Modeling of earthquake motions for seismic design of critical facilities: Revision of licensing criteria of NPP

The importance of input ground motions for the seismic safety design of nuclear power plants (NPP), in relation to the current revision of licensing criteria in Japan are discussed. The current Japanese criteria employ two levels of design basis earthquakes, which includes S1 and S2. The limit earthquake S2 is similar to SSE in US, and the safety function should be kept under any S2 event as referred by the Omote map. The building code in Japan requires a double check or two step design, a design by base shear and elastic limit design and an evaluation of the total capacity of energy absorption of a structure under a IG ground motion. The intensity, PGA and PGV, the value of peak ground motions are considered to be only a key for mechanical design. The Japan meteorological Agency and local governments have developed a seismograph network to measure JMA Intensity scale. Instrumental JMA Intensity is a peak value of ground motions normalized by frequency depending sensitivity.