Fukushima: The Tsunami Opened the Door, but the Disaster Was Prepared Beforehand

On March 11, 2011, at 2:46 p.m., a massive earthquake struck off northeastern Japan. Six reactors at Fukushima Daiichi were in different states: Units 1, 2, and 3 were operating; Units 4, 5, and 6 were shut down for maintenance or refuelling. Automatic systems immediately inserted control rods into the cores. Fission stopped. On paper, the most visible part of the safety procedure had worked.

A reactor does not become cold the moment it shuts down. Fuel rods continue to produce heat and require constant water circulation. About an hour later, a tsunami more than 14 metres high crossed the plant’s seawall. Seawater destroyed backup diesel generators, electrical switchgear, and pumps. The plant entered a total station blackout. The control rooms lost much of their instrumentation. Engineers worked in darkness without a reliable picture of water level, pressure, or core temperature.