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:
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 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 staff's review. Other considerations of which reviewers should be aware in the area of system analysis are whether the application can impact support functions in such a way as to alter the dependencies in the model, and whether the application can impact system performance to an extent that would require changes to the fault tree logic or modeling assumptions. SRP 19-A6 b. Review Guidance and Procedures When the review of one or more of the system logic models becomes necessary, this review should include a study of