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:
internal fire scenario selection and analysis are identified and characterized. The objective of the internal fire ignition frequency is to estimate the frequencies of the ignition sources postulated for the internal fire scenarios. Ignition sources consist of in situ sources, such as electrical cabinets or batteries, and other sources, such as transient fires. U.S. nuclear power industry internal fire event frequencies, possibly augmented with plant-specific experience for operating reactors, are used where available to establish the fire ignition frequencies. Other sources are generally used only for cases when the U.S. nuclear power industry does not provide the representative frequency. Internal fire ignition frequencies due to LPSD types of POS conditions that are different from conditions in at- power types of POSs should be addressed (e.g., the frequency of general transient fires or hot work fires). RG 1.247, Page 31 All POSs should be evaluated for differences in the internal fire ignition frequency sub-element. The characteristics and attributes needed to achieve the objectives of an internal fire ignition frequency PRA analysis element are as follows: • Frequencies are established for ignition sources and consequently for PAUs. • Transient fires should be postulated for all PAUs regardless of administrative controls. • Appropriate justification should be provided for the use of nonnuclear experience to determine internal fire ignition frequency. • Internal fire frequencies should be specific to POS conditions (e.g., the frequency of general transient fires or hot work fires) as appropriate. • All POSs should be evaluated for differences in the internal fire ignition frequency PRA analysis element. • The uncertainties related to the internal 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