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:
ding system design considerations, natural phenomena and site hazards design criteria, and in-service testing and maintenance considerations. This revised guide contains information applicable to both current operating plants and new plants being licensed under both 10 CFR Parts 50 and 52. Background The UHS is the system of structures and components and associated assured water supply and atmospheric condition(s) credited for functioning as a heat sink to absorb reactor decay heat and essential station heat loads after a normal reactor shutdown or a shutdown following a design-basis accident (DBA) or transient. This includes those necessary water-retaining structures (e.g., a pond, a reservoir with its dam) and the canals (aqueducts) or piping systems connecting those cooling water sources with the essential or safety-related cooling water intake structure of the nuclear power units. Non-safety systems (e.g., circulating water supply) may share this safety-related water supply. If cooling towers or portions of cooling towers are required to accomplish the UHS safety functions, they should satisfy the same requirements as the UHS. The UHS performs two principal safety functions: (1) dissipation of residual heat after reactor shutdown, and (2) dissipation of residual heat after a DBA such as a loss-of-coolant accident. For a single nuclear power unit, the UHS should be capable of providing sufficient cooling water to accomplish both of these safety functions. A UHS complex serving multiple units should be able to provide sufficient cooling water to SSCs important to safety to permit the simultaneous safe shutdown and cooldown of all units and maintain them in a safe-shutdown condition. In the event of an accident in one unit, the UHS should be able to DG-1275, Page 4 dissipate the heat for that accident safely, permit the concurrent safe shutdown and cooldown of the remaining units, and maintain them in a safe-shutdown condition. The capacity of the UHS should be