Proceedings of the Eighth International Conference on Probabilistic Safety Assessment & Management (PSAM)
106 Risk Insights Baseline Report: A Basis for Risk-Informed Decision Making in the U.S. Nuclear Regulatory Commission's High-Level Waste Repository Safety Program for the Proposed Yucca Mountain, Nevada Repository (PSAM-0304)
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The U.S. Nuclear Regulatory Commission (NRC) staff has compiled a set of system-level and detailed risk insights related to post-closure performance of the potential geologic repository system at Yucca Mountain, Nevada, in the Risk Insights Baseline Report. These risk insights are based on staff's experience in independently conducting and reviewing performance assessments for a high-level waste repository at Yucca Mountain. The staff developed the risk insights baseline by synthesizing the results of total system performance assessments, subsystem analyses, and auxiliary calculations. The report includes a discussion of the quantitative technical bases for the insights and associated uncertainties. The risk insights baseline focuses on those features, events, and processes that staff views as most important to a potential repository system. The staff rated the significance of the individual risk insights by considering the contribution to, or adverse effect on, the waste isolation capabilities of the repository system. The effect on waste isolation was evaluated by considering the potential effect on: the integrity of the waste package; the release of radionuclides from the waste package and waste form; and radionuclide transport through the geosphere and biosphere.
The U.S. Nuclear Regulatory Commission has directed its staff to carry out risk-informed and performance-based regulatory programs. Part 63 under Title 10 of the U.S. Code of Federal Regulations contains the NRC's rules for the licensing of a potential U.S. Department of Energy (DOE) geologic repository. The licensing regulations are risk-informed and performance-based, and require an estimation of risk of radiation exposure, using a performance assessment, to the reasonably maximally-exposed individual as part of the performance objectives. The NRC staff has written the Yucca Mountain Review Plan to provide guidance to the staff to evaluate a DOE license application for a geologic repository. The review plan provides that the staff will apply risk information throughout the review of the performance assessment to focus its review on those items most important to waste isolation. A DOE license application can provide risk information via the identification of, description of the capabilities of, and technical bases of barriers important to waste isolation. The Risk Insights Baseline Report, the DOE-supplied information on barriers, and the review plan, will enable the staff to conduct a risk-informed license review.
The DOE has prepared performance assessments over the past 15 years. The NRC staff is using a risk-informed approach to review some of these DOE performance assessments as part of its pre-licensing activities. This paper describes two examples (localized corrosion of waste package and radionuclide transport in the unsaturated zone) where staff is reviewing different aspects of the DOE performance assessment in a risk-informed and performance-based manner.
The NRC staff views expressed herein are preliminary and do not constitute a final judgment or determination of the matters addressed or of the acceptability of a license application for a geologic repository at Yucca Mountain.