The Fukushima Daiichi nuclear disaster (福島第一原子力発電所事故, Fukushima Dai-ichi (pronunciation) genshiryoku hatsudensho jiko) was an energy accident at the Fukushima Daiichi Nuclear Power Plant in Ōkuma, Fukushima Prefecture, initiated primarily by the tsunami following the Tōhoku earthquake on 11 March 2011. Immediately after the earthquake, the active reactors automatically shut down their sustained fission reactions. However, the ensuing tsunami disabled the emergency generators that would have provided power to control and operate the pumps necessary to cool the reactors. The insufficient cooling led to three nuclear meltdowns, hydrogen-air explosions, and the release of radioactive material in Units 1, 2 and 3 from 12 to 15 March. Loss of cooling also raised concerns over the recently loaded spent fuel pool of Reactor 4, which increased in temperature on 15 March due to the decay heat from the freshly added spent fuel rods but did not boil down to exposure. On 5 July 2012, the National Diet of Japan Fukushima Nuclear Accident Independent Investigation Commission (NAIIC) found that the causes of the accident had been foreseeable, and that the plant operator, Tokyo Electric Power Company (TEPCO), had failed to meet basic safety requirements such as risk assessment, preparing for containing collateral damage, and developing evacuation plans. On 12 October 2012, TEPCO admitted for the first time that it had failed to take necessary measures for fear of inviting lawsuits or protests against its nuclear plants. The Fukushima disaster was the most significant nuclear incident since the 26 April 1986 Chernobyl disaster and the only other disaster to be given the Level 7 event classification of the International Nuclear Event Scale. As of September 2018, one cancer fatality was the subject of a financial settlement, to the family of a former station workman. The United Nations Scientific Committee on the Effects of Atomic Radiation and World Health Organization report that there will be no increase in miscarriages, stillbirths or physical and mental disorders in babies born after the accident. Controversially, an estimated 1,600 deaths are believed to have occurred, primarily in the elderly who had earlier lived in nursing homes, due to the resultant poor evacuation conditions. There is an ongoing intensive cleanup program to both decontaminate affected areas and decommission the plant, which the plant management estimate will take 30 to 40 years. A frozen soil barrier was constructed in an attempt to prevent further contamination of seeping groundwater, which is slowing down the amount of contaminated water that is collected. The water collected is treated and all radioactive elements are removed, except for tritium. In February 2017, TEPCO released images taken inside Reactor 2 by a remote-controlled camera that show there is a 2-meter (6.5 ft) wide hole in the metal grating under the pressure vessel in the reactor's primary containment vessel, which could have been caused by fuel escaping the pressure vessel, indicating a meltdown/melt-through had occurred, through this layer of containment. Radiation levels of about 210 Sv per hour were subsequently detected inside the Unit 2 containment vessel. These values are in the context of undamaged spent fuel which has typical values of 270 Sv/h, after 10 years of cold shutdown, with no shielding.
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