Concentration of Tritium in Liquid Samples by Electrolysis problem solved LPING OUR CLIENTS SOLVE COMPLEX PROBLEMS 17 th Annual RETS – REMP Workshop Stan Morton, Ph.D. June 27, 2007 Philadelphia, PA June 27, 2007
Jan 11, 2016
Concentration of Tritium in Liquid Samples by Electrolysis
problem solved
HELPING OUR CLIENTS SOLVE COMPLEX PROBLEMS
17th Annual RETS – REMP
Workshop
Stan Morton, Ph.D.
June 27, 2007
Philadelphia, PA June 27, 2007
Tritium
problem solved
HELPING OUR CLIENTS SOLVE COMPLEX PROBLEMS
• Heavy Isotope of Hydrogen
• 12.3 year half-life
• Beta Decays to Stable He-3
• Low-energy Beta Particle– 18.6 keV beta-max– 5.7 keV beta-avg
• Hydrogen and Tritium interchangeable
Tritium Unit (TU)
problem solved
HELPING OUR CLIENTS SOLVE COMPLEX PROBLEMS
TU ≡ 0.118 Bq/L ≡ 3.19 pCi/L
Or
1 Bq/L ≡ 8.47 TU
1TU ≡ Concentration of 10-18
Sources of Tritium
problem solved
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• Cosmogenic• Nuclear Weapons – Atmospheric detonation
• By-Product Nuclear Power Reactors
– Boron
– Lithium
• Fission Process
Cosmogenic
problem solved
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• Spallation – Cosmic-rays interact with atomic nitrogen:
14N (n, 3H) → 12C
• Reaction altitude from 11 to 16 km
• Adds to Precipitation Level
Nuclear Weapons - Atmospheric
problem solved
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• Testing 1940s through 1970s
• Precipitation Levels peaked in 1963
• Additional 52 X 1018 Bq to Global Inventory
• Estimated remnant of 100 – 400 pCi/L in precipitation
Precipitation Concentrations
problem solved
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Tritium Production from Boron
problem solved
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• Boron-10 (19.9%) high thermal neutron cross section – 3835 barns
• Control rods for BWRs and PWRs
• Chemical shim and reactivity control in PWRs
10B(n,2α) → 3H10B(n,α) → 7Li(n,nα) → 3H
Tritium Production from Lithium
problem solved
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• Most acceptable hydroxide for pH control in some PWR primary coolant
• 6Li (7.5%) 940 barns
• Principle reactions:7Li(n,nα) → 3H8Li(n,α) → 3H
Tritium from Fission
problem solved
HELPING OUR CLIENTS SOLVE COMPLEX PROBLEMS
• Lesser extent from fission
• Fission yield for 235U is ~0.01%
Tritium Inventory
problem solved
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• Estimated normal releases 0.02 x 1018 Bq/year• Estimated off-normal releases 0.001 x 1018
Bq/year• Steady-state buildup 0.4 x 1018 Bq globally• Legacy release 0.4 x 1018 Bq/year• Steady-state buildup 7.4 x 1018 Bq globally
Tritium Global Inventory
problem solved
HELPING OUR CLIENTS SOLVE COMPLEX PROBLEMS
• Atmospheric detonations 50s & 60s:
185 to 240 X 1018 Bq
• Legacy today:
52 X 1018 Bq
• Combined natural and anthropogenic global inventory of approximately:
53 X 1018 Bq or ~ 10 Bq/L
Regulatory Limits
problem solved
HELPING OUR CLIENTS SOLVE COMPLEX PROBLEMS
• Weak beta and rapid elimination produce a minor constituent in dose evaluation
• EPA 1976 Drinking Water Standard is 4 mrem/yr = 20,000 pCi/L
• 1991 4 mrem/yr = 60,900; retained 1976 limit.
Dose Considerations
problem solved
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• Human retention studies provide three-component half-lives– 6 to 12 days – turnover of pool of body water– 10 to 34 days – involved in carbon-tritium
chemistry– 130 to 550 days – organic molecules with
slow turnover rates
Perception vs. Risk
problem solved
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• Braidwood – 1600 pCi/L ≡ 0.3 mrem/yr; Exelon Corporation bought the farm
• Decatur Daily headline: …TVA, NRC are ‘flippant’ over tritium leaks
• Morris Daily Herald: Dresden leak levels 25 times the allowable drinking water limits
• Arizona Republic: Palo Verde’s tritium leak may impact the groundwater.
• Harford Courant: Haddam a few gallons a day of tritium contaminated water breaches 6-foot thick concrete wall.
Concentration of Tritium by Electrolysis
problem solved
HELPING OUR CLIENTS SOLVE COMPLEX PROBLEMS
• 2006, GEL Labs recognized need
• Quantitative below 150 – 200 pCi/L
• Reliable method
• Well defined turn-around-times
• Quality driven
• Customer service
Concentration of Tritium by Electrolysis
problem solved
HELPING OUR CLIENTS SOLVE COMPLEX PROBLEMS
• Exploits slight differences in physical properties between hydrogen and tritium
• Molecule of water containing hydrogen more likely to dissociate by electrolysis than molecule of water containing tritium.
Overview
problem solved
HELPING OUR CLIENTS SOLVE COMPLEX PROBLEMS
• Aliquant of 500 mL sample screened for ‘high’ levels of tritium and extraneous emitters
• Shipped to Richland Service Center (RSC) in Richland, Washington
• Enrichment process
• Returned in closed vial for LSC
Ambient and Environmental Considerations
problem solved
HELPING OUR CLIENTS SOLVE COMPLEX PROBLEMS
• All commercial analytical labs evaporate hundreds of liters of tritium laden water
• May produce elevated levels of ambient tritium
• Environmental concentrations vary by region– Eastern and Southern states highest levels– Mid-west and Western States lowest levels
Richland Service Center
problem solved
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Electrolysis Instrumentation
problem solved
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Electrolysis Cold-Water Bath
problem solved
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RSC Tritium Laboratory
problem solved
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Procedure
problem solved
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• 300 mL distilled
• 250 mL concentrated by electrolysis for maximum sensitivity
• Batch size– 12 samples– 2 background– LCS containing NIST traceable tritium
standard
Procedure (cont’d)
problem solved
HELPING OUR CLIENTS SOLVE COMPLEX PROBLEMS
• Cold water bath (~ 5°C)
• Constant current until 25 mL remaining
• Reduce current until 12 – 15 ml
• Volume reduction and enrichment requires 12 – 14 days
• Vacuum distillation to remove NaOH
Procedure (cont’d)
problem solved
HELPING OUR CLIENTS SOLVE COMPLEX PROBLEMS
• Volume determined by weight
X = Vi / Vf
• Enrichment determined from LCSs
Y = Cf / Ci
• Transferred to LSC vial
• Returned to Charleston for beta counting
MARLAP Approach
problem solved
HELPING OUR CLIENTS SOLVE COMPLEX PROBLEMS
• Multi-Agency Radiological Laboratory Analytical Protocols (MARLAP) Manual
• Nationally consistent approach to producing analytical data
• Performance-based approach for selecting analytical protocol
• Project specific criteria
MARLAP Method Validation
problem solved
HELPING OUR CLIENTS SOLVE COMPLEX PROBLEMS
Validation Level
Applications Sample Type1
Acceptance Criteria2
Levels3 (Concentrations)
Replicates No. of Analyses
A Without
Additional Validation
Existing Validated Method
____ Method
Previously Validated B thru E
____ ____ ____
B
Same or similar Matrix
Internal PT
Measured Value Within ±2.8μMR or ±2.8φMR Known Value
3 3 9
C Similar Matrix/
New Application
Internal or
external PT
Measured Value Within ±2.9μMR or ±2.9φMR Known Value
3 3 15
D
Newly Developed or
Adapted Method
Internal or
external PT
Measured Value Within ±3.0μMR or ±3.0φMR Known Value
3 3 21
E
Newly Developed or
Adapted Method
MVRM* Samples
Measured Value Within ±3.0μMR or ±3.0φMR Known Value
3 3 21
Newly Developed Methods
problem solved
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• Newly developed use Level D or E
• Increased number of replicates
• Best estimate of precision and bias
• Unique matrix
Determination of Uncertainty
problem solved
HELPING OUR CLIENTS SOLVE COMPLEX PROBLEMS
• Method validation determines method uncertainty
• Sample uncertainty menu includes– Method uncertainty– Liquid-scintillation counting statistics– Background subtraction– NIST standards, decay time, half-life, etc.
Uncertainty Considerations
problem solved
HELPING OUR CLIENTS SOLVE COMPLEX PROBLEMS
• Uncertainty increases as activity approaches detection limit
• Because of such effects, as analyte concentrations drop, the relative uncertainty associated with the result tends to increase, first to a substantial fraction of the result and finally to the point where the (symmetric) uncertainty interval includes zero. This region is typically associated with the practical limit of detection for a given method.
Questions & Contact Information
problem solved
HELPING OUR CLIENTS SOLVE COMPLEX PROBLEMS
Contact Information:
Stan Morton, Manager, Radiobioassay Programs 303.349.8345 [email protected]
Bob Wills, Manager, Nuclear Programs 843.556.8171 [email protected]