The was a series of equipment failures, nuclear meltdowns, and releases of radioactive materials at the Fukushima I Nuclear Power Plant, following the Tōhoku earthquake and tsunami on 11 March 2011. It was the largest nuclear disaster since the Chernobyl disaster of 1986,"Analysis: A month on, Japan nuclear crisis still scarring" International Business Times (Australia). 9 April 2011, retrieved 12 April 2011; excerpt, According to James Acton, Associate of the Nuclear Policy Program at the Carnegie Endowment for International Peace, "Fukushima is not the worst nuclear accident ever but it is the most complicated and the most dramatic ... This was a crisis that played out in real time on TV. Chernobyl did not." and the radiation released exceeded official safety guidelines. Despite this, there were no deaths caused by acute radiation syndrome. Given the uncertain health effects of low-dose radiation, cancer deaths cannot be ruled out. However, studies by the World Health Organization and Tokyo University have shown that no discernible increase in the rate of cancer deaths is expected. Predicted future cancer deaths due to accumulated radiation exposures in the population living near Fukushima have ranged * in the academic literature from none to hundreds.
Many deaths are attributed to the evacuation and subsequent long-term displacement following emergency mass evacuation. For evacuation, the estimated number of deaths during and immediately after transit ranges from 34 to "greater than 50". The victims include hospital inpatients and elderly people at nursing facilities who died from causes such as hypothermia, deterioration of underlying medical problems, and dehydration. The old people and already sick, were more likely to be injured because of being relocated than damaged by radiation.
For long-term displacement, many people (mostly sick and elderly) died at an increased rate while in temporary housing and shelters. Degraded living conditions and separation from support networks are likely contributing factors. , the Fukushima prefecture government counted 2,129 "disaster-related deaths" in the prefecture. This value exceeds the number that have died in Fukushima prefecture directly from the earthquake and tsunami. "Disaster-related deaths" are deaths attributed to disasters and are not caused by direct physical trauma, but do not distinguish between people displaced by the nuclear disaster compared to the earthquake/tsunami. As of the year 2016, among those deaths, 1,368 have been listed as "related to the nuclear power plant" according to media analysis. Reports have pointed out that many of these deaths may have been caused by the evacuation period being too long, and that residents could have been allowed to return to their homes earlier in order to reduce the total related death toll. According to UNSCEAR, evacuation and sheltering measures to protect the public significantly reduced potential radiation exposures by "a factor of 10".
At least six workers have exceeded lifetime legal limits for radiation and more than 175 (0.7%) have received significant radiation doses. Workers involved in mitigating the effects of the accident do face minimally higher risks for some cancers. According to Japan's Ministry of Health, Labor and Welfare, the government awarded workers' compensation to a man who developed leukemia while working on the Fukushima cleanup in 2015 and has acknowledged that three other Fukushima workers developed leukemia and thyroid cancer after working on the plant cleanup. As of 2020, the total number of cancer and leukemia instances has risen to six cases according to the Tokyo Electric Power Company (TEPCO). In 2018 one worker died from lung cancer as a result from radiation exposure. After hearing opinions from a panel of radiologists and other experts, the ministry ruled that the man's family should be paid compensation.
The Tōhoku earthquake and tsunami killed over 15,000 people from effects unrelated to the destruction of the reactors at Fukushima.
Summary of events
The plant comprises six separate boiling water reactors originally designed by General Electric (GE), and maintained by the Tokyo Electric Power Company (TEPCO). At the time of the quake, Reactor 4 had been de-fueled while 5 and 6 were in cold shutdown for planned maintenance. Immediately after the earthquake, the remaining reactors 1–3 shut down automatically, and emergency generators came online to control electronics and coolant systems. However, the tsunami following the earthquake quickly flooded the low-lying rooms in which the emergency generators were housed. The flooded generators failed, cutting power to the critical pumps that must continuously circulate coolant water through a nuclear reactor for several days to keep it from melting down after being shut down. As the pumps stopped, the reactors overheated due to the normal high radioactive decay heat produced in the first few days after nuclear reactor shutdown (smaller amounts of this heat normally continue to be released for years, but are not enough to cause fuel melting). At this point, only prompt flooding of the reactors with seawater could have cooled the reactors quickly enough to prevent meltdown. Saltwater flooding was delayed because it would ruin the costly reactors permanently. Flooding with seawater was finally commenced only after the government ordered that seawater be used, and at this point, it was already too late to prevent a meltdown.F. Tanabe, Journal of Nuclear Science and Technology, 2011, volume 48, issue 8, pages 1135 to 1139
As the water boiled away in the reactors and the water levels in the fuel rod pools dropped, the reactor fuel rods began to overheat severely, and melt down. In the hours and days that followed, Reactors 1, 2, and 3 experienced full meltdown.
In the intense heat and pressure of the melting reactors, a reaction between the nuclear fuel metal cladding and the remaining water surrounding them produced explosive hydrogen gas. As workers struggled to cool and shut down the reactors, several strongly damaging hydrogen-air chemical explosions occurred.
Concerns about the atmospheric venting of radioactive gasses and the large hydrogen explosion at unit 1 led to a -radius evacuation around the plant. During the early days of the accident workers were temporarily evacuated at various times for radiation safety reasons. At the same time, seawater that had been exposed to the melting rods was returned to the sea heated and radioactive in large volumes for several months until recirculating units could be put in place to repeatedly cool and reuse a limited quantity of water for cooling. The earthquake damage and flooding in the wake of the tsunami hindered external assistance. Electrical power was slowly restored for some of the reactors, allowing for automated cooling.Stricken reactors may get power Sunday, The Wall Street Journal, 19 March 2011
Japanese officials initially assessed the accident as Level 4 on the International Nuclear Event Scale (INES) despite the views of other international agencies that it should be higher. The level was later raised to 5 and eventually to 7, the maximum scale value.Justin McCurry. Japan raises nuclear alert level to seven. The Guardian. 12 April 2011 The Japanese government and TEPCO have been criticized in the foreign press for poor communication with the public and improvised cleanup efforts. On 20 March, the Chief Cabinet Secretary Yukio Edano announced that the plant would be decommissioned once the crisis was over.
On 16 December 2011, Japanese authorities declared the plant stable, although it would take decades to decontaminate the surrounding areas and decommission the plant altogether.
Radiation release Experts estimate the total amount of radioactivity released into the atmosphere was approximately one-tenth as much as was released during the Chernobyl disaster. Significant amounts of radioactive material have also been released into ground and ocean waters. Measurements taken by the Japanese government 30–50 km from the plant showed caesium-137 levels high enough to cause concern, leading the government to ban the sale of food grown in the area. Tokyo officials temporarily recommended that tap water should not be used to prepare food for infants. In May 2012, TEPCO reported that at least 900 PBq had been released "into the atmosphere in March, 2011 alone".
Reports Japanese government report On 5 July 2012, the parliament appointed The Fukushima Nuclear Accident Independent Investigation Commission (NAIIC) submitted its inquiry report to the Japanese parliament, while the government appointed Investigation Committee on the Accident at the Fukushima Nuclear Power Stations of Tokyo Electric Power Company submitted its final report to the Japanese government on 23 July 2012. Tepco admitted for the first time on 12 October 2012 that it had failed to take stronger measures to prevent disasters for fear of inviting lawsuits or protests against its nuclear plants.
UNSCEAR Report Annex A of the UNSCEAR (United Nations Scientific Committee for the Effects of Atomic Radiation) 2013 report to the UN General Assembly states that the average effective dose of the 25,000 workers over the first 19 months after the accident was about 12 millisieverts (mSv). About 0.7% of the workforce received doses of more than 100 mSv (Chapter II A(b) paragraph 35). No radiation-related deaths or acute diseases have been observed among the workers and general public exposed to radiation from the accident (Chapter II A(b) paragraph 38). Adults living in the city of Fukushima were estimated to have received, on average, an effective dose of about 4 mSv (Chapter II A(a) paragraph 30). No discernible increased incidence of radiation-related health effects are expected among exposed members of the public or their descendants (Chapter II A(b) paragraph 39). Average annual exposure in the region from naturally occurring sources is about 2.1 mSv, and average lifetime exposure is 170 mSv (Chapter II A(2) paragraph 29). For comparison, the average dose from an abdominal and pelvic computed tomography (CT) scan, with and without contrast, is 20 to 30 mSv.
WHO Report In 2013, two years after the incident, the World Health Organization indicated that the residents of the area who were evacuated were exposed to so little radiation that radiation induced health impacts are likely to be below detectable levels. The health risks in the WHO assessment attributable to the Fukushima radioactivity release were calculated by largely applying the conservative Linear no-threshold model of radiation exposure, a model that assumes even the smallest amount of radiation exposure will cause a negative health effect.
The WHO calculations using this model determined that the most at risk group, infants, who were in the most affected area, would experience an absolute increase in the risk of cancer (of all types) during their lifetime, of approximately 1% due to the accident. With the lifetime risk increase for thyroid cancer, due to the accident, for a female infant, in the most affected radiation location, being estimated to be one half of one percent [0.5%]. Cancer risks for the unborn child are considered to be similar to those in 1 year old infants.
The estimated risk of cancer to people who were children and adults during the Fukushima accident, in the most affected area, was determined to be lower again when compared to the most at risk group – infants. A thyroid ultrasound screening programme is currently ongoing in the entire Fukushima prefecture, this screening programme is, due to the screening effect, likely to lead to an increase in the incidence of thyroid disease due to early detection of non-symptomatic disease cases.