Document: NUREG-0800
Document ID: e32f0820-4e33-476e-aa36-4ca8c2c64af0
Document Type: srp
Title: Use of Probabilistic Risk Assessment in Plant-Specific, Risk-Informed Decisionmaking:
Source: NUREG-0800
Source URL: https://www.nrc.gov/docs/ML0119/ML011940192.pdf
Revision Date: 2023-06
Chapter: 19
Section ID: 19.0
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are several alternative approaches to the analysis of certain elements of the PRA model. They are typically addressed by adopting a specific: model or making a specific assumption. In such cases, the licensee should document why the particular model or assumption used is SRP 19-22 appropriate both for the base case risk evaluation and for the analysis of the impact of the change. In certain cases, it may be necessary to perform sensitivity analyses using alternative reasonable models or assumptions to demonstrate the robustness of the conclusions. In deciding what are reasonable alternatives, reviewers should consider whether the alternatives have some precedent and whether they have a reasonable engineering basis. Reviewers should pay particular attention when the characterization of a model uncertainty is such that the results fall into a bimodal or multi-modal distribution, and one or more of the modes exceed the acceptance guidelines. The results should then be reviewed on the basis of an evaluation of the significance of the hypotheses associated with those modes that exceed the guidelines. * Completeness uncertainty: Reviewers should determine whether the licensee has adequately addressed the limitations in the PRA scope, and other completeness issues either by limiting the scope of the application, or by demonstrating that the impact of the unanalyzed portion of the risk on both the base case risk and on the change in risk is bounded or can be neglected. Section 111.2.2.2 of this SRP chapter discusses this further. Cumulative and Synergistic Effects from all Applications In evaluating the licensee's submittal, reviewers should consider the effects of the proposed changes in light of previously submitted changes implemented by the licensee. Optimally, the PRA used for the current application should already model the effects of past applications. However, qualitative and synergistic effects are sometimes difficult to model in the PRA. Therefore, a review of