How plants survived the Great Hanshin earthquake

The Japanese base requirements for nuclear power plants to avoid the kind of destruction recently seen in the city of Kobe as a result of the earthquake are described. Kobe is built above a series of faults. Sites for nuclear power plants are carefully selected so that there are no active faults within a radius of about 30 km. The foundations of all parts of the plant essential for safety, such as the reactor building, are located directly on the bedrock. This minimizes the vertical accelerations due to an earthquake which are magnified by relatively soft surface soil. Soil-structure interactions are also avoided in this way and soil liquefaction is prevented. In addition, nuclear plants are designed to a much higher standard than that specified by the Building Standard Law of Japan. Two design-base earthquakes are used. The first is the largest earthquake likely to occur and the second the largest earthquake which could conceivably occur from a seismological point of view. The requirement is that a reactor plant should survive essentially undamaged in the event of the first, and that there should be no release of radioactivity to the outside world in the event of the second, even if some damage occurs. (UK)