Tokyo Electric Power Company Holdings, Inc.

The Fukushima Daiichi accident began with an extraordinary earthquake and tsunami, but its accountability meaning lies in what happened after a predictable class of safety functions was lost. Flooding disabled electrical distribution, emergency power, instrumentation and heat removal across several units at once; procedures, communications and portable equipment then had to work in conditions for which they had not been adequately integrated or rehearsed. Fifteen years of investigations, court decisions, compensation, regulatory reconstruction and decommissioning provide substantial evidence of response. They do not reduce nuclear-safety assurance to a seawall height. The durable test is whether operators and regulators can prove that every reactor retains diverse ways to see, cool, depressurise and contain a severe accident when the assumed design boundary has already failed.