ML21208A222
| ML21208A222 | |
| Person / Time | |
|---|---|
| Issue date: | 07/14/2021 |
| From: | Bruce Watson Office of Nuclear Material Safety and Safeguards |
| To: | |
| Aird, Thomas - 301 415 2442 | |
| Shared Package | |
| ML21208A206 | List: |
| References | |
| Download: ML21208A222 (15) | |
Text
Survey Issues with Excavations From Recent Decommissionings Subsurface Workshop July 14-15, 2021 Bruce A. Watson, CHP Chief, Reactor Decommissioning Branch Office of Nuclear Material Safety and Safeguards 1
NRC Decommissioning Experience Cumulative Completion of Decommissioning Sites 1998-2021 90 80 70 60 50 40 30 20 10 0
Materials Sites Research Reactors Power Reactors 2
To Excavate or Not?
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Excavation Required 4
Seasonal Flooding Issues?
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Weather Impacts?
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Shallow Ground Water?
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Background Issues?
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Excavation Depth?
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Contaminant Layering and Stratification
Excavation Safety 11
Surveys of Backfill Materials
- Generally, State Regulators
- Survey Plans:
have concerns over backfill - Radionuclides from material constituents and dose Characterization and excavation surveys
- Backfill plans must be - Based on MARSSIM addressed in the - Scan Surveys of soil, typically 6-Decommissioning Plan (LTP) inch (15 cm)
- Include a Survey Plan for - Sampling for lab analysis determining the residual - Direct Measurement Sampling radioactivity to support dose
- As left surveys and sampling after modeling backfilling with 6-inch lifts.
- Need to address residual radioactivity and dose
- Backfill compression to contribution (ALARA) prevent depression
- Need to address origin and constituents of the backfill (soil, concrete debris) 12
Survey and Sampling Concerns
- Excavation sidewall issues
- Survey unit area (bottom and sides)
- Sampling of sidewalls
- Scanning of sidewalls
- Composite Sampling and averaging
- Inaccessible areas (?)
- Standing or running water
- Excavation sidewalls
- Gas pipeline and other safety concerns
- Mud, ice and snow
- Rocky substrate
Survey Concerns
- Under building subsurface activity is always a concern and the licensee needs to address in the site characterization report.
- High background count rates generally indicates that of the residual radioactivity has not been remediated.
- Based on the radionuclides present, soil lifts need to be limited to 6 (15 cm) for surveys to be effective. Reminder: MARSSIM is based on 6 inch (15 cm) depth.
- Need to verify that the survey unit has been remediated to the proper depth to remove the residual radioactivity
- Class 1 surveys require 100 % SCAN surveys, if not already in the approved Decommissioning Plan, seek Regulator input for unusual situations.
- Class 2 and 3 areas require minimal Scan Coverage, chose the most where residual activity is likely to be present.
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Subsurface Issues?
In developing guidance for subsurface surveys/sampling, many of the issues with excavation surveys, sampling and safety may be applicable.
Thank you for the opportunity to speak today!
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