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:
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 sufficient to provide cooling for the time necessary to evaluate the situation and take corrective action. A period of 30 days is considered adequate for these purposes. In addition, procedures should be available for ensuring the continued capability of the UHS beyond 30 days. A capacity of less than 30 days may be acceptable if it can be demonstrated that replenishment can be effected to ensure the continuous capability of the UHS to perform its safety functions, taking into account the availability of replenishment equipment and limitations that may be imposed on “freedom of movement” following an accident or severe natural event. Sufficient conservatism should be provided to ensure that a safety-related water supply for a 30- day cooling capacity is available (e.g., there is a 30-day supply of water available for those UHSs relying on evaporation) and that the design-basis temperatures of equipment that is important to safety are not exceeded. For UHSs where the water supply may be limited or the temperature of plant intake water from the UHS may become critical (e.g., ponds, lakes, cooling towers, or other UHSs where recirculation between plant cooling water discharge and intake can occur), transient analyses of supply and/or temperature should be performed. Techniques for selecting the meteorological conditions for minimum heat transfer and examples for performing the transient analysis for cooling ponds, spray ponds and wet cooling towers are provided in NUREG-0693, “Analysis of Ultimate Heat Sink Cooling Ponds” (Ref. 3), NUREG-0733, “Analysis of Ultimate Heat Sink Spray Ponds” (Ref. 4), and a technical report titled “Method for Analysis of Ultimate Heat Sink Cooling Tower Performance” (Ref. 5), respectively. Design inputs for wind functions and