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
CFR Part: 
CFR Title: 

Content:
ovide valuable insight on the validity of the event tree structure and logic. Specifically, reviewers should ensure that the following factors are addressed in the evaluation of the LB change: • The event trees reflect changes (if any) to the initiating event groupings. • The models and analyses are consistent with the as-built and as-operated plant, i.e., the functions necessary for safe shutdown are included, relevant systems are credited for each function, and plant emergency operating procedures (EOPs) and abnormal operating procedures (AOPs) are correctly represented. In addition, when the proposed change affects any of these elements, the change is properly modeled. • Changes to the plant's design or operations could affect the dependencies (functional, phenomenological, and operational) among the top events in event trees. Section A.4 of this appendix 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 station blackout (SBO) sequences). The impact of the change on event timing that could affect the structure or logic of the event trees should be understood. • 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