I have seen improvements in safety measures and procedures in every nuclear power plant that I have visited. The Great East Japan Earthquake of magnitude 9.0 at 2.46 pm on Friday 11 March 2011 did considerable damage in the region, and the large tsunami it created caused very much more. Fukushima accident, also called Fukushima nuclear accident or Fukushima Daiichi nuclear accident, accident in 2011 at the Fukushima Daiichi (“Number One”) plant in northern Japan, the second worst nuclear accident in the history of nuclear power generation. The reactors proved robust seismically, but vulnerable to the tsunami. (Oxidation of the zirconium cladding at high temperatures in the presence of steam produces hydrogen exothermically, with this exacerbating the fuel decay heat problem.). (There is some dry storage on site to extend the plant's capacity.). 12 March
Power, from grid or backup generators, was available to run the residual heat removal (RHR) system cooling pumps at eight of the eleven units, and despite some problems they achieved 'cold shutdown' within about four days. Most of the stored wastes have decayed to below the 8 kBq/kg level. A second, but smaller, nuclear accident took place in August 2013 when approximately 300 tonnes (330 tons) of irradiated water used in ongoing cooling operations in reactors 1, 2, and 3 was discharged into the landscape surrounding the Fukushima Daiichi facility. Tepco management ignored an instruction from the prime minister to cease the seawater injection into unit 1, and this instruction was withdrawn shortly afterwards. 20 mSv/yr was also the general limit set for children's dose rate related to outdoor activities, but there were calls to reduce this.In areas with 20-50 mSv/yr from April 2012 residency is restricted, with remediation action taken. If they reach certain levels, e.g. Prime Minister Abe then called for Tepco to decommission both units. It is being fitted in 2017, with a cover, for the 566 fuel assemblies to be removed by mid-2018. In June 2013, analysis from Japan's Nuclear Regulation Authority (NRA) showed that the most contaminated areas in the Fukushima evacuation zone had reduced in size by three-quarters over the previous two years. Apart from this recirculating loop, the cumulative treated volume was then 1.232 million cubic metres. Monitoring of seawater, soil and atmosphere is at 25 locations on the plant site, 12 locations on the boundary, and others further afield. The government may relieve the operator of liability if it determines that damage results from “a grave natural disaster of an exceptional character” (which it did not do here), and in any case total liability is unlimited. In August 2014 the Nuclear Damage Compensation and Decommissioning Facilitation Corporation (NDF) was set up by government as a planning body with management support for R&D projects, taking over IRID’s planning role. In January 2013 4.5 to 5.5 m3/hr was being added to each RPV via core spray and feed water systems, hence 370 m3 per day, and temperatures at the bottom of RPVs were 19°C in unit 1 and 32°C in units 2&3, at little above atmospheric pressure. During the initial response to the tsunami, this lack of readiness for station blackout was compounded by a lack of planning and training for severe accident mitigation. The schedule for fuel removal from the pond at unit 1 was postponed from late FY17 to FY20, while that for unit 2 was delayed from early FY20 to later the same fiscal year, and that at unit 3 from early FY15 to FY17. Of these 135 had received 100 to 150 mSv, 23 150-200 mSv, three more 200-250 mSv, and six had received over 250 mSv (309 to 678 mSv) apparently due to inhaling iodine-131 fume early on. Rising residual heat within each reactor’s core caused the fuel rods in reactors 1, 2, and 3 to overheat and partially melt down, leading at times to the release of radiation. However, they also announced that radiation levels had declined enough in some towns located just beyond the original 20-km evacuation warning zone that residents could return to their homes there. The figure is greater than for Iwate and Miyagi prefectures, with 434 and 879 respectively, though they had much higher loss of life in the earthquake and tsunami – about 14,200. Some of the Tepco staff had lost homes, and even families, in the tsunami, and were initially living in temporary accommodation under great difficulties and privation, with some personal risk. These were in two stages, and are described in the Japan Nuclear Power paper. Developments since the 2013 UNSCEAR Report on the levels and effects of radiation exposure due to the nuclear accident following the great east-Japan earthquake and tsunami - UNSCEAR White Paper, 2015 The Fukushima Daiichi Accident - IAEA, 2015 Japan moved a few metres east and the local coastline subsided half a metre. Beyond whatever insurance Tepco might carry for its reactors is the question of third party liability for the accident. The venting was designed to be through an external stack, but in the absence of power much of it apparently backflowed to the service floor at the top of the reactor building, representing a serious failure of this system (though another possibility is leakage from the drywell). In addition, an impermeable wall is being constructed on the sea-side of the reactors, and inside this a frozen soil wall will further block water flow into the reactor buildings. After conducting 900 hours of public hearings and interviews with more than 1,100 people and visiting several nuclear power plants, the commission’s report concluded that the accident was a “manmade disaster,” the result of “collusion between the government, the regulators and Tokyo Electric Power Co.” It said the “root causes were the organizational and regulatory systems that supported faulty rationales for decisions and actions.” The NAIIC criticized the regulator for insufficiently maintaining independence from the industry in developing and enforcing safety regulations, the government for inadequate emergency preparedness and management, and Tepco for its poor governance and lack of safety culture. From Tuesday 15 March attention was given to replenishing the water in the ponds of units 1, 2, 3 as well. Tsunami waves after the earthquake were up to 30 feet high. 15 March
A report from the Japanese government's Earthquake Research Committee on earthquakes and tsunamis off the Pacific coastline of northeastern Japan in February 2011 was due for release in April, and might finally have brought about changes. It lost circulation with the power outage, and temperature increased to 73°C by the time mains power and cooling were restored after two weeks. Areas with colour changes in 2012 showed approximately half the contamination as surveyed in 2011, the difference coming from decay of caesium-134 (two year half-life) and natural processes like wind and rain. The 125-volt DC back-up batteries for units 1 & 2 were flooded and failed, leaving them without instrumentation, control or lighting. The highest radiation levels on site came from debris left on the ground after the explosions at units 3&4. These reduced levels are reflected in worker doses: during January 2013, the 5702 workers at the site received an average of 0.86 mSv, with 75% of workers recorded as receiving less than 1 mSv. The United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR) is undertaking a 12-month study on the magnitude of radioactive releases to the atmosphere and ocean, and the range of radiation doses received by the public and workers. Cs-134 is also produced and dispersed, it has a two-year half-life. The main problem initially centred on Fukushima Daiichi units 1-3. Summary: A large amount of contaminated water has accumulated on site and has been treated to remove all but traces of tritium, which limits the potential to release treated water to the sea. Unit 4 became a problem on day five. By March 2016 total decay heat in units 1-3 had dropped to 1 MW for all three, about 1% of the original level, meaning that cooling water injection – then 100 m3/d – could be interrupted for up to two days. Concentrations outside these structures have been below regulatory levels since April 2011. INPO 11-005 Addendum, Aug 2012, Lessons learned from the Nuclear Accident at Fukushima Daiichi Nuclear Power Station. In February 2015 the prime minister said that restarting the four units was essentially a matter for Tepco to decide. Tepco figures submitted to NRA for the period to end January 2014 showed 173 workers had received more than 100 mSv (six more than two years earlier) and 1578 had received 50 to 100 mSv. The plant did have a sea wall to protect it but, as it had been drastically reduced in height, the sea wall failed to protect the complex from the tidal wave. NDF will also work closely with Tepco Fukushima Daiichi D&D Engineering Co. which has responsibility for operating the actual decommissioning work there. In April 2019, the first residents of Okuma, the closest town to the plant, were allowed to return home. An initial report was published in December 2011 and a final report in July 2012. The only exception are the 146 emergency workers that received radiation doses of over 100 mSv during the crisis. It then plans to remove concrete and other rubble on the top floor of the building. The meltdown was the worst nuclear accident since Chernobyl in 1986. For unit 3, fuel removal is expected to be completed in FY20. Caesium is soluble and can be taken into the body, but does not concentrate in any particular organs, and has a biological half-life of about 70 days. By December 2018, 2259 disaster-related deaths, that were not due to radiation-induced damage or to the earthquake or to the tsunami, had been identified by the Japanese authorities. Most Japanese people were exposed to additional radiation amounting to less than the typical natural background level of 2.1 mSv per year. It included a new goal of cutting the amount of groundwater flowing into the buildings to less than 100 m3 per day by April 2016. The level of 250 mSv was the allowable maximum short-term dose for Fukushima Daiichi accident clean-up workers through to December 2011, 500 mSv is the international allowable short-term dose "for emergency workers taking life-saving actions". In mid-April 2011, the first meeting was held of a panel to address compensation for nuclear-related damage. The new International Research Institute for Nuclear Decommissioning (IRID) has a focus on Fukushima 1-4. 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