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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Content:
events, or flow blockages by sludge or debris should also be considered in the analysis. • The potential for common cause failures, including those potentially resulting from the change, should have been evaluated and modeled where appropriate. Review guidance for the evaluation of common cause failures is provided in Section A.7 of this appendix. • The function of the modeled system should remain consistent with that required in the event tree models. Success criteria and event sequence conditions should be correctly modeled and consistent with the definition in the event trees. When fault tree solutions in the form of function cutsets are available, an efficient way to review for the logic in system models is to study the cutsets produced by the solution of the linked fault trees (i.e., the fault tree formed by linking the support system fault trees to the system fault tree). In performing this visual inspection, reviewers should compare the results with expectations based on their understanding of functional and support system dependencies. The effects of events such as operator actions or common cause failures can also be easily verified by an inspection of the function cutsets. When expected combinations of failures are not present, reviewers should check to see if these failures have been modeled, or if they have been truncated during model solution, or if the fault tree logic is incorrect (e.g., an AND gate in place of an OR gate). In short, a review of cutsets can be one way to focus further reviews on other parts of the system modeling analysis. c. Evaluation Findings Reviewers should verify that information provided and review activities conducted support the following conclusion: The evaluation adequately reflects changes in the plant hardware or procedures, including changes to the system design or alignments, system performance characteristics, support system dependencies, and operational procedures or operational philosophies. Where applicable,