Document: NRC Regulatory Guide
Document ID: 8a2332d3-66ca-40af-84e1-507db8b26559
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:
or do not have enough construction complete to allow physical walkdowns. • Flood areas are based on the physical barriers, mitigation features, and propagation pathways for all POSs. • Sources of model uncertainty are identified and characterized for plant partitioning. The objective of the internal flood source analysis is to identify the flood sources in each flood area that are attributable to equipment (e.g., piping, valves, pumps) and other sources internal to the plant (e.g., tanks) along with the affected SSCs. Flood mechanisms examined include failure modes of components, human-induced mechanisms, and other water-releasing events. Flood types (e.g., leak, rupture, spray) and flood sizes are determined. Plant walkdowns are performed to verify the accuracy of the information. It is recognized that at the design and initial licensing stages, plant walkdowns are not possible. All POSs should be evaluated for differences in the internal flood source analysis element. It is important that the differences in POSs are considered in evaluating flood sources. The characteristics and attributes needed to achieve the objectives of the internal flood source analysis are as follows: • The identification and characterization of the following are sufficiently detailed: o SSCs located within each area, o flood sources and flood mechanisms for all POSs, and o type of water release and capacity. • Well defined and justified screening criteria are used for the elimination of flood sources and areas. Information is verified through plant walkdowns or by evaluating available data and findings of investigations of the plant design and operations information for plants that have not started construction or do not have enough construction complete to allow physical walkdowns. The objective of the internal flood scenario analysis is to identify the potential flood scenarios for each flood source by identifying flood propagation paths of water from the flood source to its RG