Seismic response and its analysis for components of Fukushima Daiichi Nuclear Power Plants in 2011 Great East Japan Earthquake

The Fukushima Daiichi (1F) accident in unit 1 to 4 was likely to be caused by the tsunami induced loss of emergency power and seawater heat sink that is consistently elucidated based on the performance of the plants until the tsunami hit after the seismic SCRAM by Great East Japan Earthquake. However it is fact that the actual damages of components have difficulty to be completely inspected under high radioactivity, and to make clear distinction between tsunami induced damage and seismic induced damage. This paper will support above conclusion based on the result of seismic response analysis for safety related components of each plant, the result of the plant walk down in the similar unit in the same station, and also the result of analysis for the observed seismic records from the perspective of generalization of the damage possibility of nuclear components designed by Japanese seismic standards. The result of seismic response analysis using observed seismic motion shows all safety related components fulfill the seismic criteria and seem to maintain structural integrity. Also we could find few seismic induced damage in the walk down for unit 5 of 1F that shows similar result would be expected in unit 1 to 4. It is concluded that the design method using seismic static load contributes additional robustness of nuclear components, even the lower seismic class components, and that the damage by the earthquake should be quite limited based on the analysis of observed seismic motions.