Waste Technology Section, NEFW Nuclear Spectrometry and Applications Laboratory, NAPC Demonstration and review of a Mobile Unit for Site Characterization.

Waste Technology Section, NEFW Nuclear Spectrometry and Applications Laboratory , NAPC

Demonstration and review of a Mobile Unit for Site Characterization in Environmental Remediation Projects

23-27 July 2012, Gabon

Scope of the mission:

To gather together experienced professionals in designing, constructing and operating Mobile Laboratory Units for environmental measurements of radionuclides to perform a real case exercise of site characterization in areas contaminated by past activities involving NORM

Instruments:

Model Detector type

Capability Data (discarded)

PGIS 21,Envinet S.A.

NaI(Tl) (3 x 3 “).

Dose rateeU, eTh, KSpectrometry

32929(0)

High throughputReliable dose rate calibration and GPS coordinatesHeavy, but easy to carry

Instruments:

Model Detector type

Capability Data (discarded)

AT6101C,Atomtex

NaI(Tl) (2.5 x 2.5 “).+ Neutron He detector

Dose rateeU, eTh, KSpectrometry

5604(0)

High throughputReliable dose rate calibration and GPS coordinatesHeavy

Instruments:

Model Detector type

Capability Data (discarded)

StrideThermoScientific

NaI(Tl) (2 x 2 “).

Dose rateSpectrometry

35338(8.9%)

FH40G from APVL Ionization chamber

Dose rate 35338(23.8 %)

High throughputReliable dose rate calibration (NaI)Partial loses of GPS coordinates Not so easy to carry Out of calibration readings (Ioniz.Ch)

Instruments:

Model Detector type

Capability Data (discarded)

RS-125,Radiation solutions

NaI(Tl) (2 x 2 “).

Dose rateSpectrometry

1853(0)

Light weight, reliable GPS readingsDose rate readings require long accumulation time (~ 10 seconds)Biased results below 400 nSv/h

Instruments:

Model Detector type

Capability Data (discarded)

Victoreen 451PFluke

Ionization chamber

Dose rate 38441(4 %)

Dose rate readings and GPS readings very reliableHigh throughputFraction of readings transmitted out of scaleNo spectrometry

Instruments:

Model Detector type

Capability Data (discarded)

RadEye B20 from Thermo Scientific

Geiger Muller Exposure rateDose rate (calibrated)

For calibration

Light weightAccuracy (calibrated)

Instruments:

Model Detector type

Capability Data (discarded)

Niton XLt-Goldd SDD Elemental composition

Selected spots

Fast measurement time (60 s)Light weightRelative Accuracy (10 – 20 %)

Instruments:

Model Detector type

Capability Data (discarded)

Gamma Surveyor II,GF-Instruments

BGO (1.3 x 1.3 “).

Dose rateeU, eTh, KSpectrometry

100 % Discarded

Dose rate readings only reliable with long accumulation time (> 20 seconds)Not quantitative results in scan mode (1 s)

Comparison of Dose rate readings

0

1

2

3

4

5

6

7

0 500 1000 1500 2000 2500 3000 3500

1 / PGIS21

1 / Atomtex

1 / RS125

1 / Thermo

Comparison of GPS readings

Deviations < 0.00005 DecimalDegrees~ 5.5 m

Strategy followed

o Gathering background informationo Measurements around the areas (waypoints)o Grid measurements in the areas with hot spots

Hot spot: Dose rate values exceeding 10 x 114 nSv/h

114 nSv/h: Internationally accepted level for public exposure(1 mSv/year)

The site: Original Map

The site: modified map

Eyebird view

Waypoint readings

• 114 165 measurements

• 2 ½ days of measurements

Dose rate(nSv/h)

Number (%)

10 - 114 61 267 56.7

114 - 250 24 771 22.9

250 - 500 11 660 10.8

500 - 1140 5 283 4.9

1140 - 10400 5 036 4.7

Interpretation of readings

Identification of hot spots

Interpolation based on Natural Neighbor

Correlation with the features of the area

Interpolation based on Natural Neighbor

Correlation with the features of the area

Interpolation based on Natural Neighbor

Correlation with the features of the area

Interpolation based on Natural Neighbor

Correlation with the features of the area

Interpolation based on Natural Neighbor

Correlation with the features of the area

Interpolation based on Natural Neighbor

Correlation with the features of the area

Interpolation based on Natural Neighbor

Correlation with the features of the area

Interpolation based on Natural Neighbor

Correlation with the features of the area

Interpolation by Kriging

1) Analysis of variance of data in space

Model definition

Interpolation by Kriging

2) Using the model for the interpolation

Interpolation by Kriging

3) Probability of exceeding a given level

> 300 nSv/h

Gamma Spectrometry analysis

Identification of source of activity

Gamma Spectrometry analysis

Identification of source of activity

214Bi

Pressed Wood

Remediation Site

XRF Spectrometry analysis

Identification of materials based on elemental composition

Participants:

HorstDidier

MarcosRean

Eugene

Roman

Conclusions

o The mission allowed producing maps of radiological status of most of the areas of interest in the Mounana site, as requested by the counterpart

o The use of the Mobile is a cost-effective approach for the assessment of surface dose rate distribution and the identification of radiation sources

Thanks for your attention