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:
tes needed to achieve the objectives of an internal fire scenario selection and analysis PRA analysis element are as follows: • Internal fire scenarios are defined in terms of ignition sources, fire growth and propagation, fire detection, fire suppression, and cables and equipment (“targets”) damaged by fire. • The effectiveness of various fire protection features, and systems is assessed (e.g., fixed suppression systems). • Appropriate internal fire modeling tools are applied. • The technical basis is established for statistical and empirical models in the context of the internal fire scenarios (e.g., fire brigade response). • Scenarios involving the internal fire-induced failure of structural steel are identified and assessed (at least qualitatively). • Multicompartment fire propagation scenarios are also assessed and screened as appropriate. • The ability to develop internal fire scenarios 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. • The nature and amount of transient fuel sources introduced in the plant may differ for different POSs and should be evaluated. • The availability of fire protection features and systems during a POS should be evaluated for plant activities that have a bearing on their availability. For example, dependencies between activities in the plant, such as removing a fixed suppression system from service in an area while performing hot work, should be addressed. • Fire barrier failures should also be addressed in the context of those plant activities leading to the demand for that barrier. • All POSs should be evaluated for differences in the internal fire scenario selection and analysis sub-element. • The uncertainties in the 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