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:
n 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. SRP 19-B4 • Review plant operating history for failures of mitigating system trains attributable to events that might have been prevented by the proposed application. • Review accident sequence modeling for instances in which early termination of the analysis obscured challenges to affected SSCs that would normally come into play later than the termination point. Possible dispositions of the above tasks include the following results: • The item will not affect initiating event frequency or mitigating system performance under reasonably foreseeable circumstances, and the proposed change is warranted. • Although unmodeled, the item already receives and will continue to receive programmatic attention commensurate with its significance. In cases where reduced commitments are proposed, adequate justification is provided for this reduction. • The item does not currently receive sufficient programmatic attention and may be subject to tighter controls. Reviewers should verify that the safety significance of SSCs not modeled in the PRA (but affected by the proposed application) are appropriately characterized and justified. Addressing Limitations of the Risk