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:
the plant's design or operations could affect the dependencies (functional, phenonnenological, and operational) among the top events in event trees. Section A.4 of this SRP chapter presents additional detail concerning the review of the dependent failure analysis. Time-phased evaluation is normally included for sequences with significant time-dependent failure modes (e.g., batteries for station blackout sequences) and significant recoveries (e.g., AC recovery for SBO sequences). The impact of the change on event timing that could affect the structure or logic of the event trees should be understood. SRP 19-A4 It is expected that the success criteria used in the event trees will not be affected by many of the changes to the plant's design and operations. In cases where changes could affect the success criteria for front-line or support systems, reviewers should verify that these criteria (hardware requirements, number of trains required, etc.) remain consistent with the required performance criteria (flow, response time, etc.) related to functional requirements. However, even in cases where the change does not affect the success criteria, reviewers should be aware that the success criteria used in the base PRA analysis could affect the conclusions made in the evaluation of the risk change. For example, a component in a three-train system might not be risk-significant if mission success was contingent on the successful operation of one out of the three trains, but this component could become more risk-significant if the success criterion was two-out-of-three or three-out-of-three trains. Section A.5 discusses the review of the success criteria used in accident sequence modeling. c. Evaluation Findings Reviewers should verify that information provided and review activities conducted support the following conclusions: The licensee has adequately considered the effects of proposed changes on the structure and logic of the event trees. * The licensee has addressed the