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
CFR Part: 
CFR Title: 

Content:
cessary in order to relate the application to actual risk indices. Documentation of inputs to the decisionmaking panel should be part of the process. Reviewers should verify the scope and depth of the information base, especially information supplied regarding modes and/or classes of initiators unanalyzed in the PRA. Treatment of SSCs not modeled in the PRA PRAs do not model all SSCs involved in performance of safety functions for various reasons. However, this should not imply that unmodeled SSCs are not important in terms of contributions to plant risk. For example, SSCs are omitted in some cases because the analysts take credit for programmatic activities that ensure a low failure frequency for that item or a short fault exposure time in the event that it does fail. In such cases, even though the PRA results will not reflect the SSC at all, it would be inappropriate to conclude that the programmatic activity is unimportant. Consequently, one task of the integrated decisionmaking panel is to extrapolate from the PRA and other information sources to draw conclusions about SSCs that are not modeled in the PRA. This does not mean that the panel is to impute to the PRA high-level results that were not generated in the analysis; however, it does mean that if a success path is modeled in the PRA, the panel is justified in reasoning that unmodeled SSCs in that path are relied upon. If items were screened from the PRA, the panel should be aware of the screening process, in order to avoid violating the basis for the screening. For SSCs not modeled in the PRA, reviewers should verify that the decisionmaking panel has performed the following tasks: Review the PRA assumption base for instances in which initiators were screened out on the basis of credit for SSCs affected by the application. Review plant operating history for initiating events that might have been prevented by the proposed application. Review plant operating history for failures of mitigating system trains