Document: NRC Regulatory Guide
Document ID: 22ccfd5e-c5d8-4615-a02c-32369aa9f533
Document Type: regulatory_guide
Title: Acceptability of Probabilistic Risk Assessment Results for Risk-Informed Activities (Rev. 3)
Source: NRC Regulatory Guide Division 1
Source URL: https://www.nrc.gov/docs/ML1930/ML19308B636.pdf
Revision Date: 2023-06
Chapter: 
Section ID: RG-1.200
CFR Part: 
CFR Title: 

Content:
table DG-1362, Appendix C, Page C-2 approach for determining whether a change to a PRA model is classified as PRA maintenance or a PRA upgrade. The description of Step 2 of the process in Section 3 of PWROG-19027-NP, Revision 1, includes four items. The NRC staff considers the first item to be an example of when a state-of-practice method is implemented in a new context whereupon the change to the PRA would be considered a PRA upgrade. However, the last three of the four items are not considered to be examples of when a state-of-practice method is implemented in a new context, because they could represent cases where an NDM is being used without being subjected to the NDM technical adequacy assessment peer review. Newly Developed Method An NDM is a method that has either been developed separately from a state-of-practice method or is one that involves a fundamental change to a state-of-practice method with respect to use in a PRA. An NDM for a PRA may well be used by other industries or other applications, but it has not been used to meet the requirements for a PRA model as defined by a national consensus PRA standard, and as endorsed in this regulatory guide with exceptions and clarifications. Therefore, an NDM is not considered to be part of the state-of-practice in developing PRA models for a nuclear power plant. The NRC staff endorse the definition of the term NDM provided in PWROG-19027-NP, Revision 1, which has been reproduced in the Glossary of this regulatory guide for reference. As indicated in the definition of an NDM, such a method may have been developed separately from an existing method. Although the purpose and goal of the NDM may be similar to that of an existing method, the NDM’s technical bases (e.g., assumptions and data) and the tools (e.g., analyses, equations) used to formulate the method are fundamentally different than that of the existing method. Additionally, an NDM may have been developed from an existing method that has been modified. A