Document: NUREG-0800
Document ID: ac43f632-9db1-4857-9f56-bfba45965456
Document Type: srp
Title: * These are modifications to a plant’s design, operations, or other activities that require NRC approval. These modifica
Source: NUREG-0800
Source URL: https://www.nrc.gov/docs/ML0232/ML023250195.pdf
Revision Date: 2023-06
Chapter: 19
Section ID: 19
CFR Part: 
CFR Title: 

Content:
mportance, Risk Reduction Worth, and Risk Achievement Worth. However, in using these importance measures for risk-informed applications, several issues should be addressed. Most of these issues relate to technical problems that can be resolved through the use of sensitivity studies or appropriate quantification techniques, as discussed in detail later in this section. In addition, there are two issues that reviewers should ensure have been adequately addressed, namely (i) that risk rankings apply only to individual contributions and not to combinations or sets of contributors, and (ii) that risk rankings are not necessarily related to the risk changes that result from those contributor changes. When correctly applied and interpreted, component-level importance measures can provide valuable input to the integrated decisionmaking process. b. Review Guidance and Procedures Risk ranking results from a PRA can be affected by many factors, the most important being the model assumptions and techniques (e.g., for modeling of human reliability or common cause failures), the data used, and the success criteria chosen. Reviewers should therefore evaluate the licensee’s PRA as part of the overall review process. Appendix A to this SRP chapter presents guidance for this review. In addition to using a PRA of appropriate quality for the application, the licensee should 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