Document: NUREG-0800
Document ID: 7916b088-fb90-4163-84fe-027bd315bcc5
Document Type: srp
Title: REVIEW OF RISK INFORMATION USED TO SUPPORT PERMANENT PLANT-
Source: NUREG-0800
Source URL: https://www.nrc.gov/docs/ML0717/ML071700658.pdf
Revision Date: 2023-06
Chapter: 19
Section ID: 19.2
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CFR Title: 

Content:
demonstrate the robustness of risk ranking results for conditions and parameters that might not be addressed in the base PRA. Therefore, when importance measures are used to group components or human actions as low safety-significant contributors, the information to be provided to the integrated decisionmaking process should include sensitivity studies and/or other evaluations to demonstrate the sensitivity of the ranking results to the important PRA modeling techniques, assumptions, and data. In assessing this information, reviewers should consider the following issues: Different Risk Metrics: Reviewers should ensure that the licensee’s ranking process adequately considered risk in terms of both CDF and LERF. Completeness of Risk Model: Reviewers should ensure that, when determining safety significance contributions using an internal events PRA, the licensee also considered external events, as well as shutdown and low-power initiators, either by PRA modeling or by the integrated decisionmaking process (as detailed in Section C.2 of this appendix and Appendix B to this SRP section). Sensitivity Analysis for Component Data Uncertainties: The licensee should have addressed the sensitivity of component categorizations to uncertainties in the parameter values. Reviewers should be satisfied that SSC categorization is not affected by data uncertainties. Sensitivity Analysis for Common Cause Failures: CCFs are modeled in PRAs to account for dependent failures of redundant components within a system. As discussed in Appendix A to this SRP section, CCF probabilities can impact PRA results by enhancing or obscuring the importance of components. This should be addressed by the review. A component may be ranked as a high risk contributor mainly because of its contribution to CCFs, or a component may be ranked as a low risk contributor mainly because it has negligible or no contribution to CCFs. I n RIR, removing or relaxing requirements may increase the CCF contribution,