The Great East Japan Earthquake and subsequent tsunami on 11 March 2011 initiated accident conditions at several nuclear power stations on the northeast coast of Japan, and it developed into a very serious nuclear accident at Units 1-3 of the Fukushima Daiichi Nuclear Power Station (NPS). As a result, the IAEA set out a comprehensive program of work, called Action Plan on Nuclear Safety, in order to strengthen nuclear safety worldwide in 12 major areas. One of the action items is "Effectively utilize research and development". To assist relevant stakeholders in conducting necessary research and development in nuclear safety, technology and engineering, the IAEA has been identifying and organizing lessons learned from the accident, and has assimilated them into a comprehensive and concise set of lessons learned with emphasis on technical issues. This paper summarizes the event sequences during the Fukushima accident, taking into account recently published new information, and discusses technical lessons learned from the accident at the Fukushima Daiichi and Daini Nuclear Power Stations.
