Examination of aseismatic capability of underground nuclear power stations

As one of the new locating methods of nuclear power stations, the examination on the underground location is in progress in Japan and abroad. In underground nuclear power stations, the reactor containment vessels are to be installed in rock bed cavities. Generally, the earthquake force inside rock beds is small, but for the rock bed cavities containing nuclear reactors, the higher aseismatic capability than ordinary rock bed cavities is to be required. In Shiroyama underground hydropower station, earthquake observation has been carried out since July, 1976, and the behavior of the underground cavity at the time of earthquakes and the comparison of earthquake movement on ground surface and underground have been investigated. Also the stability of nuclear reactor cavities at earthquakes and the aseismatic capability of main equipment and piping in a cavity have been examined. In this report, the knowledge obtained so far on the aseismatic capability of underground nuclear power stations is summarized. The earthquake observation in an underground power station, the stability of underground cavities and the structures in a cavity at the time of earthquakes and so on are reported. (Kako, I.)