Lessons of TEPCO's Fukushima accident from human and organizational aspects and challenge for nuclear safety reform

The author participated in international experts' meeting held by IAEA on May 21, 2013 and presented the paper focusing on human and organizational aspects of the Fukushima nuclear accident. It clarified TEPCO's basic recognition: 'The cause of the accident should not be treated merely as a natural disaster due to an enormous tsunami being something difficult to anticipate and we believe it is necessary to seriously acknowledge the result that TEPCO failed to avoid an accident which might have been avoided if ample preparations had been made in advance with thorough use of human intellect' and then reconsidered the Fukushima nuclear accident: 'could we predict an enormous tsunami and take whatever countermeasures?' and 'could we respond to the accident better?' for the worldwide operators to avoid such an accident, which moved meeting's participants deeply. Presentation's contents followed 'Reassessment of the Fukushima Nuclear Accident and Nuclear Safety Reform Plan' published by TEPCO on March 29. This article described outline of the presentation. Though the only way to explore the possibility to save Unit 1 was that operators could bravely go up to the 4th floor of reactor building and open the isolation valves to start IC, it was given up without any clear communication among key decision makers for confirming the IC operational status. As for Unit 3, operators could not achieve thorough focus on ensuring core cooling such that proactive transfer from RCIC/HPCI to low pressure water injection was not challenged, mainly because of low trust on Diesel/Driven Fire Protection Pump (DDFP). During the design stage and afterward, ample consideration was not given to common cause failures originating in external events, which led to a severe situation where almost all the power supplies and safety system functions were lost. Continuous efforts to reduce risks were not ample, including the collection, analysis and utilization of information on safety enhancement measures and operational experiences in other countries and/or the consideration of new technical knowledge. Preparation for a severe accident was somewhat deficient in terms of facility and personnel deployment. Action plan for nuclear safety reform was as follows: (1) enhance safety awareness of top management, (2) establishment of Nuclear Safety Oversight Organization (NSOO), (3) improve engineering ability to propose Defense in Depth (DiD) safety measures, (4) establish risk communicator positions and Social Communication Office to build trust with local community and public, (5) reorganize emergency response team based on Incident Command System (ICS), and (6) enhance on-site staff technical capabilities. Nuclear operators' ultimate measures might be to continuously improve their own fundamental engineering capabilities and firsthand technical skills. (T. Tanaka)