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
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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 of this appendix 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: 19.2-45 June 2007 • The licensee has adequately considered the effects of proposed changes on the structure and logic of the event trees. • The licensee has addressed the effects of the application on sequence dependent failure analysis, sequence timing, and success criteria. A.3 System Modeling Analysis (Fault Trees) a. Areas of Review Fault trees are used to depict the logical interrelationships of credible plant events (component hardware failures, human errors, or other pertinent events) that can lead to particular failure modes of plant systems in the context of their environment and operation. In RIR, the majority of proposed changes would only be expected to impact the parameters that are used to quantify the event probabilities modeled in the fault trees. In such cases, the change will not affect the fault tree logic models themselves. However, in cases where the change relates to a system design change, or where the licensee is proposing temporary changes that require reconfiguration of the system into ones that are not currently modeled, the revised fault trees should be one focus of the review. Other considerations of which reviewers should be aware in the area of system analysis