Nuclear Power Plant Tornado Design Considerations

Tornadoes, which are the most violent of all atmospheric disturbances, have not usually been considered in structural design criteria except for possible provisions of emergency personnel shelters. Since 1967, the Atomic Energy Commission has required designers of nuclear reactor facilities to carefully consider the effects of tornadoes. The results of a study to determine the frequency probability of annual occurrence ranges from less than one in 10,000 to about 30 in 10,000 for certain areas. Design to resist tornadoes should consider three potential sources of damage: the force from the dynamic wind loading; the pressure differential between the inside and outside of a building which may be caused by rapid changes in barometric pressure; and the possible impact of wind driven missiles. Design of nuclear power plants for tornado resistance is not intended to prevent all damage to the enclosing structures. Rather, it is intended to prevent any loss of capability to protect the public.