High Winds

This natural hazard group can be subdivided into two categories; one, the design basis severe wind and two, the extreme wind, such as those due to tornados and hurricanes. Severe winds are based on an annual frequency of 10-2. Severe wind loads on structures are generally enveloped by seismic loads. Tornado or hurricane wind loads are generated by extreme winds with an annual frequency of 10-7. Extreme wind load needs to be combined with effects of wind bourn missiles. Regulatory Guide 1.76, “Design-Basis Tornado and Tornado Missiles for Nuclear Power Plants,” Dated April 1974, Rev 0 [10] has been used to determine tornado wind speeds and associated spectrum of missiles consistent with applicable wind velocity ranges. RG 1.76 subdivided the continental U. S. into three regions for ranges of wind speed. Recent developments in this area are further discussed in Section 8.3.2.3.

Other Natural Hazards

Other natural hazards that can affect safety are listed as follows: avalanche, biological events, drought, forest fire, hurricane, ice cover, landslide, lightning, river diversion, sandstorm, severe wind, snow, frost, hail, high temperatures, low water, low temperatures, precipitation, tornado, volcanic activity and water spouts These hazards are very site specific and many of these hazards can be eliminated based on location, site elevation, geological and tectonic setting, and other factors. However, those that cannot be eliminated should be considered in the design.

 
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