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:
e taken into account in reviews of PRA applications. The licensee should also have evaluated proposed plant changes to determine whether the changes could result in initiators that were not previously analyzed in the PRA. For example, changes might enhance the potential for spurious operation of components that might, in turn, cause initiating events, or changes might increase the likelihood for operator errors of commission that could result in plant trips. If the licensee identified mechanisms for producing new initiators, reviewers should ensure that the licensee added those initiators to the risk analysis so that their impacts can be analyzed. In PRAs, initiating events are usually grouped according to the systems required to respond to the transient. This implies that success criteria for plant systems and operator responses are similar for all events in a group. In addition, events may be screened out when it can be shown that they are bounded in probability and consequence by other similar events. In evaluating risk-informed applications that affect initiating events, reviewers should ensure that grouping criteria used in the base analysis have not been invalidated by the proposed plant changes or, when this is not true, the licensee has made appropriate changes to the event groupings. Finally, the reader should note that many PRAs model initiating events as single basic events or "black boxes." In RIR, it is preferred that the licensee model initiating events (especially those that result from the loss of support systems) using a fault tree (or equivalent) approach so that system dependencies are fully understood and accounted for. If this is not the case, reviewers should be aware of the combination of SSC failures or other events that could lead to the "failure" of the black box. This would lead to a better understanding of the risk contributors and is especially important in risk categorization applications. 19.2-43 June 2007 c. Evaluation Findings