Fukushima 1st NPPs accidents and disaster caused by the pacific coast Tsunami of Tohoku earthquake. Lessons from evaluation of the Fukushima 1st NPPs accidents

The Great East Japan earthquake (moment magnitude 9.0) occurred in March 11, 2011. The disastrous tsunami attacked Fukushima Daiichi nuclear power plants (NPPs) after automatically shutdown by the earthquake and all motor operated pumps became inoperable due to station black out. It caused severe accident of multiple plants simultaneously such as loss of cooling function, fuel damaged and vent of containment, hydrogen explosion and discharge of large amount of radioactive materials into the environment leading to nuclear power emergency that ordered resident to evacuate or remain indoors. The situation of the accident had been reported in details by mass media and most people experienced a disaster of reactor accidents and fear of radioactivity contamination. Based on the investigation and analysis of the accident at this moment, this article consisted of overview and time sequence of the accident, lessons learned from TMI and Chernobyl accidents and root cause analysis of the accident and countermeasures. Filtered containment venting system and catalyzed hydrogen recombiners were highly recommended from the point of defense-in-depth to mitigate and prevent nuclear disaster. (T. Tanaka)