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:
ncrease 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 SRP 19-A3 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. 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