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:
es, 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 modified existing method is considered an NDM when the modifications result in fundamental changes to the technical bases and tools used to formulate the method. In contrast, when a modified existing method does not result in such fundamental changes, it would be considered a revised (existing) method and not an “NDM.” DG-1362, Appendix D, Page D-1 APPENDIX D HAZARDS FOR CONSIDERATION IN A BASE PRA A key feature of a base PRA is that a wide spectrum of potential hazards in terms of magnitude and frequency of occurrence should be systematically surveyed to help ensure that significant contributors to plant risk are not inadvertently excluded from the PRA. A hazard is a category of similar challenges to plant design or operations that poses some risk to a facility. A hazard group is a set of similar hazards that are assessed in a PRA using common approaches, methods, and likelihood data for characterizing the effect on the plant. Hazards represent events or phenomena that are generally classified as either internal hazards or external hazards, based on the defined plant boundary in a PRA. Hazards categorized under the internal events, internal flood, internal fire, seismic, high wind, and external flood hazard groups are typically analyzed and modeled in detail using a PRA. However, there are a number of internal and external hazards whose risk to a facility can be assessed qualitatively and/or quantitatively, but in a simplified manner and without the need for a detailed PRA model. Regulatory position C.1.2.6 in Section C of this RG provides additional guidance on screening and conservative analyses that can be performed to this end. Conversely, some such internal and external hazards may produce impacts to a plant and a potential plant response that are too complex