ML20072N079
| ML20072N079 | |
| Person / Time | |
|---|---|
| Issue date: | 03/17/2020 |
| From: | George Alexander, Douglas Mandeville, Thomas Nicholson Office of Nuclear Material Safety and Safeguards |
| To: | |
| Mandeville D | |
| Shared Package | |
| ML20072N076 | List: |
| References | |
| Download: ML20072N079 (1) | |
Text
Long-Term Performance of Engineered Systems in Nature George Alexander, Doug Mandeville and Thomas Nicholson U.S. Nuclear Regulatory Commission (U.S. NRC)
Based on lessons learned in licensing reviews, the U.S. NRC staff has recently developed guidance pertaining to the incorporation of risk-significant features, events, and processes (FEPs) into performance assessments (PA) for low-level radioactive waste disposal systems (NUREG-2175). A FEPs analysis provides confidence that risk-significant phenomena are considered in the PA model(s). The subsequent understanding of the interactions between these phenomena and the site features and engineered system barriers is critical to the understanding of both short-term and long-term site performance. A key component of the FEPs analysis is the identification and characterization of credible scenarios and alternative conceptual site models to understand the local environmental conditions, events and processes.
Operational experience of these facilities indicate that systems evolve towards the established natural conditions of the local environment (i.e., a local equilibrium) for physical (e.g., erosion, development of soil structure, vadose zone hydrology), biotic (e.g., flora, fauna), and chemical (e.g., oxidation, dissolution, leaching, mineral precipitation) mechanisms. Because engineered systems evolve towards a long-term equilibrium, the further the systems are initially from equilibrium, the faster they evolve to the surrounding natural conditions. The recognition of this concept of system evolution has led, in some instances, to the transition from resistive barriers (i.e., rock covers) to integrated engineered systems more compatible with nature. Closure caps at uranium mill tailings sites provides an example of this paradigm shift from resistive covers to evapotranspiration covers.
NUREG-2175, Guidance for Conducting Technical Analyses for 10 CFR Part 61, Draft Report for Comment, U.S. Nuclear Regulatory Commission, Washington, DC, March 2015.
https://www.nrc.gov/reading-rm/doc-collections/nuregs/staff/sr2175/
NUREG/CR-7028, Engineered Covers for Waste Containment: Changes in Engineering Properties and Implications for Long-Term Performance Assessment, U.S. NRC, Dec. 2011.
https://www.nrc.gov/reading-rm/doc-collections/nuregs/contract/cr7028/
NUREG/CP-0312, Proceedings of the Radon Barriers Workshop, U.S. NRC, August 2019.
https://www.nrc.gov/reading-rm/doc-collections/nuregs/conference/cp0312/
NUREG/CP-0195, Proceedings of the Workshop on Engineered Barrier Performance Related to Low-Level Radioactive Waste, Decommissioning, and Uranium Mill Tailings Facilities: Held at the U.S. Nuclear Regulatory Commission Headquarters, Rockville, MD, August 3-5, 2010, U.S. NRC, August 2011. https://www.nrc.gov/reading-rm/doc-collections/nuregs/conference/cp0195/