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:
ation of the risk measures. However, the feasibility of performing such risk quantification has been questioned for those applications for which a method for evaluating the impact of the change on SSC unavailability is not obviously available. In such instances, an acceptable alternative to requantification of risk is to categorize SSCs and human actions using an integrated decisionmaking process (such as the use of an Expert Panel), with PRA importance measures as input. This appendix discusses the issues that reviewers should address for this approach. Section C.A discusses the technical issues SRP 19-Cl associated with the use cf PRA importance measures, and Section C.2 discusses the use of the importance measures by the decisionmaking panel. C.1 Use of Importance Measures a. Areas of Review In the implementation of t:he Maintenance Rule and in many industry guides for the risk-informed applications, the measures most commonly identified for use in the relative risk ranking of SSCs and human actions include the Fussell-Vesely Importance, Risk Reduction Worth, and Risk Achievement Worth. However, in using of these importance measures for risk-informed applications, several issues should be addressed. Most of these issues relate to technical problems that can be resolved through the use of sensitivity studies or appropriate quantification techniques, as discussed in detail later in this section. In addition, there are two issues that reviewers should ensure have been adequately addressed, namely i) thai: risk rankings apply only to individual contributions and not to combinations or sets of contributors, and ii) that risk rankings are not necessarily related to the risk changes which result from those contributor changes. When correctly applied and interpreted, component-level importance measures can provide valuable input to the integrated decisionmaking process. b. Review Guidance and Procedures Risk ranking results from a PRA can be affected by many factors, the