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:
releases into smaller subsets of representative source terms with emphasis on large early release and large late release Quantification • Estimation of the frequency of different containment failure modes and resulting radionuclide source terms DG-1362, Page 19 Technical Elements for Internal Flood, At-Power PRA This section identifies the technical elements for an internal flood, at-power PRA. The objective for each technical element is briefly described and the characteristics and attributes needed to achieve the objective are provided in the subsequent table. The technical elements for an internal flood, at-power PRA are: • flood area partitioning • flood source analysis • flood scenario analysis • flood scenario delineation and quantification PRA models of internal floods are based on an existing up-to-date internal events, at-power PRA model, which is modified to include the impact of the identified flood scenarios in terms of causing initiating events, and failing equipment used to respond to initiating events. The quantification task specific to internal floods is similar in nature to that for the internal events. Because of its dependence on the internal events model, the internal flood PRA incorporates the elements of regulatory positions C.1.2.1 and C.1.2.2, as necessary. Flood area partitioning divides the plant into flood areas that are used as the basis for the flood analysis. Flood areas are defined on the basis of physical barriers, mitigation features, and propagation pathways. Flood source analysis identifies 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 structures, systems, and components (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