Fukushima disaster cleanup

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The Fukushima disaster cleanup is an ongoing attempt to limit radioactive contamination from the three nuclear reactors involved in the Fukushima Daiichi nuclear disaster that followed the earthquake and tsunami on 11 March 2011. The affected reactors were adjacent to one another and accident management was made much more difficult because of the number of simultaneous hazards concentrated in a small area. Failure of emergency power following the tsunami resulted in loss of coolant from each reactor, hydrogen explosions damaging the reactor buildings, and water draining from open-air spent fuel pools. Plant workers were put in the position of trying to cope simultaneously with core meltdowns at three reactors and exposed fuel pools at three units.

Automated cooling systems were installed within 3 months from the accident. A fabric cover was built to protect the buildings from storms and heavy rainfall. New detectors were installed at the plant to track emissions of xenon gas which can be a sign of nuclear fission. Filters were installed to reduce contaminants from escaping the area of the plant into the area or atmosphere. Cement has been laid near to the seabed to control contaminants from accidentally entering the ocean.

Michio Aoyama, a scientist at Fukushima University's Institute of Environmental Radioactivity, estimated that the meltdowns and explosions released 18,000 terabecquerel (TBq) of caesium 137 (equivalent to roughly 5,600 grams (200 oz)), mostly into the Pacific Ocean. He also estimated that two years after the accident, the stricken plant was still releasing 30 gigabecquerel (30 GBq, or approximately 0.8 curie equivalent to roughly 9 milligrams (0.14 gr)) of caesium 137 and the same amount (in terms of activity, not in terms of mass - the mass of ⁹⁰
Sr amounts to roughly 5.8 milligrams (0.090 gr)) of strontium 90 into the ocean daily.^[1] For comparison, the LD50 of Caesium-137 in mice (through acute radiation syndrome) has been reported at 245 μg/kg body weight^[2] whereas experiments in the 1970s yielded a lethal dose in dogs of 44 μg/kg body weight.^[3] In a 70 kilograms (150 lb) adult human, this would imply doses of 17 milligrams (0.26 gr) and 3 milligrams (0.046 gr) respectively. In September 2013, it was reported that the level of strontium-90 detected in a drainage ditch located near a water storage tank, from which around 300 tons of water was found to have leaked, was believed to have exceeded the threshold^[which?] set by the government.^[4] Efforts to control the flow of contaminated water have included trying to isolate the plant behind a 30-meter-deep, 1.5-kilometer-long "ice wall" of frozen soil, which has had limited success.^[5]

Decommissioning the plant is estimated to cost tens of billions of dollars and last 30–40 years.^[6][7] Tokyo Electric Power Company (TEPCO) is going to remove the remaining nuclear fuel material from the plants. TEPCO completed the removal of 1535 fuel assemblies from the Unit 4 spent fuel pool in December 2014 and 566 fuel assemblies from the Unit 3 spent fuel pool in February 2021.^[8] TEPCO plans to remove all fuel rods from the spent fuel pools of Units 1, 2, 5, and 6 by 2031 and to remove the remaining molten fuel debris from the reactor containments of Units 1, 2, and 3 by 2040 or 2050.^[9]

While radioactive particles were found to have contaminated rice harvested near Fukushima City in the autumn of 2011,^[10] fears of contamination in the soil have receded as government measures to protect the food supply have appeared to be successful. Studies have shown that soil contamination in most areas of Fukushima was not serious.^[11] In 2018, Dr. Aoyama of Fukushima University released a report saying that contaminated water was still flowing into the Pacific Ocean, but at a greatly diminished rate of 2 GBq per day.^{[12][note 1]}

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