Document: NUREG-0800
Document ID: ac43f632-9db1-4857-9f56-bfba45965456
Document Type: srp
Title: * These are modifications to a plant’s design, operations, or other activities that require NRC approval. These modifica
Source: NUREG-0800
Source URL: https://www.nrc.gov/docs/ML0232/ML023250195.pdf
Revision Date: 2023-06
Chapter: 19
Section ID: 19
CFR Part: 
CFR Title: 

Content:
The direct application of PRA results will therefore be limited to those SSCs that are explicitly modeled as part of the PRA basic events. Insights for SSCs that are implicitly modeled (e.g., screened out, assumed not important) are only to be used after additional consideration of the effects of the proposed change on PRA assumptions, screening analyses, and boundary conditions. Specifically, the following relationships exist between the level of detail in the modeling of each SSC and the conclusions that can be drawn from the PRA: • If the SSCs are modeled at the basic event level, i.e., each SSC is represented by a basic event (or sometimes, more than one if different failure modes are modeled), risk insights from the PRA can be applied directly to the modeled component as long as the effects of the change are appropriately considered. • If the SSCs are included within the boundaries of other components (e.g., the governor and throttle valves being included in the pump boundary), or if they are included in "black boxes" or modules within the PRA model, or if they are modeled as part of the calculation of human error probabilities (HEPs) in recovery actions, risk insights from the PRA can be applied if the effects of the application can be mapped onto the events (e.g., modules, HEPs) in question. In these cases it should be noted that the mapping is relatively simple if the event is under the same "OR gate" with the other module or HEP events. However, if the logic involves "AND gates," the mapping is more complicated. SRP 19-16 • If the SSCs are omitted from the model because of inherent reliability, or if they are not modeled at all, risk insights for these components should be obtained through an integrated decisionmaking process (such as an Expert Panel) that revisits the assumptions or screening criteria used to support the initial omission. III.2.2.4 Quality of a PRA for Use in Risk-Informed Regulation The baseline risk profile is used to model the