Fukushima nuclear accident

The Fukushima Daiichi Nuclear Power Plant consisted of six General Electric (GE) light water boiling water reactors (BWRs). At the time of the Tōhoku earthquake on 11 March 2011, units 1–3 were operating. However, the spent fuel pools of all units still required cooling. Materials Many of the internal components and fuel assembly cladding are made from a zirconium alloy (Zircaloy) for its low neutron cross section. At normal operating temperatures (~), it is inert. However, above , Zircaloy can be oxidized by steam to form hydrogen gas Both of these reactions are exothermic. In combination with the exothermic reaction of boron carbide with stainless steel, these reactions can contribute to the overheating of a reactor. Isolated cooling systems In the event of an emergency, reactor pressure vessels (RPV) are automatically isolated from the turbines and main condenser and are instead switched to a secondary condenser system, which is designed to cool the reactor without the need for pumps powered by external power or generators. The isolation condenser (IC) system involved a closed coolant loop from the pressure vessel with a heat exchanger in a dedicated condenser tank. Steam would be forced into the heat exchanger by the reactor pressure, and the condensed coolant would be fed back into the vessel by gravity. Each reactor was initially designed to be equipped with two redundant ICs which were each capable of cooling the reactor for at least 8 hours (at which point, the condenser tank would have to be refilled). However, it was possible for the IC system to cool the reactor too rapidly after shutdown, which could result in undesirable thermal stress on the reactor pressure vessel. To avoid this, the protocol called for reactor operators to manually open and close the condenser loop using electrically operated control valves. Venting systems In the event of an emergency, operators planned to pump water into the reactors to keep them cool. This would inevitably create steam which should not be very radioactive because the fuel would still be in the primary containment vessel. Therefore, the steam would manually be released by venting valves to prevent a high pressure explosion. == Accident ==

Although AC power was lost, some DC power was still available in unit 3 and the workers were able to remotely confirm that the RCIC system was continuing to cool the reactor. However, knowing that their DC supply was limited, the workers managed to extend the backup DC supply to about 2 days by disconnecting nonessential equipment, until replacement batteries were brought from a neighboring power station on the morning of the 13th (with 7 hours between loss and restoration of DC power). At 11:36 the next day, after 20.5 hours of operation, the RCIC system failed. In response, the high-pressure coolant injection (HPCI) system was activated to alleviate the lack of cooling while workers continued to attempt to restart the RCIC. Additionally, the FP system was used to spray the PCV (mainly the SC) with water in order to slow the climbing temperatures and pressures of the PCV. Unit 4 was not fueled at the time, but the unit 4 spent fuel pool (SFP) contained a number of fuel rods. The following day, on the 16th, an aerial inspection was performed by helicopter which confirmed there was sufficient water remaining in the SFP. On the 20th, water was sprayed into the uncovered SFP, later replaced by a concrete pump truck with a boom on the 22nd. Radionuclide release Quantities of the released material are expressed in terms of the three predominant products released: caesium-137 (137Cs), iodine-131 (131I), and xenon-133. Estimates for atmospheric releases range from 7–20 PBq for 137Cs, 100–400 PBq for 131I, and 6,000–12,000 PBq for xenon-133. Thus, the majority (90~99%) of the radionuclides deposited were isotopes of iodine and caesium, with a small portion of tellurium, which almost fully vaporized out of the core due to their high vapor pressure. The remaining fraction of deposited radionuclides were of less volatile elements such as barium, antimony, and niobium, of which less than a percent evaporated from the fuel. In addition to atmospheric deposition, there was also a significant quantity of direct releases into groundwater (and eventually the ocean) through leaks of coolant which had been in direct contact with the fuel. Estimates for this release vary from 1 to 5.5 PBq 137Cs and 10–20 PBq 131I. According to the French Institute for Radiological Protection and Nuclear Safety, the release from the accident represents the most important individual oceanic emissions of artificial radioactivity ever observed. The Fukushima coast has one of the world's strongest currents (Kuroshio Current). It transported the contaminated waters far into the Pacific Ocean, dispersing the radioactivity. As of late 2011, measurements of both the seawater and the coastal sediments suggested that the consequences for marine life would be minor. Significant pollution along the coast near the plant might persist, because of the continuing arrival of radioactive material transported to the sea by surface water crossing contaminated soil. The possible presence of other radioactive substances, such as strontium-90 or plutonium, had not been sufficiently studied. Recent measurements show persistent contamination of some marine species (mostly fish) caught along the Fukushima coast. ==Consequences==

Evacuation Immediate response , February 2012 orders, and additional administrative districts that had an evacuation order are highlighted. However, due to difficulty coordinating with the national government, a 3 km evacuation order of ~6,000 residents and a 10 km shelter-in-place order for 45,000 residents was established nearly simultaneously at 21:23. The evacuation radius was expanded to 10 km at 5:44, and was then revised to 20 km at 18:25. The size of these evacuation zones was set for arbitrary reasons at the discretion of bureaucrats rather than nuclear experts. Communication between different authorities was scattered and at several times the local governments learned the status of evacuation via the televised news media. at the time of the 3 km evacuation order, the majority of residents within the zone had already evacuated. Additionally, a 30 km shelter in place order was communicated on the 15th, although some municipalities within this zone had already decided to evacuate their residents. This order was followed by a voluntary evacuation recommendation on the 25th, although the majority of residents had evacuated from the 30 km zone by then. 51 fatalities are attributed to the evacuation. However Geraldine Thomas claimed "there is a vanishingly small chance that this man's lung cancer was as a result of the radiation he was exposed to". Communication failures The Japanese public felt that the government and TEPCO provided limited information about the accident in the early weeks. There were several instances early in the accident response in which data about the accident was not properly handled. The Ministry of Education, Culture, Sports, Science and Technology (MEXT) only sent data from the SPEEDI network to the Fukushima prefectural government TEPCO officials were instructed not to use the phrase "core meltdown" in order to conceal the meltdown until they officially recognized it two months after the accident. The Japanese government did not keep records of key meetings during the crisis. In January 2015, the number of residents displaced due to the accident was around 119,000, peaking at 164,000 in June 2012. A 2014 metareview of 48 articles indexed by PubMed, PsycINFO, and EMBASE, highlighted several psychophysical consequences among the residents in Miyagi, Iwate, Ibaraki, Tochigi and Tokyo. The metareview found mass fear among Fukushima residents which was associated with depressive symptoms, anxiety, sleep disturbance, post-traumatic stress disorder, maternal distress, and distress among the employees of the nuclear plant. The rates of psychological distress among evacuated people rose fivefold compared to the Japanese average due to the experience of the accident and evacuation. An increase in childhood obesity in the area after the accident has also been attributed to recommendations that children stay indoors instead of going outside to play. Energy policy complex in Tokyo Prior to the accident, over 25% of domestic electricity generation in Japan used nuclear power and Japan had set a fairly ambitious green house gas (GHG) reduction target of 25% below 1990 levels by 2020, which involved increasing the share of nuclear power in electricity generation from 30% to 50%. However, this plan was abandoned and the target was revised to a 5.2% emissions increase by 2020 following the accident, alongside a focus on reducing dependence on nuclear power in favor of improved thermal efficiency in fossil fuel energy use and increasing the share of "renewables". The contribution of nuclear energy dropped to less than one percent following the accident This resulted in an increase in the share of fossil fuel energy use, which had increased to ~94% by 2015 (the highest of any IEA member state, with the remaining ~6% produced by renewables, an increase from 4% in 2010). As of 2013, TEPCO and eight other Japanese power companies were paying approximately 3.6 trillion JPY (37 billion USD) more in combined imported fossil fuel costs compared to 2010 to make up for the missing power. In May 2011, UK chief inspector of nuclear installations Mike Weightman traveled to Japan as the lead of an International Atomic Energy Agency (IAEA) expert mission. The main finding of this mission, as reported to the IAEA ministerial conference that month, was that risks associated with tsunamis in several sites in Japan had been underestimated. In September 2011, IAEA Director General Yukiya Amano said the Japanese nuclear disaster "caused deep public anxiety throughout the world and damaged confidence in nuclear power". In the aftermath, Germany accelerated plans to close its nuclear power reactors and decided to phase out the rest by 2022. but have undone these plans since. Italy held a national referendum, in which 94 percent voted against the government's plan to build new nuclear power plants. New nuclear projects were proceeding in some countries. The consulting firm KPMG reported in 2018 that 653 new nuclear facilities were planned or proposed for completion by 2030. In 2019, the United Kingdom was planning a major nuclear expansion despite some public objection. Russia had similar plans. In 2015, India was also pressing ahead with a large nuclear program, as was South Korea. Indian Vice President M. Hamid Ansari said in 2012 that "nuclear energy is the only option" for expanding India's energy supplies, and Prime Minister Modi announced in 2014 that India intended to build 10 more nuclear reactors in a collaboration with Russia. Radiation effects in humans , from 21 March until 5 May 2011 Radiation exposure of those living in proximity to the accident site was estimated at 12–25 millisieverts (mSv) in the year following the accident. Residents of Fukushima City were estimated to have received 4 mSv in the same time period. In comparison, the dosage of background radiation received over a lifetime is 170 mSv. Very few or no detectable cancers are expected as a result of accumulated radiation exposure. Residents who were evacuated were exposed to so little radiation that radiation-induced health effects were likely to be below detectable levels. The World Health Organization (WHO), United Nations (UN), and researchers from other groups were particularly concerned about thyroid cancer as a result of the radiation. In January 2022, six such patients who were kids at the time of the accident sued TEPCO for 616 million yen after developing thyroid cancer. The scientific consensus suggests that the increase in detectable thyroid cancer fell within statistical background noise due to the screening effect, and that the cancers did not have chromosomal aberrations consistent with exposure to ionizing radiation, except for that caused by CT scans. Leukemia, breast cancer, and other solid cancers were studied by the WHO. Increase in lifetime cancer relative to baseline risk for infants was reported because these represent an upper bound for the cancer related health risks. especially when the effects of radiation on the human body are not linear, and with obvious thresholds. The WHO reports that the radiation levels from the accident were below the thresholds for deterministic effects from radiation. Migratory pelagic species are also highly effective and rapid transporters of pollutants throughout the ocean. Elevated levels of Cs-134 appeared in migratory species off the coast of California that were not seen prior to the accident. In June 2016, the political advocacy group International Physicians for the Prevention of Nuclear War, asserted that 174,000 people have been unable to return to their homes and ecological diversity has decreased and malformations have been found in trees, birds, and mammals. Although physiological abnormalities have been reported within the vicinity of the accident zone, the scientific community has largely rejected any such findings of genetic or mutagenic damage caused by radiation, instead showing it can be attributed either to experimental error or other toxic effects. In February 2018, Japan renewed the export of fish caught off Fukushima's nearshore zone. According to prefecture officials, no seafood had been found with radiation levels exceeding Japan safety standards since April 2015. In 2018, Thailand was the first country to receive a shipment of fresh fish from Japan's Fukushima prefecture. A group campaigning to help prevent global warming has demanded the Food and Drug Administration disclose the name of the importer of fish from Fukushima and of the Japanese restaurants in Bangkok serving it. Srisuwan Janya, chairman of the Stop Global Warming Association, said the FDA must protect the rights of consumers by ordering restaurants serving Fukushima fish to make that information available to their customers, so they could decide whether to eat it or not. In February 2022, Japan suspended the sale of black rockfish from Fukushima after it was discovered that one fish from Soma had 180 times more radioactive Cesium-137 than legally permitted. The high levels of radioactivity led investigators to believe it had escaped from a breakwater at the accident site, despite nets intended to prevent fish from leaving the area. Forty-four other fish from the accident site have shown similar levels. Radiation effects in agriculture On 20 March 2011, vegetables produced in six prefectures in the Kanto and Tohoku regions exceeded provisional regulation values. The government subsequently prohibited Fukushima, Ibaraki, Tochigi and Gunma prefectures from shipping vegetables in which radioactive materials exceeding provisional regulation values had been detected. Additionally, The Federal Office for Radiation Protection found that foodstuffs were contaminated by radioactive material that was deposited on the leaves or directly on agricultural produce, such as fruit and vegetables, or that was absorbed via the roots of fruit and vegetables. Considering the use of land for crop cultivation, radiocesium concentration in the top layer of the soil had to be evaluated. Without disturbance of soil surface, radiocesium was accumulated within about 5 cm of the soil surface, which could affect food safety. The authors found that the agri-food industry in Fukushima Prefecture has been heavily impacted, with serious negative effects extending to other regions and the national food supply. Agri-food radiation regulation and food safety inspection in Japan prior to the accident were sparse, and have been characterized as inadequate. Provisional regulatory limits for radionuclides in agri-food products were introduced after Fukushima. These became the world's strictest in 2012. == Investigations ==

Three investigations into the accident showed the man-made nature of the catastrophe and its roots in regulatory capture associated with a "network of corruption, collusion, and nepotism." The three pleaded not guilty, and in September 2019, the court agreed. NAIIC The Fukushima Nuclear Accident Independent Investigation Commission (NAIIC) was the first independent investigation commission by the National Diet in the 66-year history of Japan's constitutional government. The chairman highlighted that it was foreseeable and preventable. The Commission recognized that the affected residents were still struggling and facing grave concerns, including the "health effects of radiation exposure, displacement, the dissolution of families, disruption of their lives and lifestyles and the contamination of vast areas of the environment". ICANPS The purpose of the Investigation Committee on the Accident at the Fukushima Nuclear Power Stations (ICANPS) was to identify the accident's causes and propose policies designed to minimize the damage and prevent the recurrence of similar incidents. The 10 member, government-appointed panel included scholars, journalists, lawyers, and engineers. It was supported by public prosecutors and government experts and released its final 448-page investigation report on 23 July 2012. The panel's report faulted an inadequate legal system for nuclear crisis management, a crisis-command disarray caused by the government and TEPCO, and possible excess meddling on the part of Prime Minister Naoto Kan's office in the crisis' early stage. The panel concluded that a culture of complacency about nuclear safety and poor crisis management led to the nuclear accident. == Remediation and recovery ==

team examining Unit 3 To assuage fears, the government enacted an order to decontaminate over a hundred areas where the level of additional radiation was greater than one millisievert per year. This is a much lower threshold than is necessary for protecting health. The government also sought to address the lack of education on the effects of radiation and the extent to which the average person was exposed. In September 2020, The Great East Japan Earthquake and Nuclear Disaster Memorial Museum was opened in the town of Futaba, near the power plant. The museum exhibits items and videos about the earthquake and the nuclear accident. To attract visitors from abroad, the museum offers explanations in English, Chinese, and Korean. Fuel removal TEPCO plans to remove the remaining nuclear fuel material from the plants. TEPCO completed the removal of 1535 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 plans to remove all fuel rods from the spent fuel pools of Units 1, 2, 5, and 6 by 2037 and to remove the remaining molten fuel debris from the reactor containments of Units 1, 2, and 3 by about 2050. Plant management estimated the ongoing intensive cleanup program to both decontaminate affected areas and decommission the plant will take 30 to 40 years from the accident. As of 2019, the contaminated water generation had been reduced to per day. In February 2014, NHK reported that TEPCO was reviewing its radioactivity data, after finding much higher levels of radioactivity than was reported earlier. Groundwater collected in July 2013 contained 5 MBq (0.12 millicuries) of strontium per liter () not the 0.9 MBq (0.02 millicuries) () that were initially reported. Plastic bags filled with contaminated soil and grass were also swept away by the flood waters. As of October 2019, 1.17 million cubic meters of contaminated water was stored in the plant area. The water is being treated by a purification system that can remove radionuclides, except tritium, to a level that Japanese regulations allow to be discharged to the sea. As of December 2019, 28% of the water had been purified to the required level, while the remaining 72% needed additional purification. However, tritium cannot be separated from the water. As of October 2019, the total amount of tritium in the water was about 856 terabecquerels, and the average tritium concentration was about 0.73 MBq per liter. IAEA considers that the dose calculation method is appropriate. Further, the IAEA recommended that a decision on the water disposal must be made urgently. Despite the negligible doses, the Japanese committee is concerned that the water disposal may cause reputational damage to the prefecture, especially to the fishing industry and to tourism. Tanks used to store the water were expected to be filled in 2023. In July 2022, Japan's Nuclear Regulation Authority approved discharging the treated water into the sea. Japan said the water is safe, many scientists agreed, and the decision came weeks after the UN's nuclear watchdog approved the plan; but critics say more studies need to be done and the release should be halted. In August, Japan began the discharge of treated waste water into the Pacific Ocean, sparking protests in the region and retaliation from China, who blocked all imports of seafood from Japan. Discharges were planned to occur over the subsequent 30 years to release all the water. A US State Department spokesperson supported the decision. South Korea's foreign minister and activists from Japan and South Korea protested the announcement. In April 2023, fishers and activists held protests in front of the Japanese embassy in the Philippines in opposition to the planned release of 1.3 million tons of treated water into the Pacific Ocean. Xiaoqi Zhou, an environmental sciences scholar, found that more than 60 radioactive substances have been detected in the Fukushima nuclear wastewater, such as 106Ru, 60Co, 90Sr, 137Cs and 131I. Some of these radioactive isotopes are relatively volatile fission products that can be released into the atmosphere. These particles could adhere to both the leaves and stems of plants, as well as bind firmly to clay minerals in the soil, resulting in their prolonged retention in the terrestrial ecosystems. Eventually, they can enter groundwater through rainfall and flow into the ocean. Zhou found that compared with terrestrial radioactive elements, the release of radioactive elements from the Fukushima nuclear wastewater into the ocean spreads more rapidly with ocean currents, which increases their potential to harm marine species—and, by extension, human health. In December 2016 the government estimated decontamination, compensation, decommissioning, and radioactive waste storage costs at ($ billion inflation adjusted), nearly double the 2013 estimate. By 2022, had already been spent, with on compensation, on decontamination, and on decommissioning and storage. Despite concerns, the government expected total costs to remain under budget. In March 2017, a Japanese court ruled that negligence by the Japanese government had led to the Fukushima accident by failing to use its regulatory powers to force TEPCO to take preventive measures. The Maebashi district court near Tokyo awarded ($ inflation adjusted) to 137 people who were forced to flee their homes following the accident. On 30 September 2020, the Sendai High Court ruled that the Japanese government and TEPCO are responsible for the accident, ordering them to pay $9.5 million in damages to residents for their lost livelihoods. In March 2022, Japan's Supreme Court rejected an appeal from TEPCO and upheld the order for it to pay damages of ($12 million) to about 3,700 people whose lives were harmed by the accident. Its decision covered three class-action lawsuits, among more than 30 filed against the utility. On 17 June 2022, the Supreme Court acquitted the government of any wrongdoing regarding potential compensation to over 3,700 people affected by the accident. On 13 July 2022, four former TEPCO executives were ordered to pay ($95 billion) in damages to the operator of the power plant, in the civil case brought by TEPCO shareholders. Equipment, facility, and operational changes A number of nuclear reactor safety system lessons emerged from the incident. The most obvious was that in tsunami-prone areas, a power station's sea wall must be adequately tall and robust. Eventually a wide variety of specially designed robots were employed (leading to a robotics boom in the region), but as of early 2016, three of them had promptly become non-functional due to the intensity of the radioactivity. == Prior warning ==

On 5 July 2012, the NAIIC found that the causes of the accident had been foreseeable, and that TEPCO had failed to meet basic safety requirements such as risk assessment, preparing for containing collateral damage, and developing evacuation plans. At a meeting in Vienna, Austria, three months after the accident, the IAEA faulted lax oversight by the Japanese Ministry of Economy, Trade and Industry, saying the ministry faced an inherent conflict of interest as the government agency in charge of both regulating and promoting the nuclear power industry. On 12 October 2012, TEPCO admitted that it had failed to take necessary measures for fear of inviting lawsuits or protests against its nuclear plants. Additionally, other individuals, citizen groups, and non-profits in the Tohoku region pursued alternative routes to producing and disseminating radiation data so as to make contamination and its health impacts more visible to the public. In 2002, the government earthquake research headquarters estimated that a tsunami up to could hit the power station. These findings were supported by the cabinet office's own findings which stated that the forecast by TEPCO did not cover the full range of possibility. TEPCO's in-house 2008 study identified an immediate need to better protect the facility from flooding by seawater which cited the estimate from the 2002 study. In 2009, the Active Fault and Earthquake Research Center urged TEPCO and the Nuclear and Industrial Safety Agency to revise their assumptions for possible tsunami heights upwards, based on his team's findings about the 869 Sanriku earthquake, but this was not seriously considered at the time. Unit 1 EDG disabled by flooding in 1991 On 30 October 1991, one of unit 1's EDGs failed as a result of a condensate coolant leak in the turbine building, as reported by former employees in December 2011. A TEPCO report in 2011 detailed that the room was flooded through a door and some holes for cables, but the power supply was not cut off by the flooding. An engineer reported to superiors the possibility that a tsunami could damage the generators. In response, TEPCO installed doors to prevent water from leaking into the generator rooms. Venting systems American nuclear scientists identified manually activated venting systems to be riskier than a passive approach five years prior to the accident. The venting system for unit 3 had several issues before its explosion. By 2011, new reactor designs used passive venting systems. ==See also==