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
CFR Part: 
CFR Title: 

Content:
p3lies. 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 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. SRP 19-A12 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