Document: NUREG-0800
Document ID: e32f0820-4e33-476e-aa36-4ca8c2c64af0
Document Type: srp
Title: Use of Probabilistic Risk Assessment in Plant-Specific, Risk-Informed Decisionmaking:
Source: NUREG-0800
Source URL: https://www.nrc.gov/docs/ML0119/ML011940192.pdf
Revision Date: 2023-06
Chapter: 19
Section ID: 19.0
CFR Part: 
CFR Title: 

Content:
ng 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 SRP 19-A2 plant changes or, in the case where 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 initiators have been identified, these have been added to and analyzed in the risk model. 0 The licensee has accounted for the proposed changes in the grouping of initiating events. 0 The decisionmaking process considered the dependencies between the initiating events and the plant's mitigation