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:
oses some risk to a facility. For example, internal events is a hazard group and loss-of-coolant accidents (LOCAs) are a hazard within the internal events hazard group. A hazard group is characterized as either an internal or external hazard type, where the distinction between these hazard types is defined by the plant boundary in the PRA. The hazard groups addressed in this RG include the following: • internal events • seismic events • Other Hazards • internal floods • high wind • internal fire • external flood The first six hazard groups listed represent categories of hazards that are typically analyzed and modeled in detail using a PRA. However, 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. As such, there are a number of internal and external hazards that are considered during the development of a base PRA in addition to those hazards analyzed under the first six hazard groups listed above. For many such internal and external hazards, the risk posed to a facility can be assessed qualitatively and/or quantitatively, but in a simplified way and without the need for a detailed PRA model. Regulatory position C.1.2.6 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 for a simplified analysis and should be modeled in detail using a PRA. This latter type of hazard is commonly referred to as an Other Hazard and regulatory position C.1.2.9 provides additional guidance on the modeling of such hazards. Appendix D of this RG provides a listing of and general description for the internal and external hazards that should be considered during the development of a base