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:
fined as no greater than a factor of 3 for the mean values of the failure rate or failure probability. The focus of the review should be on those parameter values that have a significant impact on the results as discussed above and that deviate significantly from the generally accepted norm. If the reviewer decides that a more detailed review of the parameter values is appropriate, the following guidance applies. For plant-specific data, reviewers should determine how the licensee used plant records to estimate the number of events or failures, the number of demands, and the operating or standby hours. Reviewers should verify the consistency between the definitions of failure modes and component boundaries used in the risk analysis and the corresponding definitions used in the plant records. When reviewing generic data, it is important to verify that the plant component is typical of the generic industry component. In cases where generic failure rates are used in combination with plant-specific data like test intervals, reviewers should verify that the generic data are applicable for the range of plant data used. When evaluating the impact of the change, it is important for reviewers to recognize the assumptions that have gone into developing the PRA model. For example, two models are commonly used for events representing the unavailability of a standby component on demand: the standby failure rate model and the constant probability of failure on demand model. The constant probability of failure on demand parameter may be estimated on the basis of an assumed number of demands, implying an average test interval. Use of such a model to investigate the impact of extending test intervals can result in large differences between the unavailabilities of components SRP 19-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