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:
confirmed. Specifically, reviewers should be confident that the licensee's evaluation process is sufficient to account for the potential effects of the proposed change on modeling simplifications and assumptions made during the quantification of risk. In addition, the reviewers should ensure that the chosen sequence truncation limits are appropriate so that important sequences are not discarded and final results are not sensitive to the chosen truncation limit. b. Review Guidance and Procedures Reviewers should verify that model simplifications and assumptions made during the quantification process are properly accounted for in evaluating of the change in risk, as illustrated by the following examples: • Reviewers should ensure that the licensee accounted for model asymmetries during the application of the PRA models. Asymmetries could result from modeling assumptions (e.g., assuming one train to be the operating train, and the second train to be the standby train), from differences in support system alignment, or from actual differences in system design or operating procedures. The licensees should have accounted for these asymmetries when evaluating changes to the affected systems. • Reviewers should ensure that, if cutset/sequence deletion is performed during quantification, these are correctly addressed in the assessment of risk change. In some quantification processes, cutsets that contain combinations of maintenance actions that are disallowed by the Technical Specifications are deleted from the accident sequence equations after the merging of functional cutset equations. This is done to avoid undue conservatism. If the PRA application deals with Technical Specification allowed outage issues, reviewers should confirm that any impacts on such deletions have been correctly addressed. • Reviewers should ensure that, if operator recovery actions are incorporated after the initial quantification, these actions are still valid in light of the proposed change.