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:
n 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, these changes are appropriately included in the PRA system models. A.4 Dependent Failure Analysis a. Areas of Review Accident progression models and system models should correctly account for dependencies between systems and operator actions needed for accident mitigation. Proposed changes to the plant's design or operations could affect these dependencies; therefore, the evaluation of the risk change should also consider system-operator dependencies. However, since the modeling of these dependencies requires detailed knowledge of the plant systems and procedures, it will not be practical (nor is it intended) for reviewers to verify that all dependencies have been included in the change evaluation. Instead, reviewers should verify that the evaluation utilized a