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:
is defined in terms of how closely the base PRA represents the plant as it is actually built and operated. In general, PRA results used to support an application must be derived from a base PRA model that represents the DG-1362, Page 12 as-built and as-operated plant to the extent needed to support the application. Consequently, the base PRA is maintained and upgraded, where necessary, to ensure it represents the as-built and as-operated plant. However, for some applications, the plant may only be in the DC or COL stage of licensing, at which point the plant may not have been built or is not yet operational. At these licensing stages, the base PRA model is intended to reflect the as-designed plant. Regulatory position C.1.4 provides guidance on plant representation in the base PRA. Scope of a Base PRA The scope of a base PRA is defined by the challenges included in the analysis, the level of analysis performed and its intended use for representing the as-built and as-operated plant. Specifically, the base PRA scope is defined in the following terms: • metrics used to characterize the risk, • POSs for which the risk is to be evaluated, and • causes of initiating events (hazard groups) that can potentially challenge and disrupt the normal operation of the plant. For currently operating reactors and for reactors at the DC or COL application stage, some applications may require a full-scope Level 1 and some aspects of a Level 2 PRA. Risk characterization is typically expressed by metrics of core damage frequency (CDF) and LERF (as surrogates for latent and early fatality risks, respectively, for operating light-water reactors). Large release frequency (LRF) is used as a risk metric for LWR DC and COL applicants, as approved in SRM-SECY-90-016, “Evolutionary Light Water Reactor (LWR) Certification Issues and Their Relationships to Current Regulatory Requirements” (Ref. 38). The CDF and LERF metrics are defined in a functional sense as follows: • Core damage