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:
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 data are available, other historical regional data (including, if available, quality assured onsite meteorological data) should be examined to determine the controlling meteorological conditions for the critical time period(s). If examination of other historical regional data indicate that the controlling meteorological conditions did not occur within the period of record for the available representative data, these conditions should be correlated with the available representative data and appropriate adjustments should be made for site conditions. (2) In rare cases, design-basis meteorological conditions less severe than those suggested in Regulatory Position C.1.e(1) may be assumed when it can be demonstrated that the consequences of actual meteorological conditions exceeding the less than design-basis DG-1275, Page 9 conditions for short time periods can be accommodated by the applicable design (for example, short-term excursions of ambient wet-bulb temperatures exceeding a cooling tower’s design-basis wet-bulb). Information on magnitude, persistence, and frequency of occurrence of controlling meteorological parameters that exceed the design-basis conditions, based on representative climatological data as discussed above, should be presented. f. The above analyses related to the 30-day cooling supply and peak UHS temperature should include sufficient information to substantiate the assumptions and analytical methods used. This information should include actual performance data for a similar cooling method operating under load near the specified design conditions, or justification that conservative evaporation, drift loss (if applicable), and heat transfer values have been used. g. A cooling capacity of less than 30 days may be acceptable if it can be demonstrated