Fukushima Daiichi nuclear power plant: a retrospective evaluation

Based on available data and personal experience in Japan at the time of the design and construction of the Fukushima Daiichi nuclear power plant (NPP), the basis of its earthquake resistant design is revisited. The relevant knowledge and technology of the time (late 1960’s to early 1970’s) are reviewed to illustrate the technical environment in which this and other plants around the world were designed. The initial structural design of the plant was based on static analysis and for structures and components needing high seismic protection, a seismic coefficient of 0.54 was used. A comparison is carried out between the design seismic loads and the inferred seismic excitations that were likely to be experienced at the Fukushima Daiichi NPP during the 11th March 2011 earthquake. It is indicated that the allowable checking stress reached the yielding material stress. The piping system and the containment structure were dynamically designed based on a pre-described response spectrum shape with peak ground acceleration of0.27g. It is concluded that structural components’ upgrading should be as much as around three times the initial seismic resistance in order for the plant to safely withstand the 2011 ground motion.