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:
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, • a mechanical draft tower with a basin1 and a lake, • a cooling lake with a submerged pond,1 and • two wet/dry forced draft towers.1 1 These are designated as Seismic Category I design. DG-1275, Page 6 The UHS complex, whether supplied by single or multiple water sources, should be capable of withstanding, without loss of the UHS safety functions, all of the following events: 1. the most severe natural phenomena expected at the site in accordance with GDC 2, 2. the site-related events (e.g., river blockage, river diversions, reservoir depletion, ship collisions, airplane crashes, oil spills, fires) that have occurred or may reasonably be expected to occur during the lifetime of the plant, 3. reasonably probable combinations of less severe natural phenomena or site-related events, and 4. failure of reservoirs, dams, and other manmade water retaining structures both upstream and downstream of the site including the potential for resultant debris to block water flow. In applying this approach, various mechanistic failure modes should be postulated. A licensee or applicant may choose to assume a complete functional loss, but this is not necessarily required. For example, the consequences of a postulated major rupture of a dam (including the time-related effects of forces imposed at the time of rupture) should be assumed. As another example, the consequences of a postulated slide of earthen canal walls should be assumed; however, it is not necessarily required to assume that waterflow ceases completely. Realistic assumptions about potential flow blockage from resultant debris should also be made. In cases where canals (aqueducts) or piping systems are required as part of the UHS, at least two should be provided, even if only one source of water can be demonstrated to be