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:
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, thereby changing the risk impact of an SSC. 19.2-76 June 2007 Consideration of Multiple Failure Modes: PRA basic events represent specific failure events and failure modes of SSCs. Reviewers should verify that the licensee performed the categorization by taking into account the combined effects of all associated basic PRA events (such as failure to start and failure to run), including indirect contributions through associated CCF event probabilities. Sensitivity Analysis for Recovery Actions: PRAs typically model recovery actions especially for dominant accident sequences. Quantification of recovery actions typically depends on the time available to diagnose the situation and perform the action, as well as the adequacy of the licensee’s training, procedures, and operator knowledge. Estimating the success probability for the recovery actions involves a certain degree of subjectivity. The concerns in this case stem from situations where very high success probabilities are assigned to a sequence, resulting in related components being ranked as low risk contributors. Furthermore, it is not desirable for the categorization of SSCs to be impacted by recovery actions that sometimes are only modeled for the dominant scenarios. Sensitivity analyses can be used to show how the SSC categorization would change if recovery actions were removed. Reviewers should ensure that the categorization has not been unduly impacted by the modeling of recovery actions. Truncation Limit: Reviewers should verify that the licensee set the sequence truncation limits low enough so that the truncated set of minimal cutsets or scenarios contains the significant contributors and their logical combinations for the application in question. Depending on the level of PRA detail (module level, component