Document: NUREG-0800
Document ID: fce5c014-cdea-4bf2-83f9-535d051f0f3b
Document Type: srp
Title: MISSILES GENERATED BY NATURAL PHENOMENA
Source: NUREG-0800
Source URL: https://www.nrc.gov/docs/ML0520/ML052070375.pdf
Revision Date: 2023-06
Chapter: 3
Section ID: 3.5.1.4
CFR Part: 
CFR Title: 

Content:
reported for the site and surrounding region. Regulatory Guide 1.76 describes a design-basis tornado based upon WASH-1300, "Technical Basis for Interim Regional Tornado Criteria" (Reference 6) that is acceptable to the NRC staff. A nuclear power plant must remain in a safe condition in the event of the most severe tornado that can reasonably be predicted. Essentially all conclusions concerning tornado properties are based upon indirect observations rather than directly sensing tornado properties. However, it is possible to characterize a set of properties that are significant and can be used to develop a definition for a design-basis tornado. Designing a nuclear plant to withstand the design-basis tornado characteristics of Regulatory Guide 1.76 ensures that there will be no undue risk to the health and safety of the public in the event of the most severe tornado conditions. Evolutionary reactors have the option of using a maximum tornado wind speed of at least 482 km/hr (300 mph) in the design-basis tornado. In SECY 93-087 and its associated Staff Requirements Memorandum (SRM) (References 7 and 8), the NRC staff found acceptable and the Commission approved, for evolutionary reactors, a departure from Regulatory Guide 1.76 guidance regarding tornado design-basis maximum wind speed. This change in tornado design-basis maximum wind speed for the evolutionary reactors is based upon updated tornado data from the National Severe Storm Forecast Center covering a 30 year period and the analysis of this data provided by NUREG/CR-4461 3.5.1.4-3 DRAFT Rev. 3 - April 1996 (Reference 9). The design-basis maximum wind speed for evolutionary reactors, although lower in some cases than Regulatory Guide 1.76 tornado wind speeds, is based upon methodology that has been shown to be appropriate and is conservative. Designing a nuclear power plant to withstand the design-basis maximum tornado wind speed ensures that SSC important to safety will be capable of performing their safety