This standard establishes guidelines to estimate the frequency of occurrence and the magnitude of parameters associated with rare meteorological events such as tornadoes, hurricanes, and extreme straight line winds at nuclear facility sites within the continental United States. The parameters addressed include the following: maximum wind speed ~e.g., translational, rotational, and total!, maximum atmospheric pressure drop, and design basis missile characteristics. Recommended values of these parameters are provided. This standard does not address the forces on structures that result from these physical phenomena.

The standard also refers to two acceptable methodologies for developing tornado wind hazard curves and recommends the use of a set of hazard curves for determining design basis tornado and hurricane wind speeds and extreme straight line wind speeds for various geographical regions within the continental United States. These curves can be used to determine design basis wind speeds for a predetermined frequency of occurrence or return period that is appropriate for the facility based on safety, relative cost, and strategic importance considerations. The selection or determination of the frequency of occurrence is not addressed in this standard.

The values of the design parameters recommended in this standard are intended to assure that public health and safety will be maintained as required in Code of Federal Regulations, Title 10, "Energy," Part 50, "Domestic Licensing of Production and Utilization Facilities," Appendix A, Criteria 2 and 4 [1]¹⁾; Code of Federal Regulations, Title 10, "Energy," Part 70, "Domestic Licensing of Special Nuclear Material" [2]; and Code of Federal Regulations, Title 10, "Energy," Part 830, "Nuclear Safety Management" [3].

The standard does not address the determination of the design basis tornado and other extreme wind effects for sites located outside the continental United States ~i.e., Alaska, Hawaii, Virgin Islands, Guam, and Puerto Rico! or over the Atlantic and Pacific Oceans and the Gulf of Mexico. Such determinations should be evaluated on a case-by-case basis. Additionally, the standard does not identify the structures, systems, and components that should be designed to withstand the effects of the design basis extreme or rare wind speeds and remain functional nor does it treat the structural design requirements for protection from these winds.

¹⁾Numbers in brackets refer to corresponding numbers in Sec. 5, "References."

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