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:
ion are both justified and reasonable. • Data used to support changes to the plant's design or operations are supported by an appropriate performance monitoring program. A.7 Modeling of Common Cause Failures a. Areas of Review Common cause failures (CCFs) represent the failures of components that are caused by common influences such as design, manufacturing, installation, calibration, or operational deficiencies. Since CCFs can fail more than one component at the same time and can occur with greater probability than would be predicted by the product of the individual component failure probabilities, they can significantly contribute to plant risk. Risk-informed applications that cover SSCs as a group have the potential to affect the CCF probabilities of SSCs within the given group. For the affected components, CCF probabilities could be low or might not even be included in the baseline PRA models based on the operational and engineering evidence driven by current requirements. With proposed changes, there should be assurance that the CCF contribution will not become more significant. In addition, the assessment of the impact of the change can be affected by the CCF probabilities for other components, and can either be exaggerated or obscured depending on the CCF probabilities. b. Review Guidance and Procedures Reviewers should verify that the PRA addressed potentially significant CCFs and that, where applicable, the CCF modeling has incorporated the effects of the proposed changes. Staff evaluation should include a review of the process used to select common cause component groups. Specific review guidelines related to risk-informed applications and the assessment of the change are as follows: • Reviewers should verify that industry and especially plant-specific experience involving the failure of two or more components (especially for the application-specific components) from the same cause was analyzed and incorporated into the risk model where appropriate.