Inside Fukushima I (Dai-Ichi), Nuclear Power Plant, Japan

On 11 March 2011 an earthquake categorised as 9.0 MW on the moment magnitude scale occurred at 14:46 Japan Standard Time (JST) off the northeast coast of Japan. Units 4, 5 and 6 had been shut down prior to the earthquake for planned maintenance. The remaining reactors were shut down automatically after the earthquake, and the remaining decay heat of the fuel was being cooled with power from emergency generators. Then, the subsequent tsunami disabled emergency generators required to cool the reactors. Over the following three weeks there was evidence of a partial nuclear meltdown in units 1, 2 and 3; visible explosions, suspected to be caused by hydrogen gas, in units 1 and 3; a suspected explosion in unit 2, that may have damaged the primary containment vessel; and a possible uncovering of the units 1, 3 and 4 spent fuel pools. Radiation releases caused large evacuations, concern over food and water supplies, and treatment of nuclear workers.
The IAEA has rated the events at units 1, 2 and 3 at Level 5 (Accident With Wider Consequences) on the International Nuclear Event Scale, and those at unit 4 as Level 3 (Serious Incident) events.
On April 3, two bodies were discovered in the basement turbine room after the workers likely fled there during the tsunami.