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The multiple nuclear reactor units involved in the Fukushima Daiichi nuclear disaster were close to one another and this proximity triggered the parallel, chain-reaction accidents that led to hydrogen explosions blowing the roofs off reactor buildings and water draining from open-air spent fuel pools. This situation was potentially more dangerous than the loss of reactor cooling itself. Because of the proximity of the reactors, 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. 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. 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. The biggest costs for the cleanup will be the final decommissioning of the reactors, a process estimated to take 10–30 years. Cleanup costs will not be fully known until the cleanup is completed and the decommissioning is complete. No strontium was released into the area from the accident; however, 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 highly toxic water was found to have leaked was believed to have exceeded the threshold set by the government.〔The Mainichi Shimbun (13 September 2013) (Toxic water may have leaked into Pacific Ocean: TEPCO )〕 Decommissioning the plant is evaluated to cost tens of billions of dollars and last 30–40 years.〔(Fukushima radiation levels 18 times higher than previously thought ) The Guardian 1 September 2013〕 Initial fears that contamination of the soil was deep have been reduced with the knowledge that current crops are safe for human consumption and the contamination of the soil was not serious; however, in July and August 2013, it was discovered that radioactive groundwater has been leaking into the sea. ==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". However, on 17 April 2011, TEPCO appeared to put forward the broad basis of a plan which 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;"〔(TEPCO Announces a "Roadmap to restoration" at Fukushima Dai-1 - IEEE Spectrum ). Spectrum.ieee.org. Retrieved on 30 April 2011.〕 (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 11 March tsunami.〔Clenfield, Jason. (14 April 2011) (Fukushima radioactive contamination leaks will continue through June, Tokyo Electric says ). Bloomberg. Retrieved on 30 April 2011.〕 Toshiba and Hitachi had both proposed plans for shuttering the facility.〔(NTI: Global Security Newswire – Japan plant emits more radiation after cooling lapse ). Global Security Newswire (14 April 2011). Retrieved on 30 April 2011. 〕 Cold shutdown was accomplished in December 11, 2011. From that point cooling was no longer required, but maintenance was still required to control large water leaks. Long term plans for Units 5 and 6 have not been announced, "but they too may need to be decommissioned".〔Tabuchi, Hiroko (Nuclear cleanup plans hinge on unknowns ), NY Times, 14 April 2011.〕 On 5 May 2011, workers were able to enter reactor buildings for the first time since the accident.〔(Workers enter reactor building ), NHK, 5 May 2011〕 The workers began to install air filtration systems to clean air of radioactive materials to allow additional workers to install water cooling systems.〔 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Fukushima disaster cleanup」の詳細全文を読む スポンサード リンク
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