TEPCO's Fukushima plant was built for a 5.7m tsunami — the wave was 15m

On March 11, 2011, a magnitude 9.0 earthquake struck off the coast of Japan, triggering a tsunami that overwhelmed the Fukushima Daiichi Nuclear Power Plant, operated by TEPCO. The plant's seawall was designed for a maximum tsunami height of 5.7 meters. The actual wave was approximately 15 meters.

The tsunami flooded the plant's backup diesel generators, which were located in basements, cutting off power to the reactor cooling systems. Without cooling, three reactors underwent meltdown, releasing radioactive material and forcing the evacuation of over 160,000 people. It was the worst nuclear disaster since Chernobyl.

The investigation found that TEPCO and Japanese regulators had ignored warnings about the risk of larger tsunamis. A 2008 internal TEPCO study had predicted a possible 15-meter tsunami, but the company did not act on it. The case illustrated how the assumption that 'it hasn't happened before' is not a safety analysis, and how regulatory capture — the close relationship between TEPCO and the regulators — can suppress the warnings that matter.