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:
l fire ignition frequencies are identified and characterized. The objective of the internal fire circuit failure analysis is to treat the impact of internal fire- induced circuit failures on the plant response for all POSs. In particular, spurious actuations from hot shorts are analyzed. The conditional probability of the particular circuit failure is identified and assigned. The characteristics and attributes needed to achieve the objectives of an internal fire circuit failure analysis PRA analysis element are as follows: • The conditional probability of occurrence of various circuit failure modes given cable damage from an internal fire is based on cable and circuit features. • The ability to develop internal fire-induced circuit failure likelihoods in the internal fire PRA is limited by the information known about the plant (i.e., the lack of as-built details) prior to construction. • Since the cable itself, its function in the plant, and cable location relative to other cables are not often affected by the LPSD type of POSs, the circuit failure analysis from at-power types of POSs is often applicable to the LPSD type of POSs, with limited potential exceptions. Differences in circuit failure analysis should be evaluated for different POSs. • The uncertainties related to the internal fire circuit failure analysis are identified and characterized. The objective of the internal fire HRA is to identify operator actions and related HFEs, both within and outside the main control room, for inclusion in the plant response model for the POS. This element also includes quantification of human error probabilities for the modeled actions. Modeled operator actions include those introduced into the plant response model resulting strictly from internal fire-related procedures and those actions retained from the internal events PRA. The latter HFEs are modified to account for internal fire effects. The characteristics and attributes needed to achieve the objectives of an