2017 年 6 巻 2 号 p. 14-19
On March 11, 2011, the Great East Japan Earthquake triggered an extremely severe nuclear accident at Fukushima Daiichi Nuclear Power Plant, owned and operated by Tokyo Electric Power Company (TEPCO). Before the accident, several experts and researchers had repeatedly pointed out a high possibility that tsunami would reach beyond the level assumed by TEPCO, as well as a possibility that such level of tsunami might cause severe accidents. However, TEPCO and the regulatory body (NISA) overlooked these warnings and did not take any preventive measure against tsunami. Consequently, Fukushima Daiichi Nuclear Power Plant was incapable of withstanding the tsunami that hit on the day. Due to these facts, the accident is regarded as a man-made disaster. Even today, more than 6 years after the accident, it has not been revealed why they underestimated the risk of tsunami and couldn't prevent the accident. This article suggests that this question can be partially answered by applying “groupthink” model which was developed by Irving Janis. This study analyzes the descriptions of two official reports on the Fukushima accident by Japanese government and National Diet. As the result, all antecedent conditions, six symptoms of groupthink and six symptoms of defective decision making are found in the accident reports. This study also suggests that an additional antecedent condition "existences of obvious and obscure risks" and a symptom of groupthink "procrastination of problem solving" could be included in the groupthink model.