Philosophy for seismic design of nuclear power plants

In Japan, earthquakes occur frequently, therefore the basic philosophy in the aseismatic design of nuclear facilities is to design so as not to cause the accident which gives to the public in the surroundings and the employes radiation injuries in the case of large earthquakes. The ''Guideline for the aseismatic design techniques for nuclear power stations'' was drawn up in 1970 as the result of studies by related government offices and organizations. The guideline for determining the earthquakes used for design was published later, and the allowable stress for equipments and pipings has been adopted in accordance with ASME Code, Section 3. The buildings and structures, equipments and pipings in nuclear facilities are classified into three classes according to their importance in aseismatic design. The power of design earthquakes is determined corresponding to the degree of importance. The determination of the standard earthquake waves is explained. The proprieth of aseismatic design is evaluated on the basis of the basic concept of the combination of loads and the allowable limit. The static analysis in accordance with the Building Standards Act is applied to the B and C classes, while the dynamic analysis is required for the A class. The aseismatic analysis of buildings and structures, equipments and pipings is outlined. Many problems to be solved still remain though the concept of aseismatic design has been clarified. (Kako, I.)