Document: NUREG-0800
Document ID: e32f0820-4e33-476e-aa36-4ca8c2c64af0
Document Type: srp
Title: Use of Probabilistic Risk Assessment in Plant-Specific, Risk-Informed Decisionmaking:
Source: NUREG-0800
Source URL: https://www.nrc.gov/docs/ML0119/ML011940192.pdf
Revision Date: 2023-06
Chapter: 19
Section ID: 19.0
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Content:
for recovery of failed components (restoration of component function, as opposed to actuation of a compensating system). When human actions are proposed as compensatory measures as part of a proposed change, licensee actions to ensure operator performance at the level credited in the risk analysis (e.g., by training, procedures, etc.) are also a part of the change request. A.9 Sequence Quantification a. Areas of Review The staff would not genel-ally anticipate the need to perform a detailed review of the quantification of the change in risk; however, some details of the quantification process SRP 19-A18 should be 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 staff 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