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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Content:
"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 Reviewers should verify that the information provided and review activities conducted support the following conclusions: • The licensee has adequately considered the effects of proposed changes on the frequencies of initiating events analyzed and those previously screened out. • The licensee has demonstrated that the changes do not result in new initiating events or, if new initiators have been identified, these have been added to and analyzed in the risk model. • The licensee has accounted for the proposed changes in the grouping of initiating events. • The decisionmaking process considered the dependencies between the initiating events and the plant's mitigation systems. A.2 Accident Sequence Analysis (Event Trees) a. Areas of Review Although the evaluation of risk change from most applications will usually not necessitate changes to the event tree structure or logic, reviewers should be aware that there will be some changes, particularly those involving changes to plant procedures, that might cause a restructuring of the event sequence logic. In addition, the application may isolate part of the PRA that is dependent on specific initiating events. Thus, these initiating events and their associated event trees would have a proportionately greater impact on the evaluation of the change in risk. In this case, these event trees could be candidates for a higher level of scrutiny. For example, if the changes involved the addition or subtraction of a diesel generator, the review would focus on the station blackout event tree and its associated structure and logic. Similarly, if changes involve modification to procedures to cross-tie electrical buses, the review might focus on the loss of offsite power event trees. b. Review Guidance and Procedures Event tree