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:
ays. b. Sufficient conservatism should be provided to ensure that a 30-day cooling supply is available and that 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 eventually 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, as appropriate, should be performed. The transient analysis for the effluent from one unit affecting the performance of an adjacent unit should also be considered, for both normal operation and accident conditions. UHS cooling towers should be designed for the potential effects of recirculation and interference. c. Where applicable, the meteorological conditions resulting in maximum cooling water loss should be the worst 30-day combination of controlling parameters. d. The meteorological conditions resulting in the maximum intake water temperature to the plant from the UHS should be the worst combination of controlling parameters, including diurnal variations, where appropriate, for the critical time period(s) unique to the specific design of the UHS. e. The bases and procedures used to select and develop critical meteorological data should be provided and justified. The following are acceptable methods for selecting these conditions: (1) Based on regional climatological information, select the most severe observation of controlling parameters or parameter combination for each critical time period(s), with substantiation of the conservatism of these values for site use. The climatological measurements used for this analysis should be based on a recent period of record at least 30 years in length and should be demonstrated to be representative of conditions that might reasonably be expected to occur at the site. If significantly less than 30 years of representative