Document: NRC Regulatory Guide
Document ID: 46049842-54a7-40a0-a0cc-ab115059f05e
Document Type: regulatory_guide
Title: Ultimate Heat Sink for Nuclear Power Plants + HISTORY - HISTORY DG-1275 , Proposed Revision 3, published 09/2013 (Rev. 3)
Source: NRC Regulatory Guide Division 1
Source URL: https://www.nrc.gov/docs/ML1304/ML13043A624.pdf
Revision Date: 2023-06
Chapter: 
Section ID: RG-1.27
CFR Part: 
CFR Title: 

Content:
ip collisions, airplane crashes, nearby pipeline explosions, or oil spills and fires. Reasonable combinations of less severe natural and accidental phenomena or conditions also should be considered to the extent needed for a consistent level of conservatism. For example, such combinations should be evaluated in cases in which the probability of their existing at the same time and having significant consequences is comparable to that associated with the most severe phenomena. For instances where the UHS structure is partially embedded in the ground or in contact with ground water, the structural design should include the buoyancy forces of ground water on the foundation. If ground water is used for makeup of UHS water supply, the potential effects of settlement or land subsidence should be evaluated. Sedimentation buildup of sand and/or silt over time should be considered in the design of the UHS. There should be a high level of assurance that the UHS’s water sources will be available when needed. For natural sources, historical experience indicates that river blockage (e.g., ice dams or flood debris) or diversion may be possible, as well as changes in ocean or lake levels as a result of severe natural events, or the effects of climate changes that might occur over the design life of the facility. For manmade portions, particularly structures above ground, failures are not uncommon. Because of these factors, a UHS comprising at least two water sources should be considered; each source should be capable of performing the UHS safety functions, unless it can be demonstrated that there is an extremely low probability of losing the capability of a single source. Examples of UHSs that the staff has found acceptable are as follows: • a large river, • a large lake, • an ocean, • two spray ponds,1 • a spray pond1 and a reservoir, • a spray pond1 and a river, • two mechanical draft towers with basins,1 • a mechanical draft tower with a basin1 and a river, •