a set of solid-free controls (No-Solids Controls) For clarity this experimental matrix is shown in Table 33 below
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Table 33 Experimental Matrix of Sorption Experiments under Aerobic Conditions
After spiking the radionuclides a precalculated amount of 10M NaOH was added to each sample
to counter the acidic radionuclide spike solutions and the pH of one of the triplicate samples was measured to ensure the proper pH range was reached The samples were then placed on and end-over-end shaker to mix at approximately 8 rpm After 24 hours the samples were removed from the shaker and the pH of each sample was measured using an Orion Ross semi-micro glass electrode calibrated against pH 4 7 and 10 buffers (Thermo) The samples were then shaken and a transfer pipette was used to transfer 35 mL of a homogenous suspension to a 5mL syringe The solution was then passed through a 100 nm nylon syringe filter The first 025-050 mL of filtrate was discarded and the remaining filtrate was collected in a clean polyethylene vial Then 10 mL of the filtrate was removed and diluted in 90 mL 2 HNO3 The mass of each phase was determined and recorded gravimetrically Then 10 mL of the remaining filtrate was transferred to a clean Falcon BlueMax 15mL vial and diluted with 90 mL of trap solution for 127I analysis Again the volume of each phase was monitored gravimetrically After the 24 hour sampling event the samples were put back on the shaker to mix for three additional days On day four the above sampling procedure was repeated
The 237Np 242Pu and 99Tc samples can be run on the Thermo Scientific ICP-MS using the standard setup and procedure which included a standard flow glass nebulizer and bulb spray chamber However for the 127I analysis the ICP-MS must be reconfigured to accommodate the basic reducing trap solution This is to alleviate problems with iodine signal stability over time frequently observed in ICP-MS analysis The reconfigured instrument uses an Elemental Science Microflow PFA-100 Teflon nebulizer with a flow rate of 100microLmin along with a sapphire torch and a Teflon spray chamber This configuration must be run with a low pump speed to prevent back pressure on the system Two 30 minute stability tests were performed using a 50 ppb iodate solution Each experiment consisted of 40 separate measurements After each experiment was completed the uncorrected mass counts were examined and found to stay steady over the sampling period The relative standard deviation ( RSD) over all samples for each experiment was 1866 and 1460 respectively This shows that there was no significant ldquomemoryrdquo or loss of the iodine signal over time and that the reconfigured instrument has a stable iodine signal over time However as will be discussed below some difficulty has been encountered in finding an adequate internal standard for iodine analysis
35 Experimental Protocol for Sorption Experiments under Anerobic Conditions In order to examine the effects of reducing conditions of sorption of each isotope to the various cementitious samples a series of sorption experiments were performed in an anaerobic glovebox under a 2 H2(g) 98 N2(g) atmosphere Based on the measured pH and EH of these systems as discussed below these systems were at the point of reducing water Therefore they are expected to represent a lower end of the possible range for reducing conditions expected in the porewater available within cementitious materials
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Preparation of Calcite for Reducing Conditions Approximately 35 L of DDI water was boiled for 45 minutes Argon was slowly bubbled through the water as it cooled Once it cooled to below 500C approximately 3 g of calcite was added This solution mixed overnight under a continuous Ar flow After 12 hours the solution was moved into an oxygen free glove bag for filtration as described in 3231 After filtration the calcite solution was moved into the glove box
Preparation of Working Solutions under Reducing Conditions The calcite and solid solutions
were prepared in the glove box using the previously mentioned procedure used under aerobic conditions The radionuclide working solutions were transferred to the glovebox and stirred open to the reducing atmosphere for at least three days The concentration of each isotope in the working solutions was measured to determine any change in the concentration due to evaporation while the solutions were equilibrating
The preparation and spiking of samples for sorption experiments was performed exactly as described for the oxidizing conditions except all sample handling was performed in the glovebox After the 1 day and 4 day equilibration the samples were filtered within the glovebox then transferred outside for dilution and ICP-MS analysis similar to the description provided about for the oxidizing conditions For these experiments only 4 mL of either 2 HNO3 or trap solution were used to dilute the filtrate instead of the 90 mL used above for experiments performed under oxidizing conditions
36 Examination of Sorption to Vial Walls for Solids and No Solids Controls
As will be discussed below the solid-free controls samples indicated significant loss of Np and Pu Once the one and four days samples were collected and run on the ICP-MS it was necessary to determine the degree each radionuclide was sorbing to the vial walls The remaining suspensions and controls were emptied into a waste container Then 5 mL of the calcite solution was added to each vial using a calibrated pipette The vials were sonicated for approximately one minute and then emptied into the waste container Another 5 mL of calcite solution was added for the second wash and then discarded into the waste container This procedure was expected to remove any soluble Pu from the system or Pu associated with colloidal particles After each vial was washed 10 mL of 2 HNO3 was added using a calibrated pipette The acid solution is expected to remove any Tc Np or Pu associated with the vial walls This procedure has been shown to complete mass balances of Pu in similar sorption experiments using Pu (Powell et al 2002) This process was performed for both the solid suspension and the no solids controls The samples were then run on the ICP-MS to determine the concentration of 99Tc 237Np and 242Pu sorbed to the vial walls
37 Data Analysis The solubilities of 242Pu and 237Np were calculated by using the formula
nuclide
nuclide
nuclideMSICP
sol Mg
gCC
)(10 6
microminus
minus
= (Equation 31)
Csol = observed nuclide solubility (molnuclidekgsolution) CICP-MS = aqueous concentration of nuclide from ICP-MS measurement (ppb micrognuclidekgsolution) Mnuclide = molecular mass of nuclide (gnuclidemolnuclide)
In order to determine the Kd values one first needs to determine the concentration on the solid by using
SRNL-STI-2009-00636 Revision 0
24
solid
calcitespikeaqspikecalcite
spikestock
solid m
mmCmmmC
C)(
)()(
+⎥⎥⎦
⎤
⎢⎢⎣
⎡minus
+
lowast
= (Equation 32)
Csolid = calculated solid phase concentration of the nuclide (ppb) Cstock = concentration of the nuclide stock solution (ppb) mspike = mass of nuclide spiked into the saltstone suspension (g) mcalcite = total mass of calcite solution used in the saltstone suspension (g) Caq = aqueous concentration of nuclide from ICP-MS measurement (ppb) msolid = mass of the saltstone used in the suspension (g)
The Kd can be calculated using the equation
aq
solidd C
CK = (Equation 33)
Kd = solid-water partitioning coefficient (gsolutiongsolid assuming density of 10 gmL traditional
unit of mLsolutiongsolid can be obtained) This Kd Equation (33) is numerically equivalent to the traditional Kd equation proposed in ASTM D-4646 which has been used in previous saltstone experiments (Kaplan et al 2007 Kaplan et al 2008)
40 Results and Discussion
41 Radionuclide Sorption to Cementitious Formulations under Oxidizing Conditions
Figure 41 shows Pu Kd values ranging from 104 to gt105 mLg Generally for each solid the Kd increases with increasing initial Pu concentrations typical behavior of systems where the aqueous concentrations of the radionuclides are solubility controlled This is not expected because the Kd expression indicates that the Kd value should remain constant with increasing total Pu concentrations It was noted that aqueous phase concentration of Pu remained relatively constant in all samples (see discussion below regarding Pu solubility) Therefore the sorption capacity of each solid phase for Pu has not been overcome For each of these solid phases it appears the solutions had reached equilibrium before the first samples were taken at 24 hours In each case the Kd values for the one day and four day are similar A trend between the solid phases is not discernible The aged cement with no reducing slag was expected to have the lowest Kd values but in actuality it has the highest Kd Also there is no correlation with the concentration of reducing slag The Vault 2 samples with 17 dry wt- reducing slag has a Kd similar to that of the TR547 (45 dry wt- slag) while the saltstone with the most slag TR545 (90 dry wt- slag) has the lowest Kd value Others have observed that Pu Kd values of cementitious materials are similar in the absence and presence of slag (Allard et al 1984 Hoaglund et al 1985)
It was observed that similar aqueous concentrations of Pu were observed regardless of the solid phase present Figure 42 shows the average aqueous phase concentrations measured after one day and four days for all solids As stated above triplicate samples were prepared for each solid phase and each initial concentration Therefore each of the reported solubility values in Figure 42 is an average of nine measurements Using the highest reported value with the expected maximum error (0018 ppb for solid TR545) the maximum expected aqueous concentration of Pu in the pore water associated with the
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saltstone formulations will be approximately 7 x 10-11 molL as calculated using Equation 31 This is on the same order as the solubility of Pu hydrous oxide solid phases (Neck and Kim 2001)
Figure 41 Plutonium Kd Values under Oxidizing Conditions Plutonium Kd values for various saltstone formulations measured after one-day equilibration (1d) and four-day equilibration (4d under oxidizing conditions Total plutonium concentrations in each system were 1 ppb 5 ppb and 10 ppb Sample prepared in triplicate and error bars represent standard deviation of samples except as follows value for dataset TR547-4d 10 ppb is reported based on duplicate samples
Figure 42 Plutonium solubility for various saltstone formulations measured after one-day equilibration (1d) and four-day equilibration (4d) under oxidizing conditions Total plutonium concentrations in each system were 1 ppb 5 ppb and 10 ppb as noted Samples prepared in triplicate and an average of all samples (9) was used to determine average solubility The error bars represent standard deviation of samples
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Overall the Kd values for Np range from 105 to gt106 with only a few outliers The most significant outlier is the 1 ppb solution in the TR545 sample after the four-day equilibration It drops two orders of magnitude while the 5 and 10 ppb solutions remain constant However this result is most likely an analytical artifact from working at the detection limits of the ICP-MS In the one-day equilibration samples only one of the triplicates S-2-E had detectable Np while in the four-day equilibration samples only S-2-F had detectable amounts present The graph also shows that with the exception of the 5 ppb sample in the aged cement Np sorption to TR545 (90 dry-wt- slag) and TR547 (45 dry wt- slag) have Kd values approximately one order of magnitude over the aged cement (no slag) and Vault 2 (17 dry wt- slag) samples
It was observed that similar aqueous concentrations of Np were observed regardless of the solid phase present Figure 44 shows the average aqueous phase concentrations measured after one day and four-day equilibrations for all solids As stated above triplicate samples were prepared for each solid phase and each initial concentration Therefore each of the reported solubility values in Figure 44 is an average of nine measurements of Np concentration unless stated otherwise Using the highest reported value with the expected maximum error (00026 ppb for solid TR545) the maximum expected aqueous concentration of Pu in the pore water associated with the saltstone formulations will be approximately 2 x 10-11 molL
Figure 43 Neptunium Kd values under oxidizing conditions Neptunium Kd values for various saltstone formulations measured after one-day equilibration (1d) and four-day equilibration (4d) under oxidizing conditions Total plutonium concentrations in each system were 1 ppb 5 ppb and 10 ppb as noted Samples prepared in triplicate and error bars represent standard deviation of samples except as follows value for datasets TR545-1d 1ppb TR545-4d 1 ppb TR547 4d 1 ppb TR545-4d 10 ppb TR547-1d 1ppb TR547-4d 10 ppb are reported based on a single sample and for dataset TR545-1d 5ppb is reported based on duplicate samples Kd values limited to gt106 were at instrumental background
The Kd values for Tc are significantly lower than that of Pu or Np As a whole the values are
comparable The values for the one-day and four-day equilibrations solutions in the Vault 2 (17 dry wt- slag) and TR545 (90 dry wt- slag) remained constant within reasonable error with just a slight increase from the one-day to four-day equilibration However the Aged Cement (no slag) and TR547 (45 dry wt- slag) showed a noticeable decrease from day one to day four (Figure 45)
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Figure 44 Average solubility of Np under oxidizing conditions Neptunium solubility for various saltstone formulations measured after one-day equilibration (1d) and four-day equilibration (4d) under oxidizing conditions Total Np concentrations in each system were 1 ppb 5 ppb and 10 ppb Samples prepared in triplicate and an average of all samples (9) was used to determine average solubility except as follows TR545-1d is based on 6 samples TR545- 4d on 5 samples TR547-1d on 7 samples and TR547- 4d on 5 samples The error bars represent standard deviation
Figure 45 Technetium Kd values under oxidizing conditions Tc Kd values for various saltstone formulations measured after one-day equilibration (1d) and four-day equilibration (4d) under oxidizing conditions Total Tc concentrations in each system were 1 ppb 5 ppb and 10 ppb as noted above Samples were prepared in triplicate and the error bars represent standard deviation of samples except as follows data sets for Vault 2-1d 1ppb were duplicates and TR547- 4d 10 ppb is based on a single dataset
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Similar to the Tc Kd values the 127I Kd values are much lower than those of Pu and Np The amount of reducing slag present in each of the solids does not appear to have a drastic effect on the 127I Kd values In fact the initial (one day) Aged Cement (0 slag) samples had a Kd almost two orders of magnitude above those with reducing slag The cause of this behavior is not known but it has been shown that iodate IO3
- the oxidized form of iodine sorbs more strongly than iodide I- to charged surfaces (Schwehr et al 2009 Yoshida et al 1992 Fukui et al 1996) It is possible that the slag is reducing the iodine to the I- form converting it to a species that is less likely to sorb to saltstone Additional work would be required to confirm the oxidation state of iodine when associated with saltstone
Figure 46 Iodine Kd Values under Oxidizing Conditions Iodine Kd values for various cementitious formulations measured after one-day equilibration (1d) and four-day equilibration (4d) under oxidizing conditions Total iodine concentrations in the systems were 100ppb 500 ppb and 1000 ppb as noted above Samples were prepared in triplicate and the error bars represent standard deviation of samples except as follows duplicates were used for dataset TR545- 1d 100ppb
42 Radionuclide Sorption to Vial Walls Under Oxidizing Conditions
Figure 47 shows the aqueous fractions found in the no-solids controls It provides a measure of the solubility of each radionuclide as well as examines the fraction of each radionuclide sorbed to the vial walls After one day only 25 of the Pu remained in solution and the concentration decreased even more after four days The loss of Pu from the aqueous phase may be due to sorption of Pu to the vial walls or precipitation of a Pu hydrous oxide solid (discussed with respect to Figure 49 below) Additional experiments would be required to examine the solubility of the Pu in high pH calcite saturated solutions
After one day about 80 of the Np remained in solution However the aqueous concentration in the initially 1-ppb solution was significantly reduced after four days Approximately 60 of the Np remained soluble in the initially 10-ppb solution Once again this drop could be due to sorption to the vial wall The Tc present after one day ranged from about 88 to about 95 and was virtually 100 after four days These values are consistent with internal standards used to monitor Tc detection performance on the ICP-MS Greater than 50 of the I remained in solution after the one-day and four-day equilibrations As shown in Figure 48 the standard deviation between the triplicate I control samples was
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quite large Additional control samples are required to understand the mechanism by which I is being lost from the aqueous phase in these samples
Figure 47 Plutonium Neptunium and Technetium Aqueous Fractions Fraction of Pu Np and Tc remaining in the aqueous phase for the No Solids controls after a one-day equilibration (1d) and four-day equilibration (4d) under oxidizing conditions The total concentration for each radionuclide 10 ppb as noted above Samples were prepared in triplicate and the error bars represent the standard deviation of the samples
Figure 48 Iodine Aqueous Fraction Iodine aqueous fraction for the no-solids controls after a one-day equilibration (1d) and four-day equilibration (4d) under oxidizing conditions The total concentration of iodine was 1000 ppb as noted above Samples were prepared in triplicate and the error bars represent the standard deviation of the samples
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As discussed above the loss of Np and Pu from the no-solids control (Figure 47) could be due to
precipitation of Np and Pu hydrous oxides or sorption to the vial walls To quantify the differences between these possible sinks the vials were washed as described in Section 36 The data in Figure 49 indicate that significant sorption of Np and Pu to the vial walls may occur When combining the mass of Np represented in Figure 47 and Figure 49 there is almost 100 mass recovery of the Np sorbed to the vial wall and the aqueous fraction measured Therefore no precipitation of Np is expected However because 100 recovery was not achieved for Pu a Pu hydrous oxide phase could be precipitating which was washed out of the vial during the cleaning procedure The data in Figure 47 represent the no-solids control samples where there was no solid phase present for Np or Pu to sorb to besides the vial walls However when a cementitious solid phase is present in the sample there will be competition between the vial walls and the cement for sorption of Np and Pu Based on the affinity of metals for metal oxide surfaces as opposed to the polypropylene surface and the much higher surface site density expected for the cementitious samples it is assumed that the cementitious samples will out-compete the vial walls for sorption sites This thesis was tested by taking one of the triplicate samples from each sorption experiment with a solid phase present removing the solid phase from the tubes and leaching any sorbed Np and Pu from the tubes with acid as described in Section 36 Figure 410 and Figure 411 show that although some of the Pu and Np sorbed to the vial walls of the samples this amount accounted for less than 2 in all samples Therefore sorption of Np and Pu to the vial walls does not appear to be a significant factor in experiments where the solid phase is present Note these results do not discount the possibility that Pu hydrous oxide precipitates were forming in both the no-solid control experiments and experiments with cement formulations present Based on the observation of a constant aqueous phase concentration of Pu regardless of the initial Pu concentration the presence of a solubility limiting Pu phase cannot be discounted based on these data Further experiments examining the solubility of Pu in high pH calcite saturated solutions are required
Like Pu Np shows little affinity for the vial walls in the presence of a solid phase In each case tested there was significantly less than 1 of the total Np sorbed to the vial walls This behavior is consistent with the ~100 mass balance on Np achieve in the solid-free controls The majority of Np remained soluble in the solid-free control experiments Therefore it is expected that sorption of Np to the vial walls was the primary reason for the loss of Np from the aqueous phase in the no-solids systems rather than precipitation of a Np solid phase similar to the process discussed for Pu above This assumption is based on the relative solubility of Np(V) as compared with Pu(IV)
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Figure 49 Percent Pu and Np sorbed to vial walls of the no solids controls after the aqueous phases were discarded and the vials were washed Both the 10 ppb and 1 ppb datasets were prepared in triplicate and the error bars show the standard deviation
Figure 410 Percent Pu sorbed to vial walls after the solids and aqueous phases were removed and the vials were washed The graph illustrates one sample from each of the 1 ppb 5 ppb and 10 ppb systems Therefore no error bars are present
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Figure 411 Percent Np sorbed to vial walls after the solids and aqueous phases were removed and the vials were washed The graph illustrates one sample from each of the 1 ppb 5 ppb and 10 ppb systems Therefore no error bars are present
43 Radionuclide Sorption to Cementitious Formulations under Reducing Conditions
Similar to the Pu Kd values under oxidizing conditions Pu Kd values ranged from 104 to gt105 under reducing conditions (Figure 412) Also similar to the results under oxidizing conditions the Kd increases with increasing initial Pu concentration Again this behavior is indicative of the aqueous phase concentration of Pu being controlled by solubility of Pu rather than by sorption In each case the samples appeared to reach steady state within 24 hours This equilibration is evident because the Kd values after one day and four days are very similar Also it appears that the amount of reducing slag does not make a significant difference in the Kd value In fact the TR547 solid consists of 45 reducing grout but produces approximately the same Kd values of the aged cement which does not have any reducing grout Each of these Kd values are higher than the TR545 which is 90 reducing grout These findings are in agreement with those conducted by Allard et al (1984) and Hoglund et al (1985) who reported that concrete containing reducing agents (slag similar to that used in our study) did not have greater Pu Kd values than those that did not contain slag
Similar aqueous concentrations of Pu were observed regardless of the solid phase present Figure 36 shows the average aqueous phase concentrations measured after one day and four days for all solids As stated above triplicate samples were prepared for each solid phase and each initial concentration Therefore each of the reported solubility values in Figure 412 is an average of up to nine measurements of the Pu aqueous concentrations Using the highest reported value with the expected maximum error (00045 ppb for solid Vault 2) the maximum expected aqueous concentration of Pu in the pore water associated with the cementitious formulations will be approximately 2 x 10-11 molL (calculated from Equation 31) This value is on the same order as the solubility of Pu hydrous oxide solid phases (Neck and Kim 2001) A best value would be 10-12 molL
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Figure 412 Pu Kd Values under Reducing Conditions Plutonium Kd values for various cementitious formulations measured after one-day equilibration (1d) and four-day equilibration (4d) under reducing conditions Total plutonium concentrations in each system were 1ppb 5 ppb and 10 ppb Samples prepared in triplicate and error bars represent standard deviation
Figure 413 Average Solubility of Plutonium under Reducing Conditions Plutonium solubility for various cementitious formulations measured after one-day equilibration (1d) and four-day equilibration (4d) under reducing conditions Total plutonium concentrations in each system were 1ppb 5 ppb and 10 ppb as noted Samples prepared in triplicate and an average of all samples (9) was used to determine average solubility The error bars represent standard deviation of samples
The Np Kd values reported in Figure 414 obtained under reducing conditions are very similar to
those obtained under oxidizing conditions In each case the samples appeared to reach steady state within 24 hours This equilibration is evident because the Kd values between the one-day and fourndashday equilibrations are similar As was the case with Pu the amount of slag present in each solid does not
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seem to have a significant effect on the Kd values Again the aged cement with no slag has as high a Kd as the TR545 with 90 reducing slag
Similar aqueous concentrations of Np were observed regardless of the solid phase present Figure 314 shows the average aqueous phase concentrations measured after one day and four days for all solids All Kd values were gt 105 mLg which is considerably larger than those reported by Kaplan and Coates (2007) who reported Np Kd values to 1300 to 1600 mLg This difference can be attributed to two important experimental differences 1) the experiment was designed to permit larger Kd values to be measured (eg solid to liquid ratios and spike concentrations) and more importantly 2) a more sensitive analytical method ICP-MS was used instead of conventional low-energy gamma spectroscopy or liquid scintillation counting (LSC) analysis As stated above triplicate samples were prepared for each solid phase and each initial concentration Therefore each of the reported solubility values in Figure 415 is an average of up to nine measurements Using the highest reported value (to provide the most conservative most soluble values) with the expected maximum error (00045 ppb for solid TR545) the maximum expected aqueous concentration of Np in the pore water associated with the cementitious formulations will be approximately 2 x 10-11 molL A best value taking into consideration the less-than values which are depicted in Figure 414 as running off the top of the plot would be 10-12 molL
Figure 414 Np Kd Values under Reducing Conditions Neptunium Kd values for various cementitious formulations measured after one-day equilibration (1d) and four-day equilibration (4d) under reducing conditions Total Np concentrations in each system were 1 ppb 5 ppb and 10 ppb Samples were prepared in triplicate and the error bars represent standard deviation Kd values limited to gt106 were at instrumental background
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Figure 415 Average Solubility of Neptunium under Reducing Conditions Neptunium solubility for various cementitious formulations measured after one day equilibration (1d) and four day equilibration (4d) under reducing conditions Total plutonium concentrations in each system were 1ppb 5 ppb and 10 ppb Samples prepared in triplicate and an average of all samples (9) was used to determine average solubility The error bars represent standard deviation
A plot of the Tc Kd values for each cementitious formulations under reducing conditions is shown
in Figure 416 (log y-axis) and Figure 417 (reduced scale linear y-axis) The Kd values for each of the initial Tc concentrations are relatively similar This behavior is consistent with the Kd expression However the increasing Kd values from the one-day to four-day day equilibrations for each solid indicate that steady state was not reached within one day and it is unclear whether steady state was reached after four days A possible explanation for this behavior is that Tc(VII) was being reduced to Tc(IV) in these systems due to the reducing conditions As Tc(VII) was reduced the Kd would increase based on the high affinity of Tc(IV) for solid phases This proposed mechanism was observed by Lukens et al (2005) using an SRS saltstone material similar but not identical to TR547 Using synchrotron X-ray absorption fine structure spectroscopy they observed over a 453 month period that Tc(VII) incorporated into SRS saltstone slowly converted to Tc(IV) and that the nearest neighbor was initially predominantly oxygen and eventually became predominantly sulfur (described as a Tc(IV) phase TcSx) Lacking in Lukens et al (2005) is quantification of the solubility of Tc This analysis still needs to be completed along with re-oxidation studies (ie what is the rate that reduced Tc reoxidizes under ambient natural saltstone conditions)
Unlike Np and Pu Tc Kd values changed with the amount of slag included in the formulation Tc Kd values noticeable increase as the amount of slag in the formulation increased TR547 (45 dry-wt- slag) Kd value is visibly higher than the Aged Cement and Vault 2 Kd values while the most reducing TR545 (90 dry wt- slag) Kd value is significantly higher than the others Following a similar trend the reduction capacity that is the total quantity of reductant in the saltstone on a mass basis (units of milli-equivalents of charge per g) of TR547 had slightly greater or equal reduction capacity to that of TR545 (Roberts and Kaplan 2009)
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Figure 416 Tc Kd Values under Reducing Conditions Tc Kd values for various cementitious formulations measured after one-day equilibration (1d) and four-day equilibration (4d) under reducing conditions Total Tc concentrations in each system were 1 ppb 5 ppb and 10 ppb Sample prepared in triplicate and error bars represent standard deviation except as follows TR547-1d 1 ppb is based on a single dataset and datasets Vault 2-1d 5 ppb Vault 2- 4d 1 ppb Aged Cement-1d 5 ppb and Aged Cement-4d 1 ppb are duplicates
Figure 417 Data from Figure 416 replotted on a reduced linear scale for easier viewing Each sample was prepared in triplicate except as follows TR547-1d 1 ppb is based on a single dataset Vault 2-1d 5 ppb Vault 2- 4d 1 ppb Aged Cement-1d 5 ppb and Aged Cement-4d 1 ppb are duplicate datasets
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The calculated Kd values for I sorption to cementitious samples under reducing conditions are shown in Figure 418 Before discussing the data it should be noted that spiked QAQC samples which were analyzed on the ICP-MS along with the samples used to generate the data in Figure 418 were off by an average of 195 with one outlier of approximately 40 This dataset did not include the use of internal standards as discussed in Section 31 above1 Due to a lack of an internal standard the iodine results presented in this report should be considered with a minimum error estimate of 20
The iodine Kd values under reducing conditions are different from those observed under oxidizing conditions Under oxidizing conditions it appears they are at a steady state by day one However under reducing conditions there is a noticeable difference between days one and four indicating steady state was not reached by day one and possibly not by day four Another interesting observation is that the Kd values are decreasing from day one to four A possible reason for this behavior may be due to redox chemistry of iodine in this system If iodine partially or entirely exists in the form as iodate (IO3
-) it is possible it could be reduced to iodide I- within the reducing cementitious system These two iodine species sorb differently iodate sorbing to minerals more strongly than iodide (Denham et al 2009 Schwehr et al 2009 Fukui et al 1996 Yoshida et al 1992) It is hypothesized that the reducing environment of the saltstone is sufficient to reduce iodate ions to the more weakly binding form of iodine iodide
This is one of the few datasets (along with Tc) in this study where there may be a difference between the various solids The degree of iodate reduction would be expected to increase as the slag content increases As mentioned above reduction of iodate to iodide should result in a decrease in sorption Therefore higher Kd values should be observed for solids with less slag such as the Aged Cement (0 dry wt- slag) and Vault 2 (17 dry wt- slag) This is generally the case in Figure 418 where the highest Kd values are reported for the Aged Cement and the lowest values are for solid TR547 However this trend does not hold completely where the saltstone sample containing 90 slag (TR545) has generally equal or higher Kd values than the saltstone containing 45 dry wt- slag (TR547)
1 Clemson University is presently investigating appropriate internal standards for iodine analyses for ICP-MS Of those tested rhenium and molybdenum have shown some promise
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Figure 418 Iodine Kd Values under Reducing Conditions I Kd Values for various cementitious formulations measured after one day equilibration (1d) and four day equilibration (4d) under reducing conditions Total iodine concentrations in each system were 100 ppb 500 ppb and 1000 ppb as noted Sample prepared in triplicate and error bars represent standard deviation of samples except as follows Vault 2-4 d 100 ppb is a single dataset while the datasets for Vault 2-1 d 100 ppb 4 d 1000 ppb TR545-4 d 1000 ppb 100 ppb TR547-4 d 1000 ppb 500 ppb 100 ppb and Aged Cement- 4 d 1000 ppb and 100 ppb are all based on duplicates
44 Radionuclide Sorption to Vial Walls under Reducing Conditions
The aqueous concentrations for Pu Np and Tc in the no solids controls are shown in Figure 419 The results are similar to those presented for experiments performed under oxidizing conditions above The 1 ppb Pu aqueous fraction is approximately three times greater than the 10 ppb fraction at day one This fraction decreases over time and by day four they are approximately equal when taking error into account This behavior is similar to the aqueous fraction under oxidizing conditions The 1 ppb Np aqueous fraction is significantly higher on both day one and day four than the aqueous fraction of the 10 ppb samples However each remained constant from day one to day four The 10 ppb aqueous fraction is twice as low as under oxidizing conditions which suggests either higher sorption to the vial walls or more precipitating out under the reducing conditions Like Pu and Np Tc shows a decrease from day one to day four especially for the 1 ppb samples The decrease in the 10 ppb sample is minimal and the aqueous fraction remains around 09 This value is slightly lower than that under oxidizing conditions
To examine the degree of sorption to the vial walls the tubes were washed again as performed for the experiments under oxidizing conditions above and similar results were found Ninety percent of the 1 ppb Pu sample was sorbed to the vial wall upon completion of the experiment which gives a 100 mass recovery when comparing this value to that found in Figure 419 However this result is not the case with the 10 ppb samples where approximately 75 of the mass remains unaccounted It is noteworthy that approximately 25 of the Pu from the 10 ppb solution sorbed to the vial walls under both oxidizing
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and reducing conditions Np follows the same trend as Pu while less than 005 of the Tc sorbed to the wall
Figure 419 Plutonium Neptunium and Technetium No-Solids Aqueous Fractions under Reducing Conditions Pu Np and Tc aqueous fractions of No Solids controls after a one-day equilibration (1d) and four-day equilibration (4 d) under reducing conditions Total concentration for each radionuclide was 1 ppb and 10 ppb Samples were prepared in triplicate and the error bars represent the standard deviation
Figure 420 Percent of Pu Np and Tc sorbed to the vial walls of the No Solids control samples under reducing conditions Each the 1 ppb and 10 ppb samples were prepared in triplicate and the error bars represent the standard deviations of triplicate samples
Under reducing conditions the fraction of I remaining in the aqueous phase was around 90 with
almost 100 mass recovery of the 100 ppb I after the four-day equilibration These graphs show that
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under reducing conditions there will only be a small fraction of I sorbing to the vial wall or coming out of solution This result is a much better mass recovery than under oxidizing conditions (Figure 48) which had a mass recovery of approximately 65 after four days This result is also consistent with the interpretation that there may be a iodine speciation change between the two redox treatments
Figure 421 Iodine No-Solids Aqueous Fractions under Reducing Conditions I aqueous fractions of No-Solids controls after a one-day equilibration (1d) and four-day equilibration (4d) under reducing conditions The total concentration for each system was 100 ppb and 1000 ppb Samples were prepared in triplicate and the error bars represent the standard deviation
50 Comparison of Radionuclide Sorption under Oxidizing and Reducing Conditions
In the following figures (Figure 51 through Figure 54) the data shown above has been replotted to allow comparison between the oxidizing and reducing conditions for each cementitious formulation General observations based on these data follow Vault 2 Observations (Figure 51)
bull Pu Kds are greater than 104 under both oxidizing and reducing conditions and Pu Kds are slightly lower under reducing conditions This could possibly be due to reduction of Pu(IV) to Pu(III) However no oxidation state analysis was performed in this work
bull Np Kds are generally greater than 104 under both oxidizing and reducing conditions Interestingly Np Kds are higher under reducing conditions by almost an order of magnitude This could possibly be due to reduction of Np(V) to Np(IV) However no oxidation state analysis was performed in this work
bull Regardless of the initial Np or Pu concentration similar aqueous phase concentrations of Np or Pu were observed in all samples This trend indicates that ldquosorptionrdquo of Np and Pu in these systems may be a combination of adsorption absorption and (co)precipitation processes
bull Tc appears to reach a steady state within four days under oxidizing conditions This behavior does not appear to be the case under reducing conditions After four days similar Kd values are reached under both oxidizing and reducing conditions It is unclear
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whether the Kd value of Tc will continue to increase under reducing conditions consistent with reduction of Tc(VII) to Tc(IV) The similarity in Kd values under both oxidizing and reducing conditions is an interesting observation and certainly warrants additional studies
bull I Kd values are similar under both oxidizing and reducing conditions However reducing condition systems may not be at steady state after four days while systems under oxidizing conditions appeared to reach a steady state The difference in rates may be due to reduction of iodate to iodine
bull For all isotopes examined the sorption behavior to each of the solid phases is very similar
TR545 and TR547 Observations (Figure 52 and Figure 53) bull Similar to the discussion above with respect to Vault 2 Pu Np and Tc all appear to reach
a steady state under oxidizing conditions and approach steady state slower under reducing conditions
bull Np and Pu Kd values are greater than 104 for all systems and time steps The aqueous phase concentrations of Np and Pu appear to be better described as a solubility in terms of the aqueous phase concentration of Np and Pu Similar aqueous phase concentrations of both Np and Pu were reached The data indicate that the initial Np and Pu concentration generally does not affect the aqueous phase concentration at an apparent steady state The presence of each solid phase appears to limit the aqueous phase concentration of both Np and Pu on the order of 10-11 molL
bull Tc shows significantly higher Kd values under reducing conditions versus oxidizing conditions
bull For all isotopes examined the sorption behavior to each of the solid phases is very similar
Aged Cement Observations (Figure 54) bull Pu appears to be close to steady state for each solid by day one with similar Kd values
reached on between day one and day four bull Np has a higher Kd under reducing conditions than oxidizing (105 under oxidizing
conditions and gt105 under reducing conditions) bull Neither set of Tc data was at steady state by day one and rates of sorptiondesorption
reactions appear to be different Tc Kds decrease from day one to four under oxidizing conditions but increase under reducing conditions
bull The Kd values for I under oxidizing conditions were considerably higher than those measured for I with any other solid Similar Kd values obtained for the same solids under reducing conditions indicate that the reported Kd values under oxidizing conditions appear to be suspect However analysis of the raw data gives no indication of an experimental artifact As discussed above these observations may be explained based upon the amount of slag contained within the solids which will affect the reducing capacity (ie No reducing slag is in the aged cement which could be reason the reduction of iodate to iodide (speculated in other samples) is not evident)
bull The difference in sorption behavior of iodine to the aged cement between oxidizing and reducing conditions also indicates that the reducing conditions of the solution may affect I redox behavior in addition to any reactivity expected in the solid phases
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Figure 51 Comparison of Tc I Np and Pu sorption to Vault 2 solid under oxidizing and reducing conditions
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Figure 52 Comparison of Tc I Np and Pu sorption to TR 545 solid under oxidizing and reducing conditions
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Figure 53 Comparison of Tc I Np and Pu sorption to TR547 solid under oxidizing and reducing conditions
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Figure 54 Comparison of Tc I Np and Pu sorption to Aged Cement under oxidizing and reducing conditions
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60 Comparison of Radionuclide Sorption and Solubility under Oxidizing and Reducing Conditions
To further summarize the data the following tables provide either the average solubility
(for Np and Pu) or average Kd (for Tc and I) determined under both oxidizing and reducing conditions for each cementitious formulation Each table lists the average value standard deviation and the number of replicate samples used to calculate the reported values
The solubility of Pu in the presence of each solid under oxidizing and reducing conditions is shown in Table 61 (this is taken from experiments equilibrated for four days not one day) Under oxidizing conditions the apparent solubility values associated with the Aged Cement (0 dry wt- slag) Vault 2 (17 dry wt- slag) and TR547 (45 dry wt- slag) are all similar with only a slight increase in solubility as the amount of reducing slag increases There is a significant increase of almost an order of magnitude for the most reducing saltstone TR545 (90 dry wt- slag) However these samples also have a standard deviation on the same order of magnitude as the solubility itself which when taken into account brings the solubility back into the range of the others Under reducing conditions the apparent solubility values are slightly lower than under oxidizing conditions In this set of samples the Vault 2 saltstone with 10 dry wt- reducing slag had the highest apparent solubility but once again when considering the standard deviation the values are similar
Table 61 Comparison of plutonium apparent solubility values under oxidizing and reducing conditions
Table 62 lists the apparent solubility values of Np in the presence of each cementitious
formulation under both oxidizing and reducing conditions Under oxidizing conditions the cementitious formulation does not appear to have a dramatic effect on the solubility The apparent solubility values are similar to those of Pu under similar conditions except the Np standard deviations are much higher The high standard deviations are an analytical artifact since the measured concentrations were close to or at the detection limit of the ICP-MS There does appear to be a slight decrease in Np solubility under reducing conditions However the statistical significance of this decrease was not calculated
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47
Table 62 Comparison of neptunium apparent solubility values under oxidizing and reducing conditions
Unlike the apparent solubility values of Pu and Np the aqueousatmospheric conditions
and cementitious formulation seem to have an effect on the Tc Kd values (Table 63) Under oxidizing conditions there is not a discernible difference among the different cementitious formulations especially when taking the respective standard deviations into account However when experiments were run under reducing conditions the specific formulation had a noticeable effect The two saltstone samples with the least amount of reducing slag Aged Cement (0 dry-wt- slag) and Vault 2 (17 dry wt- slag) had Kd values which were similar to those observed under oxidizing conditions However the TR547 (45 dry-wt- slag) increased by almost an order of magnitude while the TR545 (90 dry wt- slag) increased by about three orders of magnitude Although the respective standard deviations are large the higher Kd values do appear to be significant
Table 63 Comparison of technetium Kd values under oxidizing and reducing conditions
Unlike Tc I does not seem to be as affected by cementitious formulation and redox status (Table 64) The only treatment (possible outlier) that does not follow this trend is the Aged Cement under oxidizing conditions This Kd value is higher than the others but also has a much higher standard deviation which when accounted for gives a value similar to the others All other treatments had near identical Kd values irrespective of solid phase or redox condition But again the Aged Cement data cannot be discounted at this time given the possibility of the influence that redox may have on iodine speciation and the strong influence I speciation has on sorption to cementitious materials
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Table 64 Comparison of iodine Kd values under oxidizing and reducing conditions
71 Comparison with Previous Data The increased sensitivity of the ICP-MS over conventional low-energy gamma
spectroscopy or liquid scintillation counting (LSC) analysis allowed for much more accurate Kd values and apparent solubility values in this work than were previously obtainable Generally radioanalytical detection methods start with activities on the order of 103 to 104 counts per minute (cpm) and approach background levels of 1 to 5 cpm for strongly sorbing radionuclides Therefore the accuracy of the Kd value will be the difference in analytical sensitivity when the initial aqueous activity decreases by a factor of approximately 5000 (ie the aqueous activity drops from approximately 5000 cpm to the instrument background of 1 cpm following almost complete sorption) As a result the reported Kd values can only be reliably reported up for a Kd of 103 to 104 This constraint is believed to be the difference between the observed Kd values for 237Np of gt 105 observed in this work when compared with the Kd values between 3000 and 4000 reported by Kaplan et al (2008) A similar observation was made for Pu because 242Pu was used for ICP-MS analysis and 238Pu was used in the work of Kaplan et al (2008) This constrint may account for the different Kd value of gt104 reported in Kaplan et al (2008) compared with the value of gt105 observed in this work
In the case of Tc Kaplan et al (2008) reported a Kd of 023 mLg for Vault 2 under oxidizing conditions and 093 mLg under reducing conditions while the above experiment determined the Vault 2 Kd to be 505 mLg under oxidizing conditions and 557 mLg under reducing conditions Unlike the discrepancy in the Kd values for Np Pu and Tc between the above findings and those in Kaplan et al (2008) the reported Kd values for iodine are similar For Vault 2 Kaplan et al (2008) found 125I to have a Kd of 894 mLg under oxidizing conditions and 715 mLg under reducing conditions These values are similar to the Kd values of 766 mLg and 725 mLg observed under oxidizing and reducing conditions respectively in this work These findings appear to confirm the previously accepted Kd values of 0-10 mLg depending on the cementitious formulation
72 Suggested Future Work The above data demonstrate several areas that require further examination The
increasing Tc Kd values over time dataset suggest that steady state had not been achieved It would be beneficial to determine the amount of time required to reach steady state and allow determination of a more accurate Kd value (an assumption of the Kd construct is that it be measured at steady state) Also kinetic studies of both Tc and I are needed to better understand their respective interactions with the different cementitious formulations As for the I additional
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49
tests should be performed to test the hypothesis that iodine may in part exist as iodate which may initially sorb to the saltstone then undergo reduction to iodine or iodide and then desorbs causing a decrease in Kd
A final area of future work is to examine the possible causes for the similar behavior of each cementitious formulation despite the different slag content This discrepancy is not only observed in the above experiments but also in Kaplan et al (2008) which is illustrated in Table 31 and by recent work in measurements of saltstone reduction capacity (Roberts and Kaplan 2009) The reduction capacity (units in milli-equivalentsg solid) equivalents of the Aged Cement with no slag is 855 plusmn 101 and adding 10 slag gives a reducing equivalent of 2398 plusmn 311 However increasing the slag content to 23 causes the reducing capacity to increase to 8218 plusmn 81 which is almost equivalent to the 8324 plusmn 49 of the 100 slag Understanding the chemistry behind the reducing capacity of each cementitious formulation will help to define what reactions are important for controlling radionuclide release from the saltstone
80 References Allard B L Eliasson S Hoglund and K Andersson 1984 ldquoSorption of Cs I and actinides in
concrete systemsrdquo SKB Technical Report SKBKBS TR-84-15 DKB Stockholm Sweden
Denham M D I Kaplan and C Yeager2009 ldquoGroundwater radioiodine Prevalence biogeochemistry and potential remedial approachesrdquo SRNL-STI-2009-00463 Savannah River National Laboratory Aiken SC
Dixon K L M A Phifer and J R Harbour 2008 ldquoFY09 PACA Maintenance Program Additional Saltstone Property Testingrdquo SRNL-L3100-2009-00019 Rev0 Savannah River National Laboratory Aiken SC
Fukui M Fujikawa Y and Satta N 1996 ldquoFactors affecting interaction of radioiodide and iodate species with soilrdquo Journal of Environmental Radioactivity 31 199-216
Hoglund S L Eliasson B Allard K Andersson and B Torstenfelt 1985 ldquoSorption of some fission products and actinides in concrete systemsrdquo Mat Res Soc Symp Proc 50 683-690
Kaplan D I 2007 Geochemical Data Package for Performance Assessment Calculations Related to the Savannah River Site WSRC-TR-2006-00004 Rev 1 Washington Savannah River Company Aiken SC
Kaplan D I and Coates J 2007 ldquoPartitioning of Dissolved Radionuclides to Concrete under Scenarios Appropriate for Tank Closure Performance Assessmentsrdquo WSRC-STI-2007-00640 Rev 0 Washington Savannah River Company Aiken SC 29808
Kaplan D I Roberts K Coates J Siegfried M Serkiz S 2008 ldquoSaltstone and concrete interactions with radionuclides Sorption (Kd) desorption and reduction capacity measurementsrdquo SRNS-STI-2008-00045 Savannah River National Laboratory Aiken SC 2008
SRNL-STI-2009-00636 Revision 0
50
Neck V and Kim J I 2001 ldquoSolubility and hydrolysis of tetravalent actinidesrdquo Radiochim Acta 89 1
Powell B A Fjeld R A Coates J T Kaplan D I Serkiz S M 2002 ldquoPlutonium Oxidation State Geochemistry in the SRS Subsurface Environmentrdquo WSRC-TR-2003-00035 Westinghouse Savannah River Company US DOE Savannah River Site Aiken SC
Roberts K A and D I Kaplan 2009 Reduction Capacity of Saltstone and Saltstone Componentsrdquo SRNL-STI-2009-00637 Rev0 Savannah River National Laboratory Aiken SC
Schwehr K A Santschi P H D I Kaplan C M Yeager and R Brinkmeyer 2009 ldquoOrgano-iodine formation in soils and aquifer sediments at ambient concentrationsrdquo Environ Sci Technol 437258-7264
Yoshida S Muramatsu Y and Uchida S 1992 ldquoStudies on the sorption of I-(iodide) and IO3-
(iodate) onto andosolsrdquo Water Air and Soil Pollution 63 321-329
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51
90 Appendix A Data Tables of Radionuclide Sorption to Saltstone under Oxidizing Conditions
The following tables represent data collected for the no solids controls each saltstone and testing of radionuclide sorption to the vial walls The no solids controls tables include the concentration (ppb) of the radionuclide spiked into the sample along with the concentration of the radionuclide (ppb) measured in the aqueous phase after the given equilibration time The pH at the time the sample was taken is also recorded along with the fraction of the radionuclide which stayed in the aqueous phase The tables for the cementitious formulation data include the data above along with the addition of a Kd value The tables of the data for the radionuclides sorbed to the vial walls include the initial concentration (ppb) of the spike the concentration (ppb) of the radionuclide that had sorbed to the vial wall during the experiment and the percentage of the total concentration this represents Important Notes
BDL- Below Detection Limit lt01 denotes no notable sorption occurred
91 Data Tables for No Solid Controls
Table 91 Plutonium no solids control after one day
A 9264165178 402285E‐05 1181 434238E‐06 9980817 B 9352537276 0000110618 1183 118276E‐05 3616813 C 9363541597 705331E‐05 118 753273E‐06 5401186 D 0993110568 BDL 12 NA NA E 0977247222 300794E‐05 1199 307797E‐05 1280331 F 0962441315 BDL 1198 NA NA G 4059128499 BDL 1186 NA NA H 4065161486 705198E‐05 1188 173473E‐05 2380003 I 4116819691 0000110748 1189 269014E‐05 1555864
Table 920 TR545- neptunium after four days
Sample ID
Initial Aq Conc (ppb)
Equil Aq Conc (ppb) pH
Fraction Aq Kd
A 92641652 NA 1188 NA NA B 93525373 00001935 1185 2069E‐05 2067199C 93635416 4119E‐05 1185 44E‐06 9247818D 09931106 BDL 1197 NA NA E 09772472 BDL 12 NA NA F 09624413 00066817 1206 00069424 562421G 40591285 00003289 1196 8103E‐05 5148274H 40651615 00025316 1196 00006228 6625737I 41168197 00001018 1194 2474E‐05 1692126
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Table 921 TR545- technetium after one day
Sample ID
Initial Aq Conc (ppb)
Equil Aq Conc (ppb) pH Fraction Aq Kd
A 9655146069 820460082 1181 0849764546 8998984 B 9356176321 7703053505 1183 0823312135 1051242 C 9114122586 7978297395 118 0875377451 7062663 D 1042349157 0853053814 12 0818395456 9099556 E 0983206046 0871198263 1199 0886079033 5196709 F 0905148405 0803451372 1198 0887646013 5098696 G 4950156706 4275082341 1186 0863625658 7213934 H 4889067068 4173762594 1188 0853693053 7687519 I 4854463762 4147024058 1189 0854270268 7771045
A 1048950046 0002141023 1149 0000204111 2112281 B 1039943573 0001770549 1157 0000170254 2460487 C 1084651695 0001127533 1153 0000103953 4014918 D 1088686867 0001201087 1172 0001103244 3564524 E 1119673887 0000783288 1177 0000699568 5709897 F 1045722787 0000914861 1181 000087486 4495324 G 5387981131 0001444832 1169 0000268158 1494715 H 5412748988 0001143483 1169 0000211257 1965749 I 5373948758 00010003 1164 0000186139 2280472
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Table 926 TR547- plutonium after four days
Sample ID
Initial Aq Conc (ppb)
Equil Aq Conc (ppb) pH
Fraction Aq Kd
A 104895 NA 116 NA NA B 10399436 0001828 1165 00001758 2383132C 10846517 00010788 1164 9946E‐05 4196159D 10886869 00009131 1184 00008388 4689778E 11196739 00010624 1189 00009488 4208928F 10457228 00007967 1191 00007619 516258G 53879811 00007915 1173 00001469 2728993H 5412749 00008355 1175 00001544 2690641I 53739488 00006103 1174 00001136 3737892
Table 927 TR547- neptunium after one day
Sample ID
Initial Aq Conc (ppb)
Equil Aq Conc (ppb) pH Fraction Aq Kd
A 9589772032 0000454463 1149 473903E‐05 9116335 B 9293228768 0000260081 1157 27986E‐05 1499475 C 1008725504 0000302018 1153 299405E‐05 1397125 D 0952173007 000019177 1172 0000201403 1954603 E 0992224074 BDL NA NA F 0967815522 402137E‐05 1181 41551E‐05 9474699 G 4068405786 0000222282 1169 546361E‐05 7336986 H 409543171 0000531619 1169 0000129808 3199152 I 4017406611 0000410123 1164 0000102086 4157807
Table 928 TR547- neptunium after four days
Sample ID
Initial Aq Conc (ppb)
Equil Aq Conc (ppb) pH Fraction Aq Kd
A 9589772 NA 116 NA NA B 92932288 00002145 1165 2308E‐05 1818463C 10087255 00001628 1164 1614E‐05 2591215D 0952173 BDL 1184 NA NA E 09922241 BDL NA NA F 09678155 5107E‐05 1191 5277E‐05 7460375G 40684058 00001336 1173 3284E‐05 1220544H 40954317 8151E‐05 1175 199E‐05 2086795I 40174066 00001322 1174 3292E‐05 1289605
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Table 929 TR547- technetium after one day
Sample ID
Initial Aq Conc (ppb)
Equil Aq Conc (ppb) pH Fraction Aq Kd
A 9466799266 8233850788 1149 0869760788 8220086 B 9439556236 817653394 1157 0866198975 8165745 C 9383493063 8086024379 1153 0861728604 8430884 D 1061939876 0919992065 1172 0866331594 6241759 E 0991827343 0836511397 1177 0843404251 7590958 F 0971981155 0839862696 1181 0864073024 6354378 G 4883337077 414858839 1169 0849539633 7903986 H 4691440077 3996173112 1169 0851800949 8038249 I 486993937 4291285586 1164 0881178442 6558707
Table 930 TR547- technetium after four days
Sample ID
Initial Aq Conc (ppb)
Equil Aq Conc (ppb) pH
Fraction Aq Kd
A 94667993 NA 116 NA NA B 94395562 85812109 1165 09090693 5885474C 93834931 84622373 1164 09018217 6279204D 10619399 09580683 1184 09021869 4435663E 09918273 08881507 1189 08954691 4835506F 09719812 09036489 1191 0929698 3138862G 48833371 4490415 1173 09195382 4312104H 46914401 42054182 1175 08964024 5612948I 48699394 43843193 1174 09002821 5536503
Table 931 TR547- iodine after one day
Sample ID
Initial Aq Conc (ppb)
Equil Aq Conc (ppb) pH Fraction Aq Kd
A 9944920441 8813152965 1149 0886196427 738241 B 9956006121 8747156303 1157 0878580848 8007767 C 9822152291 8664470934 1153 0882135674 7988892 D 1002391846 9333490632 1172 0931121963 3368509 E 9918273427 6625075445 1177 0667966607 1551748 F 9918175056 8931364957 1181 0900504872 4773862 G 5166570628 4445386532 1169 0860413387 7961604 H 4847821413 410447427 1169 084666367 8664303 I 4850381381 4266693706 1164 0879661489 6413801
100 Appendix B Data Tables of Radionuclide Sorption to Saltstone Under Reducing Conditions
The following tables represent data collected for the no solids controls each cementitious solid and testing of radionuclide sorption to the vial walls The no solids controls tables include the concentration (ppb) of the radionuclide spiked into the sample along with the concentration of the radionuclide (ppb) measured in the aqueous phase after the given equilibration time The pH at the time the sample was taken is also recorded along with the fraction of the radionuclide which stayed in the aqueous phase The tables for the cementitious solidsrsquo data include the data above along with the addition of a Kd value The tables of the data for the radionuclides sorbed to the vial walls include the initial concentration (ppb) of the spike the concentration (ppb) of the radionuclide that had sorbed to the vial wall during the experiment and the percentage of the total concentration this represents Important Notes
BDL= Below Detection Limit lt01 denotes no notable sorption occurred
101 Data Tables for No-Solid Controls
Table 101 Plutonium no solids control after one day
A 9405892 0007019 111 0000746258 5681206 B 9602498 0003294 1117 0000342992 123554 C 9630619 0002936 1114 0000304893 1396318 D 4945396 0001795 113 0000363011 1171688 E 4964945 0001373 1131 0000276484 1493015 F 4441601 0001516 113 0000341219 1389674 G 1079602 0001109 1142 0001027508 4215519 H 1031512 0000883 1143 0000855983 4820576 I 0939294 0000978 1143 0001040992 4550255
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Table 1011 Vault 2- neptunium after one day
Sample ID Initial Aq Conc (ppb)
Equil Aq Conc (ppb) pH Fraction Aq
A 9425042625 0001709054 1105 0000181331 B 9611386476 0001184125 1110 00001232 C 9579553607 0001155517 1104 0000120623 D 4974000414 0000672325 1125 0000135168 E 4916731623 0000675371 1128 0000137362 F 4373142817 0000570681 1120 0000130497 G 0943366414 0000389738 1129 0000413136 H 1011745587 0000565648 1132 0000559081 I 0865252712 0000379545 1133 0000438653
A 8849444124 0000306309 1150 346133E‐05 1289533 B 8447823057 0000150131 1155 177715E‐05 2711019 C 8590597085 0000199185 1153 231864E‐05 2044057 D 4491250244 517162E‐05 1156 115149E‐05 4020064 E 4391894479 204591E‐05 1158 465838E‐06 9846089 F 4210703646 204376E‐05 1158 485374E‐06 9816203 G 086381524 522216E‐06 1160 604546E‐06 7577764 H 0870501884 BDL 1160 NA NA I 0861953838 BDL 1162 NA NA
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Table 1036 Aged cement- neptunium after four days
Sample ID
Initial Aq Conc (ppb)
Equil Aq Conc (ppb) pH Fraction Aq Kd
A 8849444 0000131 1145 148418E‐05 3007445B 8447823 0000111 1146 131529E‐05 3662996C 8590597 656E‐05 1146 76328E‐06 6209405D 449125 BDL 1155 NA NA E 4391894 BDL 1156 NA NA F 4210704 BDL 1155 NA NA G 0863815 BDL 1165 NA NA H 0870502 BDL 1162 NA NA I 0861954 BDL 1164 NA NA
Table 1037 Aged cement- technetium after one day
Sample ID
Initial Aq Conc (ppb)
Equil Aq Conc (ppb) pH Fraction Aq Kd
A 8426518355 833290075 1150 098889012 0476492 B 8638001423 7823321167 1155 0905686487 4413063 C 9323317745 925927516 1153 0993130923 0294664 D 442651005 4300859603 1156 0971614106 1242837 E 4426849405 4336992073 1158 0979701742 0855315 F 3929483125 3938204338 1158 100221943 lt01 G 0817864386 081693181 1160 0998859743 0049487 H 0878958929 0792412508 1160 0901535306 4510199 I 0772205665 0871436364 1162 1128502941 lt01
Table 1038 Aged cement- technetium after four days
110 Appendix C Dixon et al (2009) FY09 PACA Maintenance Program Additional Saltstone Property Testing SRNL L3100-2009-00019 Rev 0
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83
SRNL L3100-2009-00019 Rev 0
December 16 2008
Keywords Performance Permeability Modulus
L B Romanowski
Waste Determinations From K L Dixon M A Phifer and J R Harbour
FY09 PACA Maintenance Program Additional Saltstone Property Testing
BACKGROUND
Additional tests have been identified for measurement of important hydraulic and physical properties of saltstone The initial phase of this work [1] was completed last year and the results were detailed in an internal report [2] The proposed testing for FY09 includes measurement of saturated hydraulic conductivity porosity bulk density particle density water retention and Youngrsquos modulus of simulated Saltstone grouts For completeness the bleed volumes and gel times for each mix will also be measured
The testing will be based on a projected salt solution composition for the ARPMCU stream that will be fed to the Saltstone Production Facility over the next few years The scope for FY09 will include testing to determine the impact of (1) admixtures (2) organics (3) wcm ratio (4) aluminate concentration and (5) temperature of curing on the hydraulic properties of saltstone mixes Samples of selected batches prepared as part of this task will be provided to Dan Kaplan for measurement of Kd through leaching tests The eleven mixes that will be batched and tested are detailed in Table 1
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Table 1 The Eleven Mixes That will be Batched and Tested
BFS is Blast Furnace Slag FA is Fly Ash and PC is Portland Cement
TEST DETAILS
Test 1 Control (Mix 1)
A control mix will be based on the baseline mix modified by exclusion of the Class F fly ash Consequently the cementitious materials premix will be a mixture of 90 blast furnace slag and 10 portland cement The degree of reaction will be much greater than with the normal premix and therefore should result in a lower porosity and a lower permeability This bounding test at 060 wcm ratio is expected to yield a hydraulic conductivity at or below the detection limit for the Mactec permeameter measurement system Therefore this test should demonstrate the lowest level of detection of the Mactec system as well as show a resolvable difference between measurements of the control mix and the control mix with the normal premix composition
Test 2 ndashImpact of Admixtures (Mixes 2 and 3)
Recent saltstone batches have required both a set retarder (Daratard 17) and an antifoam agent (Q2) for processing of the saltstone Therefore the baseline mix will be prepared with and without nominal levels of these two admixtures to determine whether these admixtures appreciably affect the hydraulic and physical properties of saltstone at these nominal concentrations
Test 3ndashImpact of Organics (Mixes 2 and 4)
The solvent extraction process is expected to result in some carryover of organics [3]
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Consequently a test will be performed on the impact of Caustic Side Solvent Extraction (CSSX) organics at 100 microliters per 1600 gram batch The CSSX solvent consists of 075 M 1-(2233-tetrafluoropropoxy)-3-(4-sec-butylphenoxy)-2-propanol (Cs-7SB) and 0003 M tri-n-octylamine (TOA) in an Isoparreg L diluent Test 4ndashImpact of Combination of Admixtures and Organics (Mixes 2 5 10 and 11)
This test will determine the impact of a combination of admixtures (Test 2) and organics (Test 3) together in the mix vs the baseline case without admixtures and organics
Test 5ndash Impact of wcm Ratio (Mixes 2 6 and 7)
It is well known that decreasing the wcm ratio in a mix will improve permeability in normal portland cement water mixes This test will measure the variation in permeability for the case of the MCU salt solution at three different wcm ratios The initial selection of wcm ratios is 055 060 and 065 However if the mix at an as-batched 065 wcm ratio has significant bleed water and the resulting actual wcm ratio is close to 060 then the three ratios will be adjusted to provide a more evenly spaced set of values However the baseline mix at 060 will be included as one of the three mixes
Test 6 ndash Impact of Aluminate Concentration (Mixes 8 9 and 10)
The DWPF has modified its process flowsheet to include a caustic washing of HLW sludge to remove some of the aluminum from the HLW prior to vitrification The resulting aluminate stream will then be blended with tank 50 material and fed to the SPF This increased aluminate concentration in the salt solution has significant impact on heat of hydration and set times and consequently it is likely that it will also impact permeability Therefore a set of three samples will be made at wcm ratios of 055 060 and 065 (as in Test 3) with a higher level of aluminate (028 M) for testing
Test 7 ndash Impact of Increased Curing Temperature (Mix 11)
In an ongoing task there is evidence that Youngrsquos modulus (a performance indicator) [4] is reduced by increasing the curing temperature of the mix Since the vault temperature increases during curing as a result of the exothermic hydration reactions one of the baseline mixes with a combination of admixtures and organics will be cured at 60
o
C rather than the normal 22
o
C to determine the impact of curing temperature on the permeability
SRNL-STI-2009-00636 Revision 0
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SCHEDULE
The schedule for the task of batching and testing of the samples is provided in Table 2 This schedule is based on the fact that the cementitious materials will be available for the testing as needed
Table 2 Additional Saltstone Hydraulic and Physical Property Tests
Item Schedule Start Work 12108 Test Plan Complete 1509 Preparation of 1st set of Samples Complete 11909 90-Day Cure Period for 1st set of Samples Complete 42009
SRNL-STI-2009-00636 Revision 0
87
SRNL-STI-2009-00636 Revision 0
SRNL-STI-2009-00636 Revision 0
DISTRIBUTION Savannah River Site
A B Barnes 999-W Rm 336 H H Burns 999-W Rm 381 B T Butcher 773-43A Rm 212 A D Cozzi 999-W Rm 337 D A Crowley 773-43A Rm 216 M E Denham 773-42A Rm 218 J C Griffin 773-A Rm A-231 J R Harbour 999-W Rm 348 C A Langton 773-43A Rm 219 M H Layton 705-1C Rm 14 D I Kaplan (3 copies) 773-43A Rm 215 S L Marra 773A Rm A-230 A M Murray 773-A Rm 229 K A Roberts 773-43A Rm 225 T C Robinson 705-1C Rm 13 L B Romanowski 705-1C Rm 19 K H Rosenberger 705-1C Rm 16 F M Smith 705-1C Rm 24 RPA File (2 copies) 773-43A Rm 213
Clemson University Environmental Engineering and Earth Sciences 372 Computer Court LG Rich Environmental Laboratory Anderson SC 29625
Figure 31 Screen capture of a typical 242Pu calibration curve using Thermo PlasmaLab software to control the data collection and analysis R2=0999872 Intercept Conc (Detection Limit) = 0000044 ppb 16
Figure 32 Screen capture of a typical 237Np calibration curve using Thermo PlasmaLab software to control the data collection and analysis R2=0999981 Intercept Conc (Detection Limit) = 0000026 ppb 17
Figure 33 Screen capture of a typical 99Tc calibration curve using Thermo PlasmaLab software to control the data collection and analysis R2=0999984 Intercept Conc (Detection Limit) = 0000013 ppb 18
Figure 34 Screen capture of a typical 127I calibration curve using Thermo PlasmaLab software to control the data collection and analysis R2=0999991 Intercept Conc (Detection Limit) = 024 ppb 19
Figure 41 Plutonium Kd Values under Oxidizing Conditions Plutonium Kd values for various saltstone formulations measured after one-day equilibration (1d) and four-day equilibration (4d under oxidizing conditions Total plutonium concentrations in each system were 1 ppb 5 ppb and 10 ppb Sample prepared in triplicate and error bars represent standard deviation of samples except as follows value for dataset TR547-4d 10 ppb is reported based on duplicate samples 25
Figure 42 Plutonium solubility for various saltstone formulations measured after one-day equilibration (1d) and four-day equilibration (4d) under oxidizing conditions Total plutonium concentrations in each system were 1 ppb 5 ppb and 10 ppb as noted Samples prepared in triplicate and an average of all samples (9) was used to determine average solubility The error bars represent standard deviation of samples 25
Figure 43 Neptunium Kd values under oxidizing conditions Neptunium Kd values for various saltstone formulations measured after one-day equilibration (1d) and four-day equilibration (4d) under oxidizing conditions Total plutonium concentrations in each system were 1 ppb 5 ppb and 10 ppb as noted Samples prepared in triplicate and error bars represent standard deviation of samples except as follows value for datasets TR545-1d 1ppb TR545-4d 1 ppb TR547 4d 1 ppb TR545-4d 10 ppb TR547-1d 1ppb TR547-4d 10 ppb are reported based on a single sample and for dataset TR545-1d 5ppb is reported based on duplicate samples Kd values limited to gt106 were at instrumental background 26
Figure 44 Average solubility of Np under oxidizing conditions Neptunium solubility for various saltstone formulations measured after one-day equilibration (1d) and four-day equilibration (4d) under oxidizing conditions Total Np concentrations in each system were 1 ppb 5 ppb and 10 ppb Samples prepared in triplicate and an average of all samples (9) was used to determine average solubility except as follows TR545-1d is based on 6 samples TR545- 4d on 5 samples TR547-1d on 7 samples and TR547- 4d on 5 samples The error bars represent standard deviation 27
Figure 45 Technetium Kd values under oxidizing conditions Tc Kd values for various saltstone formulations measured after one-day equilibration (1d) and four-day equilibration (4d) under oxidizing conditions Total Tc concentrations in each system were 1 ppb 5 ppb and 10 ppb as noted above Samples were prepared in triplicate and the error bars represent standard deviation
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xii
of samples except as follows data sets for Vault 2-1d 1ppb were duplicates and TR547- 4d 10 ppb is based on a single dataset 27
Figure 46 Iodine Kd Values under Oxidizing Conditions Iodine Kd values for various cementitious formulations measured after one-day equilibration (1d) and four-day equilibration (4d) under oxidizing conditions Total iodine concentrations in the systems were 100ppb 500 ppb and 1000 ppb as noted above Samples were prepared in triplicate and the error bars represent standard deviation of samples except as follows duplicates were used for dataset TR545- 1d 100ppb 28
Figure 47 Plutonium Neptunium and Technetium Aqueous Fractions Fraction of Pu Np and Tc remaining in the aqueous phase for the No Solids controls after a one-day equilibration (1d) and four-day equilibration (4d) under oxidizing conditions The total concentration for each radionuclide 10 ppb as noted above Samples were prepared in triplicate and the error bars represent the standard deviation of the samples 29
Figure 48 Iodine Aqueous Fraction Iodine aqueous fraction for the no-solids controls after a one-day equilibration (1d) and four-day equilibration (4d) under oxidizing conditions The total concentration of iodine was 1000 ppb as noted above Samples were prepared in triplicate and the error bars represent the standard deviation of the samples 29
Figure 49 Percent Pu and Np sorbed to vial walls of the no solids controls after the aqueous phases were discarded and the vials were washed Both the 10 ppb (blueleft) and 1 ppb (redright)) datasets were prepared in triplicate and the error bars show the standard deviation 31
Figure 410 Percent Pu sorbed to vial walls after the solids and aqueous phases were removed and the vials were washed The graph illustrates one sample from each of the 1 ppb (redleft) 5 ppb (greenmiddle) and 10 ppb (blueright) systems Therefore no error bars are present 31
Figure 411 Percent Np sorbed to vial walls after the solids and aqueous phases were removed and the vials were washed The graph illustrates one sample from each of the 1 ppb (redleft) 5 ppb (greenmiddle) and 10 ppb (blueright) systems Therefore no error bars are present 32
Figure 412 Pu Kd Values under Reducing Conditions Plutonium Kd values for various cementitious formulations measured after one-day equilibration (1d) and four-day equilibration (4d) under reducing conditions Total plutonium concentrations in each system were 1ppb 5 ppb and 10 ppb Samples prepared in triplicate and error bars represent standard deviation 33
Figure 413 Average Solubility of Plutonium under Reducing Conditions Plutonium solubility for various cementitious formulations measured after one-day equilibration (1d) and four-day equilibration (4d) under reducing conditions Total plutonium concentrations in each system were 1ppb 5 ppb and 10 ppb as noted Samples prepared in triplicate and an average of all samples (9) was used to determine average solubility The error bars represent standard deviation of samples 33
Figure 414 Np Kd Values under Reducing Conditions Neptunium Kd values for various cementitious formulations measured after one-day equilibration (1d) and four-day equilibration (4d) under reducing conditions Total Np concentrations in each system were 1 ppb 5 ppb and 10 ppb Samples were prepared in triplicate and the error bars represent standard deviation Kd values limited to gt106 were at instrumental background 34
Figure 415 Average Solubility of Neptunium under Reducing Conditions Neptunium solubility for various cementitious formulations measured after one day equilibration (1d) and four day
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xiii
equilibration (4d) under reducing conditions Total plutonium concentrations in each system were 1ppb 5 ppb and 10 ppb Samples prepared in triplicate and an average of all samples (9) was used to determine average solubility The error bars represent standard deviation 35
Figure 416 Tc Kd Values under Reducing Conditions Tc Kd values for various cementitious formulations measured after one-day equilibration (1d) and four-day equilibration (4d) under reducing conditions Total Tc concentrations in each system were 1 ppb 5 ppb and 10 ppb Sample prepared in triplicate and error bars represent standard deviation except as follows TR547-1d 1 ppb is based on a single dataset and datasets Vault 2-1d 5 ppb Vault 2- 4d 1 ppb Aged Cement-1d 5 ppb and Aged Cement-4d 1 ppb are duplicates 36
Figure 417 Data from Figure 416 replotted on a reduced linear scale for easier viewing Each sample was prepared in triplicate except as follows TR547-1d 1 ppb is based on a single dataset Vault 2-1d 5 ppb Vault 2- 4d 1 ppb Aged Cement-1d 5 ppb and Aged Cement-4d 1 ppb are duplicate datasets 36
Figure 418 Iodine Kd Values under Reducing Conditions I Kd Values for various cementitious formulations measured after one day equilibration (1d) and four day equilibration (4d) under reducing conditions Total iodine concentrations in each system were 100 ppb 500 ppb and 1000 ppb as noted Sample prepared in triplicate and error bars represent standard deviation of samples except as follows Vault 2-4 d 100 ppb is a single dataset while the datasets for Vault 2-1 d 100 ppb 4 d 1000 ppb TR545-4 d 1000 ppb 100 ppb TR547-4 d 1000 ppb 500 ppb 100 ppb and Aged Cement- 4 d 1000 ppb and 100 ppb are all based on duplicates 38
Figure 419 Plutonium Neptunium and Technetium No-Solids Aqueous Fractions under Reducing Conditions Pu Np and Tc aqueous fractions of No Solids controls after a one-day equilibration (1d) and four-day equilibration (4 d) under reducing conditions Total concentration for each radionuclide was 1 ppb and 10 ppb Samples were prepared in triplicate and the error bars represent the standard deviation 39
Figure 420 Percent of Pu Np and Tc sorbed to the vial walls of the No Solids control samples under reducing conditions Each the 1 ppb and 10 ppb samples were prepared in triplicate and the error bars represent the standard deviations of triplicate samples 39
Figure 421 Iodine No-Solids Aqueous Fractions under Reducing Conditions I aqueous fractions of No-Solids controls after a one-day equilibration (1d) and four-day equilibration (4d) under reducing conditions The total concentration for each system was 100 ppb and 1000 ppb Samples were prepared in triplicate and the error bars represent the standard deviation 40
Figure 51 Comparison of Tc I Np and Pu sorption to Vault 2 solid under oxidizing and reducing conditions 42
Figure 52 Comparison of Tc I Np and Pu sorption to TR 545 solid under oxidizing and reducing conditions 43
Figure 53 Comparison of Tc I Np and Pu sorption to TR547 solid under oxidizing and reducing conditions 44
Figure 54 Comparison of Tc I Np and Pu sorption to Aged Cement under oxidizing and reducing conditions 45
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xiv
LIST OF ABBREVIATIONS
DDI water Distilled deionized water ICP-MS Inductively coupled plasma ndash mass spectrometer
Kd Distribution coefficient LSC liquid scintillation counting NOM Natural organic matter PA Performance Assessment ppb parts per billion ppq parts per quadrillion QAQC Quality AssuranceQuality Control SA Special Analyses SRNL Savannah River National Laboratory SRS Savannah River Site
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10 Introduction Performance Assessments (PA) are risk calculations designed to determine (1) the maximum
amount of radioactivity that can be safely buried in a subsurface facility and (2) the potential human risk associated with disposing of radioactive waste in a subsurface facility Special Analyses (SAs) are similar to PAs except that they are designed to address specific issues related to PAs such as a new discovery since the PA was issued Commonly parameters describing the extent that a radionuclide interacts with solids at the source vadose zone and aquifer influence the extent of calculated human risk The two parameters that the SRS use to represent radionuclidesolid interactions are Kd and apparent solubility values together these parameters are referred to as sorption values Sorption values vary with radionuclides groundwater chemistry and the type of solid phase (and for cementitious materials by the age of the material during the calculation) In this work Kd and apparent solubility values are reported for 99Tc 127I 237Np and 242Pu sorption to various cementitious formulations
20 Objectives
The objectives of this work were to 1 Determine the influence of cementitious formulation on technetium (Tc) iodine (I) neptunium
(Np) and plutonium (Pu) sorption under oxidizing conditions The specific formulations that were evaluated included 1) an aged cement recovered from a 30-year old outdoor concrete pad on the SRS 2) Vault 2 concrete 3) TR545 saltstone and 4) TR547 saltstone (additional details are presented in Section 30 Materials and Methods)
2 Measure Tc I Np and Pu sorption to the cementitious formulations under reducing conditions
30 Materials and Methods
31 Preparation of ICP-MS Standards Stock Solutions and Working Solutions
311 242Pu
A National Institute of Standards and Technology Standard Reference Material (NIST SRM 434H) was used to prepare a stock 242Pu solution by dilution in 2 Aristar Optima HNO3 All volume additions were monitored gravimetrically This working solution was then used to make a set of 001 005 1 2 5 10 parts per billion (ppb) standards by dilution using 2 HNO3 Again all volume additions were monitored gravimetrically These standards were used to calibrate the Thermo Scientific X Series 2 inductively coupled plasma ndash mass spectrometer (ICP-MS) for quantification of 242Pu A representative calibration curve for 242Pu is shown in Figure 31 The instrument performance was monitored using 209Bi 232Th and 238U as internal standards The recovery of each sample during analysis was corrected based on the internal standard recovery The internal standard recoveries remained within standard quality assurancequality control QAQC protocols for the instrument (between 80 and 120)
A 242Pu stock solution was prepared by dissolving 1mg of Pu(NO3)4 obtained as a Certified Reference Material from New Brunswick Laboratory (CRM 130) This CRM is gt999 242Pu by atom percent The CRM was dissolved in 20mL of 8M HNO3 (Aristar Optima Grade) Because no chemicals or heat have been introduced to manipulate the Pu oxidation state it can be assumed that Pu(IV) is the predominant oxidation state in this stock solution A working solution to be used in spiking 242Pu experiments was prepared by diluting 25 mL of the CRM stock solution with 100 mL 10 M Aristar Optima HNO3 The concentration of 242Pu in this stock solution was determined using ICP-MS calibrated using the NIST SRM standards The concentration of Pu in this stock solution was 1065 ppb The total Pu
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concentration was also determined using liquid scintillation counting using the isotopic ratios reported for CRM 130 These compared favorably with the ICP-MS results but are reported here as a rigorous standardization because the isotopic ratios of CRM 130 have not yet been certified
Figure 31 Screen capture of a typical 242Pu calibration curve using Thermo PlasmaLab software to control the data collection and analysis R2=0999872 Intercept Conc (Detection Limit) = 0000044 ppb
312 237Np
A National Institute of Standards and Technology Standard Reference Material (NIST SRM 4341) was used to prepare a stock 237Np solution by dilution in 2 Aristar Optima HNO3 All volume additions were monitored gravimetrically This working solution was then used to make a set of 001 005 1 2 5 10 ppb standards by dilution using 2 HNO3 Again all volume additions were monitored gravimetrically These standards were used to calibrate the Thermo Scientific X Series 2 ICP-MS for quantification of 237Np A representative calibration curve for 237Np is shown in Figure 32 The instrument performance was monitored using 209Bi 232Th and 238U as internal standards The recovery of each sample during analysis was corrected based on the internal standard recovery The internal standard recoveries remained within standard QAQC protocols for the instrument (between 80 and 120)
A compiled 237Np stock solution from the Environmental Engineering and Earth Science (EEampES) inventory (primarily purchased from Isotope Products Valencia CA) was evaporated to dryness then the residue was brought up in approximately 5mL 80 M HNO3 Then 10 M hydroxylamine hydrochloride (NH2OHHCl EMD Chemicals ACS grade) and water were added to achieve a 3M HNO303M NH2OHHCl solution This solution was purified by extraction chromatography using Eichrom TEVA resin packed in a Bio-Rad poly-prep column The 3M HNO303 M NH2OHHCl neptunium solution was loaded on a 2 mL column and washed with 3 column volumes of 3 M HNO3 The Np(IV) was eluted with 002 M HCl + 02 M HF The effluent was evaporated to dryness then redissolved in 10 M HNO3 Additional 10 M HNO3 was added to maintain a approximately 10 mL then the solution was evaporated to incipient dryness and redissolved in a 50 mL of 10 M HNO3 An aliquot of the stock solution was evaporated to dryness on a stainless steel planchet and counted on the EGampG Ortec Alpha Spectrometer (Octete PC Detectors) No other alpha energies besides 237Np were observed The approximate concentration was determined using liquid scintillation counting and little 233Pa was observed The fuming in HNO3 as performed at the end of the purification procedure will drive Np to the soluble pentavalent state This is the stable oxidation state of Np under the experimental conditions Therefore experiments performed here can be assumed to be initially Np(V) The exact Np
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concentration in this solution was determined using ICP-MS calibrated with a NIST standard as discussed in section 312 below
A 237Np working solution (Working Solution 1) was created by pipetting an aliquot of the 237Np stock solution into a 100 mL Nalgene Teflon bottle and diluting with 2 BDH Aristar Ultra HNO3 to give a working solution concentration of 820 ppb All volumes were monitored gravimetrically Analysis on the ICP-MS calibrated against NIST Standards as described below gave a concentration of 820 ppb in Working Solution 1
Figure 32 Screen capture of a typical 237Np calibration curve using Thermo PlasmaLab software to control the data collection and analysis R2=0999981 Intercept Conc (Detection Limit) = 0000026 ppb
313 99Tc
A 99Tc working solution was prepared by diluting a stock solution of 99Tc (from the EEampES inventory purchased from Isotope Products Valencia CA) in distilled-deionized water (DDI Resistivity gt18 MΩcm) The oxidation state of Tc was not measured However based on the aqueous concentration in the DDI water solution Tc(VII) is the expected oxidation state The reduced Tc(IV) oxidation state would not be soluble under these conditions The expected concentration of 950 ppb based on the dilution was verified using liquid scintillation counting The 99Tc working solution was used to make 001 005 1 2 5 and 10 ppb standards by dilution using 2 HNO3 These standards were used to calibrate the Thermo Scientific X Series 2 ICP-MS for quantification of 99Tc A screen shot of a representative calibration curve is shown in Figure 33 The instrument performance was monitored by interpolating between 89Y and 115In internal standards The recovery of each sample during analysis was corrected based on the internal standard recovery The internal standard recoveries remained within standard QAQC protocols for the instrument (between 80 and 120)
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Figure 33 Screen capture of a typical 99Tc calibration curve using Thermo PlasmaLab software to control the data collection and analysis R2=0999984 Intercept Conc (Detection Limit) = 0000013 ppb
314 127I
A 100 microgmL iodate (IO3-) stock solution from High Purity Standards (Charleston SC) was used
to make 1 5 10 50 and 100 ppb standards by dilution using the ldquotraprdquo solution (discussed in Section 32 below) These standards were used to calibrate the Thermo Scientific X Series 2 ICP-MS for quantification of 127I A screen shot of a representative calibration curve is shown in Figure 34 The use of a reducing basic trap solution for iodine analysis limits the number of available internal standards that can be used to monitor ICP-MS instrument performance during iodine analysis Experiments are underway to identify acceptable internal standards However the data presented in this work did not use any internal standards prior to rigorous testing and analysis of representative standards As with the analyses for all isotopes (Tc I Np and Pu) spiked QAQC samples were frequently analyzed throughout the analysis as a check on instrument performance While these values cannot be used to correct individual samples in the same manner that the internal standards can they can be used to ensure accurate measurements of each isotope In almost all cases QAQC standards were within 10 of the expected value Because the average internal standard recovery ranges between 80 and 120 for the ICP-MS the iodine QAQC standard appears to be acceptable However a significant amount of ongoing work is testing various internal standards to improve the accuracy of iodine analysis using ICP-MS In one experiment (discussed in detail below) the QAQC standards deviated by an average value of 195 This will be specifically discussed below
Because experiments were performed with 127I concentrations up to 1000 ppb the 100 microgmL (ppm) stock iodate solution from High Purity Standards was used as the working solution
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Figure 34 Screen capture of a typical 127I calibration curve using Thermo PlasmaLab software to control the data collection and analysis R2=0999991 Intercept Conc (Detection Limit) = 024 ppb
315 Cementitious Materials Selected for Experiments There were four cementitious materials selected for this sorption study The first referred to as Aged Cement is a 30 year old sample that does not contain any reducing slag The aggregate from the Vault 2 cement had its aggregate removed prior to conducted tests in an effort to make subsamples more uniform This was necessary because some of the aggregate were larger than the 05 g subsamples used in individual sorption tests The Vault 2 cementitious material contained 17 dry wt- reducing slag on a dry weight basis before the water was added to the mix (Table 31) The TR547 and TR545 saltstone formulations contain 45 dry wt- and 90 dry wt- reducing slag respectively
Table 31 Characteristics of saltstone formulations used in this work Kaplan et al (2008)
Sample Percent Reducing Slag (dry wt-) (c)
Percent Portland Cement
(dry wt-) (c)
Percent Fly Ash
(dry wt-) (c)
Percent Aggregatesand ( dry wt-) (c)
Reducing Equivalents
(microeqg)
Aged Cement 0 10 45 45 855 plusmn 101(a)
Vault 2 Cement 17 10 45 0 178(b)
TR547 45 10 45 0 607(b) TR545 90 10 0 0 681(b) Blast furnace slag 100 0 0 0 819(b) (a) Kaplan et al (2008) (b) Roberts and Kaplan (2009) (c) All percentages of saltstone formulations are reported on a dry weight percentage basis that is the weight of the ingredients before water was added (d) Based on Table 8 in Dixon et al (2008 SRNL-STI-2008-00421) which shows the following quantity (lbscu yd) for saltstone Vault 2 Mix 1 concrete formulation 201 cement (1271 wt-) 268 slag (1695 wt-) 447 silica fume (283 wt-) 1563 fly ash (989 wt-) 911 fine sand (5762 wt-) The large aggregate was removed before the sorption tests were conducted The large aggregate accounted for 75 wt- of the original field sample not the sample used in these test before water was added to the mix TR547 is referred to as the Baseline by Dixon et al (2008) and is described in more detail in Appendix C (Mix 2) by Dixon et al (2008) (Control-BFSPC) and 1 (Baseline)
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TR545 saltstone contains 90 reducing slag and it is Mix 1 in Dixon et al (2008) and is described as
ldquoA control mix will be based on the baseline mix modified by exclusion of the Class F fly ash Consequently the cementitious materials premix will be a mixture of 90 blast furnace slag and 10 Portland cement The degree of reaction will be much greater than with the normal premix and therefore should result in a lower porosity and a lower permeability This bounding test at 060 wcm ratio is expected to yield a hydraulic conductivity at or below the detection limit for the Mactec permeameter measurement system Therefore this test should demonstrate the lowest level of detection of the Mactec system as well as show a resolvable difference between measurements of the control mix and the control mix with the normal premix compositionrdquo
32 ICP-MS Detection Limits
The PlasmaLab software platform determines a detection limit for each isotope based upon the intercept concentration A new calibration curve was generated for each experimental run and curves were very similar Using representative calibrations curves the detection limits for each isotope were as listed in Table 32 Note the higher detection limit for 127I is primarily due to the higher background count rate observed on the instrument This is believed to be due to the minimum purity levels of chemicals required for the iodine ldquotraprdquo solution as discussed in Section 33 below Therefore experiments were run with initial iodate concentrations higher than Tc Np and Pu to maintain analytical sensitivity
Table 32 Detection limits for each isotope based on representative calibration curves generated in PlasmaLab software associated with the ICP-MS
33 Experimental Methods
The experimental methods used in this work followed closely those previously described for experiments examining radionuclide sorption to saltstone (Kaplan et al 2007 Kaplan et al 2008) Brief descriptions of each method are provided below
Preparation of Calcite Solution Using a hotstirring plate 10 L of distilled-deionized (DDI)
water was heated to 3-100C above room temperature Then 001 g CaCO3 (EM Science ACS grade) was added to the solution and the resulting suspension was mixed for 24 hours at the elevated temperature The solution was then vacuum filtered through a 045-microm filter to ensure no solid CaCO3 remained in solution
Preparation of 2 HNO3 Analysis of Tc Np and Pu on the ICP-MS required dilution in 2
HNO3 This was prepared by adding 28 mL of Aristar Optima HNO3 from a clean graduated cylinder (designated to 2 HNO3) into a 1 L volumetric flask (designated to 2 HNO3) partially filled with DDI water and then further diluted to volume
Preparation of Trap Solution for Iodine Analysis Analysis of I required the use of a reducing
basic solution that was capable of reducing iodate to iodine and holding the iodine in solution This minimized the loss of I during sample analysis A 1 L trap solution was prepared by weighing out 00500 g NaHSO3 (Fisher Scientific ACS Grade) on a calibrated Sartorous LA 230S scale and adding it to a 1L volumetric flask Then 40 mL of 25 ww tetramethylammonium hydroxide (Alfa Aesar electronic grade) and 10 mL CFA-C solution (Spectrasol Inc) were added to the volumetric flask via a calibrated 1000-5000 microL Eppendorf Research pipette The solution was then diluted to volume with DDI water
34 Experimental Protocol for Sorption Experiments under Aerobic Conditions
Falcon BlueMax 15mL polypropylene vials were labeled and weighed to within 0001 g on a calibrated Sartorious LA 230S scale The scale was then zeroed and 025 +- 001 g of a given solid were added to each tube and the weight was recorded to within 0001g
For each of the four solids three sets of triplicate samples were prepared The three sets of samples were used to allow for experiments to be run with varying concentrations of each isotope Target initial concentrations for 99Tc 237Np and 242Pu samples were 1 ppb 5 ppb and 10 ppb Target initial concentrations for the 127I samples were 100 ppb 500 ppb and 1000 ppb A set of no solids controls at initial concentrations of 1 ppb and 10 ppb for 99Tc 237Np and 242Pu and initial concentrations of 100 ppb and 1000 ppb 127I were also prepared by adding the calcite solution to pre-weighed pre-labeled centrifuge tubes as discussed above
The solids were equilibrated with the calcite solution before spiking with the radionuclides This was done by adding 10 plusmn 01 mL of calcite solution to each tube and recording the mass The samples were then placed on a Thermo Scientific shaker overnight After 24 hours the solutions were allowed to settle for 1 hour The pH was then measured and the samples were then centrifuged for 15 minutes at 8000 rpm to further separate the solids The aqueous phase was then decanted and 10 plusmn 01 mL of calcite solution was added to each tube The weight of the tube (labeled tube + solid + calcite solution) was measured to within 0001g During this washing process the pH was monitored and held steady throughout the process The pH ranged from 11-12 depending on the particular saltstone used During the experiments the exact pH for all samples at all equilibration times was measured and is reported in Appendix A and B
The resulting suspensions were then spiked with 127I 237Np 242Pu and 99Tc It is important to note that all four isotopes were added to the same vial Use of the ICP-MS to determine the concentration of each isotope allows for a single solution to contain all analytes of concern This allowed for a greater variability in the sample set and increased replicates as opposed to running individual sorption tests for each isotope For the systems with initial 99Tc 237Np and 242Pu concentrations of 10 ppb and initial 127I concentration of 100 ppb a 100 microL aliquot of each radionuclide working solution was added to the first three tubes for each solid The addition was made with the tube resting on a tared analytical balance so that the exact mass of each radionuclide solution added was recorded and the solution was gently swirled before the next radionuclide was added The 5 ppb 237Np 242Pu and 99Tc and 500 ppb 127I samples were prepared in the same manner but adding 50 microL of the respective spike solutions The final three tubes with initial 237Np 242Pu and 99Tc concentrations of 1 ppb and 100 ppb 127I were prepared by using 10 microL of the spike solutions for all four solids as well as a set of solid-free controls (No-Solids Controls) For clarity this experimental matrix is shown in Table 33 below
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Table 33 Experimental Matrix of Sorption Experiments under Aerobic Conditions
After spiking the radionuclides a precalculated amount of 10M NaOH was added to each sample
to counter the acidic radionuclide spike solutions and the pH of one of the triplicate samples was measured to ensure the proper pH range was reached The samples were then placed on and end-over-end shaker to mix at approximately 8 rpm After 24 hours the samples were removed from the shaker and the pH of each sample was measured using an Orion Ross semi-micro glass electrode calibrated against pH 4 7 and 10 buffers (Thermo) The samples were then shaken and a transfer pipette was used to transfer 35 mL of a homogenous suspension to a 5mL syringe The solution was then passed through a 100 nm nylon syringe filter The first 025-050 mL of filtrate was discarded and the remaining filtrate was collected in a clean polyethylene vial Then 10 mL of the filtrate was removed and diluted in 90 mL 2 HNO3 The mass of each phase was determined and recorded gravimetrically Then 10 mL of the remaining filtrate was transferred to a clean Falcon BlueMax 15mL vial and diluted with 90 mL of trap solution for 127I analysis Again the volume of each phase was monitored gravimetrically After the 24 hour sampling event the samples were put back on the shaker to mix for three additional days On day four the above sampling procedure was repeated
The 237Np 242Pu and 99Tc samples can be run on the Thermo Scientific ICP-MS using the standard setup and procedure which included a standard flow glass nebulizer and bulb spray chamber However for the 127I analysis the ICP-MS must be reconfigured to accommodate the basic reducing trap solution This is to alleviate problems with iodine signal stability over time frequently observed in ICP-MS analysis The reconfigured instrument uses an Elemental Science Microflow PFA-100 Teflon nebulizer with a flow rate of 100microLmin along with a sapphire torch and a Teflon spray chamber This configuration must be run with a low pump speed to prevent back pressure on the system Two 30 minute stability tests were performed using a 50 ppb iodate solution Each experiment consisted of 40 separate measurements After each experiment was completed the uncorrected mass counts were examined and found to stay steady over the sampling period The relative standard deviation ( RSD) over all samples for each experiment was 1866 and 1460 respectively This shows that there was no significant ldquomemoryrdquo or loss of the iodine signal over time and that the reconfigured instrument has a stable iodine signal over time However as will be discussed below some difficulty has been encountered in finding an adequate internal standard for iodine analysis
35 Experimental Protocol for Sorption Experiments under Anerobic Conditions In order to examine the effects of reducing conditions of sorption of each isotope to the various cementitious samples a series of sorption experiments were performed in an anaerobic glovebox under a 2 H2(g) 98 N2(g) atmosphere Based on the measured pH and EH of these systems as discussed below these systems were at the point of reducing water Therefore they are expected to represent a lower end of the possible range for reducing conditions expected in the porewater available within cementitious materials
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Preparation of Calcite for Reducing Conditions Approximately 35 L of DDI water was boiled for 45 minutes Argon was slowly bubbled through the water as it cooled Once it cooled to below 500C approximately 3 g of calcite was added This solution mixed overnight under a continuous Ar flow After 12 hours the solution was moved into an oxygen free glove bag for filtration as described in 3231 After filtration the calcite solution was moved into the glove box
Preparation of Working Solutions under Reducing Conditions The calcite and solid solutions
were prepared in the glove box using the previously mentioned procedure used under aerobic conditions The radionuclide working solutions were transferred to the glovebox and stirred open to the reducing atmosphere for at least three days The concentration of each isotope in the working solutions was measured to determine any change in the concentration due to evaporation while the solutions were equilibrating
The preparation and spiking of samples for sorption experiments was performed exactly as described for the oxidizing conditions except all sample handling was performed in the glovebox After the 1 day and 4 day equilibration the samples were filtered within the glovebox then transferred outside for dilution and ICP-MS analysis similar to the description provided about for the oxidizing conditions For these experiments only 4 mL of either 2 HNO3 or trap solution were used to dilute the filtrate instead of the 90 mL used above for experiments performed under oxidizing conditions
36 Examination of Sorption to Vial Walls for Solids and No Solids Controls
As will be discussed below the solid-free controls samples indicated significant loss of Np and Pu Once the one and four days samples were collected and run on the ICP-MS it was necessary to determine the degree each radionuclide was sorbing to the vial walls The remaining suspensions and controls were emptied into a waste container Then 5 mL of the calcite solution was added to each vial using a calibrated pipette The vials were sonicated for approximately one minute and then emptied into the waste container Another 5 mL of calcite solution was added for the second wash and then discarded into the waste container This procedure was expected to remove any soluble Pu from the system or Pu associated with colloidal particles After each vial was washed 10 mL of 2 HNO3 was added using a calibrated pipette The acid solution is expected to remove any Tc Np or Pu associated with the vial walls This procedure has been shown to complete mass balances of Pu in similar sorption experiments using Pu (Powell et al 2002) This process was performed for both the solid suspension and the no solids controls The samples were then run on the ICP-MS to determine the concentration of 99Tc 237Np and 242Pu sorbed to the vial walls
37 Data Analysis The solubilities of 242Pu and 237Np were calculated by using the formula
nuclide
nuclide
nuclideMSICP
sol Mg
gCC
)(10 6
microminus
minus
= (Equation 31)
Csol = observed nuclide solubility (molnuclidekgsolution) CICP-MS = aqueous concentration of nuclide from ICP-MS measurement (ppb micrognuclidekgsolution) Mnuclide = molecular mass of nuclide (gnuclidemolnuclide)
In order to determine the Kd values one first needs to determine the concentration on the solid by using
SRNL-STI-2009-00636 Revision 0
24
solid
calcitespikeaqspikecalcite
spikestock
solid m
mmCmmmC
C)(
)()(
+⎥⎥⎦
⎤
⎢⎢⎣
⎡minus
+
lowast
= (Equation 32)
Csolid = calculated solid phase concentration of the nuclide (ppb) Cstock = concentration of the nuclide stock solution (ppb) mspike = mass of nuclide spiked into the saltstone suspension (g) mcalcite = total mass of calcite solution used in the saltstone suspension (g) Caq = aqueous concentration of nuclide from ICP-MS measurement (ppb) msolid = mass of the saltstone used in the suspension (g)
The Kd can be calculated using the equation
aq
solidd C
CK = (Equation 33)
Kd = solid-water partitioning coefficient (gsolutiongsolid assuming density of 10 gmL traditional
unit of mLsolutiongsolid can be obtained) This Kd Equation (33) is numerically equivalent to the traditional Kd equation proposed in ASTM D-4646 which has been used in previous saltstone experiments (Kaplan et al 2007 Kaplan et al 2008)
40 Results and Discussion
41 Radionuclide Sorption to Cementitious Formulations under Oxidizing Conditions
Figure 41 shows Pu Kd values ranging from 104 to gt105 mLg Generally for each solid the Kd increases with increasing initial Pu concentrations typical behavior of systems where the aqueous concentrations of the radionuclides are solubility controlled This is not expected because the Kd expression indicates that the Kd value should remain constant with increasing total Pu concentrations It was noted that aqueous phase concentration of Pu remained relatively constant in all samples (see discussion below regarding Pu solubility) Therefore the sorption capacity of each solid phase for Pu has not been overcome For each of these solid phases it appears the solutions had reached equilibrium before the first samples were taken at 24 hours In each case the Kd values for the one day and four day are similar A trend between the solid phases is not discernible The aged cement with no reducing slag was expected to have the lowest Kd values but in actuality it has the highest Kd Also there is no correlation with the concentration of reducing slag The Vault 2 samples with 17 dry wt- reducing slag has a Kd similar to that of the TR547 (45 dry wt- slag) while the saltstone with the most slag TR545 (90 dry wt- slag) has the lowest Kd value Others have observed that Pu Kd values of cementitious materials are similar in the absence and presence of slag (Allard et al 1984 Hoaglund et al 1985)
It was observed that similar aqueous concentrations of Pu were observed regardless of the solid phase present Figure 42 shows the average aqueous phase concentrations measured after one day and four days for all solids As stated above triplicate samples were prepared for each solid phase and each initial concentration Therefore each of the reported solubility values in Figure 42 is an average of nine measurements Using the highest reported value with the expected maximum error (0018 ppb for solid TR545) the maximum expected aqueous concentration of Pu in the pore water associated with the
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saltstone formulations will be approximately 7 x 10-11 molL as calculated using Equation 31 This is on the same order as the solubility of Pu hydrous oxide solid phases (Neck and Kim 2001)
Figure 41 Plutonium Kd Values under Oxidizing Conditions Plutonium Kd values for various saltstone formulations measured after one-day equilibration (1d) and four-day equilibration (4d under oxidizing conditions Total plutonium concentrations in each system were 1 ppb 5 ppb and 10 ppb Sample prepared in triplicate and error bars represent standard deviation of samples except as follows value for dataset TR547-4d 10 ppb is reported based on duplicate samples
Figure 42 Plutonium solubility for various saltstone formulations measured after one-day equilibration (1d) and four-day equilibration (4d) under oxidizing conditions Total plutonium concentrations in each system were 1 ppb 5 ppb and 10 ppb as noted Samples prepared in triplicate and an average of all samples (9) was used to determine average solubility The error bars represent standard deviation of samples
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Overall the Kd values for Np range from 105 to gt106 with only a few outliers The most significant outlier is the 1 ppb solution in the TR545 sample after the four-day equilibration It drops two orders of magnitude while the 5 and 10 ppb solutions remain constant However this result is most likely an analytical artifact from working at the detection limits of the ICP-MS In the one-day equilibration samples only one of the triplicates S-2-E had detectable Np while in the four-day equilibration samples only S-2-F had detectable amounts present The graph also shows that with the exception of the 5 ppb sample in the aged cement Np sorption to TR545 (90 dry-wt- slag) and TR547 (45 dry wt- slag) have Kd values approximately one order of magnitude over the aged cement (no slag) and Vault 2 (17 dry wt- slag) samples
It was observed that similar aqueous concentrations of Np were observed regardless of the solid phase present Figure 44 shows the average aqueous phase concentrations measured after one day and four-day equilibrations for all solids As stated above triplicate samples were prepared for each solid phase and each initial concentration Therefore each of the reported solubility values in Figure 44 is an average of nine measurements of Np concentration unless stated otherwise Using the highest reported value with the expected maximum error (00026 ppb for solid TR545) the maximum expected aqueous concentration of Pu in the pore water associated with the saltstone formulations will be approximately 2 x 10-11 molL
Figure 43 Neptunium Kd values under oxidizing conditions Neptunium Kd values for various saltstone formulations measured after one-day equilibration (1d) and four-day equilibration (4d) under oxidizing conditions Total plutonium concentrations in each system were 1 ppb 5 ppb and 10 ppb as noted Samples prepared in triplicate and error bars represent standard deviation of samples except as follows value for datasets TR545-1d 1ppb TR545-4d 1 ppb TR547 4d 1 ppb TR545-4d 10 ppb TR547-1d 1ppb TR547-4d 10 ppb are reported based on a single sample and for dataset TR545-1d 5ppb is reported based on duplicate samples Kd values limited to gt106 were at instrumental background
The Kd values for Tc are significantly lower than that of Pu or Np As a whole the values are
comparable The values for the one-day and four-day equilibrations solutions in the Vault 2 (17 dry wt- slag) and TR545 (90 dry wt- slag) remained constant within reasonable error with just a slight increase from the one-day to four-day equilibration However the Aged Cement (no slag) and TR547 (45 dry wt- slag) showed a noticeable decrease from day one to day four (Figure 45)
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Figure 44 Average solubility of Np under oxidizing conditions Neptunium solubility for various saltstone formulations measured after one-day equilibration (1d) and four-day equilibration (4d) under oxidizing conditions Total Np concentrations in each system were 1 ppb 5 ppb and 10 ppb Samples prepared in triplicate and an average of all samples (9) was used to determine average solubility except as follows TR545-1d is based on 6 samples TR545- 4d on 5 samples TR547-1d on 7 samples and TR547- 4d on 5 samples The error bars represent standard deviation
Figure 45 Technetium Kd values under oxidizing conditions Tc Kd values for various saltstone formulations measured after one-day equilibration (1d) and four-day equilibration (4d) under oxidizing conditions Total Tc concentrations in each system were 1 ppb 5 ppb and 10 ppb as noted above Samples were prepared in triplicate and the error bars represent standard deviation of samples except as follows data sets for Vault 2-1d 1ppb were duplicates and TR547- 4d 10 ppb is based on a single dataset
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Similar to the Tc Kd values the 127I Kd values are much lower than those of Pu and Np The amount of reducing slag present in each of the solids does not appear to have a drastic effect on the 127I Kd values In fact the initial (one day) Aged Cement (0 slag) samples had a Kd almost two orders of magnitude above those with reducing slag The cause of this behavior is not known but it has been shown that iodate IO3
- the oxidized form of iodine sorbs more strongly than iodide I- to charged surfaces (Schwehr et al 2009 Yoshida et al 1992 Fukui et al 1996) It is possible that the slag is reducing the iodine to the I- form converting it to a species that is less likely to sorb to saltstone Additional work would be required to confirm the oxidation state of iodine when associated with saltstone
Figure 46 Iodine Kd Values under Oxidizing Conditions Iodine Kd values for various cementitious formulations measured after one-day equilibration (1d) and four-day equilibration (4d) under oxidizing conditions Total iodine concentrations in the systems were 100ppb 500 ppb and 1000 ppb as noted above Samples were prepared in triplicate and the error bars represent standard deviation of samples except as follows duplicates were used for dataset TR545- 1d 100ppb
42 Radionuclide Sorption to Vial Walls Under Oxidizing Conditions
Figure 47 shows the aqueous fractions found in the no-solids controls It provides a measure of the solubility of each radionuclide as well as examines the fraction of each radionuclide sorbed to the vial walls After one day only 25 of the Pu remained in solution and the concentration decreased even more after four days The loss of Pu from the aqueous phase may be due to sorption of Pu to the vial walls or precipitation of a Pu hydrous oxide solid (discussed with respect to Figure 49 below) Additional experiments would be required to examine the solubility of the Pu in high pH calcite saturated solutions
After one day about 80 of the Np remained in solution However the aqueous concentration in the initially 1-ppb solution was significantly reduced after four days Approximately 60 of the Np remained soluble in the initially 10-ppb solution Once again this drop could be due to sorption to the vial wall The Tc present after one day ranged from about 88 to about 95 and was virtually 100 after four days These values are consistent with internal standards used to monitor Tc detection performance on the ICP-MS Greater than 50 of the I remained in solution after the one-day and four-day equilibrations As shown in Figure 48 the standard deviation between the triplicate I control samples was
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quite large Additional control samples are required to understand the mechanism by which I is being lost from the aqueous phase in these samples
Figure 47 Plutonium Neptunium and Technetium Aqueous Fractions Fraction of Pu Np and Tc remaining in the aqueous phase for the No Solids controls after a one-day equilibration (1d) and four-day equilibration (4d) under oxidizing conditions The total concentration for each radionuclide 10 ppb as noted above Samples were prepared in triplicate and the error bars represent the standard deviation of the samples
Figure 48 Iodine Aqueous Fraction Iodine aqueous fraction for the no-solids controls after a one-day equilibration (1d) and four-day equilibration (4d) under oxidizing conditions The total concentration of iodine was 1000 ppb as noted above Samples were prepared in triplicate and the error bars represent the standard deviation of the samples
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As discussed above the loss of Np and Pu from the no-solids control (Figure 47) could be due to
precipitation of Np and Pu hydrous oxides or sorption to the vial walls To quantify the differences between these possible sinks the vials were washed as described in Section 36 The data in Figure 49 indicate that significant sorption of Np and Pu to the vial walls may occur When combining the mass of Np represented in Figure 47 and Figure 49 there is almost 100 mass recovery of the Np sorbed to the vial wall and the aqueous fraction measured Therefore no precipitation of Np is expected However because 100 recovery was not achieved for Pu a Pu hydrous oxide phase could be precipitating which was washed out of the vial during the cleaning procedure The data in Figure 47 represent the no-solids control samples where there was no solid phase present for Np or Pu to sorb to besides the vial walls However when a cementitious solid phase is present in the sample there will be competition between the vial walls and the cement for sorption of Np and Pu Based on the affinity of metals for metal oxide surfaces as opposed to the polypropylene surface and the much higher surface site density expected for the cementitious samples it is assumed that the cementitious samples will out-compete the vial walls for sorption sites This thesis was tested by taking one of the triplicate samples from each sorption experiment with a solid phase present removing the solid phase from the tubes and leaching any sorbed Np and Pu from the tubes with acid as described in Section 36 Figure 410 and Figure 411 show that although some of the Pu and Np sorbed to the vial walls of the samples this amount accounted for less than 2 in all samples Therefore sorption of Np and Pu to the vial walls does not appear to be a significant factor in experiments where the solid phase is present Note these results do not discount the possibility that Pu hydrous oxide precipitates were forming in both the no-solid control experiments and experiments with cement formulations present Based on the observation of a constant aqueous phase concentration of Pu regardless of the initial Pu concentration the presence of a solubility limiting Pu phase cannot be discounted based on these data Further experiments examining the solubility of Pu in high pH calcite saturated solutions are required
Like Pu Np shows little affinity for the vial walls in the presence of a solid phase In each case tested there was significantly less than 1 of the total Np sorbed to the vial walls This behavior is consistent with the ~100 mass balance on Np achieve in the solid-free controls The majority of Np remained soluble in the solid-free control experiments Therefore it is expected that sorption of Np to the vial walls was the primary reason for the loss of Np from the aqueous phase in the no-solids systems rather than precipitation of a Np solid phase similar to the process discussed for Pu above This assumption is based on the relative solubility of Np(V) as compared with Pu(IV)
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Figure 49 Percent Pu and Np sorbed to vial walls of the no solids controls after the aqueous phases were discarded and the vials were washed Both the 10 ppb and 1 ppb datasets were prepared in triplicate and the error bars show the standard deviation
Figure 410 Percent Pu sorbed to vial walls after the solids and aqueous phases were removed and the vials were washed The graph illustrates one sample from each of the 1 ppb 5 ppb and 10 ppb systems Therefore no error bars are present
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Figure 411 Percent Np sorbed to vial walls after the solids and aqueous phases were removed and the vials were washed The graph illustrates one sample from each of the 1 ppb 5 ppb and 10 ppb systems Therefore no error bars are present
43 Radionuclide Sorption to Cementitious Formulations under Reducing Conditions
Similar to the Pu Kd values under oxidizing conditions Pu Kd values ranged from 104 to gt105 under reducing conditions (Figure 412) Also similar to the results under oxidizing conditions the Kd increases with increasing initial Pu concentration Again this behavior is indicative of the aqueous phase concentration of Pu being controlled by solubility of Pu rather than by sorption In each case the samples appeared to reach steady state within 24 hours This equilibration is evident because the Kd values after one day and four days are very similar Also it appears that the amount of reducing slag does not make a significant difference in the Kd value In fact the TR547 solid consists of 45 reducing grout but produces approximately the same Kd values of the aged cement which does not have any reducing grout Each of these Kd values are higher than the TR545 which is 90 reducing grout These findings are in agreement with those conducted by Allard et al (1984) and Hoglund et al (1985) who reported that concrete containing reducing agents (slag similar to that used in our study) did not have greater Pu Kd values than those that did not contain slag
Similar aqueous concentrations of Pu were observed regardless of the solid phase present Figure 36 shows the average aqueous phase concentrations measured after one day and four days for all solids As stated above triplicate samples were prepared for each solid phase and each initial concentration Therefore each of the reported solubility values in Figure 412 is an average of up to nine measurements of the Pu aqueous concentrations Using the highest reported value with the expected maximum error (00045 ppb for solid Vault 2) the maximum expected aqueous concentration of Pu in the pore water associated with the cementitious formulations will be approximately 2 x 10-11 molL (calculated from Equation 31) This value is on the same order as the solubility of Pu hydrous oxide solid phases (Neck and Kim 2001) A best value would be 10-12 molL
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Figure 412 Pu Kd Values under Reducing Conditions Plutonium Kd values for various cementitious formulations measured after one-day equilibration (1d) and four-day equilibration (4d) under reducing conditions Total plutonium concentrations in each system were 1ppb 5 ppb and 10 ppb Samples prepared in triplicate and error bars represent standard deviation
Figure 413 Average Solubility of Plutonium under Reducing Conditions Plutonium solubility for various cementitious formulations measured after one-day equilibration (1d) and four-day equilibration (4d) under reducing conditions Total plutonium concentrations in each system were 1ppb 5 ppb and 10 ppb as noted Samples prepared in triplicate and an average of all samples (9) was used to determine average solubility The error bars represent standard deviation of samples
The Np Kd values reported in Figure 414 obtained under reducing conditions are very similar to
those obtained under oxidizing conditions In each case the samples appeared to reach steady state within 24 hours This equilibration is evident because the Kd values between the one-day and fourndashday equilibrations are similar As was the case with Pu the amount of slag present in each solid does not
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seem to have a significant effect on the Kd values Again the aged cement with no slag has as high a Kd as the TR545 with 90 reducing slag
Similar aqueous concentrations of Np were observed regardless of the solid phase present Figure 314 shows the average aqueous phase concentrations measured after one day and four days for all solids All Kd values were gt 105 mLg which is considerably larger than those reported by Kaplan and Coates (2007) who reported Np Kd values to 1300 to 1600 mLg This difference can be attributed to two important experimental differences 1) the experiment was designed to permit larger Kd values to be measured (eg solid to liquid ratios and spike concentrations) and more importantly 2) a more sensitive analytical method ICP-MS was used instead of conventional low-energy gamma spectroscopy or liquid scintillation counting (LSC) analysis As stated above triplicate samples were prepared for each solid phase and each initial concentration Therefore each of the reported solubility values in Figure 415 is an average of up to nine measurements Using the highest reported value (to provide the most conservative most soluble values) with the expected maximum error (00045 ppb for solid TR545) the maximum expected aqueous concentration of Np in the pore water associated with the cementitious formulations will be approximately 2 x 10-11 molL A best value taking into consideration the less-than values which are depicted in Figure 414 as running off the top of the plot would be 10-12 molL
Figure 414 Np Kd Values under Reducing Conditions Neptunium Kd values for various cementitious formulations measured after one-day equilibration (1d) and four-day equilibration (4d) under reducing conditions Total Np concentrations in each system were 1 ppb 5 ppb and 10 ppb Samples were prepared in triplicate and the error bars represent standard deviation Kd values limited to gt106 were at instrumental background
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Figure 415 Average Solubility of Neptunium under Reducing Conditions Neptunium solubility for various cementitious formulations measured after one day equilibration (1d) and four day equilibration (4d) under reducing conditions Total plutonium concentrations in each system were 1ppb 5 ppb and 10 ppb Samples prepared in triplicate and an average of all samples (9) was used to determine average solubility The error bars represent standard deviation
A plot of the Tc Kd values for each cementitious formulations under reducing conditions is shown
in Figure 416 (log y-axis) and Figure 417 (reduced scale linear y-axis) The Kd values for each of the initial Tc concentrations are relatively similar This behavior is consistent with the Kd expression However the increasing Kd values from the one-day to four-day day equilibrations for each solid indicate that steady state was not reached within one day and it is unclear whether steady state was reached after four days A possible explanation for this behavior is that Tc(VII) was being reduced to Tc(IV) in these systems due to the reducing conditions As Tc(VII) was reduced the Kd would increase based on the high affinity of Tc(IV) for solid phases This proposed mechanism was observed by Lukens et al (2005) using an SRS saltstone material similar but not identical to TR547 Using synchrotron X-ray absorption fine structure spectroscopy they observed over a 453 month period that Tc(VII) incorporated into SRS saltstone slowly converted to Tc(IV) and that the nearest neighbor was initially predominantly oxygen and eventually became predominantly sulfur (described as a Tc(IV) phase TcSx) Lacking in Lukens et al (2005) is quantification of the solubility of Tc This analysis still needs to be completed along with re-oxidation studies (ie what is the rate that reduced Tc reoxidizes under ambient natural saltstone conditions)
Unlike Np and Pu Tc Kd values changed with the amount of slag included in the formulation Tc Kd values noticeable increase as the amount of slag in the formulation increased TR547 (45 dry-wt- slag) Kd value is visibly higher than the Aged Cement and Vault 2 Kd values while the most reducing TR545 (90 dry wt- slag) Kd value is significantly higher than the others Following a similar trend the reduction capacity that is the total quantity of reductant in the saltstone on a mass basis (units of milli-equivalents of charge per g) of TR547 had slightly greater or equal reduction capacity to that of TR545 (Roberts and Kaplan 2009)
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Figure 416 Tc Kd Values under Reducing Conditions Tc Kd values for various cementitious formulations measured after one-day equilibration (1d) and four-day equilibration (4d) under reducing conditions Total Tc concentrations in each system were 1 ppb 5 ppb and 10 ppb Sample prepared in triplicate and error bars represent standard deviation except as follows TR547-1d 1 ppb is based on a single dataset and datasets Vault 2-1d 5 ppb Vault 2- 4d 1 ppb Aged Cement-1d 5 ppb and Aged Cement-4d 1 ppb are duplicates
Figure 417 Data from Figure 416 replotted on a reduced linear scale for easier viewing Each sample was prepared in triplicate except as follows TR547-1d 1 ppb is based on a single dataset Vault 2-1d 5 ppb Vault 2- 4d 1 ppb Aged Cement-1d 5 ppb and Aged Cement-4d 1 ppb are duplicate datasets
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The calculated Kd values for I sorption to cementitious samples under reducing conditions are shown in Figure 418 Before discussing the data it should be noted that spiked QAQC samples which were analyzed on the ICP-MS along with the samples used to generate the data in Figure 418 were off by an average of 195 with one outlier of approximately 40 This dataset did not include the use of internal standards as discussed in Section 31 above1 Due to a lack of an internal standard the iodine results presented in this report should be considered with a minimum error estimate of 20
The iodine Kd values under reducing conditions are different from those observed under oxidizing conditions Under oxidizing conditions it appears they are at a steady state by day one However under reducing conditions there is a noticeable difference between days one and four indicating steady state was not reached by day one and possibly not by day four Another interesting observation is that the Kd values are decreasing from day one to four A possible reason for this behavior may be due to redox chemistry of iodine in this system If iodine partially or entirely exists in the form as iodate (IO3
-) it is possible it could be reduced to iodide I- within the reducing cementitious system These two iodine species sorb differently iodate sorbing to minerals more strongly than iodide (Denham et al 2009 Schwehr et al 2009 Fukui et al 1996 Yoshida et al 1992) It is hypothesized that the reducing environment of the saltstone is sufficient to reduce iodate ions to the more weakly binding form of iodine iodide
This is one of the few datasets (along with Tc) in this study where there may be a difference between the various solids The degree of iodate reduction would be expected to increase as the slag content increases As mentioned above reduction of iodate to iodide should result in a decrease in sorption Therefore higher Kd values should be observed for solids with less slag such as the Aged Cement (0 dry wt- slag) and Vault 2 (17 dry wt- slag) This is generally the case in Figure 418 where the highest Kd values are reported for the Aged Cement and the lowest values are for solid TR547 However this trend does not hold completely where the saltstone sample containing 90 slag (TR545) has generally equal or higher Kd values than the saltstone containing 45 dry wt- slag (TR547)
1 Clemson University is presently investigating appropriate internal standards for iodine analyses for ICP-MS Of those tested rhenium and molybdenum have shown some promise
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Figure 418 Iodine Kd Values under Reducing Conditions I Kd Values for various cementitious formulations measured after one day equilibration (1d) and four day equilibration (4d) under reducing conditions Total iodine concentrations in each system were 100 ppb 500 ppb and 1000 ppb as noted Sample prepared in triplicate and error bars represent standard deviation of samples except as follows Vault 2-4 d 100 ppb is a single dataset while the datasets for Vault 2-1 d 100 ppb 4 d 1000 ppb TR545-4 d 1000 ppb 100 ppb TR547-4 d 1000 ppb 500 ppb 100 ppb and Aged Cement- 4 d 1000 ppb and 100 ppb are all based on duplicates
44 Radionuclide Sorption to Vial Walls under Reducing Conditions
The aqueous concentrations for Pu Np and Tc in the no solids controls are shown in Figure 419 The results are similar to those presented for experiments performed under oxidizing conditions above The 1 ppb Pu aqueous fraction is approximately three times greater than the 10 ppb fraction at day one This fraction decreases over time and by day four they are approximately equal when taking error into account This behavior is similar to the aqueous fraction under oxidizing conditions The 1 ppb Np aqueous fraction is significantly higher on both day one and day four than the aqueous fraction of the 10 ppb samples However each remained constant from day one to day four The 10 ppb aqueous fraction is twice as low as under oxidizing conditions which suggests either higher sorption to the vial walls or more precipitating out under the reducing conditions Like Pu and Np Tc shows a decrease from day one to day four especially for the 1 ppb samples The decrease in the 10 ppb sample is minimal and the aqueous fraction remains around 09 This value is slightly lower than that under oxidizing conditions
To examine the degree of sorption to the vial walls the tubes were washed again as performed for the experiments under oxidizing conditions above and similar results were found Ninety percent of the 1 ppb Pu sample was sorbed to the vial wall upon completion of the experiment which gives a 100 mass recovery when comparing this value to that found in Figure 419 However this result is not the case with the 10 ppb samples where approximately 75 of the mass remains unaccounted It is noteworthy that approximately 25 of the Pu from the 10 ppb solution sorbed to the vial walls under both oxidizing
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and reducing conditions Np follows the same trend as Pu while less than 005 of the Tc sorbed to the wall
Figure 419 Plutonium Neptunium and Technetium No-Solids Aqueous Fractions under Reducing Conditions Pu Np and Tc aqueous fractions of No Solids controls after a one-day equilibration (1d) and four-day equilibration (4 d) under reducing conditions Total concentration for each radionuclide was 1 ppb and 10 ppb Samples were prepared in triplicate and the error bars represent the standard deviation
Figure 420 Percent of Pu Np and Tc sorbed to the vial walls of the No Solids control samples under reducing conditions Each the 1 ppb and 10 ppb samples were prepared in triplicate and the error bars represent the standard deviations of triplicate samples
Under reducing conditions the fraction of I remaining in the aqueous phase was around 90 with
almost 100 mass recovery of the 100 ppb I after the four-day equilibration These graphs show that
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under reducing conditions there will only be a small fraction of I sorbing to the vial wall or coming out of solution This result is a much better mass recovery than under oxidizing conditions (Figure 48) which had a mass recovery of approximately 65 after four days This result is also consistent with the interpretation that there may be a iodine speciation change between the two redox treatments
Figure 421 Iodine No-Solids Aqueous Fractions under Reducing Conditions I aqueous fractions of No-Solids controls after a one-day equilibration (1d) and four-day equilibration (4d) under reducing conditions The total concentration for each system was 100 ppb and 1000 ppb Samples were prepared in triplicate and the error bars represent the standard deviation
50 Comparison of Radionuclide Sorption under Oxidizing and Reducing Conditions
In the following figures (Figure 51 through Figure 54) the data shown above has been replotted to allow comparison between the oxidizing and reducing conditions for each cementitious formulation General observations based on these data follow Vault 2 Observations (Figure 51)
bull Pu Kds are greater than 104 under both oxidizing and reducing conditions and Pu Kds are slightly lower under reducing conditions This could possibly be due to reduction of Pu(IV) to Pu(III) However no oxidation state analysis was performed in this work
bull Np Kds are generally greater than 104 under both oxidizing and reducing conditions Interestingly Np Kds are higher under reducing conditions by almost an order of magnitude This could possibly be due to reduction of Np(V) to Np(IV) However no oxidation state analysis was performed in this work
bull Regardless of the initial Np or Pu concentration similar aqueous phase concentrations of Np or Pu were observed in all samples This trend indicates that ldquosorptionrdquo of Np and Pu in these systems may be a combination of adsorption absorption and (co)precipitation processes
bull Tc appears to reach a steady state within four days under oxidizing conditions This behavior does not appear to be the case under reducing conditions After four days similar Kd values are reached under both oxidizing and reducing conditions It is unclear
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whether the Kd value of Tc will continue to increase under reducing conditions consistent with reduction of Tc(VII) to Tc(IV) The similarity in Kd values under both oxidizing and reducing conditions is an interesting observation and certainly warrants additional studies
bull I Kd values are similar under both oxidizing and reducing conditions However reducing condition systems may not be at steady state after four days while systems under oxidizing conditions appeared to reach a steady state The difference in rates may be due to reduction of iodate to iodine
bull For all isotopes examined the sorption behavior to each of the solid phases is very similar
TR545 and TR547 Observations (Figure 52 and Figure 53) bull Similar to the discussion above with respect to Vault 2 Pu Np and Tc all appear to reach
a steady state under oxidizing conditions and approach steady state slower under reducing conditions
bull Np and Pu Kd values are greater than 104 for all systems and time steps The aqueous phase concentrations of Np and Pu appear to be better described as a solubility in terms of the aqueous phase concentration of Np and Pu Similar aqueous phase concentrations of both Np and Pu were reached The data indicate that the initial Np and Pu concentration generally does not affect the aqueous phase concentration at an apparent steady state The presence of each solid phase appears to limit the aqueous phase concentration of both Np and Pu on the order of 10-11 molL
bull Tc shows significantly higher Kd values under reducing conditions versus oxidizing conditions
bull For all isotopes examined the sorption behavior to each of the solid phases is very similar
Aged Cement Observations (Figure 54) bull Pu appears to be close to steady state for each solid by day one with similar Kd values
reached on between day one and day four bull Np has a higher Kd under reducing conditions than oxidizing (105 under oxidizing
conditions and gt105 under reducing conditions) bull Neither set of Tc data was at steady state by day one and rates of sorptiondesorption
reactions appear to be different Tc Kds decrease from day one to four under oxidizing conditions but increase under reducing conditions
bull The Kd values for I under oxidizing conditions were considerably higher than those measured for I with any other solid Similar Kd values obtained for the same solids under reducing conditions indicate that the reported Kd values under oxidizing conditions appear to be suspect However analysis of the raw data gives no indication of an experimental artifact As discussed above these observations may be explained based upon the amount of slag contained within the solids which will affect the reducing capacity (ie No reducing slag is in the aged cement which could be reason the reduction of iodate to iodide (speculated in other samples) is not evident)
bull The difference in sorption behavior of iodine to the aged cement between oxidizing and reducing conditions also indicates that the reducing conditions of the solution may affect I redox behavior in addition to any reactivity expected in the solid phases
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Figure 51 Comparison of Tc I Np and Pu sorption to Vault 2 solid under oxidizing and reducing conditions
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Figure 52 Comparison of Tc I Np and Pu sorption to TR 545 solid under oxidizing and reducing conditions
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Figure 53 Comparison of Tc I Np and Pu sorption to TR547 solid under oxidizing and reducing conditions
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Figure 54 Comparison of Tc I Np and Pu sorption to Aged Cement under oxidizing and reducing conditions
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60 Comparison of Radionuclide Sorption and Solubility under Oxidizing and Reducing Conditions
To further summarize the data the following tables provide either the average solubility
(for Np and Pu) or average Kd (for Tc and I) determined under both oxidizing and reducing conditions for each cementitious formulation Each table lists the average value standard deviation and the number of replicate samples used to calculate the reported values
The solubility of Pu in the presence of each solid under oxidizing and reducing conditions is shown in Table 61 (this is taken from experiments equilibrated for four days not one day) Under oxidizing conditions the apparent solubility values associated with the Aged Cement (0 dry wt- slag) Vault 2 (17 dry wt- slag) and TR547 (45 dry wt- slag) are all similar with only a slight increase in solubility as the amount of reducing slag increases There is a significant increase of almost an order of magnitude for the most reducing saltstone TR545 (90 dry wt- slag) However these samples also have a standard deviation on the same order of magnitude as the solubility itself which when taken into account brings the solubility back into the range of the others Under reducing conditions the apparent solubility values are slightly lower than under oxidizing conditions In this set of samples the Vault 2 saltstone with 10 dry wt- reducing slag had the highest apparent solubility but once again when considering the standard deviation the values are similar
Table 61 Comparison of plutonium apparent solubility values under oxidizing and reducing conditions
Table 62 lists the apparent solubility values of Np in the presence of each cementitious
formulation under both oxidizing and reducing conditions Under oxidizing conditions the cementitious formulation does not appear to have a dramatic effect on the solubility The apparent solubility values are similar to those of Pu under similar conditions except the Np standard deviations are much higher The high standard deviations are an analytical artifact since the measured concentrations were close to or at the detection limit of the ICP-MS There does appear to be a slight decrease in Np solubility under reducing conditions However the statistical significance of this decrease was not calculated
SRNL-STI-2009-00636 Revision 0
47
Table 62 Comparison of neptunium apparent solubility values under oxidizing and reducing conditions
Unlike the apparent solubility values of Pu and Np the aqueousatmospheric conditions
and cementitious formulation seem to have an effect on the Tc Kd values (Table 63) Under oxidizing conditions there is not a discernible difference among the different cementitious formulations especially when taking the respective standard deviations into account However when experiments were run under reducing conditions the specific formulation had a noticeable effect The two saltstone samples with the least amount of reducing slag Aged Cement (0 dry-wt- slag) and Vault 2 (17 dry wt- slag) had Kd values which were similar to those observed under oxidizing conditions However the TR547 (45 dry-wt- slag) increased by almost an order of magnitude while the TR545 (90 dry wt- slag) increased by about three orders of magnitude Although the respective standard deviations are large the higher Kd values do appear to be significant
Table 63 Comparison of technetium Kd values under oxidizing and reducing conditions
Unlike Tc I does not seem to be as affected by cementitious formulation and redox status (Table 64) The only treatment (possible outlier) that does not follow this trend is the Aged Cement under oxidizing conditions This Kd value is higher than the others but also has a much higher standard deviation which when accounted for gives a value similar to the others All other treatments had near identical Kd values irrespective of solid phase or redox condition But again the Aged Cement data cannot be discounted at this time given the possibility of the influence that redox may have on iodine speciation and the strong influence I speciation has on sorption to cementitious materials
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Table 64 Comparison of iodine Kd values under oxidizing and reducing conditions
71 Comparison with Previous Data The increased sensitivity of the ICP-MS over conventional low-energy gamma
spectroscopy or liquid scintillation counting (LSC) analysis allowed for much more accurate Kd values and apparent solubility values in this work than were previously obtainable Generally radioanalytical detection methods start with activities on the order of 103 to 104 counts per minute (cpm) and approach background levels of 1 to 5 cpm for strongly sorbing radionuclides Therefore the accuracy of the Kd value will be the difference in analytical sensitivity when the initial aqueous activity decreases by a factor of approximately 5000 (ie the aqueous activity drops from approximately 5000 cpm to the instrument background of 1 cpm following almost complete sorption) As a result the reported Kd values can only be reliably reported up for a Kd of 103 to 104 This constraint is believed to be the difference between the observed Kd values for 237Np of gt 105 observed in this work when compared with the Kd values between 3000 and 4000 reported by Kaplan et al (2008) A similar observation was made for Pu because 242Pu was used for ICP-MS analysis and 238Pu was used in the work of Kaplan et al (2008) This constrint may account for the different Kd value of gt104 reported in Kaplan et al (2008) compared with the value of gt105 observed in this work
In the case of Tc Kaplan et al (2008) reported a Kd of 023 mLg for Vault 2 under oxidizing conditions and 093 mLg under reducing conditions while the above experiment determined the Vault 2 Kd to be 505 mLg under oxidizing conditions and 557 mLg under reducing conditions Unlike the discrepancy in the Kd values for Np Pu and Tc between the above findings and those in Kaplan et al (2008) the reported Kd values for iodine are similar For Vault 2 Kaplan et al (2008) found 125I to have a Kd of 894 mLg under oxidizing conditions and 715 mLg under reducing conditions These values are similar to the Kd values of 766 mLg and 725 mLg observed under oxidizing and reducing conditions respectively in this work These findings appear to confirm the previously accepted Kd values of 0-10 mLg depending on the cementitious formulation
72 Suggested Future Work The above data demonstrate several areas that require further examination The
increasing Tc Kd values over time dataset suggest that steady state had not been achieved It would be beneficial to determine the amount of time required to reach steady state and allow determination of a more accurate Kd value (an assumption of the Kd construct is that it be measured at steady state) Also kinetic studies of both Tc and I are needed to better understand their respective interactions with the different cementitious formulations As for the I additional
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49
tests should be performed to test the hypothesis that iodine may in part exist as iodate which may initially sorb to the saltstone then undergo reduction to iodine or iodide and then desorbs causing a decrease in Kd
A final area of future work is to examine the possible causes for the similar behavior of each cementitious formulation despite the different slag content This discrepancy is not only observed in the above experiments but also in Kaplan et al (2008) which is illustrated in Table 31 and by recent work in measurements of saltstone reduction capacity (Roberts and Kaplan 2009) The reduction capacity (units in milli-equivalentsg solid) equivalents of the Aged Cement with no slag is 855 plusmn 101 and adding 10 slag gives a reducing equivalent of 2398 plusmn 311 However increasing the slag content to 23 causes the reducing capacity to increase to 8218 plusmn 81 which is almost equivalent to the 8324 plusmn 49 of the 100 slag Understanding the chemistry behind the reducing capacity of each cementitious formulation will help to define what reactions are important for controlling radionuclide release from the saltstone
80 References Allard B L Eliasson S Hoglund and K Andersson 1984 ldquoSorption of Cs I and actinides in
concrete systemsrdquo SKB Technical Report SKBKBS TR-84-15 DKB Stockholm Sweden
Denham M D I Kaplan and C Yeager2009 ldquoGroundwater radioiodine Prevalence biogeochemistry and potential remedial approachesrdquo SRNL-STI-2009-00463 Savannah River National Laboratory Aiken SC
Dixon K L M A Phifer and J R Harbour 2008 ldquoFY09 PACA Maintenance Program Additional Saltstone Property Testingrdquo SRNL-L3100-2009-00019 Rev0 Savannah River National Laboratory Aiken SC
Fukui M Fujikawa Y and Satta N 1996 ldquoFactors affecting interaction of radioiodide and iodate species with soilrdquo Journal of Environmental Radioactivity 31 199-216
Hoglund S L Eliasson B Allard K Andersson and B Torstenfelt 1985 ldquoSorption of some fission products and actinides in concrete systemsrdquo Mat Res Soc Symp Proc 50 683-690
Kaplan D I 2007 Geochemical Data Package for Performance Assessment Calculations Related to the Savannah River Site WSRC-TR-2006-00004 Rev 1 Washington Savannah River Company Aiken SC
Kaplan D I and Coates J 2007 ldquoPartitioning of Dissolved Radionuclides to Concrete under Scenarios Appropriate for Tank Closure Performance Assessmentsrdquo WSRC-STI-2007-00640 Rev 0 Washington Savannah River Company Aiken SC 29808
Kaplan D I Roberts K Coates J Siegfried M Serkiz S 2008 ldquoSaltstone and concrete interactions with radionuclides Sorption (Kd) desorption and reduction capacity measurementsrdquo SRNS-STI-2008-00045 Savannah River National Laboratory Aiken SC 2008
SRNL-STI-2009-00636 Revision 0
50
Neck V and Kim J I 2001 ldquoSolubility and hydrolysis of tetravalent actinidesrdquo Radiochim Acta 89 1
Powell B A Fjeld R A Coates J T Kaplan D I Serkiz S M 2002 ldquoPlutonium Oxidation State Geochemistry in the SRS Subsurface Environmentrdquo WSRC-TR-2003-00035 Westinghouse Savannah River Company US DOE Savannah River Site Aiken SC
Roberts K A and D I Kaplan 2009 Reduction Capacity of Saltstone and Saltstone Componentsrdquo SRNL-STI-2009-00637 Rev0 Savannah River National Laboratory Aiken SC
Schwehr K A Santschi P H D I Kaplan C M Yeager and R Brinkmeyer 2009 ldquoOrgano-iodine formation in soils and aquifer sediments at ambient concentrationsrdquo Environ Sci Technol 437258-7264
Yoshida S Muramatsu Y and Uchida S 1992 ldquoStudies on the sorption of I-(iodide) and IO3-
(iodate) onto andosolsrdquo Water Air and Soil Pollution 63 321-329
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51
90 Appendix A Data Tables of Radionuclide Sorption to Saltstone under Oxidizing Conditions
The following tables represent data collected for the no solids controls each saltstone and testing of radionuclide sorption to the vial walls The no solids controls tables include the concentration (ppb) of the radionuclide spiked into the sample along with the concentration of the radionuclide (ppb) measured in the aqueous phase after the given equilibration time The pH at the time the sample was taken is also recorded along with the fraction of the radionuclide which stayed in the aqueous phase The tables for the cementitious formulation data include the data above along with the addition of a Kd value The tables of the data for the radionuclides sorbed to the vial walls include the initial concentration (ppb) of the spike the concentration (ppb) of the radionuclide that had sorbed to the vial wall during the experiment and the percentage of the total concentration this represents Important Notes
BDL- Below Detection Limit lt01 denotes no notable sorption occurred
91 Data Tables for No Solid Controls
Table 91 Plutonium no solids control after one day
A 9264165178 402285E‐05 1181 434238E‐06 9980817 B 9352537276 0000110618 1183 118276E‐05 3616813 C 9363541597 705331E‐05 118 753273E‐06 5401186 D 0993110568 BDL 12 NA NA E 0977247222 300794E‐05 1199 307797E‐05 1280331 F 0962441315 BDL 1198 NA NA G 4059128499 BDL 1186 NA NA H 4065161486 705198E‐05 1188 173473E‐05 2380003 I 4116819691 0000110748 1189 269014E‐05 1555864
Table 920 TR545- neptunium after four days
Sample ID
Initial Aq Conc (ppb)
Equil Aq Conc (ppb) pH
Fraction Aq Kd
A 92641652 NA 1188 NA NA B 93525373 00001935 1185 2069E‐05 2067199C 93635416 4119E‐05 1185 44E‐06 9247818D 09931106 BDL 1197 NA NA E 09772472 BDL 12 NA NA F 09624413 00066817 1206 00069424 562421G 40591285 00003289 1196 8103E‐05 5148274H 40651615 00025316 1196 00006228 6625737I 41168197 00001018 1194 2474E‐05 1692126
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58
Table 921 TR545- technetium after one day
Sample ID
Initial Aq Conc (ppb)
Equil Aq Conc (ppb) pH Fraction Aq Kd
A 9655146069 820460082 1181 0849764546 8998984 B 9356176321 7703053505 1183 0823312135 1051242 C 9114122586 7978297395 118 0875377451 7062663 D 1042349157 0853053814 12 0818395456 9099556 E 0983206046 0871198263 1199 0886079033 5196709 F 0905148405 0803451372 1198 0887646013 5098696 G 4950156706 4275082341 1186 0863625658 7213934 H 4889067068 4173762594 1188 0853693053 7687519 I 4854463762 4147024058 1189 0854270268 7771045
A 1048950046 0002141023 1149 0000204111 2112281 B 1039943573 0001770549 1157 0000170254 2460487 C 1084651695 0001127533 1153 0000103953 4014918 D 1088686867 0001201087 1172 0001103244 3564524 E 1119673887 0000783288 1177 0000699568 5709897 F 1045722787 0000914861 1181 000087486 4495324 G 5387981131 0001444832 1169 0000268158 1494715 H 5412748988 0001143483 1169 0000211257 1965749 I 5373948758 00010003 1164 0000186139 2280472
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Table 926 TR547- plutonium after four days
Sample ID
Initial Aq Conc (ppb)
Equil Aq Conc (ppb) pH
Fraction Aq Kd
A 104895 NA 116 NA NA B 10399436 0001828 1165 00001758 2383132C 10846517 00010788 1164 9946E‐05 4196159D 10886869 00009131 1184 00008388 4689778E 11196739 00010624 1189 00009488 4208928F 10457228 00007967 1191 00007619 516258G 53879811 00007915 1173 00001469 2728993H 5412749 00008355 1175 00001544 2690641I 53739488 00006103 1174 00001136 3737892
Table 927 TR547- neptunium after one day
Sample ID
Initial Aq Conc (ppb)
Equil Aq Conc (ppb) pH Fraction Aq Kd
A 9589772032 0000454463 1149 473903E‐05 9116335 B 9293228768 0000260081 1157 27986E‐05 1499475 C 1008725504 0000302018 1153 299405E‐05 1397125 D 0952173007 000019177 1172 0000201403 1954603 E 0992224074 BDL NA NA F 0967815522 402137E‐05 1181 41551E‐05 9474699 G 4068405786 0000222282 1169 546361E‐05 7336986 H 409543171 0000531619 1169 0000129808 3199152 I 4017406611 0000410123 1164 0000102086 4157807
Table 928 TR547- neptunium after four days
Sample ID
Initial Aq Conc (ppb)
Equil Aq Conc (ppb) pH Fraction Aq Kd
A 9589772 NA 116 NA NA B 92932288 00002145 1165 2308E‐05 1818463C 10087255 00001628 1164 1614E‐05 2591215D 0952173 BDL 1184 NA NA E 09922241 BDL NA NA F 09678155 5107E‐05 1191 5277E‐05 7460375G 40684058 00001336 1173 3284E‐05 1220544H 40954317 8151E‐05 1175 199E‐05 2086795I 40174066 00001322 1174 3292E‐05 1289605
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Table 929 TR547- technetium after one day
Sample ID
Initial Aq Conc (ppb)
Equil Aq Conc (ppb) pH Fraction Aq Kd
A 9466799266 8233850788 1149 0869760788 8220086 B 9439556236 817653394 1157 0866198975 8165745 C 9383493063 8086024379 1153 0861728604 8430884 D 1061939876 0919992065 1172 0866331594 6241759 E 0991827343 0836511397 1177 0843404251 7590958 F 0971981155 0839862696 1181 0864073024 6354378 G 4883337077 414858839 1169 0849539633 7903986 H 4691440077 3996173112 1169 0851800949 8038249 I 486993937 4291285586 1164 0881178442 6558707
Table 930 TR547- technetium after four days
Sample ID
Initial Aq Conc (ppb)
Equil Aq Conc (ppb) pH
Fraction Aq Kd
A 94667993 NA 116 NA NA B 94395562 85812109 1165 09090693 5885474C 93834931 84622373 1164 09018217 6279204D 10619399 09580683 1184 09021869 4435663E 09918273 08881507 1189 08954691 4835506F 09719812 09036489 1191 0929698 3138862G 48833371 4490415 1173 09195382 4312104H 46914401 42054182 1175 08964024 5612948I 48699394 43843193 1174 09002821 5536503
Table 931 TR547- iodine after one day
Sample ID
Initial Aq Conc (ppb)
Equil Aq Conc (ppb) pH Fraction Aq Kd
A 9944920441 8813152965 1149 0886196427 738241 B 9956006121 8747156303 1157 0878580848 8007767 C 9822152291 8664470934 1153 0882135674 7988892 D 1002391846 9333490632 1172 0931121963 3368509 E 9918273427 6625075445 1177 0667966607 1551748 F 9918175056 8931364957 1181 0900504872 4773862 G 5166570628 4445386532 1169 0860413387 7961604 H 4847821413 410447427 1169 084666367 8664303 I 4850381381 4266693706 1164 0879661489 6413801
100 Appendix B Data Tables of Radionuclide Sorption to Saltstone Under Reducing Conditions
The following tables represent data collected for the no solids controls each cementitious solid and testing of radionuclide sorption to the vial walls The no solids controls tables include the concentration (ppb) of the radionuclide spiked into the sample along with the concentration of the radionuclide (ppb) measured in the aqueous phase after the given equilibration time The pH at the time the sample was taken is also recorded along with the fraction of the radionuclide which stayed in the aqueous phase The tables for the cementitious solidsrsquo data include the data above along with the addition of a Kd value The tables of the data for the radionuclides sorbed to the vial walls include the initial concentration (ppb) of the spike the concentration (ppb) of the radionuclide that had sorbed to the vial wall during the experiment and the percentage of the total concentration this represents Important Notes
BDL= Below Detection Limit lt01 denotes no notable sorption occurred
101 Data Tables for No-Solid Controls
Table 101 Plutonium no solids control after one day
A 9405892 0007019 111 0000746258 5681206 B 9602498 0003294 1117 0000342992 123554 C 9630619 0002936 1114 0000304893 1396318 D 4945396 0001795 113 0000363011 1171688 E 4964945 0001373 1131 0000276484 1493015 F 4441601 0001516 113 0000341219 1389674 G 1079602 0001109 1142 0001027508 4215519 H 1031512 0000883 1143 0000855983 4820576 I 0939294 0000978 1143 0001040992 4550255
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Table 1011 Vault 2- neptunium after one day
Sample ID Initial Aq Conc (ppb)
Equil Aq Conc (ppb) pH Fraction Aq
A 9425042625 0001709054 1105 0000181331 B 9611386476 0001184125 1110 00001232 C 9579553607 0001155517 1104 0000120623 D 4974000414 0000672325 1125 0000135168 E 4916731623 0000675371 1128 0000137362 F 4373142817 0000570681 1120 0000130497 G 0943366414 0000389738 1129 0000413136 H 1011745587 0000565648 1132 0000559081 I 0865252712 0000379545 1133 0000438653
A 8849444124 0000306309 1150 346133E‐05 1289533 B 8447823057 0000150131 1155 177715E‐05 2711019 C 8590597085 0000199185 1153 231864E‐05 2044057 D 4491250244 517162E‐05 1156 115149E‐05 4020064 E 4391894479 204591E‐05 1158 465838E‐06 9846089 F 4210703646 204376E‐05 1158 485374E‐06 9816203 G 086381524 522216E‐06 1160 604546E‐06 7577764 H 0870501884 BDL 1160 NA NA I 0861953838 BDL 1162 NA NA
SRNL-STI-2009-00636 Revision 0
79
Table 1036 Aged cement- neptunium after four days
Sample ID
Initial Aq Conc (ppb)
Equil Aq Conc (ppb) pH Fraction Aq Kd
A 8849444 0000131 1145 148418E‐05 3007445B 8447823 0000111 1146 131529E‐05 3662996C 8590597 656E‐05 1146 76328E‐06 6209405D 449125 BDL 1155 NA NA E 4391894 BDL 1156 NA NA F 4210704 BDL 1155 NA NA G 0863815 BDL 1165 NA NA H 0870502 BDL 1162 NA NA I 0861954 BDL 1164 NA NA
Table 1037 Aged cement- technetium after one day
Sample ID
Initial Aq Conc (ppb)
Equil Aq Conc (ppb) pH Fraction Aq Kd
A 8426518355 833290075 1150 098889012 0476492 B 8638001423 7823321167 1155 0905686487 4413063 C 9323317745 925927516 1153 0993130923 0294664 D 442651005 4300859603 1156 0971614106 1242837 E 4426849405 4336992073 1158 0979701742 0855315 F 3929483125 3938204338 1158 100221943 lt01 G 0817864386 081693181 1160 0998859743 0049487 H 0878958929 0792412508 1160 0901535306 4510199 I 0772205665 0871436364 1162 1128502941 lt01
Table 1038 Aged cement- technetium after four days
110 Appendix C Dixon et al (2009) FY09 PACA Maintenance Program Additional Saltstone Property Testing SRNL L3100-2009-00019 Rev 0
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83
SRNL L3100-2009-00019 Rev 0
December 16 2008
Keywords Performance Permeability Modulus
L B Romanowski
Waste Determinations From K L Dixon M A Phifer and J R Harbour
FY09 PACA Maintenance Program Additional Saltstone Property Testing
BACKGROUND
Additional tests have been identified for measurement of important hydraulic and physical properties of saltstone The initial phase of this work [1] was completed last year and the results were detailed in an internal report [2] The proposed testing for FY09 includes measurement of saturated hydraulic conductivity porosity bulk density particle density water retention and Youngrsquos modulus of simulated Saltstone grouts For completeness the bleed volumes and gel times for each mix will also be measured
The testing will be based on a projected salt solution composition for the ARPMCU stream that will be fed to the Saltstone Production Facility over the next few years The scope for FY09 will include testing to determine the impact of (1) admixtures (2) organics (3) wcm ratio (4) aluminate concentration and (5) temperature of curing on the hydraulic properties of saltstone mixes Samples of selected batches prepared as part of this task will be provided to Dan Kaplan for measurement of Kd through leaching tests The eleven mixes that will be batched and tested are detailed in Table 1
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84
Table 1 The Eleven Mixes That will be Batched and Tested
BFS is Blast Furnace Slag FA is Fly Ash and PC is Portland Cement
TEST DETAILS
Test 1 Control (Mix 1)
A control mix will be based on the baseline mix modified by exclusion of the Class F fly ash Consequently the cementitious materials premix will be a mixture of 90 blast furnace slag and 10 portland cement The degree of reaction will be much greater than with the normal premix and therefore should result in a lower porosity and a lower permeability This bounding test at 060 wcm ratio is expected to yield a hydraulic conductivity at or below the detection limit for the Mactec permeameter measurement system Therefore this test should demonstrate the lowest level of detection of the Mactec system as well as show a resolvable difference between measurements of the control mix and the control mix with the normal premix composition
Test 2 ndashImpact of Admixtures (Mixes 2 and 3)
Recent saltstone batches have required both a set retarder (Daratard 17) and an antifoam agent (Q2) for processing of the saltstone Therefore the baseline mix will be prepared with and without nominal levels of these two admixtures to determine whether these admixtures appreciably affect the hydraulic and physical properties of saltstone at these nominal concentrations
Test 3ndashImpact of Organics (Mixes 2 and 4)
The solvent extraction process is expected to result in some carryover of organics [3]
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85
Consequently a test will be performed on the impact of Caustic Side Solvent Extraction (CSSX) organics at 100 microliters per 1600 gram batch The CSSX solvent consists of 075 M 1-(2233-tetrafluoropropoxy)-3-(4-sec-butylphenoxy)-2-propanol (Cs-7SB) and 0003 M tri-n-octylamine (TOA) in an Isoparreg L diluent Test 4ndashImpact of Combination of Admixtures and Organics (Mixes 2 5 10 and 11)
This test will determine the impact of a combination of admixtures (Test 2) and organics (Test 3) together in the mix vs the baseline case without admixtures and organics
Test 5ndash Impact of wcm Ratio (Mixes 2 6 and 7)
It is well known that decreasing the wcm ratio in a mix will improve permeability in normal portland cement water mixes This test will measure the variation in permeability for the case of the MCU salt solution at three different wcm ratios The initial selection of wcm ratios is 055 060 and 065 However if the mix at an as-batched 065 wcm ratio has significant bleed water and the resulting actual wcm ratio is close to 060 then the three ratios will be adjusted to provide a more evenly spaced set of values However the baseline mix at 060 will be included as one of the three mixes
Test 6 ndash Impact of Aluminate Concentration (Mixes 8 9 and 10)
The DWPF has modified its process flowsheet to include a caustic washing of HLW sludge to remove some of the aluminum from the HLW prior to vitrification The resulting aluminate stream will then be blended with tank 50 material and fed to the SPF This increased aluminate concentration in the salt solution has significant impact on heat of hydration and set times and consequently it is likely that it will also impact permeability Therefore a set of three samples will be made at wcm ratios of 055 060 and 065 (as in Test 3) with a higher level of aluminate (028 M) for testing
Test 7 ndash Impact of Increased Curing Temperature (Mix 11)
In an ongoing task there is evidence that Youngrsquos modulus (a performance indicator) [4] is reduced by increasing the curing temperature of the mix Since the vault temperature increases during curing as a result of the exothermic hydration reactions one of the baseline mixes with a combination of admixtures and organics will be cured at 60
o
C rather than the normal 22
o
C to determine the impact of curing temperature on the permeability
SRNL-STI-2009-00636 Revision 0
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SCHEDULE
The schedule for the task of batching and testing of the samples is provided in Table 2 This schedule is based on the fact that the cementitious materials will be available for the testing as needed
Table 2 Additional Saltstone Hydraulic and Physical Property Tests
Item Schedule Start Work 12108 Test Plan Complete 1509 Preparation of 1st set of Samples Complete 11909 90-Day Cure Period for 1st set of Samples Complete 42009
SRNL-STI-2009-00636 Revision 0
87
SRNL-STI-2009-00636 Revision 0
SRNL-STI-2009-00636 Revision 0
DISTRIBUTION Savannah River Site
A B Barnes 999-W Rm 336 H H Burns 999-W Rm 381 B T Butcher 773-43A Rm 212 A D Cozzi 999-W Rm 337 D A Crowley 773-43A Rm 216 M E Denham 773-42A Rm 218 J C Griffin 773-A Rm A-231 J R Harbour 999-W Rm 348 C A Langton 773-43A Rm 219 M H Layton 705-1C Rm 14 D I Kaplan (3 copies) 773-43A Rm 215 S L Marra 773A Rm A-230 A M Murray 773-A Rm 229 K A Roberts 773-43A Rm 225 T C Robinson 705-1C Rm 13 L B Romanowski 705-1C Rm 19 K H Rosenberger 705-1C Rm 16 F M Smith 705-1C Rm 24 RPA File (2 copies) 773-43A Rm 213
Clemson University Environmental Engineering and Earth Sciences 372 Computer Court LG Rich Environmental Laboratory Anderson SC 29625
of samples except as follows data sets for Vault 2-1d 1ppb were duplicates and TR547- 4d 10 ppb is based on a single dataset 27
Figure 46 Iodine Kd Values under Oxidizing Conditions Iodine Kd values for various cementitious formulations measured after one-day equilibration (1d) and four-day equilibration (4d) under oxidizing conditions Total iodine concentrations in the systems were 100ppb 500 ppb and 1000 ppb as noted above Samples were prepared in triplicate and the error bars represent standard deviation of samples except as follows duplicates were used for dataset TR545- 1d 100ppb 28
Figure 47 Plutonium Neptunium and Technetium Aqueous Fractions Fraction of Pu Np and Tc remaining in the aqueous phase for the No Solids controls after a one-day equilibration (1d) and four-day equilibration (4d) under oxidizing conditions The total concentration for each radionuclide 10 ppb as noted above Samples were prepared in triplicate and the error bars represent the standard deviation of the samples 29
Figure 48 Iodine Aqueous Fraction Iodine aqueous fraction for the no-solids controls after a one-day equilibration (1d) and four-day equilibration (4d) under oxidizing conditions The total concentration of iodine was 1000 ppb as noted above Samples were prepared in triplicate and the error bars represent the standard deviation of the samples 29
Figure 49 Percent Pu and Np sorbed to vial walls of the no solids controls after the aqueous phases were discarded and the vials were washed Both the 10 ppb (blueleft) and 1 ppb (redright)) datasets were prepared in triplicate and the error bars show the standard deviation 31
Figure 410 Percent Pu sorbed to vial walls after the solids and aqueous phases were removed and the vials were washed The graph illustrates one sample from each of the 1 ppb (redleft) 5 ppb (greenmiddle) and 10 ppb (blueright) systems Therefore no error bars are present 31
Figure 411 Percent Np sorbed to vial walls after the solids and aqueous phases were removed and the vials were washed The graph illustrates one sample from each of the 1 ppb (redleft) 5 ppb (greenmiddle) and 10 ppb (blueright) systems Therefore no error bars are present 32
Figure 412 Pu Kd Values under Reducing Conditions Plutonium Kd values for various cementitious formulations measured after one-day equilibration (1d) and four-day equilibration (4d) under reducing conditions Total plutonium concentrations in each system were 1ppb 5 ppb and 10 ppb Samples prepared in triplicate and error bars represent standard deviation 33
Figure 413 Average Solubility of Plutonium under Reducing Conditions Plutonium solubility for various cementitious formulations measured after one-day equilibration (1d) and four-day equilibration (4d) under reducing conditions Total plutonium concentrations in each system were 1ppb 5 ppb and 10 ppb as noted Samples prepared in triplicate and an average of all samples (9) was used to determine average solubility The error bars represent standard deviation of samples 33
Figure 414 Np Kd Values under Reducing Conditions Neptunium Kd values for various cementitious formulations measured after one-day equilibration (1d) and four-day equilibration (4d) under reducing conditions Total Np concentrations in each system were 1 ppb 5 ppb and 10 ppb Samples were prepared in triplicate and the error bars represent standard deviation Kd values limited to gt106 were at instrumental background 34
Figure 415 Average Solubility of Neptunium under Reducing Conditions Neptunium solubility for various cementitious formulations measured after one day equilibration (1d) and four day
SRNL-STI-2009-00636 Revision 0
xiii
equilibration (4d) under reducing conditions Total plutonium concentrations in each system were 1ppb 5 ppb and 10 ppb Samples prepared in triplicate and an average of all samples (9) was used to determine average solubility The error bars represent standard deviation 35
Figure 416 Tc Kd Values under Reducing Conditions Tc Kd values for various cementitious formulations measured after one-day equilibration (1d) and four-day equilibration (4d) under reducing conditions Total Tc concentrations in each system were 1 ppb 5 ppb and 10 ppb Sample prepared in triplicate and error bars represent standard deviation except as follows TR547-1d 1 ppb is based on a single dataset and datasets Vault 2-1d 5 ppb Vault 2- 4d 1 ppb Aged Cement-1d 5 ppb and Aged Cement-4d 1 ppb are duplicates 36
Figure 417 Data from Figure 416 replotted on a reduced linear scale for easier viewing Each sample was prepared in triplicate except as follows TR547-1d 1 ppb is based on a single dataset Vault 2-1d 5 ppb Vault 2- 4d 1 ppb Aged Cement-1d 5 ppb and Aged Cement-4d 1 ppb are duplicate datasets 36
Figure 418 Iodine Kd Values under Reducing Conditions I Kd Values for various cementitious formulations measured after one day equilibration (1d) and four day equilibration (4d) under reducing conditions Total iodine concentrations in each system were 100 ppb 500 ppb and 1000 ppb as noted Sample prepared in triplicate and error bars represent standard deviation of samples except as follows Vault 2-4 d 100 ppb is a single dataset while the datasets for Vault 2-1 d 100 ppb 4 d 1000 ppb TR545-4 d 1000 ppb 100 ppb TR547-4 d 1000 ppb 500 ppb 100 ppb and Aged Cement- 4 d 1000 ppb and 100 ppb are all based on duplicates 38
Figure 419 Plutonium Neptunium and Technetium No-Solids Aqueous Fractions under Reducing Conditions Pu Np and Tc aqueous fractions of No Solids controls after a one-day equilibration (1d) and four-day equilibration (4 d) under reducing conditions Total concentration for each radionuclide was 1 ppb and 10 ppb Samples were prepared in triplicate and the error bars represent the standard deviation 39
Figure 420 Percent of Pu Np and Tc sorbed to the vial walls of the No Solids control samples under reducing conditions Each the 1 ppb and 10 ppb samples were prepared in triplicate and the error bars represent the standard deviations of triplicate samples 39
Figure 421 Iodine No-Solids Aqueous Fractions under Reducing Conditions I aqueous fractions of No-Solids controls after a one-day equilibration (1d) and four-day equilibration (4d) under reducing conditions The total concentration for each system was 100 ppb and 1000 ppb Samples were prepared in triplicate and the error bars represent the standard deviation 40
Figure 51 Comparison of Tc I Np and Pu sorption to Vault 2 solid under oxidizing and reducing conditions 42
Figure 52 Comparison of Tc I Np and Pu sorption to TR 545 solid under oxidizing and reducing conditions 43
Figure 53 Comparison of Tc I Np and Pu sorption to TR547 solid under oxidizing and reducing conditions 44
Figure 54 Comparison of Tc I Np and Pu sorption to Aged Cement under oxidizing and reducing conditions 45
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xiv
LIST OF ABBREVIATIONS
DDI water Distilled deionized water ICP-MS Inductively coupled plasma ndash mass spectrometer
Kd Distribution coefficient LSC liquid scintillation counting NOM Natural organic matter PA Performance Assessment ppb parts per billion ppq parts per quadrillion QAQC Quality AssuranceQuality Control SA Special Analyses SRNL Savannah River National Laboratory SRS Savannah River Site
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15
10 Introduction Performance Assessments (PA) are risk calculations designed to determine (1) the maximum
amount of radioactivity that can be safely buried in a subsurface facility and (2) the potential human risk associated with disposing of radioactive waste in a subsurface facility Special Analyses (SAs) are similar to PAs except that they are designed to address specific issues related to PAs such as a new discovery since the PA was issued Commonly parameters describing the extent that a radionuclide interacts with solids at the source vadose zone and aquifer influence the extent of calculated human risk The two parameters that the SRS use to represent radionuclidesolid interactions are Kd and apparent solubility values together these parameters are referred to as sorption values Sorption values vary with radionuclides groundwater chemistry and the type of solid phase (and for cementitious materials by the age of the material during the calculation) In this work Kd and apparent solubility values are reported for 99Tc 127I 237Np and 242Pu sorption to various cementitious formulations
20 Objectives
The objectives of this work were to 1 Determine the influence of cementitious formulation on technetium (Tc) iodine (I) neptunium
(Np) and plutonium (Pu) sorption under oxidizing conditions The specific formulations that were evaluated included 1) an aged cement recovered from a 30-year old outdoor concrete pad on the SRS 2) Vault 2 concrete 3) TR545 saltstone and 4) TR547 saltstone (additional details are presented in Section 30 Materials and Methods)
2 Measure Tc I Np and Pu sorption to the cementitious formulations under reducing conditions
30 Materials and Methods
31 Preparation of ICP-MS Standards Stock Solutions and Working Solutions
311 242Pu
A National Institute of Standards and Technology Standard Reference Material (NIST SRM 434H) was used to prepare a stock 242Pu solution by dilution in 2 Aristar Optima HNO3 All volume additions were monitored gravimetrically This working solution was then used to make a set of 001 005 1 2 5 10 parts per billion (ppb) standards by dilution using 2 HNO3 Again all volume additions were monitored gravimetrically These standards were used to calibrate the Thermo Scientific X Series 2 inductively coupled plasma ndash mass spectrometer (ICP-MS) for quantification of 242Pu A representative calibration curve for 242Pu is shown in Figure 31 The instrument performance was monitored using 209Bi 232Th and 238U as internal standards The recovery of each sample during analysis was corrected based on the internal standard recovery The internal standard recoveries remained within standard quality assurancequality control QAQC protocols for the instrument (between 80 and 120)
A 242Pu stock solution was prepared by dissolving 1mg of Pu(NO3)4 obtained as a Certified Reference Material from New Brunswick Laboratory (CRM 130) This CRM is gt999 242Pu by atom percent The CRM was dissolved in 20mL of 8M HNO3 (Aristar Optima Grade) Because no chemicals or heat have been introduced to manipulate the Pu oxidation state it can be assumed that Pu(IV) is the predominant oxidation state in this stock solution A working solution to be used in spiking 242Pu experiments was prepared by diluting 25 mL of the CRM stock solution with 100 mL 10 M Aristar Optima HNO3 The concentration of 242Pu in this stock solution was determined using ICP-MS calibrated using the NIST SRM standards The concentration of Pu in this stock solution was 1065 ppb The total Pu
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concentration was also determined using liquid scintillation counting using the isotopic ratios reported for CRM 130 These compared favorably with the ICP-MS results but are reported here as a rigorous standardization because the isotopic ratios of CRM 130 have not yet been certified
Figure 31 Screen capture of a typical 242Pu calibration curve using Thermo PlasmaLab software to control the data collection and analysis R2=0999872 Intercept Conc (Detection Limit) = 0000044 ppb
312 237Np
A National Institute of Standards and Technology Standard Reference Material (NIST SRM 4341) was used to prepare a stock 237Np solution by dilution in 2 Aristar Optima HNO3 All volume additions were monitored gravimetrically This working solution was then used to make a set of 001 005 1 2 5 10 ppb standards by dilution using 2 HNO3 Again all volume additions were monitored gravimetrically These standards were used to calibrate the Thermo Scientific X Series 2 ICP-MS for quantification of 237Np A representative calibration curve for 237Np is shown in Figure 32 The instrument performance was monitored using 209Bi 232Th and 238U as internal standards The recovery of each sample during analysis was corrected based on the internal standard recovery The internal standard recoveries remained within standard QAQC protocols for the instrument (between 80 and 120)
A compiled 237Np stock solution from the Environmental Engineering and Earth Science (EEampES) inventory (primarily purchased from Isotope Products Valencia CA) was evaporated to dryness then the residue was brought up in approximately 5mL 80 M HNO3 Then 10 M hydroxylamine hydrochloride (NH2OHHCl EMD Chemicals ACS grade) and water were added to achieve a 3M HNO303M NH2OHHCl solution This solution was purified by extraction chromatography using Eichrom TEVA resin packed in a Bio-Rad poly-prep column The 3M HNO303 M NH2OHHCl neptunium solution was loaded on a 2 mL column and washed with 3 column volumes of 3 M HNO3 The Np(IV) was eluted with 002 M HCl + 02 M HF The effluent was evaporated to dryness then redissolved in 10 M HNO3 Additional 10 M HNO3 was added to maintain a approximately 10 mL then the solution was evaporated to incipient dryness and redissolved in a 50 mL of 10 M HNO3 An aliquot of the stock solution was evaporated to dryness on a stainless steel planchet and counted on the EGampG Ortec Alpha Spectrometer (Octete PC Detectors) No other alpha energies besides 237Np were observed The approximate concentration was determined using liquid scintillation counting and little 233Pa was observed The fuming in HNO3 as performed at the end of the purification procedure will drive Np to the soluble pentavalent state This is the stable oxidation state of Np under the experimental conditions Therefore experiments performed here can be assumed to be initially Np(V) The exact Np
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concentration in this solution was determined using ICP-MS calibrated with a NIST standard as discussed in section 312 below
A 237Np working solution (Working Solution 1) was created by pipetting an aliquot of the 237Np stock solution into a 100 mL Nalgene Teflon bottle and diluting with 2 BDH Aristar Ultra HNO3 to give a working solution concentration of 820 ppb All volumes were monitored gravimetrically Analysis on the ICP-MS calibrated against NIST Standards as described below gave a concentration of 820 ppb in Working Solution 1
Figure 32 Screen capture of a typical 237Np calibration curve using Thermo PlasmaLab software to control the data collection and analysis R2=0999981 Intercept Conc (Detection Limit) = 0000026 ppb
313 99Tc
A 99Tc working solution was prepared by diluting a stock solution of 99Tc (from the EEampES inventory purchased from Isotope Products Valencia CA) in distilled-deionized water (DDI Resistivity gt18 MΩcm) The oxidation state of Tc was not measured However based on the aqueous concentration in the DDI water solution Tc(VII) is the expected oxidation state The reduced Tc(IV) oxidation state would not be soluble under these conditions The expected concentration of 950 ppb based on the dilution was verified using liquid scintillation counting The 99Tc working solution was used to make 001 005 1 2 5 and 10 ppb standards by dilution using 2 HNO3 These standards were used to calibrate the Thermo Scientific X Series 2 ICP-MS for quantification of 99Tc A screen shot of a representative calibration curve is shown in Figure 33 The instrument performance was monitored by interpolating between 89Y and 115In internal standards The recovery of each sample during analysis was corrected based on the internal standard recovery The internal standard recoveries remained within standard QAQC protocols for the instrument (between 80 and 120)
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Figure 33 Screen capture of a typical 99Tc calibration curve using Thermo PlasmaLab software to control the data collection and analysis R2=0999984 Intercept Conc (Detection Limit) = 0000013 ppb
314 127I
A 100 microgmL iodate (IO3-) stock solution from High Purity Standards (Charleston SC) was used
to make 1 5 10 50 and 100 ppb standards by dilution using the ldquotraprdquo solution (discussed in Section 32 below) These standards were used to calibrate the Thermo Scientific X Series 2 ICP-MS for quantification of 127I A screen shot of a representative calibration curve is shown in Figure 34 The use of a reducing basic trap solution for iodine analysis limits the number of available internal standards that can be used to monitor ICP-MS instrument performance during iodine analysis Experiments are underway to identify acceptable internal standards However the data presented in this work did not use any internal standards prior to rigorous testing and analysis of representative standards As with the analyses for all isotopes (Tc I Np and Pu) spiked QAQC samples were frequently analyzed throughout the analysis as a check on instrument performance While these values cannot be used to correct individual samples in the same manner that the internal standards can they can be used to ensure accurate measurements of each isotope In almost all cases QAQC standards were within 10 of the expected value Because the average internal standard recovery ranges between 80 and 120 for the ICP-MS the iodine QAQC standard appears to be acceptable However a significant amount of ongoing work is testing various internal standards to improve the accuracy of iodine analysis using ICP-MS In one experiment (discussed in detail below) the QAQC standards deviated by an average value of 195 This will be specifically discussed below
Because experiments were performed with 127I concentrations up to 1000 ppb the 100 microgmL (ppm) stock iodate solution from High Purity Standards was used as the working solution
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Figure 34 Screen capture of a typical 127I calibration curve using Thermo PlasmaLab software to control the data collection and analysis R2=0999991 Intercept Conc (Detection Limit) = 024 ppb
315 Cementitious Materials Selected for Experiments There were four cementitious materials selected for this sorption study The first referred to as Aged Cement is a 30 year old sample that does not contain any reducing slag The aggregate from the Vault 2 cement had its aggregate removed prior to conducted tests in an effort to make subsamples more uniform This was necessary because some of the aggregate were larger than the 05 g subsamples used in individual sorption tests The Vault 2 cementitious material contained 17 dry wt- reducing slag on a dry weight basis before the water was added to the mix (Table 31) The TR547 and TR545 saltstone formulations contain 45 dry wt- and 90 dry wt- reducing slag respectively
Table 31 Characteristics of saltstone formulations used in this work Kaplan et al (2008)
Sample Percent Reducing Slag (dry wt-) (c)
Percent Portland Cement
(dry wt-) (c)
Percent Fly Ash
(dry wt-) (c)
Percent Aggregatesand ( dry wt-) (c)
Reducing Equivalents
(microeqg)
Aged Cement 0 10 45 45 855 plusmn 101(a)
Vault 2 Cement 17 10 45 0 178(b)
TR547 45 10 45 0 607(b) TR545 90 10 0 0 681(b) Blast furnace slag 100 0 0 0 819(b) (a) Kaplan et al (2008) (b) Roberts and Kaplan (2009) (c) All percentages of saltstone formulations are reported on a dry weight percentage basis that is the weight of the ingredients before water was added (d) Based on Table 8 in Dixon et al (2008 SRNL-STI-2008-00421) which shows the following quantity (lbscu yd) for saltstone Vault 2 Mix 1 concrete formulation 201 cement (1271 wt-) 268 slag (1695 wt-) 447 silica fume (283 wt-) 1563 fly ash (989 wt-) 911 fine sand (5762 wt-) The large aggregate was removed before the sorption tests were conducted The large aggregate accounted for 75 wt- of the original field sample not the sample used in these test before water was added to the mix TR547 is referred to as the Baseline by Dixon et al (2008) and is described in more detail in Appendix C (Mix 2) by Dixon et al (2008) (Control-BFSPC) and 1 (Baseline)
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TR545 saltstone contains 90 reducing slag and it is Mix 1 in Dixon et al (2008) and is described as
ldquoA control mix will be based on the baseline mix modified by exclusion of the Class F fly ash Consequently the cementitious materials premix will be a mixture of 90 blast furnace slag and 10 Portland cement The degree of reaction will be much greater than with the normal premix and therefore should result in a lower porosity and a lower permeability This bounding test at 060 wcm ratio is expected to yield a hydraulic conductivity at or below the detection limit for the Mactec permeameter measurement system Therefore this test should demonstrate the lowest level of detection of the Mactec system as well as show a resolvable difference between measurements of the control mix and the control mix with the normal premix compositionrdquo
32 ICP-MS Detection Limits
The PlasmaLab software platform determines a detection limit for each isotope based upon the intercept concentration A new calibration curve was generated for each experimental run and curves were very similar Using representative calibrations curves the detection limits for each isotope were as listed in Table 32 Note the higher detection limit for 127I is primarily due to the higher background count rate observed on the instrument This is believed to be due to the minimum purity levels of chemicals required for the iodine ldquotraprdquo solution as discussed in Section 33 below Therefore experiments were run with initial iodate concentrations higher than Tc Np and Pu to maintain analytical sensitivity
Table 32 Detection limits for each isotope based on representative calibration curves generated in PlasmaLab software associated with the ICP-MS
33 Experimental Methods
The experimental methods used in this work followed closely those previously described for experiments examining radionuclide sorption to saltstone (Kaplan et al 2007 Kaplan et al 2008) Brief descriptions of each method are provided below
Preparation of Calcite Solution Using a hotstirring plate 10 L of distilled-deionized (DDI)
water was heated to 3-100C above room temperature Then 001 g CaCO3 (EM Science ACS grade) was added to the solution and the resulting suspension was mixed for 24 hours at the elevated temperature The solution was then vacuum filtered through a 045-microm filter to ensure no solid CaCO3 remained in solution
Preparation of 2 HNO3 Analysis of Tc Np and Pu on the ICP-MS required dilution in 2
HNO3 This was prepared by adding 28 mL of Aristar Optima HNO3 from a clean graduated cylinder (designated to 2 HNO3) into a 1 L volumetric flask (designated to 2 HNO3) partially filled with DDI water and then further diluted to volume
Preparation of Trap Solution for Iodine Analysis Analysis of I required the use of a reducing
basic solution that was capable of reducing iodate to iodine and holding the iodine in solution This minimized the loss of I during sample analysis A 1 L trap solution was prepared by weighing out 00500 g NaHSO3 (Fisher Scientific ACS Grade) on a calibrated Sartorous LA 230S scale and adding it to a 1L volumetric flask Then 40 mL of 25 ww tetramethylammonium hydroxide (Alfa Aesar electronic grade) and 10 mL CFA-C solution (Spectrasol Inc) were added to the volumetric flask via a calibrated 1000-5000 microL Eppendorf Research pipette The solution was then diluted to volume with DDI water
34 Experimental Protocol for Sorption Experiments under Aerobic Conditions
Falcon BlueMax 15mL polypropylene vials were labeled and weighed to within 0001 g on a calibrated Sartorious LA 230S scale The scale was then zeroed and 025 +- 001 g of a given solid were added to each tube and the weight was recorded to within 0001g
For each of the four solids three sets of triplicate samples were prepared The three sets of samples were used to allow for experiments to be run with varying concentrations of each isotope Target initial concentrations for 99Tc 237Np and 242Pu samples were 1 ppb 5 ppb and 10 ppb Target initial concentrations for the 127I samples were 100 ppb 500 ppb and 1000 ppb A set of no solids controls at initial concentrations of 1 ppb and 10 ppb for 99Tc 237Np and 242Pu and initial concentrations of 100 ppb and 1000 ppb 127I were also prepared by adding the calcite solution to pre-weighed pre-labeled centrifuge tubes as discussed above
The solids were equilibrated with the calcite solution before spiking with the radionuclides This was done by adding 10 plusmn 01 mL of calcite solution to each tube and recording the mass The samples were then placed on a Thermo Scientific shaker overnight After 24 hours the solutions were allowed to settle for 1 hour The pH was then measured and the samples were then centrifuged for 15 minutes at 8000 rpm to further separate the solids The aqueous phase was then decanted and 10 plusmn 01 mL of calcite solution was added to each tube The weight of the tube (labeled tube + solid + calcite solution) was measured to within 0001g During this washing process the pH was monitored and held steady throughout the process The pH ranged from 11-12 depending on the particular saltstone used During the experiments the exact pH for all samples at all equilibration times was measured and is reported in Appendix A and B
The resulting suspensions were then spiked with 127I 237Np 242Pu and 99Tc It is important to note that all four isotopes were added to the same vial Use of the ICP-MS to determine the concentration of each isotope allows for a single solution to contain all analytes of concern This allowed for a greater variability in the sample set and increased replicates as opposed to running individual sorption tests for each isotope For the systems with initial 99Tc 237Np and 242Pu concentrations of 10 ppb and initial 127I concentration of 100 ppb a 100 microL aliquot of each radionuclide working solution was added to the first three tubes for each solid The addition was made with the tube resting on a tared analytical balance so that the exact mass of each radionuclide solution added was recorded and the solution was gently swirled before the next radionuclide was added The 5 ppb 237Np 242Pu and 99Tc and 500 ppb 127I samples were prepared in the same manner but adding 50 microL of the respective spike solutions The final three tubes with initial 237Np 242Pu and 99Tc concentrations of 1 ppb and 100 ppb 127I were prepared by using 10 microL of the spike solutions for all four solids as well as a set of solid-free controls (No-Solids Controls) For clarity this experimental matrix is shown in Table 33 below
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Table 33 Experimental Matrix of Sorption Experiments under Aerobic Conditions
After spiking the radionuclides a precalculated amount of 10M NaOH was added to each sample
to counter the acidic radionuclide spike solutions and the pH of one of the triplicate samples was measured to ensure the proper pH range was reached The samples were then placed on and end-over-end shaker to mix at approximately 8 rpm After 24 hours the samples were removed from the shaker and the pH of each sample was measured using an Orion Ross semi-micro glass electrode calibrated against pH 4 7 and 10 buffers (Thermo) The samples were then shaken and a transfer pipette was used to transfer 35 mL of a homogenous suspension to a 5mL syringe The solution was then passed through a 100 nm nylon syringe filter The first 025-050 mL of filtrate was discarded and the remaining filtrate was collected in a clean polyethylene vial Then 10 mL of the filtrate was removed and diluted in 90 mL 2 HNO3 The mass of each phase was determined and recorded gravimetrically Then 10 mL of the remaining filtrate was transferred to a clean Falcon BlueMax 15mL vial and diluted with 90 mL of trap solution for 127I analysis Again the volume of each phase was monitored gravimetrically After the 24 hour sampling event the samples were put back on the shaker to mix for three additional days On day four the above sampling procedure was repeated
The 237Np 242Pu and 99Tc samples can be run on the Thermo Scientific ICP-MS using the standard setup and procedure which included a standard flow glass nebulizer and bulb spray chamber However for the 127I analysis the ICP-MS must be reconfigured to accommodate the basic reducing trap solution This is to alleviate problems with iodine signal stability over time frequently observed in ICP-MS analysis The reconfigured instrument uses an Elemental Science Microflow PFA-100 Teflon nebulizer with a flow rate of 100microLmin along with a sapphire torch and a Teflon spray chamber This configuration must be run with a low pump speed to prevent back pressure on the system Two 30 minute stability tests were performed using a 50 ppb iodate solution Each experiment consisted of 40 separate measurements After each experiment was completed the uncorrected mass counts were examined and found to stay steady over the sampling period The relative standard deviation ( RSD) over all samples for each experiment was 1866 and 1460 respectively This shows that there was no significant ldquomemoryrdquo or loss of the iodine signal over time and that the reconfigured instrument has a stable iodine signal over time However as will be discussed below some difficulty has been encountered in finding an adequate internal standard for iodine analysis
35 Experimental Protocol for Sorption Experiments under Anerobic Conditions In order to examine the effects of reducing conditions of sorption of each isotope to the various cementitious samples a series of sorption experiments were performed in an anaerobic glovebox under a 2 H2(g) 98 N2(g) atmosphere Based on the measured pH and EH of these systems as discussed below these systems were at the point of reducing water Therefore they are expected to represent a lower end of the possible range for reducing conditions expected in the porewater available within cementitious materials
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Preparation of Calcite for Reducing Conditions Approximately 35 L of DDI water was boiled for 45 minutes Argon was slowly bubbled through the water as it cooled Once it cooled to below 500C approximately 3 g of calcite was added This solution mixed overnight under a continuous Ar flow After 12 hours the solution was moved into an oxygen free glove bag for filtration as described in 3231 After filtration the calcite solution was moved into the glove box
Preparation of Working Solutions under Reducing Conditions The calcite and solid solutions
were prepared in the glove box using the previously mentioned procedure used under aerobic conditions The radionuclide working solutions were transferred to the glovebox and stirred open to the reducing atmosphere for at least three days The concentration of each isotope in the working solutions was measured to determine any change in the concentration due to evaporation while the solutions were equilibrating
The preparation and spiking of samples for sorption experiments was performed exactly as described for the oxidizing conditions except all sample handling was performed in the glovebox After the 1 day and 4 day equilibration the samples were filtered within the glovebox then transferred outside for dilution and ICP-MS analysis similar to the description provided about for the oxidizing conditions For these experiments only 4 mL of either 2 HNO3 or trap solution were used to dilute the filtrate instead of the 90 mL used above for experiments performed under oxidizing conditions
36 Examination of Sorption to Vial Walls for Solids and No Solids Controls
As will be discussed below the solid-free controls samples indicated significant loss of Np and Pu Once the one and four days samples were collected and run on the ICP-MS it was necessary to determine the degree each radionuclide was sorbing to the vial walls The remaining suspensions and controls were emptied into a waste container Then 5 mL of the calcite solution was added to each vial using a calibrated pipette The vials were sonicated for approximately one minute and then emptied into the waste container Another 5 mL of calcite solution was added for the second wash and then discarded into the waste container This procedure was expected to remove any soluble Pu from the system or Pu associated with colloidal particles After each vial was washed 10 mL of 2 HNO3 was added using a calibrated pipette The acid solution is expected to remove any Tc Np or Pu associated with the vial walls This procedure has been shown to complete mass balances of Pu in similar sorption experiments using Pu (Powell et al 2002) This process was performed for both the solid suspension and the no solids controls The samples were then run on the ICP-MS to determine the concentration of 99Tc 237Np and 242Pu sorbed to the vial walls
37 Data Analysis The solubilities of 242Pu and 237Np were calculated by using the formula
nuclide
nuclide
nuclideMSICP
sol Mg
gCC
)(10 6
microminus
minus
= (Equation 31)
Csol = observed nuclide solubility (molnuclidekgsolution) CICP-MS = aqueous concentration of nuclide from ICP-MS measurement (ppb micrognuclidekgsolution) Mnuclide = molecular mass of nuclide (gnuclidemolnuclide)
In order to determine the Kd values one first needs to determine the concentration on the solid by using
SRNL-STI-2009-00636 Revision 0
24
solid
calcitespikeaqspikecalcite
spikestock
solid m
mmCmmmC
C)(
)()(
+⎥⎥⎦
⎤
⎢⎢⎣
⎡minus
+
lowast
= (Equation 32)
Csolid = calculated solid phase concentration of the nuclide (ppb) Cstock = concentration of the nuclide stock solution (ppb) mspike = mass of nuclide spiked into the saltstone suspension (g) mcalcite = total mass of calcite solution used in the saltstone suspension (g) Caq = aqueous concentration of nuclide from ICP-MS measurement (ppb) msolid = mass of the saltstone used in the suspension (g)
The Kd can be calculated using the equation
aq
solidd C
CK = (Equation 33)
Kd = solid-water partitioning coefficient (gsolutiongsolid assuming density of 10 gmL traditional
unit of mLsolutiongsolid can be obtained) This Kd Equation (33) is numerically equivalent to the traditional Kd equation proposed in ASTM D-4646 which has been used in previous saltstone experiments (Kaplan et al 2007 Kaplan et al 2008)
40 Results and Discussion
41 Radionuclide Sorption to Cementitious Formulations under Oxidizing Conditions
Figure 41 shows Pu Kd values ranging from 104 to gt105 mLg Generally for each solid the Kd increases with increasing initial Pu concentrations typical behavior of systems where the aqueous concentrations of the radionuclides are solubility controlled This is not expected because the Kd expression indicates that the Kd value should remain constant with increasing total Pu concentrations It was noted that aqueous phase concentration of Pu remained relatively constant in all samples (see discussion below regarding Pu solubility) Therefore the sorption capacity of each solid phase for Pu has not been overcome For each of these solid phases it appears the solutions had reached equilibrium before the first samples were taken at 24 hours In each case the Kd values for the one day and four day are similar A trend between the solid phases is not discernible The aged cement with no reducing slag was expected to have the lowest Kd values but in actuality it has the highest Kd Also there is no correlation with the concentration of reducing slag The Vault 2 samples with 17 dry wt- reducing slag has a Kd similar to that of the TR547 (45 dry wt- slag) while the saltstone with the most slag TR545 (90 dry wt- slag) has the lowest Kd value Others have observed that Pu Kd values of cementitious materials are similar in the absence and presence of slag (Allard et al 1984 Hoaglund et al 1985)
It was observed that similar aqueous concentrations of Pu were observed regardless of the solid phase present Figure 42 shows the average aqueous phase concentrations measured after one day and four days for all solids As stated above triplicate samples were prepared for each solid phase and each initial concentration Therefore each of the reported solubility values in Figure 42 is an average of nine measurements Using the highest reported value with the expected maximum error (0018 ppb for solid TR545) the maximum expected aqueous concentration of Pu in the pore water associated with the
SRNL-STI-2009-00636 Revision 0
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saltstone formulations will be approximately 7 x 10-11 molL as calculated using Equation 31 This is on the same order as the solubility of Pu hydrous oxide solid phases (Neck and Kim 2001)
Figure 41 Plutonium Kd Values under Oxidizing Conditions Plutonium Kd values for various saltstone formulations measured after one-day equilibration (1d) and four-day equilibration (4d under oxidizing conditions Total plutonium concentrations in each system were 1 ppb 5 ppb and 10 ppb Sample prepared in triplicate and error bars represent standard deviation of samples except as follows value for dataset TR547-4d 10 ppb is reported based on duplicate samples
Figure 42 Plutonium solubility for various saltstone formulations measured after one-day equilibration (1d) and four-day equilibration (4d) under oxidizing conditions Total plutonium concentrations in each system were 1 ppb 5 ppb and 10 ppb as noted Samples prepared in triplicate and an average of all samples (9) was used to determine average solubility The error bars represent standard deviation of samples
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Overall the Kd values for Np range from 105 to gt106 with only a few outliers The most significant outlier is the 1 ppb solution in the TR545 sample after the four-day equilibration It drops two orders of magnitude while the 5 and 10 ppb solutions remain constant However this result is most likely an analytical artifact from working at the detection limits of the ICP-MS In the one-day equilibration samples only one of the triplicates S-2-E had detectable Np while in the four-day equilibration samples only S-2-F had detectable amounts present The graph also shows that with the exception of the 5 ppb sample in the aged cement Np sorption to TR545 (90 dry-wt- slag) and TR547 (45 dry wt- slag) have Kd values approximately one order of magnitude over the aged cement (no slag) and Vault 2 (17 dry wt- slag) samples
It was observed that similar aqueous concentrations of Np were observed regardless of the solid phase present Figure 44 shows the average aqueous phase concentrations measured after one day and four-day equilibrations for all solids As stated above triplicate samples were prepared for each solid phase and each initial concentration Therefore each of the reported solubility values in Figure 44 is an average of nine measurements of Np concentration unless stated otherwise Using the highest reported value with the expected maximum error (00026 ppb for solid TR545) the maximum expected aqueous concentration of Pu in the pore water associated with the saltstone formulations will be approximately 2 x 10-11 molL
Figure 43 Neptunium Kd values under oxidizing conditions Neptunium Kd values for various saltstone formulations measured after one-day equilibration (1d) and four-day equilibration (4d) under oxidizing conditions Total plutonium concentrations in each system were 1 ppb 5 ppb and 10 ppb as noted Samples prepared in triplicate and error bars represent standard deviation of samples except as follows value for datasets TR545-1d 1ppb TR545-4d 1 ppb TR547 4d 1 ppb TR545-4d 10 ppb TR547-1d 1ppb TR547-4d 10 ppb are reported based on a single sample and for dataset TR545-1d 5ppb is reported based on duplicate samples Kd values limited to gt106 were at instrumental background
The Kd values for Tc are significantly lower than that of Pu or Np As a whole the values are
comparable The values for the one-day and four-day equilibrations solutions in the Vault 2 (17 dry wt- slag) and TR545 (90 dry wt- slag) remained constant within reasonable error with just a slight increase from the one-day to four-day equilibration However the Aged Cement (no slag) and TR547 (45 dry wt- slag) showed a noticeable decrease from day one to day four (Figure 45)
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Figure 44 Average solubility of Np under oxidizing conditions Neptunium solubility for various saltstone formulations measured after one-day equilibration (1d) and four-day equilibration (4d) under oxidizing conditions Total Np concentrations in each system were 1 ppb 5 ppb and 10 ppb Samples prepared in triplicate and an average of all samples (9) was used to determine average solubility except as follows TR545-1d is based on 6 samples TR545- 4d on 5 samples TR547-1d on 7 samples and TR547- 4d on 5 samples The error bars represent standard deviation
Figure 45 Technetium Kd values under oxidizing conditions Tc Kd values for various saltstone formulations measured after one-day equilibration (1d) and four-day equilibration (4d) under oxidizing conditions Total Tc concentrations in each system were 1 ppb 5 ppb and 10 ppb as noted above Samples were prepared in triplicate and the error bars represent standard deviation of samples except as follows data sets for Vault 2-1d 1ppb were duplicates and TR547- 4d 10 ppb is based on a single dataset
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Similar to the Tc Kd values the 127I Kd values are much lower than those of Pu and Np The amount of reducing slag present in each of the solids does not appear to have a drastic effect on the 127I Kd values In fact the initial (one day) Aged Cement (0 slag) samples had a Kd almost two orders of magnitude above those with reducing slag The cause of this behavior is not known but it has been shown that iodate IO3
- the oxidized form of iodine sorbs more strongly than iodide I- to charged surfaces (Schwehr et al 2009 Yoshida et al 1992 Fukui et al 1996) It is possible that the slag is reducing the iodine to the I- form converting it to a species that is less likely to sorb to saltstone Additional work would be required to confirm the oxidation state of iodine when associated with saltstone
Figure 46 Iodine Kd Values under Oxidizing Conditions Iodine Kd values for various cementitious formulations measured after one-day equilibration (1d) and four-day equilibration (4d) under oxidizing conditions Total iodine concentrations in the systems were 100ppb 500 ppb and 1000 ppb as noted above Samples were prepared in triplicate and the error bars represent standard deviation of samples except as follows duplicates were used for dataset TR545- 1d 100ppb
42 Radionuclide Sorption to Vial Walls Under Oxidizing Conditions
Figure 47 shows the aqueous fractions found in the no-solids controls It provides a measure of the solubility of each radionuclide as well as examines the fraction of each radionuclide sorbed to the vial walls After one day only 25 of the Pu remained in solution and the concentration decreased even more after four days The loss of Pu from the aqueous phase may be due to sorption of Pu to the vial walls or precipitation of a Pu hydrous oxide solid (discussed with respect to Figure 49 below) Additional experiments would be required to examine the solubility of the Pu in high pH calcite saturated solutions
After one day about 80 of the Np remained in solution However the aqueous concentration in the initially 1-ppb solution was significantly reduced after four days Approximately 60 of the Np remained soluble in the initially 10-ppb solution Once again this drop could be due to sorption to the vial wall The Tc present after one day ranged from about 88 to about 95 and was virtually 100 after four days These values are consistent with internal standards used to monitor Tc detection performance on the ICP-MS Greater than 50 of the I remained in solution after the one-day and four-day equilibrations As shown in Figure 48 the standard deviation between the triplicate I control samples was
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quite large Additional control samples are required to understand the mechanism by which I is being lost from the aqueous phase in these samples
Figure 47 Plutonium Neptunium and Technetium Aqueous Fractions Fraction of Pu Np and Tc remaining in the aqueous phase for the No Solids controls after a one-day equilibration (1d) and four-day equilibration (4d) under oxidizing conditions The total concentration for each radionuclide 10 ppb as noted above Samples were prepared in triplicate and the error bars represent the standard deviation of the samples
Figure 48 Iodine Aqueous Fraction Iodine aqueous fraction for the no-solids controls after a one-day equilibration (1d) and four-day equilibration (4d) under oxidizing conditions The total concentration of iodine was 1000 ppb as noted above Samples were prepared in triplicate and the error bars represent the standard deviation of the samples
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As discussed above the loss of Np and Pu from the no-solids control (Figure 47) could be due to
precipitation of Np and Pu hydrous oxides or sorption to the vial walls To quantify the differences between these possible sinks the vials were washed as described in Section 36 The data in Figure 49 indicate that significant sorption of Np and Pu to the vial walls may occur When combining the mass of Np represented in Figure 47 and Figure 49 there is almost 100 mass recovery of the Np sorbed to the vial wall and the aqueous fraction measured Therefore no precipitation of Np is expected However because 100 recovery was not achieved for Pu a Pu hydrous oxide phase could be precipitating which was washed out of the vial during the cleaning procedure The data in Figure 47 represent the no-solids control samples where there was no solid phase present for Np or Pu to sorb to besides the vial walls However when a cementitious solid phase is present in the sample there will be competition between the vial walls and the cement for sorption of Np and Pu Based on the affinity of metals for metal oxide surfaces as opposed to the polypropylene surface and the much higher surface site density expected for the cementitious samples it is assumed that the cementitious samples will out-compete the vial walls for sorption sites This thesis was tested by taking one of the triplicate samples from each sorption experiment with a solid phase present removing the solid phase from the tubes and leaching any sorbed Np and Pu from the tubes with acid as described in Section 36 Figure 410 and Figure 411 show that although some of the Pu and Np sorbed to the vial walls of the samples this amount accounted for less than 2 in all samples Therefore sorption of Np and Pu to the vial walls does not appear to be a significant factor in experiments where the solid phase is present Note these results do not discount the possibility that Pu hydrous oxide precipitates were forming in both the no-solid control experiments and experiments with cement formulations present Based on the observation of a constant aqueous phase concentration of Pu regardless of the initial Pu concentration the presence of a solubility limiting Pu phase cannot be discounted based on these data Further experiments examining the solubility of Pu in high pH calcite saturated solutions are required
Like Pu Np shows little affinity for the vial walls in the presence of a solid phase In each case tested there was significantly less than 1 of the total Np sorbed to the vial walls This behavior is consistent with the ~100 mass balance on Np achieve in the solid-free controls The majority of Np remained soluble in the solid-free control experiments Therefore it is expected that sorption of Np to the vial walls was the primary reason for the loss of Np from the aqueous phase in the no-solids systems rather than precipitation of a Np solid phase similar to the process discussed for Pu above This assumption is based on the relative solubility of Np(V) as compared with Pu(IV)
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Figure 49 Percent Pu and Np sorbed to vial walls of the no solids controls after the aqueous phases were discarded and the vials were washed Both the 10 ppb and 1 ppb datasets were prepared in triplicate and the error bars show the standard deviation
Figure 410 Percent Pu sorbed to vial walls after the solids and aqueous phases were removed and the vials were washed The graph illustrates one sample from each of the 1 ppb 5 ppb and 10 ppb systems Therefore no error bars are present
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Figure 411 Percent Np sorbed to vial walls after the solids and aqueous phases were removed and the vials were washed The graph illustrates one sample from each of the 1 ppb 5 ppb and 10 ppb systems Therefore no error bars are present
43 Radionuclide Sorption to Cementitious Formulations under Reducing Conditions
Similar to the Pu Kd values under oxidizing conditions Pu Kd values ranged from 104 to gt105 under reducing conditions (Figure 412) Also similar to the results under oxidizing conditions the Kd increases with increasing initial Pu concentration Again this behavior is indicative of the aqueous phase concentration of Pu being controlled by solubility of Pu rather than by sorption In each case the samples appeared to reach steady state within 24 hours This equilibration is evident because the Kd values after one day and four days are very similar Also it appears that the amount of reducing slag does not make a significant difference in the Kd value In fact the TR547 solid consists of 45 reducing grout but produces approximately the same Kd values of the aged cement which does not have any reducing grout Each of these Kd values are higher than the TR545 which is 90 reducing grout These findings are in agreement with those conducted by Allard et al (1984) and Hoglund et al (1985) who reported that concrete containing reducing agents (slag similar to that used in our study) did not have greater Pu Kd values than those that did not contain slag
Similar aqueous concentrations of Pu were observed regardless of the solid phase present Figure 36 shows the average aqueous phase concentrations measured after one day and four days for all solids As stated above triplicate samples were prepared for each solid phase and each initial concentration Therefore each of the reported solubility values in Figure 412 is an average of up to nine measurements of the Pu aqueous concentrations Using the highest reported value with the expected maximum error (00045 ppb for solid Vault 2) the maximum expected aqueous concentration of Pu in the pore water associated with the cementitious formulations will be approximately 2 x 10-11 molL (calculated from Equation 31) This value is on the same order as the solubility of Pu hydrous oxide solid phases (Neck and Kim 2001) A best value would be 10-12 molL
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Figure 412 Pu Kd Values under Reducing Conditions Plutonium Kd values for various cementitious formulations measured after one-day equilibration (1d) and four-day equilibration (4d) under reducing conditions Total plutonium concentrations in each system were 1ppb 5 ppb and 10 ppb Samples prepared in triplicate and error bars represent standard deviation
Figure 413 Average Solubility of Plutonium under Reducing Conditions Plutonium solubility for various cementitious formulations measured after one-day equilibration (1d) and four-day equilibration (4d) under reducing conditions Total plutonium concentrations in each system were 1ppb 5 ppb and 10 ppb as noted Samples prepared in triplicate and an average of all samples (9) was used to determine average solubility The error bars represent standard deviation of samples
The Np Kd values reported in Figure 414 obtained under reducing conditions are very similar to
those obtained under oxidizing conditions In each case the samples appeared to reach steady state within 24 hours This equilibration is evident because the Kd values between the one-day and fourndashday equilibrations are similar As was the case with Pu the amount of slag present in each solid does not
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seem to have a significant effect on the Kd values Again the aged cement with no slag has as high a Kd as the TR545 with 90 reducing slag
Similar aqueous concentrations of Np were observed regardless of the solid phase present Figure 314 shows the average aqueous phase concentrations measured after one day and four days for all solids All Kd values were gt 105 mLg which is considerably larger than those reported by Kaplan and Coates (2007) who reported Np Kd values to 1300 to 1600 mLg This difference can be attributed to two important experimental differences 1) the experiment was designed to permit larger Kd values to be measured (eg solid to liquid ratios and spike concentrations) and more importantly 2) a more sensitive analytical method ICP-MS was used instead of conventional low-energy gamma spectroscopy or liquid scintillation counting (LSC) analysis As stated above triplicate samples were prepared for each solid phase and each initial concentration Therefore each of the reported solubility values in Figure 415 is an average of up to nine measurements Using the highest reported value (to provide the most conservative most soluble values) with the expected maximum error (00045 ppb for solid TR545) the maximum expected aqueous concentration of Np in the pore water associated with the cementitious formulations will be approximately 2 x 10-11 molL A best value taking into consideration the less-than values which are depicted in Figure 414 as running off the top of the plot would be 10-12 molL
Figure 414 Np Kd Values under Reducing Conditions Neptunium Kd values for various cementitious formulations measured after one-day equilibration (1d) and four-day equilibration (4d) under reducing conditions Total Np concentrations in each system were 1 ppb 5 ppb and 10 ppb Samples were prepared in triplicate and the error bars represent standard deviation Kd values limited to gt106 were at instrumental background
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Figure 415 Average Solubility of Neptunium under Reducing Conditions Neptunium solubility for various cementitious formulations measured after one day equilibration (1d) and four day equilibration (4d) under reducing conditions Total plutonium concentrations in each system were 1ppb 5 ppb and 10 ppb Samples prepared in triplicate and an average of all samples (9) was used to determine average solubility The error bars represent standard deviation
A plot of the Tc Kd values for each cementitious formulations under reducing conditions is shown
in Figure 416 (log y-axis) and Figure 417 (reduced scale linear y-axis) The Kd values for each of the initial Tc concentrations are relatively similar This behavior is consistent with the Kd expression However the increasing Kd values from the one-day to four-day day equilibrations for each solid indicate that steady state was not reached within one day and it is unclear whether steady state was reached after four days A possible explanation for this behavior is that Tc(VII) was being reduced to Tc(IV) in these systems due to the reducing conditions As Tc(VII) was reduced the Kd would increase based on the high affinity of Tc(IV) for solid phases This proposed mechanism was observed by Lukens et al (2005) using an SRS saltstone material similar but not identical to TR547 Using synchrotron X-ray absorption fine structure spectroscopy they observed over a 453 month period that Tc(VII) incorporated into SRS saltstone slowly converted to Tc(IV) and that the nearest neighbor was initially predominantly oxygen and eventually became predominantly sulfur (described as a Tc(IV) phase TcSx) Lacking in Lukens et al (2005) is quantification of the solubility of Tc This analysis still needs to be completed along with re-oxidation studies (ie what is the rate that reduced Tc reoxidizes under ambient natural saltstone conditions)
Unlike Np and Pu Tc Kd values changed with the amount of slag included in the formulation Tc Kd values noticeable increase as the amount of slag in the formulation increased TR547 (45 dry-wt- slag) Kd value is visibly higher than the Aged Cement and Vault 2 Kd values while the most reducing TR545 (90 dry wt- slag) Kd value is significantly higher than the others Following a similar trend the reduction capacity that is the total quantity of reductant in the saltstone on a mass basis (units of milli-equivalents of charge per g) of TR547 had slightly greater or equal reduction capacity to that of TR545 (Roberts and Kaplan 2009)
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Figure 416 Tc Kd Values under Reducing Conditions Tc Kd values for various cementitious formulations measured after one-day equilibration (1d) and four-day equilibration (4d) under reducing conditions Total Tc concentrations in each system were 1 ppb 5 ppb and 10 ppb Sample prepared in triplicate and error bars represent standard deviation except as follows TR547-1d 1 ppb is based on a single dataset and datasets Vault 2-1d 5 ppb Vault 2- 4d 1 ppb Aged Cement-1d 5 ppb and Aged Cement-4d 1 ppb are duplicates
Figure 417 Data from Figure 416 replotted on a reduced linear scale for easier viewing Each sample was prepared in triplicate except as follows TR547-1d 1 ppb is based on a single dataset Vault 2-1d 5 ppb Vault 2- 4d 1 ppb Aged Cement-1d 5 ppb and Aged Cement-4d 1 ppb are duplicate datasets
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The calculated Kd values for I sorption to cementitious samples under reducing conditions are shown in Figure 418 Before discussing the data it should be noted that spiked QAQC samples which were analyzed on the ICP-MS along with the samples used to generate the data in Figure 418 were off by an average of 195 with one outlier of approximately 40 This dataset did not include the use of internal standards as discussed in Section 31 above1 Due to a lack of an internal standard the iodine results presented in this report should be considered with a minimum error estimate of 20
The iodine Kd values under reducing conditions are different from those observed under oxidizing conditions Under oxidizing conditions it appears they are at a steady state by day one However under reducing conditions there is a noticeable difference between days one and four indicating steady state was not reached by day one and possibly not by day four Another interesting observation is that the Kd values are decreasing from day one to four A possible reason for this behavior may be due to redox chemistry of iodine in this system If iodine partially or entirely exists in the form as iodate (IO3
-) it is possible it could be reduced to iodide I- within the reducing cementitious system These two iodine species sorb differently iodate sorbing to minerals more strongly than iodide (Denham et al 2009 Schwehr et al 2009 Fukui et al 1996 Yoshida et al 1992) It is hypothesized that the reducing environment of the saltstone is sufficient to reduce iodate ions to the more weakly binding form of iodine iodide
This is one of the few datasets (along with Tc) in this study where there may be a difference between the various solids The degree of iodate reduction would be expected to increase as the slag content increases As mentioned above reduction of iodate to iodide should result in a decrease in sorption Therefore higher Kd values should be observed for solids with less slag such as the Aged Cement (0 dry wt- slag) and Vault 2 (17 dry wt- slag) This is generally the case in Figure 418 where the highest Kd values are reported for the Aged Cement and the lowest values are for solid TR547 However this trend does not hold completely where the saltstone sample containing 90 slag (TR545) has generally equal or higher Kd values than the saltstone containing 45 dry wt- slag (TR547)
1 Clemson University is presently investigating appropriate internal standards for iodine analyses for ICP-MS Of those tested rhenium and molybdenum have shown some promise
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Figure 418 Iodine Kd Values under Reducing Conditions I Kd Values for various cementitious formulations measured after one day equilibration (1d) and four day equilibration (4d) under reducing conditions Total iodine concentrations in each system were 100 ppb 500 ppb and 1000 ppb as noted Sample prepared in triplicate and error bars represent standard deviation of samples except as follows Vault 2-4 d 100 ppb is a single dataset while the datasets for Vault 2-1 d 100 ppb 4 d 1000 ppb TR545-4 d 1000 ppb 100 ppb TR547-4 d 1000 ppb 500 ppb 100 ppb and Aged Cement- 4 d 1000 ppb and 100 ppb are all based on duplicates
44 Radionuclide Sorption to Vial Walls under Reducing Conditions
The aqueous concentrations for Pu Np and Tc in the no solids controls are shown in Figure 419 The results are similar to those presented for experiments performed under oxidizing conditions above The 1 ppb Pu aqueous fraction is approximately three times greater than the 10 ppb fraction at day one This fraction decreases over time and by day four they are approximately equal when taking error into account This behavior is similar to the aqueous fraction under oxidizing conditions The 1 ppb Np aqueous fraction is significantly higher on both day one and day four than the aqueous fraction of the 10 ppb samples However each remained constant from day one to day four The 10 ppb aqueous fraction is twice as low as under oxidizing conditions which suggests either higher sorption to the vial walls or more precipitating out under the reducing conditions Like Pu and Np Tc shows a decrease from day one to day four especially for the 1 ppb samples The decrease in the 10 ppb sample is minimal and the aqueous fraction remains around 09 This value is slightly lower than that under oxidizing conditions
To examine the degree of sorption to the vial walls the tubes were washed again as performed for the experiments under oxidizing conditions above and similar results were found Ninety percent of the 1 ppb Pu sample was sorbed to the vial wall upon completion of the experiment which gives a 100 mass recovery when comparing this value to that found in Figure 419 However this result is not the case with the 10 ppb samples where approximately 75 of the mass remains unaccounted It is noteworthy that approximately 25 of the Pu from the 10 ppb solution sorbed to the vial walls under both oxidizing
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and reducing conditions Np follows the same trend as Pu while less than 005 of the Tc sorbed to the wall
Figure 419 Plutonium Neptunium and Technetium No-Solids Aqueous Fractions under Reducing Conditions Pu Np and Tc aqueous fractions of No Solids controls after a one-day equilibration (1d) and four-day equilibration (4 d) under reducing conditions Total concentration for each radionuclide was 1 ppb and 10 ppb Samples were prepared in triplicate and the error bars represent the standard deviation
Figure 420 Percent of Pu Np and Tc sorbed to the vial walls of the No Solids control samples under reducing conditions Each the 1 ppb and 10 ppb samples were prepared in triplicate and the error bars represent the standard deviations of triplicate samples
Under reducing conditions the fraction of I remaining in the aqueous phase was around 90 with
almost 100 mass recovery of the 100 ppb I after the four-day equilibration These graphs show that
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under reducing conditions there will only be a small fraction of I sorbing to the vial wall or coming out of solution This result is a much better mass recovery than under oxidizing conditions (Figure 48) which had a mass recovery of approximately 65 after four days This result is also consistent with the interpretation that there may be a iodine speciation change between the two redox treatments
Figure 421 Iodine No-Solids Aqueous Fractions under Reducing Conditions I aqueous fractions of No-Solids controls after a one-day equilibration (1d) and four-day equilibration (4d) under reducing conditions The total concentration for each system was 100 ppb and 1000 ppb Samples were prepared in triplicate and the error bars represent the standard deviation
50 Comparison of Radionuclide Sorption under Oxidizing and Reducing Conditions
In the following figures (Figure 51 through Figure 54) the data shown above has been replotted to allow comparison between the oxidizing and reducing conditions for each cementitious formulation General observations based on these data follow Vault 2 Observations (Figure 51)
bull Pu Kds are greater than 104 under both oxidizing and reducing conditions and Pu Kds are slightly lower under reducing conditions This could possibly be due to reduction of Pu(IV) to Pu(III) However no oxidation state analysis was performed in this work
bull Np Kds are generally greater than 104 under both oxidizing and reducing conditions Interestingly Np Kds are higher under reducing conditions by almost an order of magnitude This could possibly be due to reduction of Np(V) to Np(IV) However no oxidation state analysis was performed in this work
bull Regardless of the initial Np or Pu concentration similar aqueous phase concentrations of Np or Pu were observed in all samples This trend indicates that ldquosorptionrdquo of Np and Pu in these systems may be a combination of adsorption absorption and (co)precipitation processes
bull Tc appears to reach a steady state within four days under oxidizing conditions This behavior does not appear to be the case under reducing conditions After four days similar Kd values are reached under both oxidizing and reducing conditions It is unclear
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whether the Kd value of Tc will continue to increase under reducing conditions consistent with reduction of Tc(VII) to Tc(IV) The similarity in Kd values under both oxidizing and reducing conditions is an interesting observation and certainly warrants additional studies
bull I Kd values are similar under both oxidizing and reducing conditions However reducing condition systems may not be at steady state after four days while systems under oxidizing conditions appeared to reach a steady state The difference in rates may be due to reduction of iodate to iodine
bull For all isotopes examined the sorption behavior to each of the solid phases is very similar
TR545 and TR547 Observations (Figure 52 and Figure 53) bull Similar to the discussion above with respect to Vault 2 Pu Np and Tc all appear to reach
a steady state under oxidizing conditions and approach steady state slower under reducing conditions
bull Np and Pu Kd values are greater than 104 for all systems and time steps The aqueous phase concentrations of Np and Pu appear to be better described as a solubility in terms of the aqueous phase concentration of Np and Pu Similar aqueous phase concentrations of both Np and Pu were reached The data indicate that the initial Np and Pu concentration generally does not affect the aqueous phase concentration at an apparent steady state The presence of each solid phase appears to limit the aqueous phase concentration of both Np and Pu on the order of 10-11 molL
bull Tc shows significantly higher Kd values under reducing conditions versus oxidizing conditions
bull For all isotopes examined the sorption behavior to each of the solid phases is very similar
Aged Cement Observations (Figure 54) bull Pu appears to be close to steady state for each solid by day one with similar Kd values
reached on between day one and day four bull Np has a higher Kd under reducing conditions than oxidizing (105 under oxidizing
conditions and gt105 under reducing conditions) bull Neither set of Tc data was at steady state by day one and rates of sorptiondesorption
reactions appear to be different Tc Kds decrease from day one to four under oxidizing conditions but increase under reducing conditions
bull The Kd values for I under oxidizing conditions were considerably higher than those measured for I with any other solid Similar Kd values obtained for the same solids under reducing conditions indicate that the reported Kd values under oxidizing conditions appear to be suspect However analysis of the raw data gives no indication of an experimental artifact As discussed above these observations may be explained based upon the amount of slag contained within the solids which will affect the reducing capacity (ie No reducing slag is in the aged cement which could be reason the reduction of iodate to iodide (speculated in other samples) is not evident)
bull The difference in sorption behavior of iodine to the aged cement between oxidizing and reducing conditions also indicates that the reducing conditions of the solution may affect I redox behavior in addition to any reactivity expected in the solid phases
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Figure 51 Comparison of Tc I Np and Pu sorption to Vault 2 solid under oxidizing and reducing conditions
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Figure 52 Comparison of Tc I Np and Pu sorption to TR 545 solid under oxidizing and reducing conditions
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Figure 53 Comparison of Tc I Np and Pu sorption to TR547 solid under oxidizing and reducing conditions
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Figure 54 Comparison of Tc I Np and Pu sorption to Aged Cement under oxidizing and reducing conditions
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60 Comparison of Radionuclide Sorption and Solubility under Oxidizing and Reducing Conditions
To further summarize the data the following tables provide either the average solubility
(for Np and Pu) or average Kd (for Tc and I) determined under both oxidizing and reducing conditions for each cementitious formulation Each table lists the average value standard deviation and the number of replicate samples used to calculate the reported values
The solubility of Pu in the presence of each solid under oxidizing and reducing conditions is shown in Table 61 (this is taken from experiments equilibrated for four days not one day) Under oxidizing conditions the apparent solubility values associated with the Aged Cement (0 dry wt- slag) Vault 2 (17 dry wt- slag) and TR547 (45 dry wt- slag) are all similar with only a slight increase in solubility as the amount of reducing slag increases There is a significant increase of almost an order of magnitude for the most reducing saltstone TR545 (90 dry wt- slag) However these samples also have a standard deviation on the same order of magnitude as the solubility itself which when taken into account brings the solubility back into the range of the others Under reducing conditions the apparent solubility values are slightly lower than under oxidizing conditions In this set of samples the Vault 2 saltstone with 10 dry wt- reducing slag had the highest apparent solubility but once again when considering the standard deviation the values are similar
Table 61 Comparison of plutonium apparent solubility values under oxidizing and reducing conditions
Table 62 lists the apparent solubility values of Np in the presence of each cementitious
formulation under both oxidizing and reducing conditions Under oxidizing conditions the cementitious formulation does not appear to have a dramatic effect on the solubility The apparent solubility values are similar to those of Pu under similar conditions except the Np standard deviations are much higher The high standard deviations are an analytical artifact since the measured concentrations were close to or at the detection limit of the ICP-MS There does appear to be a slight decrease in Np solubility under reducing conditions However the statistical significance of this decrease was not calculated
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Table 62 Comparison of neptunium apparent solubility values under oxidizing and reducing conditions
Unlike the apparent solubility values of Pu and Np the aqueousatmospheric conditions
and cementitious formulation seem to have an effect on the Tc Kd values (Table 63) Under oxidizing conditions there is not a discernible difference among the different cementitious formulations especially when taking the respective standard deviations into account However when experiments were run under reducing conditions the specific formulation had a noticeable effect The two saltstone samples with the least amount of reducing slag Aged Cement (0 dry-wt- slag) and Vault 2 (17 dry wt- slag) had Kd values which were similar to those observed under oxidizing conditions However the TR547 (45 dry-wt- slag) increased by almost an order of magnitude while the TR545 (90 dry wt- slag) increased by about three orders of magnitude Although the respective standard deviations are large the higher Kd values do appear to be significant
Table 63 Comparison of technetium Kd values under oxidizing and reducing conditions
Unlike Tc I does not seem to be as affected by cementitious formulation and redox status (Table 64) The only treatment (possible outlier) that does not follow this trend is the Aged Cement under oxidizing conditions This Kd value is higher than the others but also has a much higher standard deviation which when accounted for gives a value similar to the others All other treatments had near identical Kd values irrespective of solid phase or redox condition But again the Aged Cement data cannot be discounted at this time given the possibility of the influence that redox may have on iodine speciation and the strong influence I speciation has on sorption to cementitious materials
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Table 64 Comparison of iodine Kd values under oxidizing and reducing conditions
71 Comparison with Previous Data The increased sensitivity of the ICP-MS over conventional low-energy gamma
spectroscopy or liquid scintillation counting (LSC) analysis allowed for much more accurate Kd values and apparent solubility values in this work than were previously obtainable Generally radioanalytical detection methods start with activities on the order of 103 to 104 counts per minute (cpm) and approach background levels of 1 to 5 cpm for strongly sorbing radionuclides Therefore the accuracy of the Kd value will be the difference in analytical sensitivity when the initial aqueous activity decreases by a factor of approximately 5000 (ie the aqueous activity drops from approximately 5000 cpm to the instrument background of 1 cpm following almost complete sorption) As a result the reported Kd values can only be reliably reported up for a Kd of 103 to 104 This constraint is believed to be the difference between the observed Kd values for 237Np of gt 105 observed in this work when compared with the Kd values between 3000 and 4000 reported by Kaplan et al (2008) A similar observation was made for Pu because 242Pu was used for ICP-MS analysis and 238Pu was used in the work of Kaplan et al (2008) This constrint may account for the different Kd value of gt104 reported in Kaplan et al (2008) compared with the value of gt105 observed in this work
In the case of Tc Kaplan et al (2008) reported a Kd of 023 mLg for Vault 2 under oxidizing conditions and 093 mLg under reducing conditions while the above experiment determined the Vault 2 Kd to be 505 mLg under oxidizing conditions and 557 mLg under reducing conditions Unlike the discrepancy in the Kd values for Np Pu and Tc between the above findings and those in Kaplan et al (2008) the reported Kd values for iodine are similar For Vault 2 Kaplan et al (2008) found 125I to have a Kd of 894 mLg under oxidizing conditions and 715 mLg under reducing conditions These values are similar to the Kd values of 766 mLg and 725 mLg observed under oxidizing and reducing conditions respectively in this work These findings appear to confirm the previously accepted Kd values of 0-10 mLg depending on the cementitious formulation
72 Suggested Future Work The above data demonstrate several areas that require further examination The
increasing Tc Kd values over time dataset suggest that steady state had not been achieved It would be beneficial to determine the amount of time required to reach steady state and allow determination of a more accurate Kd value (an assumption of the Kd construct is that it be measured at steady state) Also kinetic studies of both Tc and I are needed to better understand their respective interactions with the different cementitious formulations As for the I additional
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tests should be performed to test the hypothesis that iodine may in part exist as iodate which may initially sorb to the saltstone then undergo reduction to iodine or iodide and then desorbs causing a decrease in Kd
A final area of future work is to examine the possible causes for the similar behavior of each cementitious formulation despite the different slag content This discrepancy is not only observed in the above experiments but also in Kaplan et al (2008) which is illustrated in Table 31 and by recent work in measurements of saltstone reduction capacity (Roberts and Kaplan 2009) The reduction capacity (units in milli-equivalentsg solid) equivalents of the Aged Cement with no slag is 855 plusmn 101 and adding 10 slag gives a reducing equivalent of 2398 plusmn 311 However increasing the slag content to 23 causes the reducing capacity to increase to 8218 plusmn 81 which is almost equivalent to the 8324 plusmn 49 of the 100 slag Understanding the chemistry behind the reducing capacity of each cementitious formulation will help to define what reactions are important for controlling radionuclide release from the saltstone
80 References Allard B L Eliasson S Hoglund and K Andersson 1984 ldquoSorption of Cs I and actinides in
concrete systemsrdquo SKB Technical Report SKBKBS TR-84-15 DKB Stockholm Sweden
Denham M D I Kaplan and C Yeager2009 ldquoGroundwater radioiodine Prevalence biogeochemistry and potential remedial approachesrdquo SRNL-STI-2009-00463 Savannah River National Laboratory Aiken SC
Dixon K L M A Phifer and J R Harbour 2008 ldquoFY09 PACA Maintenance Program Additional Saltstone Property Testingrdquo SRNL-L3100-2009-00019 Rev0 Savannah River National Laboratory Aiken SC
Fukui M Fujikawa Y and Satta N 1996 ldquoFactors affecting interaction of radioiodide and iodate species with soilrdquo Journal of Environmental Radioactivity 31 199-216
Hoglund S L Eliasson B Allard K Andersson and B Torstenfelt 1985 ldquoSorption of some fission products and actinides in concrete systemsrdquo Mat Res Soc Symp Proc 50 683-690
Kaplan D I 2007 Geochemical Data Package for Performance Assessment Calculations Related to the Savannah River Site WSRC-TR-2006-00004 Rev 1 Washington Savannah River Company Aiken SC
Kaplan D I and Coates J 2007 ldquoPartitioning of Dissolved Radionuclides to Concrete under Scenarios Appropriate for Tank Closure Performance Assessmentsrdquo WSRC-STI-2007-00640 Rev 0 Washington Savannah River Company Aiken SC 29808
Kaplan D I Roberts K Coates J Siegfried M Serkiz S 2008 ldquoSaltstone and concrete interactions with radionuclides Sorption (Kd) desorption and reduction capacity measurementsrdquo SRNS-STI-2008-00045 Savannah River National Laboratory Aiken SC 2008
SRNL-STI-2009-00636 Revision 0
50
Neck V and Kim J I 2001 ldquoSolubility and hydrolysis of tetravalent actinidesrdquo Radiochim Acta 89 1
Powell B A Fjeld R A Coates J T Kaplan D I Serkiz S M 2002 ldquoPlutonium Oxidation State Geochemistry in the SRS Subsurface Environmentrdquo WSRC-TR-2003-00035 Westinghouse Savannah River Company US DOE Savannah River Site Aiken SC
Roberts K A and D I Kaplan 2009 Reduction Capacity of Saltstone and Saltstone Componentsrdquo SRNL-STI-2009-00637 Rev0 Savannah River National Laboratory Aiken SC
Schwehr K A Santschi P H D I Kaplan C M Yeager and R Brinkmeyer 2009 ldquoOrgano-iodine formation in soils and aquifer sediments at ambient concentrationsrdquo Environ Sci Technol 437258-7264
Yoshida S Muramatsu Y and Uchida S 1992 ldquoStudies on the sorption of I-(iodide) and IO3-
(iodate) onto andosolsrdquo Water Air and Soil Pollution 63 321-329
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51
90 Appendix A Data Tables of Radionuclide Sorption to Saltstone under Oxidizing Conditions
The following tables represent data collected for the no solids controls each saltstone and testing of radionuclide sorption to the vial walls The no solids controls tables include the concentration (ppb) of the radionuclide spiked into the sample along with the concentration of the radionuclide (ppb) measured in the aqueous phase after the given equilibration time The pH at the time the sample was taken is also recorded along with the fraction of the radionuclide which stayed in the aqueous phase The tables for the cementitious formulation data include the data above along with the addition of a Kd value The tables of the data for the radionuclides sorbed to the vial walls include the initial concentration (ppb) of the spike the concentration (ppb) of the radionuclide that had sorbed to the vial wall during the experiment and the percentage of the total concentration this represents Important Notes
BDL- Below Detection Limit lt01 denotes no notable sorption occurred
91 Data Tables for No Solid Controls
Table 91 Plutonium no solids control after one day
A 9264165178 402285E‐05 1181 434238E‐06 9980817 B 9352537276 0000110618 1183 118276E‐05 3616813 C 9363541597 705331E‐05 118 753273E‐06 5401186 D 0993110568 BDL 12 NA NA E 0977247222 300794E‐05 1199 307797E‐05 1280331 F 0962441315 BDL 1198 NA NA G 4059128499 BDL 1186 NA NA H 4065161486 705198E‐05 1188 173473E‐05 2380003 I 4116819691 0000110748 1189 269014E‐05 1555864
Table 920 TR545- neptunium after four days
Sample ID
Initial Aq Conc (ppb)
Equil Aq Conc (ppb) pH
Fraction Aq Kd
A 92641652 NA 1188 NA NA B 93525373 00001935 1185 2069E‐05 2067199C 93635416 4119E‐05 1185 44E‐06 9247818D 09931106 BDL 1197 NA NA E 09772472 BDL 12 NA NA F 09624413 00066817 1206 00069424 562421G 40591285 00003289 1196 8103E‐05 5148274H 40651615 00025316 1196 00006228 6625737I 41168197 00001018 1194 2474E‐05 1692126
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Table 921 TR545- technetium after one day
Sample ID
Initial Aq Conc (ppb)
Equil Aq Conc (ppb) pH Fraction Aq Kd
A 9655146069 820460082 1181 0849764546 8998984 B 9356176321 7703053505 1183 0823312135 1051242 C 9114122586 7978297395 118 0875377451 7062663 D 1042349157 0853053814 12 0818395456 9099556 E 0983206046 0871198263 1199 0886079033 5196709 F 0905148405 0803451372 1198 0887646013 5098696 G 4950156706 4275082341 1186 0863625658 7213934 H 4889067068 4173762594 1188 0853693053 7687519 I 4854463762 4147024058 1189 0854270268 7771045
A 1048950046 0002141023 1149 0000204111 2112281 B 1039943573 0001770549 1157 0000170254 2460487 C 1084651695 0001127533 1153 0000103953 4014918 D 1088686867 0001201087 1172 0001103244 3564524 E 1119673887 0000783288 1177 0000699568 5709897 F 1045722787 0000914861 1181 000087486 4495324 G 5387981131 0001444832 1169 0000268158 1494715 H 5412748988 0001143483 1169 0000211257 1965749 I 5373948758 00010003 1164 0000186139 2280472
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Table 926 TR547- plutonium after four days
Sample ID
Initial Aq Conc (ppb)
Equil Aq Conc (ppb) pH
Fraction Aq Kd
A 104895 NA 116 NA NA B 10399436 0001828 1165 00001758 2383132C 10846517 00010788 1164 9946E‐05 4196159D 10886869 00009131 1184 00008388 4689778E 11196739 00010624 1189 00009488 4208928F 10457228 00007967 1191 00007619 516258G 53879811 00007915 1173 00001469 2728993H 5412749 00008355 1175 00001544 2690641I 53739488 00006103 1174 00001136 3737892
Table 927 TR547- neptunium after one day
Sample ID
Initial Aq Conc (ppb)
Equil Aq Conc (ppb) pH Fraction Aq Kd
A 9589772032 0000454463 1149 473903E‐05 9116335 B 9293228768 0000260081 1157 27986E‐05 1499475 C 1008725504 0000302018 1153 299405E‐05 1397125 D 0952173007 000019177 1172 0000201403 1954603 E 0992224074 BDL NA NA F 0967815522 402137E‐05 1181 41551E‐05 9474699 G 4068405786 0000222282 1169 546361E‐05 7336986 H 409543171 0000531619 1169 0000129808 3199152 I 4017406611 0000410123 1164 0000102086 4157807
Table 928 TR547- neptunium after four days
Sample ID
Initial Aq Conc (ppb)
Equil Aq Conc (ppb) pH Fraction Aq Kd
A 9589772 NA 116 NA NA B 92932288 00002145 1165 2308E‐05 1818463C 10087255 00001628 1164 1614E‐05 2591215D 0952173 BDL 1184 NA NA E 09922241 BDL NA NA F 09678155 5107E‐05 1191 5277E‐05 7460375G 40684058 00001336 1173 3284E‐05 1220544H 40954317 8151E‐05 1175 199E‐05 2086795I 40174066 00001322 1174 3292E‐05 1289605
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Table 929 TR547- technetium after one day
Sample ID
Initial Aq Conc (ppb)
Equil Aq Conc (ppb) pH Fraction Aq Kd
A 9466799266 8233850788 1149 0869760788 8220086 B 9439556236 817653394 1157 0866198975 8165745 C 9383493063 8086024379 1153 0861728604 8430884 D 1061939876 0919992065 1172 0866331594 6241759 E 0991827343 0836511397 1177 0843404251 7590958 F 0971981155 0839862696 1181 0864073024 6354378 G 4883337077 414858839 1169 0849539633 7903986 H 4691440077 3996173112 1169 0851800949 8038249 I 486993937 4291285586 1164 0881178442 6558707
Table 930 TR547- technetium after four days
Sample ID
Initial Aq Conc (ppb)
Equil Aq Conc (ppb) pH
Fraction Aq Kd
A 94667993 NA 116 NA NA B 94395562 85812109 1165 09090693 5885474C 93834931 84622373 1164 09018217 6279204D 10619399 09580683 1184 09021869 4435663E 09918273 08881507 1189 08954691 4835506F 09719812 09036489 1191 0929698 3138862G 48833371 4490415 1173 09195382 4312104H 46914401 42054182 1175 08964024 5612948I 48699394 43843193 1174 09002821 5536503
Table 931 TR547- iodine after one day
Sample ID
Initial Aq Conc (ppb)
Equil Aq Conc (ppb) pH Fraction Aq Kd
A 9944920441 8813152965 1149 0886196427 738241 B 9956006121 8747156303 1157 0878580848 8007767 C 9822152291 8664470934 1153 0882135674 7988892 D 1002391846 9333490632 1172 0931121963 3368509 E 9918273427 6625075445 1177 0667966607 1551748 F 9918175056 8931364957 1181 0900504872 4773862 G 5166570628 4445386532 1169 0860413387 7961604 H 4847821413 410447427 1169 084666367 8664303 I 4850381381 4266693706 1164 0879661489 6413801
100 Appendix B Data Tables of Radionuclide Sorption to Saltstone Under Reducing Conditions
The following tables represent data collected for the no solids controls each cementitious solid and testing of radionuclide sorption to the vial walls The no solids controls tables include the concentration (ppb) of the radionuclide spiked into the sample along with the concentration of the radionuclide (ppb) measured in the aqueous phase after the given equilibration time The pH at the time the sample was taken is also recorded along with the fraction of the radionuclide which stayed in the aqueous phase The tables for the cementitious solidsrsquo data include the data above along with the addition of a Kd value The tables of the data for the radionuclides sorbed to the vial walls include the initial concentration (ppb) of the spike the concentration (ppb) of the radionuclide that had sorbed to the vial wall during the experiment and the percentage of the total concentration this represents Important Notes
BDL= Below Detection Limit lt01 denotes no notable sorption occurred
101 Data Tables for No-Solid Controls
Table 101 Plutonium no solids control after one day
A 9405892 0007019 111 0000746258 5681206 B 9602498 0003294 1117 0000342992 123554 C 9630619 0002936 1114 0000304893 1396318 D 4945396 0001795 113 0000363011 1171688 E 4964945 0001373 1131 0000276484 1493015 F 4441601 0001516 113 0000341219 1389674 G 1079602 0001109 1142 0001027508 4215519 H 1031512 0000883 1143 0000855983 4820576 I 0939294 0000978 1143 0001040992 4550255
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Table 1011 Vault 2- neptunium after one day
Sample ID Initial Aq Conc (ppb)
Equil Aq Conc (ppb) pH Fraction Aq
A 9425042625 0001709054 1105 0000181331 B 9611386476 0001184125 1110 00001232 C 9579553607 0001155517 1104 0000120623 D 4974000414 0000672325 1125 0000135168 E 4916731623 0000675371 1128 0000137362 F 4373142817 0000570681 1120 0000130497 G 0943366414 0000389738 1129 0000413136 H 1011745587 0000565648 1132 0000559081 I 0865252712 0000379545 1133 0000438653
A 8849444124 0000306309 1150 346133E‐05 1289533 B 8447823057 0000150131 1155 177715E‐05 2711019 C 8590597085 0000199185 1153 231864E‐05 2044057 D 4491250244 517162E‐05 1156 115149E‐05 4020064 E 4391894479 204591E‐05 1158 465838E‐06 9846089 F 4210703646 204376E‐05 1158 485374E‐06 9816203 G 086381524 522216E‐06 1160 604546E‐06 7577764 H 0870501884 BDL 1160 NA NA I 0861953838 BDL 1162 NA NA
SRNL-STI-2009-00636 Revision 0
79
Table 1036 Aged cement- neptunium after four days
Sample ID
Initial Aq Conc (ppb)
Equil Aq Conc (ppb) pH Fraction Aq Kd
A 8849444 0000131 1145 148418E‐05 3007445B 8447823 0000111 1146 131529E‐05 3662996C 8590597 656E‐05 1146 76328E‐06 6209405D 449125 BDL 1155 NA NA E 4391894 BDL 1156 NA NA F 4210704 BDL 1155 NA NA G 0863815 BDL 1165 NA NA H 0870502 BDL 1162 NA NA I 0861954 BDL 1164 NA NA
Table 1037 Aged cement- technetium after one day
Sample ID
Initial Aq Conc (ppb)
Equil Aq Conc (ppb) pH Fraction Aq Kd
A 8426518355 833290075 1150 098889012 0476492 B 8638001423 7823321167 1155 0905686487 4413063 C 9323317745 925927516 1153 0993130923 0294664 D 442651005 4300859603 1156 0971614106 1242837 E 4426849405 4336992073 1158 0979701742 0855315 F 3929483125 3938204338 1158 100221943 lt01 G 0817864386 081693181 1160 0998859743 0049487 H 0878958929 0792412508 1160 0901535306 4510199 I 0772205665 0871436364 1162 1128502941 lt01
Table 1038 Aged cement- technetium after four days
110 Appendix C Dixon et al (2009) FY09 PACA Maintenance Program Additional Saltstone Property Testing SRNL L3100-2009-00019 Rev 0
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83
SRNL L3100-2009-00019 Rev 0
December 16 2008
Keywords Performance Permeability Modulus
L B Romanowski
Waste Determinations From K L Dixon M A Phifer and J R Harbour
FY09 PACA Maintenance Program Additional Saltstone Property Testing
BACKGROUND
Additional tests have been identified for measurement of important hydraulic and physical properties of saltstone The initial phase of this work [1] was completed last year and the results were detailed in an internal report [2] The proposed testing for FY09 includes measurement of saturated hydraulic conductivity porosity bulk density particle density water retention and Youngrsquos modulus of simulated Saltstone grouts For completeness the bleed volumes and gel times for each mix will also be measured
The testing will be based on a projected salt solution composition for the ARPMCU stream that will be fed to the Saltstone Production Facility over the next few years The scope for FY09 will include testing to determine the impact of (1) admixtures (2) organics (3) wcm ratio (4) aluminate concentration and (5) temperature of curing on the hydraulic properties of saltstone mixes Samples of selected batches prepared as part of this task will be provided to Dan Kaplan for measurement of Kd through leaching tests The eleven mixes that will be batched and tested are detailed in Table 1
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Table 1 The Eleven Mixes That will be Batched and Tested
BFS is Blast Furnace Slag FA is Fly Ash and PC is Portland Cement
TEST DETAILS
Test 1 Control (Mix 1)
A control mix will be based on the baseline mix modified by exclusion of the Class F fly ash Consequently the cementitious materials premix will be a mixture of 90 blast furnace slag and 10 portland cement The degree of reaction will be much greater than with the normal premix and therefore should result in a lower porosity and a lower permeability This bounding test at 060 wcm ratio is expected to yield a hydraulic conductivity at or below the detection limit for the Mactec permeameter measurement system Therefore this test should demonstrate the lowest level of detection of the Mactec system as well as show a resolvable difference between measurements of the control mix and the control mix with the normal premix composition
Test 2 ndashImpact of Admixtures (Mixes 2 and 3)
Recent saltstone batches have required both a set retarder (Daratard 17) and an antifoam agent (Q2) for processing of the saltstone Therefore the baseline mix will be prepared with and without nominal levels of these two admixtures to determine whether these admixtures appreciably affect the hydraulic and physical properties of saltstone at these nominal concentrations
Test 3ndashImpact of Organics (Mixes 2 and 4)
The solvent extraction process is expected to result in some carryover of organics [3]
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85
Consequently a test will be performed on the impact of Caustic Side Solvent Extraction (CSSX) organics at 100 microliters per 1600 gram batch The CSSX solvent consists of 075 M 1-(2233-tetrafluoropropoxy)-3-(4-sec-butylphenoxy)-2-propanol (Cs-7SB) and 0003 M tri-n-octylamine (TOA) in an Isoparreg L diluent Test 4ndashImpact of Combination of Admixtures and Organics (Mixes 2 5 10 and 11)
This test will determine the impact of a combination of admixtures (Test 2) and organics (Test 3) together in the mix vs the baseline case without admixtures and organics
Test 5ndash Impact of wcm Ratio (Mixes 2 6 and 7)
It is well known that decreasing the wcm ratio in a mix will improve permeability in normal portland cement water mixes This test will measure the variation in permeability for the case of the MCU salt solution at three different wcm ratios The initial selection of wcm ratios is 055 060 and 065 However if the mix at an as-batched 065 wcm ratio has significant bleed water and the resulting actual wcm ratio is close to 060 then the three ratios will be adjusted to provide a more evenly spaced set of values However the baseline mix at 060 will be included as one of the three mixes
Test 6 ndash Impact of Aluminate Concentration (Mixes 8 9 and 10)
The DWPF has modified its process flowsheet to include a caustic washing of HLW sludge to remove some of the aluminum from the HLW prior to vitrification The resulting aluminate stream will then be blended with tank 50 material and fed to the SPF This increased aluminate concentration in the salt solution has significant impact on heat of hydration and set times and consequently it is likely that it will also impact permeability Therefore a set of three samples will be made at wcm ratios of 055 060 and 065 (as in Test 3) with a higher level of aluminate (028 M) for testing
Test 7 ndash Impact of Increased Curing Temperature (Mix 11)
In an ongoing task there is evidence that Youngrsquos modulus (a performance indicator) [4] is reduced by increasing the curing temperature of the mix Since the vault temperature increases during curing as a result of the exothermic hydration reactions one of the baseline mixes with a combination of admixtures and organics will be cured at 60
o
C rather than the normal 22
o
C to determine the impact of curing temperature on the permeability
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SCHEDULE
The schedule for the task of batching and testing of the samples is provided in Table 2 This schedule is based on the fact that the cementitious materials will be available for the testing as needed
Table 2 Additional Saltstone Hydraulic and Physical Property Tests
Item Schedule Start Work 12108 Test Plan Complete 1509 Preparation of 1st set of Samples Complete 11909 90-Day Cure Period for 1st set of Samples Complete 42009
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87
SRNL-STI-2009-00636 Revision 0
SRNL-STI-2009-00636 Revision 0
DISTRIBUTION Savannah River Site
A B Barnes 999-W Rm 336 H H Burns 999-W Rm 381 B T Butcher 773-43A Rm 212 A D Cozzi 999-W Rm 337 D A Crowley 773-43A Rm 216 M E Denham 773-42A Rm 218 J C Griffin 773-A Rm A-231 J R Harbour 999-W Rm 348 C A Langton 773-43A Rm 219 M H Layton 705-1C Rm 14 D I Kaplan (3 copies) 773-43A Rm 215 S L Marra 773A Rm A-230 A M Murray 773-A Rm 229 K A Roberts 773-43A Rm 225 T C Robinson 705-1C Rm 13 L B Romanowski 705-1C Rm 19 K H Rosenberger 705-1C Rm 16 F M Smith 705-1C Rm 24 RPA File (2 copies) 773-43A Rm 213
Clemson University Environmental Engineering and Earth Sciences 372 Computer Court LG Rich Environmental Laboratory Anderson SC 29625