Document: NRC Regulatory Guide
Document ID: cde52d5a-adf9-49be-9d1f-59449dfca895
Document Type: regulatory_guide
Title: TRIAL - Acceptability of Probabilistic Risk Assessment Results for Non-Light Water Reactor Risk-Informed Activities
Source: NRC Regulatory Guide Division 1
Source URL: https://www.nrc.gov/docs/ML2123/ML21235A008.pdf
Revision Date: 2023-05
Chapter: 
Section ID: RG-1.247
CFR Part: 
CFR Title: 

Content:
nges to plant operations that poses some risk to a facility. For example, internal events are a hazard group, whereas a reactor containment building (RCB) breach is a hazard within the internal events hazard group. A hazard group is characterized as either an internal or external hazard type; the distinction between these hazard types is defined by the plant boundary in the PRA. This RG addresses the following seven hazard groups: • internal events, • internal flood, • internal fire, • seismic events, • high wind, • external flood, and • other hazards. 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 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. Such a systematic survey of hazards should initially be conducted independent of any pre-determined list of hazards to avoid anchoring bias—the potential for decisions about what hazards should be considered to be influenced by a specific reference point. However, after such an independent survey of hazards is complete, it is reasonable that the results could subsequently be compared to relevant, existing lists of hazards to further assess completeness of the set of hazards to be considered. Thus, a number of internal and external hazards are considered during the development of a 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, quantitatively, or both but in a simplified way and without the need for a detailed PRA model. Regulatory Position C.1.3.11 provides additional guidance on screening and conservative analyses that can be performed to this end. A hazard that is not