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
CFR Part: 
CFR Title: 

Content:
ied upon in the plant's response to an initiating event. Reviewers should then verify that at least some elements of each of the important systems identified above are considered "safety significant." If this is not the case, reviewers should ascertain what performance is allocated to these items in the PRA, and whether the programmatic activities allocated to these elements are commensurate with the given performance level. If a system is identified as being important, but none of its elements is, reviewers should carefully evaluate the licensee’s justification. As an example, consider the case of a system that contains many redundant flowpaths. Single event importance analysis will tend to dismiss the flowpaths one at a time, effectively dismissing the group as a whole. The focus of the above guidance is that the redundant flowpaths (considered as a subsystem, and recognizing the function they perform), are important and deserve some attention, even though conventional importance measures would not highlight them. However, in the case of redundant systems, the solution need not always be to assign every redundant path to the high-risk contributor category. In this example, especially if the paths are essentially similar, it is arguably necessary to consider CCF. Thus, a program that addresses CCF potential by monitoring component performance may provide the necessary protection against loss of the function, while still allowing a decrease in some level of commitment on the individual members of the group. Verification of Low Safety Significance: In evaluating the qualitative risk-informed categorization, reviewers should consider the integrated decisionmaking process and criteria used by the licensee. In reviews of the licensee’s determination of low safety significance for SSCs or operator actions, reviewers should verify that the licensee appropriately applied risk importance measures and accounted for the results of sensitivity studies. Reviewers should