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:
-A13 for which the test intervals differ significantly. Reviewers should be sensitive to this effect, and should ascertain that licensees use appropriate models and parameters for such evaluations. As another example, in considering plant-specific failure data, poorly performing individual components may have been grouped with other components, allowing their poor performance to be averaged over all components of that type. Poor performance may arise because of inherent characteristics of one member of what would otherwise be considered a uniform population, or may arise because components are operating in a more demanding environment. If these components are grouped together with others for which the operating conditions are more favorable, the failure rates used for the poor performers could be artificially lowered. If requirements are relaxed on the basis of the group failure rate, reduced programmatic attention to these poor performers could lead to a greater-than-expected probability of experiencing an inservice failure of one of these components. Reviewers should be aware of such effects, and should ensure that the components are grouped appropriately. When the impact of the change is modeled as a change in the parameter values associated with specific basic events representing modes of unavailability of SSCs, reviewers should focus on whether the change in parameter values is appropriate and reasonable. The licensee is expected to document the rationale behind the change in parameter values, and that rationale should be carefully reviewed. If generic values are used for the base case parameter values that are candidates for change, reviewers should verify that the conditions under which the generic data apply do not correspond to those which would be more appropriate for a plant with the change incorporated. This should only be a real concern if the plant being changed is somewhat atypical with respect to the issue being addressed by the change. This would