The Fukushima accident cleanup is an ongoing attempt to limit radioactive contamination from the three nuclear reactors involved in the Fukushima nuclear accident 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 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 ), 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 ) of caesium 137 and the same amount (in terms of activity, not in terms of mass – the mass of amounts to roughly ) of strontium 90 into the ocean daily. For comparison, the LD50 of Caesium-137 in mice (through acute radiation syndrome) has been reported at 245 μg/kg body weight whereas experiments in the 1970s yielded a lethal dose in dogs of 44 μg/kg body weight. In a adult human, this would imply doses of and 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 of water was found to have leaked, was believed to have exceeded the threshold set by the government. Efforts to control the flow of contaminated water have included trying to isolate the plant behind a , ice wall of frozen soil, which has had limited success.
Decommissioning the plant was estimated to cost tens of billions of dollars in 2013/2014 and last 30 to 40 years. In November 2016, Japan's trade ministry put the cost of the clean up of radioactive contamination and compensation for victims at (20 trillion yen). Tokyo Electric Power Company (TEPCO) is going to remove the remaining nuclear fuel material from the plants. TEPCO completed the removal of 1,535 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. TEPCO and
While radioactive particles were found to have contaminated rice harvested near Fukushima City in the autumn of 2011, 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. In 2018, it was reported that contaminated water was still flowing into the Pacific Ocean, but at a diminished rate of 2 GBq per day.
Overview At the time of the initial event, 50 TEPCO employees remained onsite in the immediate aftermath to work to stabilize the plant and begin cleanup.
Initially, TEPCO did not put forward a strategy to regain control of the situation in the reactors. Helmut Hirsch, a German physicist and nuclear expert, said "they are improvising with tools that were not intended for this type of situation". On 17 April 2011, however, TEPCO appeared to put forward the broad basis of a plan that included: (1) reaching "cold shutdown in about six to nine months;" (2) "restoring stable cooling to the reactors and spent fuel pools in about three months;" (3) putting "special covers" on Units 1, 3, and 4 starting in June; (4) installing "additional storage containers for the radioactive water that has been pooling in the turbine basements and outside trenches;" (5) using radio-controlled equipment to clean up the site; and (6) using silt fences to limit ocean contamination. Previously, TEPCO publicly committed to installing new emergency generators 20 m above sea level, twice the height of the generators destroyed by the tsunami on 11 March. Toshiba and Hitachi had both proposed plans for shuttering the facility.
"Cold shutdown" was accomplished on 11 December 2011. From that point active cooling was no longer needed, but water injection was still required due to large water leaks. Long-term plans for Units 5 and 6 have not been announced, "but they too may need to be decommissioned".
On 5 May 2011, workers entered reactor buildings for the first time since the accident. The workers began to install air filtration systems to clean air of radioactive materials to allow additional workers to install water cooling systems.
In 2017, TEPCO announced that remote-controlled robots sent into the destroyed Unit 3 reactor buildings had found the reactor's melted uranium fuel, which had burned through the floor of the reactor vessel and settled in clumps on the concrete floor below.
Scope of cleanup Japanese reactor maker Toshiba said it could decommission the earthquake-damaged Fukushima nuclear power plant in about 10 years, three times quicker than the American Three Mile Island plant. As a comparison, at Three Mile Island the vessel of the partially melted core was first opened 11 years after the accident, with cleanup activities taking several more years.
TEPCO announced it restored the automated cooling systems in the damaged reactors in about three months, and had the reactors put into cold shutdown status in six months.Kyodo News, "Reactor shutdowns nine months away", Japan Times, 18 April 2011.
First estimates included costs as high as (), as cited by the Japanese Prime Minister at the time, Yoshihiko Noda (野田 佳彦). This estimate was made before the scope of the problem was known, however. It seems that the contamination was less than feared. No strontium is detectable in the soil, and though the crops of the year of the disaster were contaminated, the crops produced by the area now are safe for human consumption.
In 2016, Japan's Ministry of Economy, Trade and Industry estimated the total cost of dealing with the Fukushima accident at (), almost twice the previous estimate of (). A rise in compensation for victims of the accident from () to () was expected, with decontamination costs estimated to rise from () to (), costs for interim storage of radioactive material to increase from () to (), and costs of decommissioning reactors to increase from () to ().
Working conditions at the plant
There has been concern that the plant would be dangerous for workers. Two workers suffered skin burns from radiation, but no serious injuries or fatalities have been documented to have been caused by radiation at Fukushima Dai-ichi.
Workers in dorms exposed to radiation Two shelters for people working at the Fukushima site were not listed as part of the radiation management zones although radiation levels in the shelters exceeded the legal limits. The consequence was that the workers did not get paid the extra "danger allowance" that was paid to workers in these "radiation management zones". The shelters were constructed by Toshiba Corporation and the Kajima Corporation at a place some 2 kilometers west of the damaged reactors, just outside the plant compound, but near reactors 1 to 4. The shelters were built after the shelters at the plant compound became overcrowded. At 7 October 2011, radiation levels were between 2 and 16 microsieverts per hour in the Toshiba building, and 2 to 8.5 in the Kajima dorm. The Industrial Safety and Health Law on the prevention of health damage through ionizing radiation had set the limit for accumulated radiation dosage in radiation management zones at 1.3 millisieverts over three months, so the maximum level is 2.6 microsieverts/hour. In both dorms, the radiation levels were higher. These doses are, however, well below the level to affect human health. According to the law, the "business operator" is responsible for "managing radiation dosage and the prevention of contamination", Toshiba and Kajima said that TEPCO was responsible, but a TEPCO official commented, "From the perspective of protecting workers from radiation, the business operators (that constructed the shelters) are managing radiation dosage and the prevention of contamination", in this way suggesting that Toshiba and Kajima were to take the care of the zone management.The Mainichi Daily News (31 October 2011) Workers in shelters just outside gates of nuclear complex miss out on allowance
Preventing hydrogen explosions On 26 September 2011, after the discovery of hydrogen in a pipe leading to the containment vessel of reactor no.1, NISA instructed TEPCO to check whether hydrogen was building up in reactor no. 2 and 3 as well. TEPCO announced that measurements of hydrogen would be taken in reactor no. 1, before any nitrogen was injected to prevent explosions. When hydrogen would be detected at the other reactors, nitrogen injections would follow.JAIF (26 September 2011). Earthquake-report 216: Hydrogen check ordered at No. 2, 3 reactors .
After the discovery of hydrogen concentrations between 61 and 63 percent in pipes of the containment of reactor no. 1, nitrogen injections were started on 8 October. On 10 October, TEPCO announced that the concentrations were, at that moment, low enough to prevent explosions, and even if the concentration would rise again, it would not exceed 4 percent, the lowest level that would pose the risk of an explosion. On the evening of 9 October, two holes were drilled into a pipe to install a filter for radioactive substances inside the containment vessel; this was 2 weeks behind the schedule TEPCO had set for itself.JAIF (10 October 2011). Earthquake-report 230: Hydrogen level falls at Fukushima plant .
Investigations inside the reactors On 19 January 2012, the interior of the primary containment vessel of reactor 2 was inspected with an industrial endoscope. This device, 8.5 millimeters in diameter, was equipped with a 360 degrees-view camera and a thermometer to measure the temperature and the cooling water inside, in an attempt to calibrate the existing temperature measurements that could have an error margin of 20 degrees. The device was brought in by a hole at 2.5 meters above the floor where the vessel is located. The procedure lasted 70 minutes.The Mainichi Daily news (19 January 2012). TEPCO uses endoscope to look inside crippled Fukushima reactor . The photos showed parts of the walls and pipes inside the containment vessel. But they were unclear and blurred, most likely due to water vapors and the radiation inside. According to TEPCO the photos showed no serious damage. The temperature measured inside was 44.7 degrees Celsius, and did not differ much from the 42.6 degrees measured outside the vessel.JAIF (20 January 2012). Earthquake-report 323: TEPCO fails to clearly see inside damaged reactor .nu.nl (20 January 2012). TEPCO films in reactor 2 (footage comments in Dutch).
Inspections of the suppression chambers reactor no. 2 and 3