ML26027A168
| ML26027A168 | |
| Person / Time | |
|---|---|
| Site: | Fort Calhoun  |
| Issue date: | 03/08/2024 |
| From: | Davis L Energy Solutions, Omaha Public Power District |
| To: | Division of Decommissioning, Uranium Recovery and Waste Programs |
| Shared Package | |
| ML26027A165 | List: |
| References | |
| EPID L-2025-LLN-0012 FC-24-001, Rev 0 | |
| Download: ML26027A168 (0) | |
Text
Page 1 of 13 FC-24-001 Revision 0 Use of In-Situ Gamma Spectroscopy for Scan Surveys of Building Surfaces Prepared By:
LJ Davis Date Reviewed By:
Date Approved By:
Date L. J. Davis 030/08/2024 3-7-24 3/8/2024 Gregory Astrauckas, Sr Health Physicist Jason Q. Spaide Digitally signed by Jason Q.
Spaide Date: 2024.03.08 13:17:24 -06'00'
Use of In-Situ Gamma Spectroscopy for Scan Surveys of Building Surfaces FC-24-001 Revision 0 Page 2 of 13 1.0 PURPOSE The purpose of this TSD is to describe the use of in-situ gamma spectroscopy to perform scan surveys, including Final Status Surveys (FSS), of the surfaces of end state structures. This TSD assumes the use of Mirions In-Situ Object Counting System (ISOCS).
2.0 DISCUSSION 2.1 ISOCS Scan Methodology The ISOCS scanning technique provides scan coverage over a defined area to preset a-priori detection limits. These detection limits must be at or below the required investigation levels to facilitate any required follow-up investigations.
The ability of ISOCS to perform radionuclide identification is beneficial where influences from background radioactivity impede conventional survey efforts.
Count times can be tailored to achieve required detection sensitivities and the detector can be collimated to minimize the influence from sources outside the detector's field of view.
In Class 1 survey units where 100% scan coverage is required, the detector Fields of View between adjacent measurements will be overlapped to ensure that there are no gaps in coverage.
The ISOCS efficiency calibrations assume a uniform areal distribution of residual radioactivity. The effects of non-uniform areal distributions are evaluated to ensure that a conservative estimate of total activity inventory is generated for a reasonable range of distributions. An assumption is made that a potential one square meter of elevated radioactivity exists at the edge of the area being evaluated by any single inset measurement.
Radionuclide-specific investigation levels are developed and are based on the detector's field-of-view and adjusted for the smallest area of concern (i.e., 1 m2).
When an investigation level is discovered, investigatory protocols will be initiated to evaluate the presence of elevated activity and bound the region as necessary.
Such evaluations may employ both hand-held field instrumentation as well as the ISOCS system.
Field conditions (e.g. temperatures, rain, etc.) may significantly influence the practical applicability of the ISOCS as a field instrument. Caution must be used in the application of geometries for ISOCS scanning. Careful verification that the environmental conditions and geometric arrangement are appropriate to the detector geometry are essential to ensuring the accuracy of the results.
Use of In-Situ Gamma Spectroscopy for Scan Surveys of Building Surfaces FC-24-001 Revision 0 Page 3 of 13 2.2 Source Term Geometry for ISOCS Efficiency Calibration Knowledge of the source terms attributes (i.e., concentration depth profile and areal distribution of the residual radioactivity within the structure) is required to generate efficiency curves for the ISOCS measurements.
Procedure FCSD-RA-LT-217 Calibration of the Aegis LabSOCS/ISOCS Genie-2000 Portable Gamma Spectroscopy System contains instructions on the use of the Geometry Composer software. The Geometry Composer software contains a number of geometry templates that allow physical parameters to be varied to determine efficiency curves for a variety of source term geometries.
The geometries must be reviewed by a qualified Competent Person to ensure they are correctly developed, and accurately, or conservatively represent the media being measured. A Competent Person is someone who has acquired through training or experience the knowledge and skills to carry out a specific task. Qualification of a Competent Person should be documented.
The efficiency calibrations are intended to be conservative. If the ISOCS measurement results are such that a reduction in conservatism is deemed necessary for a given measurement or survey unit, additional characterization or data analysis may be performed to refine the efficiency calibration.
Due to the nature of the environment and surfaces being evaluated, input parameters for the ISOCS efficiency calibrations will be reviewed on a case-by-case basis to ensure the applicability of the resultant efficiency. The efficiency calibrations may be modified during survey design as necessary, using the general approach and methods described in this TSD.
3.0 ISOCS EFFICIENCY CALIBRATION CONSIDERATIONS 3.1 Areal Distribution of Contamination The depths of contamination found during various characterization activities are shown in Tables 1-3 below. The depth of contamination within a survey unit must be assessed to determine the appropriate value for use in the relevant ISOCS geometry.
Use of In-Situ Gamma Spectroscopy for Scan Surveys of Building Surfaces FC-24-001 Revision 0 Page 4 of 13 Table 1 2019 Characterization 6" Depth Samples 2019 Characterization 6" Samples Depth (inches)
% of Cs-137 Activity 0.0 - 0.5 92.40%
0.5 - 1.0 2.86%
1.0 - 1.5 1.46%
1.5 - 2.0 2.60%
2.0 - 4.0 0.34%
4.0 - 6.0 0.33%
Table 2 2019 Characterization 1.5" Depth Samples 2019 Characterization 1.5" Samples Depth (inches)
% of Cs-137 Activity 0.0 - 0.5 89.06%
0.5 - 1.0 7.43%
1.0 - 1.5 3.51%
Table 3 2024 989' East Trench Continuing Characterization Samples 2024 East Trench Continuing Characterization Samples Depth (inches)
% of Cs-137 Activity 0.0 - 0.5 99.95%
0.5 - 1.0 0.05%
3.2 FCS Concrete Density The material densities applied to efficiency calibrations will be documented. In order to develop a representative concrete density, the volume and mass of a 0.5 puck from 12 concrete core samples was determined and the density calculated. As seen in Table 5, the average density was 2.54 g/cm3. This measured concrete density will be used in the geometry composer software as the density for concrete surfaces.
Use of In-Situ Gamma Spectroscopy for Scan Surveys of Building Surfaces FC-24-001 Revision 0 Page 5 of 13 Table 4 Concrete Density Data 3.3 Sensitivity to Non-uniform Areal Distribution As noted earlier, a conservative assumption made is that a potential one-square-meter of elevated radioactivity exists at the edge of the area being evaluated by a single in-situ measurement. This is referred to as an offset geometry. Chapter 9 Sample ID Thickness (cm)
Radius (cm)
Weight (g)
Volume (cm3)
Density (g/cm3) 2002X-1-CJ-FCV2-001 1.1 2.15 46.1 15.97 2.89 2002X-1-CJ-FCV2-014 1.4 2.15 51.2 20.32 2.52 2002X-1-CJ-FCV3-001 1.3 2.15 48.6 18.87 2.58 2002X-1-CJ-FCV3-003 1.3 2.2 49.3 19.76 2.50 2002X-1-CJ-FCV3-008 1.3 2.1 44.1 18.00 2.45 2002X-1-CJ-FCV4-001 1.3 2.15 45.7 18.87 2.42 2002X-1-CJ-FCV4-003 1.2 2.15 45.3 17.42 2.60 2002X-1-CJ-FCV4-013 1.3 2.15 48.4 18.87 2.57 2002X-1-CJ-FCV4-014 1.3 2.15 49.0 18.87 2.60 2002X-1-CJ-FCV4-015 1.4 2.1 50.5 19.39 2.60 2002X-1-CJ-FCV4-017 1.4 2.15 46.2 20.32 2.27 Maximum 2.89 Minimum 2.27 Std. Dev.
0.15 Average 2.54
Use of In-Situ Gamma Spectroscopy for Scan Surveys of Building Surfaces FC-24-001 Revision 0 Page 6 of 13 of the Advanced ISOCS Measurements Training Course Manual contains details on performing the offset geometry evaluation.
This offset geometry is used to create an adjustment referred to as the offset geometry correction factor. To develop this correction factor, two different efficiency calibrations (i.e. geometries) are generated. The first scenario assumes radioactivity uniformly distributed over the detector's full field-of-view.
The second scenario assumes radioactivity localized over a 1-m2 situated at the edge of the detector's field-of-view.
The offset geometry adjustment factor will vary for different geometries. If different geometries are employed, this value will be determined on a case-by-case basis using the methodology presented in this TSD and will be documented in the applicable survey records.
The Nuclide Line Efficiencies for the Radionuclides of Concern (ROCs) are taken from Geometry Composer and the ISOCS Calibration Reports. The resultant efficiency values are then compared to characterize the difference in detection efficiencies between the two scenarios. The efficiency ratios are applied as the off-set geometry correction factor for each nuclide.
Correction Factor = Offset Efficiency/Full FOV Efficiency Where: CF = Offset Geometry Correction Factor Offset Efficiency = Offset Geometry Energy Line Efficiency Full FOV Efficiency = Full FOV Geometry Energy Line Efficiency 4.0 CALCULATION OF INVESTIGATION LEVELS For calculation of an effective investigation value for each radionuclide of concern The investigation levels are calculated as follows:
Nuclide Derived Investigation Level (pCi/m2) = Derived Concentration Guideline (DCGL)
- CF Where: DCGL = (DCGLw or DCGLEMC), and CF = offset geometry Correction Factor An example of how the Correction Factor is calculated and applied is presented in Table 6 below. The Geometry Composer and ISOCS Calibration Reports for this example are included in Attachment 1.
Use of In-Situ Gamma Spectroscopy for Scan Surveys of Building Surfaces FC-24-001 Revision 0 Page 7 of 13 Table 5 Correction Factor and Derived Investigation Level Calculation 5.0 REFERENCE 5.1 FCSD-RA-LT-217 Calibration of the Aegis LabSOCS/ISOCS Genie-2000 Portable Gamma Spectroscopy System 5.2 SU-476-3, Advanced ISOCS Measurements Training Course Manual, (Mirion, 2018) 5.3 Fort Calhoun Station Decommissioning Project License Termination Plan Revision 1, 2023.
5.4 TSD FC-24-004 Summary of DCGLs, Remediation Strategy and Survey Methodology for Auxiliary Building East Trenches, 2024.
6.0 ATTACHMENTS 6.1 : Geometry Composer and ISOCS Calibration Reports Nuclide Line Energy DCGL (pCi/m2) 1 m2 Line Efficiency w/ offset 5.25 m2 Line Efficiency Adjustment factor Derived Investigation Level (pCi/m2)
Cs-137 661.7 2.44E+07 8.44E-06 9.15E-06 9.23E-01 3.88E+07 Co-60 1332.5 1.99E+07 5.38E-06 5.81E-06 9.26E-01 1.99E+07
FC-18-008 Revision 0 Page 8 of 13
FC-18-008 Revision 0 Page 9 of 13
FC-18-008 Revision 0 Page 10 of 13
FC-18-008 Revision 0 Page 11 of 13
FC-18-008 Revision 0 Page 12 of 13
FC-18-008 Revision 0 Page 13 of 13