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:
und on the PRA review, the reader is referred to the bibliography provided in Section A.11 of this appendix. A.1 Initiating Event Analysis a. Areas of Review Whether or not a PRA includes a particular initiating event depends on the scope of the PRA, the frequency of the given event, the plant systems or other features available to mitigate the event, and the consequences of the event if unmitigated. Proposed plant changes could affect the frequency of initiating events, the probability of mitigating event initiators, and in some cases, event consequences. In addition, plant changes could potentially introduce new initiating events or increase the importance of events that were previously screened out. SRP 19-A2 b. Review Guidance and Procedures For risk-informed applications, reviewers should determine whether the licensee followed a systematic approach to determine whether initiating events and anticipated plant response are affected by the proposed changes. Reviewers should also determine whether the licensee’s process includes provisions to evaluate whether the proposed changes can (i) increase the frequency of an initiator already included in the PRA, (ii) increase the frequency of initiators that were initially screened out in the PRA, (iii) introduce new initiating events, or (iv) affect the grouping of initiating events. These considerations are discussed in more detail in the following paragraphs. Applications that change the frequency of an initiator or the ability of the plant to respond to event initiators are relatively easy to model in the risk analysis if the initiators are already included in the base analysis. In such cases, the licensee should have evaluated the impact of the changes directly from the risk model. In cases where initiators are not included in the original risk analysis based on screening analyses, the licensee should have determined whether initiating events previously screened out because of low frequency might now be above the