Fukushima nuclear accident

In March 2011 a great earthquake and tsunami knocked out the power and cooling systems of the Fukushima Daiichi nuclear power plant on the north-east coast of Japan. Three reactor cores overheated and melted, hydrogen explosions wrecked several reactor buildings, and radioactive material spread over land and sea. Rated at Level 7, the top of the international scale, it was the worst nuclear accident since Chernobyl in 1986, and it forced well over 100,000 people from their homes.

Fukushima Daiichi, in the town of Ōkuma, had six boiling water reactors of General Electric design, run by the Tokyo Electric Power Company (TEPCO). On 11 March 2011 units 1 to 3 were operating; units 4 to 6 were shut down, but their pools of spent fuel still needed constant cooling. The plant's emergency diesel generators, and in several units its backup batteries, were housed in basements close to the sea, protected only by a seawall.

The magnitude 9.0 Tōhoku earthquake struck at 14:46 that afternoon. The three running reactors shut down automatically, and when the grid connection failed the diesel generators started to keep the cooling systems going. About fifty minutes later the largest tsunami wave, 13 to 14 metres high, poured over the seawall and the site, which stood ten metres above the sea. It flooded the turbine and reactor buildings and destroyed the seawater pumps, most of the generators and much of the electrical equipment. Units 1 to 5 lost all alternating-current power, and some units also lost their batteries. Two workers were killed by the wave.

Without power, operators could not run the normal cooling systems and had little information about conditions inside the reactors. They struggled to vent pressure and to pump in water with fire engines, at first fresh water and then seawater. The fuel in units 1, 2 and 3 melted. Hydrogen produced by the overheated fuel leaked into the buildings and exploded: in unit 1 on 12 March, in unit 3 on 14 March, and on 15 March in unit 4, probably from gas that had travelled from unit 3 through shared pipes. TEPCO did not officially acknowledge the meltdowns until about two months later.

The authorities ordered evacuations that widened in stages, from 2 kilometres around the plant on the first evening to 20 kilometres, with people further out told to shelter indoors. The overlapping orders sent many people from one temporary refuge to another. At least 164,000 people were displaced, some permanently. Among about 2,220 hospital patients and elderly care-home residents in the zone, 51 deaths were attributed to the evacuation itself, from causes such as hypothermia and dehydration. A United Nations scientific committee later reported that no harm to residents' health had been documented as directly caused by radiation from the plant.

Investigations, including the first independent commission ever appointed by Japan's parliament, concluded that the accident was foreseeable and preventable, and criticised both TEPCO and the regulators for collusion and poor planning. Three former TEPCO executives were later tried for negligence and acquitted in 2019.

Before 2011 nuclear power supplied more than a quarter of Japan's electricity. After the accident every reactor in the country was shut down by 2013, and the country turned heavily to imported fossil fuels. In 2016 the trade ministry estimated the cost of clean-up and compensation at 20 trillion yen.

TEPCO plans to remove the molten fuel debris from units 1, 2 and 3 by about 2050. Hundreds of tonnes of water a day had to be pumped through the damaged reactors and treated, and an underground wall of frozen soil was built to hold back groundwater. In August 2023 Japan began releasing treated water, still containing tritium, into the Pacific, a programme planned to last about thirty years. The release was approved by the UN nuclear watchdog but drew protests in the region, and China banned all seafood imports from Japan.

Our 2010 map shows Japan as it was the year before the accident. For an earlier nuclear emergency, see the Three Mile Island accident.