Document: NRC Regulatory Guide
Document ID: c7b1689b-ff17-4083-9fb1-f91b6965ea1a
Document Type: regulatory_guide
Title: Design Basis Floods for Nuclear Power Plants + HISTORY - HISTORY 02/2022 – DG-1290 , Proposed Revision 3 09/2014 – Periodic Review of Revision 2 – Revise 07/1980 – Errata to Revision 2 07/2024 – DG-1290 Revision 1 (Rev. 2)
Source: NRC Regulatory Guide Division 1
Source URL: https://www.nrc.gov/docs/ML0037/ML003740388.pdf
Revision Date: 2023-06
Chapter: 
Section ID: RG-1.59
CFR Part: 
CFR Title: 

Content:
smic events should also be 6Probable Maximum Gradient Wind is defined as a gradient wind of a designated duration, which there is virtually no risk of ex ceeding. considered to the extent needed for a consistent level of conservatism. The effect of such combinations on the flood conditions at the plant site should be evaluated in cases where the probability of such com binations occurring at the same time and having significant consequences is at least comparable to the probability associated with the most severe hydrometeorological or seismically induced flood. For relatively large streams, examples of acceptable combinations of runoff floods and seismic events that could affect the flood conditions at the plant arc con tained in Appendix A. Less-severe flood conditions, associated with the above seismic events, may be ac ceptable for small streams, that exhibit relatively short periods of flooding. e. The effects of coincident wind-generated wave activity to the water levels associated with the worst site-related flood possible (as determined from paragraphs a, b, c, or d above) should be added to generally define the upper limit of flood potential. Acceptable procedures are contained in Appendix A of this guide. 2. As an alternative to designing hardened proteo ton' for all safety-related structures, systems, And components as specified in Regulatory Position 1 above, it is permissible not to provide hardened protection for some of these features if: a. S ufficientt'warning time is shown to be available to shut the plant down and implement ade quate emergency procedures; b. All safety-related structures, systems, and components identified in Regulatory Guide 1.29 (see footnote 3) arc designed to withstand the flood condi tions resulting from a Standard Project events with attendant wind-generated wave activity that may be produced by the worst winds of record and remain functional; c. In addition to the analyses in paragraph 2.b -above, reasonable combinations of