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:
ical review, parameter values will have been judged to be appropriate, whether they have been evaluated using generic or plant-specific data. However, since the review was focused on the PRA as a base case model, a different perspective on the appropriateness of parameter values may be required for specific applications. Therefore, in evaluating PRA applications, reviewers should focus on those parameter values that have the potential to change the conclusions of the analysis. For example, parameters associated with SSCs that appear in the same cutsets or scenarios as the affected SSCs have the potential to distort the conclusions by decreasing the assessed importance of the change if their values are too low, or by increasing it if their values are too high. Similarly, parameters that contribute to the cutsets or scenarios that do not contain affected SSC.. can decrease the importance of the change by being too high, or increase it by being too .lcw. The failure rates and probabilities used, especially those that directly affect the proposed application, should appropriately consider both plant-specific and generic data. The staff expects that these values will be consistent with generally accepted values from PRAs of similar plants, or the licensee should justify significant deviations on the basis of plant-specific factors. "Significant" in this context can be defined 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 thal 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 ap3lies. 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.