Appendix D: Commentary on Wind Design and Evaluation Criteria

DOE-STD-1020-2002

Appendix D

Commentary on Wind Design and Evaluation Criteria

Key points in the approach employed for the design and evaluation of facilities for

straight winds, hurricanes and tornadoes are discussed in this appendix.

D.1

Wind Design Criteria

Design goals are established for SSCs in Performance Categories 1 through 4. Design or

evaluation of SSCs requires that the performance goals be met by selecting an appropriate hazard

exceedance probability and utilizing sufficient conservatism in the methodologies and

assumptions to assure the performance goals are met or exceeded.

A consensus standard, ANSI/ANS 2.3-1983 (Ref. D-1), which provides guidelines for

estimating tornado and straight wind characteristics at nuclear power plant sites is an acceptable

alternative approach to wind hazard assessment and design. However, the standard, which

establishes tornado hazard probabilities at the 10-5, 10-6, and 10-7 levels on a regional basis,

was not adopted by the Natural Phenomena Hazards Panel for the following reasons:

(a)

The document is intended for siting of commercial nuclear power plants.

Criteria are not necessarily appropriate for DOE SSCs.

(b)

Site-specific hazard assessments were performed for each DOE site; it is

not necessary nor desirable to use regional criteria

(c)

Although published in 1983, the ANSI/ANS Standard is based on 15 year

old technology

(d)

Although ANSI/ANS Standard is a consensus document, it has not been

approved by the U.S. Nuclear Regulatory Commission.

Instead of the ANSI/ANS Standard, a uniform approach to wind design is proposed

herein, which is based on procedures of ASCE 7. The ASCE 7 document is widely accepted as

the most technologically sound censuses wind load standard in the U.S.

The uniform approach to design for wind loads treats the types of windstorms (straight,

hurricane and tornado) the same. Since ASCE 7 already treats straight winds and hurricanes the

same, all that remains is to demonstrate the applicability of the approach to tornado resistant

design. The procedure of ASCE 7 is applied for determining wind pressures on structures or net

forces on systems and components. The additional effects of atmospheric pressure change

(APC) and missile impact produced by tornadoes must also be considered at some sites.

D-1