ML20072N077
| ML20072N077 | |
| Person / Time | |
|---|---|
| Issue date: | 03/17/2020 |
| From: | George Alexander, Freeman V, Douglas Mandeville, Thomas Nicholson Office of Nuclear Material Safety and Safeguards, Pacific Northwest National Laboratory |
| To: | |
| Mandeville D | |
| Shared Package | |
| ML20072N076 | List: |
| References | |
| Download: ML20072N077 (15) | |
Text
Long-Term Performance of Engineered Systems in Nature George Alexander1, Doug Mandeville1, Thomas Nicholson1, and Vicky Freedman2 1U.S. Nuclear Regulatory Commission 2Pacific Northwest National Laboratory March 17, 2020
Overview
- FEPs Analysis - George Alexander
- Uranium Mill Tailings Sites - Doug Mandeville
- Closure Cap Monitoring - Vicky Freedman 2
Performance Assessment and FEPs Analysis NUREG-2175 Guidance for Conducting Technical Analyses for 10 CFR Part 61, Draft Final Report, October 2016.
Performance Assessment (PA) is a type of risk analysis that addresses: (1) what can happen, (2) how likely it is to happen, and (3) what are the resulting impacts (Eisenberg et al., 1999)
A PA shall consider Features, Events, and Processes (FEPs) that might affect demonstration of compliance (with the performance objective in 10 CFR 61.41) 3 How are we making progress in incorporating natural processes, features and conditions in our conceptual and numerical models, and in designing monitoring networks?
Feature - An object, structure, or characteristic that has a potential to affect system performance (e.g.,
rocks within an erosion layer of a cover)
Event - A natural or human-caused phenomenon that has a potential to affect system performance and occurs over a short period of time relative to the period of performance (e.g., earthquakes, floods, well drilling, excavation)
Process - A natural or human-caused phenomenon that has the potential to affect repository system performance and occurs over a significant part of the period of performance (e.g., erosion, leaching, transport, differential settlement)
Risk-informed approach - FEPs analysis (and documentation) commensurate with risk What is a FEPs Analysis How are we making progress in incorporating natural processes, features and conditions in our conceptual and numerical models, and in designing monitoring networks?
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Formal FEP analysis for performance assessment of disposal systems consists of the systematic implementation of the following steps:
- FEP Identification
- FEP Screening FEP analysis supports:
- Scenario Development
- Implementation in a Model These steps are performed and refined over multiple iterations 5
What is a FEPs Analysis Freeze, G. Features, Events, and Processes (FEPs) Analysis for Radioactive Waste Disposal: Rationale and Application.
NRC Workshop on PA of Near Surface Disposal. August 29, 2012. ML13053A280
FEP Identification and Screening Are we explicitly considering human processes and behaviors, and consequent natural responses?
FEP Identification (i.e., comprehensiveness of the FEP List )
A comprehensive set of FEPs should capture all of the features and phenomena that are potentially relevant to system performance Formal FEP analysis provides objective evidence that all potentially relevant FEPs have been addressed How do we determine the natural processes, features, and conditions to include in conceptual models and monitoring programs?
FEP Screening (i.e., model completeness)
The process of using regulatory, probability, and consequence criteria to eliminate FEPs from further consideration that will not significantly impact the performance of the disposal system Screened in FEPS are combined to form a limited number of scenarios for consequence analysis If a FEP cannot be excluded, then it must be included 6
Evolution of Engineered Systems Engineered systems evolve towards local equilibria Often, the further the system is from equilibrium, the faster the evolution of properties towards the surrounding environment Designing with nature can:
Reduce changes to the system over time Reduce long-term maintenance 7
Benson, C. et al., Engineered Covers for Waste Containment: Changes in Engineering Properties and Implications for Long-Term Performance Assessment, NUREG/CR-7028, 2011. ML12005A110
Uranium Mill Tailings Sites
- Doug Mandeville
- U.S. Nuclear Regulatory Commission Source - Wyoming Mining Association, Kennecott Sweetwater Mill
- under licensee control 8
Regulatory Requirements
Uranium Mill Tailings Radiation Control Act of 1978 (UMTRCA)
Title I - inactive uranium mill tailings piles (circa 1978)
Title II - facilities with NRC licenses after 1978
Regulations 40 CFR Part 192 (EPA) Generally Applicable Standards 10 CFR Part 40 Appendix A to Part 40
What NRC regulates Milling - any activity that produces byproduct material Byproduct Material - tailings or wastes produced by extraction of U or Th for its source material content NRC does not regulate mining or exploration UMETCO site near Gas Hills, WY - under licensee control 9
Goals
- Permanent isolation of tailings and associated contaminants
- Minimize disturbance and dispersion by natural forces
- No reliance on ongoing maintenance
- 10 CFR Part 40 Appendix A has 13 Criteria that address these goals Homestake site near Grants, NM - under licensee control 10
Goals - Working with Nature While isolation of tailings will be a function of both site and engineering design, overriding consideration must be given to siting features given the long-term nature of tailings hazards. from Criterion 1 in 10 CFR Part 40 Appendix A Canonsburg site, PA - under long term surveillance by DOE 11
Risks
- Wind and water erosion of cover
- Groundwater contamination from tailings liquids in the near surface aquifer
- Radon flux from tailings
- Embankment stability
Past Approach
- Resistive Barriers
- Armored Rock Covers
- Construction completed in mid to late 1990s
- Similar to many of the covers from that time period
- Research on near term performance of covers identified changes in engineering properties of soils Ambrosia Lake, NM site - under long term surveillance by DOE 13
Transition to ET Covers
- Recognition that working with nature may be more effective in the long run
- Licensees and DOE-LM trending towards evapotranspirative (ET) covers
- Thicker cover with vegetation to remove water from the cover system
- Try to mimic surroundings
- Both rock covers and vegetative covers can meet NRC regulations Crescent Junction Disposal Cell, UT - DOE EM relocating tailings from Moab, UT 14
Monitoring DOE/licensee develop long term surveillance plans prior to termination (NRC reviews and accepts)
Surveillance is site specific, depending on the features of the site Cover performance (qualitative)
Groundwater monitoring at many sites Annual reporting to NRC Increased interest from DOE in pursuing remote monitoring for cover performance
- Settlement
- Water storage in cover system
- Vegetation Open to other ideas and approaches When does a change in performance indicate a problem?
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