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
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components that might contribute to initiating event occurrence, mitigating system components that were not modeled in the PRA because their failure was not expected to dominate system failure in the baseline configuration, and components in systems that do not play a direct role in accident mitigation but do interface with accident mitigating systems. The process applied by the licensee to overcome limitations of PRA was appropriate. Where decisions were made that do not follow straightforwardly from the PRA, a technical basis was provided that shows how the PRA information and the supplementary information validly combine to support the finding. No findings contradict the PRA in a fundamental way. SRP 19-B5 APPENDIX C CATEGORIZATION OF PLANT ELEMENTS WITH RESPECT TO SAFETY SIGNIFICANCE For several proposed applications in risk-informed regulation, one of the principal activities is the categorization of SSCs and human actions with respect to their safety-significance. This appendix discusses how to review approaches that may be used in this categorization process. The first review consideration is the definition of safety-significance as it applies to SSCs and human actions for a specific application. A related, but not identical concept, is that of risk significance. For example, an individual SSC can be identified as being risk-significant if it can be demonstrated that its failure or unavailability contributes significantly to the measures of risk (e.g., CDF and LERF). Safety significance, on the other hand, can be thought of as being related to the role the SSC or human action plays in preventing the occurrence of the undesired end state. Thus, the SSCs and human actions considered when constructing the PRA model have the potential to be safety significant, since they play a role in preventing core damage or large early release. These SSCs and human actions may include those that do not necessarily appear in the final quantified model because they have