Fukushima nuclear accident

• 1. Introduction

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  At 14:46 on the 11th of March 2011, a 9.0 magnitude earthquake struck off the east coast of Japan's Tōhoku region. At the Fukushima Daiichi Nuclear Power Plant in Ōkuma, three reactors were running. All three shut down automatically the instant seismic sensors detected the shaking. For a moment, the emergency systems did exactly what they were designed to do. Then the ocean arrived.

  The tsunami that followed was 13-14 meters high. The plant's seawall stood at 10 meters. Within hours, the site had lost nearly every source of electrical power, the cooling systems were failing, and the fuel inside three reactors was beginning to melt. The United Nations Scientific Committee on the Effects of Atomic Radiation would later classify it as the worst nuclear incident since Chernobyl.

  What followed over the next weeks and years was not simply a story about radiation. It was a story about the limits of backup systems, the cost of regulatory failure, the dangers of mass evacuation, and the question of what to do with more than a million cubic meters of contaminated water sitting in tanks that were starting to degrade. Four former TEPCO executives would eventually be ordered to pay the equivalent of $95 billion in civil damages. Over 164,000 people were displaced from their homes. And a cleanup expected to take 30 to 40 years was only just beginning.

• 2. The Machinery of Failure

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  The Fukushima Daiichi plant was built around six General Electric light water boiling water reactors. Unit 1 was a GE type 3. Units 2 through 5 were type 4. Unit 6 was type 5. The plant's design included layered backup systems intended to prevent exactly the kind of meltdown that occurred.

  Each reactor had what engineers called an isolation condenser system: a closed coolant loop that could cool the reactor for at least 8 hours using only reactor pressure and gravity, with no external power required. Newer units used a different system called reactor core isolation cooling, which drove a pump using steam from the reactor vessel itself. Both systems were designed to work when the grid went dark.

  But both depended on electricity in subtler ways. The isolation condensers needed electrically operated control valves to manage cooling rates and prevent thermal stress on the reactor vessel. The RCIC systems needed direct current to allow remote control and alternating current to power isolation valves. When the tsunami flooded the turbine and reactor buildings at approximately 15:41, it knocked out ten of the plant's thirteen emergency diesel generators. The generators had been placed in basements 7-8 meters below ground, cooled by seawater pumps sitting unprotected on the shoreline. The third air-cooled diesel generator, positioned inland at higher elevation, survived. It served only unit 6.

  The DC backup batteries, designed to power the station for roughly 8 hours, were also submerged in units 1, 2, and 4. In unit 1, operators did not know the isolation condenser had stopped functioning because the loss of DC power had automatically closed the AC-powered isolation valves. They would spend hours attempting to restart a system that could no longer receive their commands.

• 3. Three Reactors, Three Failures

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  Unit 1 lost cooling for approximately 18 hours after a hydrogen explosion at 15:36 on the 12th of March damaged the mobile generator and the seawater injection lines. A second explosion in unit 3 on the 14th interrupted attempts to restore cooling to unit 1 again. Computer simulations from 2013 later suggested that the melted fuel in unit 1 had breached the bottom of the primary containment vessel and eaten into its concrete foundation, coming within about 30 centimeters of leaking into the ground. A Kyoto University nuclear engineer described the uncertainty plainly: "We just can't be sure until we actually see the inside of the reactors."

  Unit 2 had a quieter but more alarming sequence. Its RCIC system operated without operator intervention for nearly three days. Workers sent to inspect it at 02:55 on the 12th of March found it still functioning normally. But the condensate storage tank was nearly empty, so at 05:00 operators reconfigured the system to draw from the suppression chamber instead. The RCIC pump for unit 2 finally failed at 13:00 on the 14th after 68 hours of continuous operation. With no way to vent the containment and no cooling water, workers had few options left. An explosion was heard at 06:15 on the 15th of March.

  Unit 3 presented a different challenge. Workers managed to extend DC power by disconnecting nonessential equipment, buying roughly 2 additional days before replacement batteries arrived from a neighboring station with 7 hours to spare. When the HPCI system showed signs of malfunction on the morning of the 13th, workers tried to depressurize the reactor using batteries collected from nearby automobiles. The approach worked long enough to allow water injection. But a hydrogen explosion struck unit 3's reactor building at 11:01 on the 14th, damaging coolant lines and forcing another evacuation.

• 4. The Human Cost of Evacuation

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  Within hours of the tsunami, a 2 km evacuation order covering approximately 1,900 residents was issued at 20:50. A 3 km order covering around 6,000 residents and a 10 km shelter-in-place order for 45,000 more followed at 21:23. By 18:25 the next day, the evacuation radius had expanded to 20 km. Many of the zone boundaries were set by bureaucrats rather than nuclear experts. Twenty percent of residents within the initial 2 km radius were forced to evacuate more than six times.

  Of the roughly 2,220 patients and elderly residents within hospitals and nursing homes inside the 20 km zone, 51 died during the evacuation. Dr. Arifumi Hasegawa identified hypothermia, dehydration, and deterioration of underlying medical conditions as the suspected causes of death. The lack of medical support before, during, and after the evacuation was regarded as the major reason those lives were lost. The evacuation itself was later accused of causing more harm than it prevented.

  A 2012 survey of approximately 1,743 evacuees conducted by the Iitate local government found that 60 percent reported their health and their family's health had deteriorated after evacuating. About 34.7 percent had suffered salary cuts of 50 percent or more. One third of surveyed families were living apart from their children. Japanese health specialist Shunichi Yamashita drew directly on the Soviet experience: "We know from Chernobyl that the psychological consequences are enormous. Life expectancy of the evacuees dropped from 65 to 58 years - not because of cancer, but because of depression, alcoholism, and suicide." A 2014 review of 48 published studies found that rates of psychological distress among evacuated people rose fivefold compared to the Japanese average. Ten years after the accident, over 41,000 people from Fukushima were still living as evacuees.

• 5. What the Radiation Actually Did

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  Radiation exposure for residents living near the accident site was estimated at 12-25 millisieverts in the year following the accident. Residents of Fukushima City specifically were estimated to have received 4 mSv over the same period. For comparison, the total background radiation a person receives over an entire lifetime is approximately 170 mSv.

  The United Nations Scientific Committee on the Effects of Atomic Radiation stated that "no adverse health effects among Fukushima residents have been documented that are directly attributable to radiation exposure from the Fukushima Daiichi nuclear plant accident." Insurance compensation was paid for one death from lung cancer in a plant worker who had been exposed to 74 mSv since the accident, though researchers noted this did not establish a causal relationship. Six other people were reported to have developed cancer or leukemia. Two workers were hospitalized for radiation burns.

  Thyroid cancer drew particular attention from the World Health Organization and the United Nations. In January 2022, six patients who were children at the time of the accident sued TEPCO for 616 million yen after developing thyroid cancer. The scientific consensus holds that the detected increase in thyroid cancer falls within statistical background noise from the screening effect, and that the cancers did not show chromosomal aberrations consistent with ionizing radiation exposure, except from CT scans. The WHO modeled increased lifetime cancer risk relative to baseline for infants, as an upper bound: 4 percent for all solid cancers, 7 percent for leukemia, and 70 percent for thyroid cancer - though thyroid cancer has an extremely low baseline rate, which inflates that figure.

  In the ocean, caesium isotope concentrations reached 10 to 1,000 times above pre-accident levels in waters off Japan. Cs-134 was detected in migratory tuna off the coast of California. Studies from 2011 to 2015 found elevated cesium in marine life, though levels remained below thresholds considered harmful to marine animals or human consumers. In February 2022, Japan suspended black rockfish sales from Fukushima after one fish from Soma was found to contain 180 times more Cesium-137 than legally permitted.

• 6. The Inquiry and Its Findings

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  Three separate investigations ultimately concluded that the accident was man-made. Their reports pointed to regulatory capture, a culture of deference, and what one commission described as "conventions of Japanese culture" such as obedience, reluctance to question authority, and groupism.

  The Fukushima Nuclear Accident Independent Investigation Commission, known as the NAIIC, was the first independent investigation commission in the 66-year history of Japan's constitutional government to be established by the National Diet. Its chairman stated plainly that the accident was foreseeable and preventable. The commission found that both the government and TEPCO lacked any sense that they were personally responsible for protecting society: "They effectively betrayed the nation's right to be safe from nuclear accidents."

  The government-appointed Investigation Committee on the Accident at the Fukushima Nuclear Power Stations, ICANPS, released a 448-page final report on the 23rd of July 2012. It faulted an inadequate legal framework for nuclear crisis management and possible excess intervention by Prime Minister Naoto Kan's office. It also concluded that a culture of complacency had made accident prevention structurally difficult.

  A pattern of concealment worsened the public's distrust. TEPCO officials were instructed not to use the phrase "core meltdown" in public. The company officially acknowledged the meltdown two months after it occurred. The Ministry of Education, Culture, Sports, Science and Technology sent data from the radiation monitoring network only to the Fukushima prefectural government and delayed sharing it with the U.S. military. The U.S. military produced a detailed contamination map using aircraft and provided it to a Japanese ministry on the 18th of March; the data was not forwarded to the Nuclear Safety Commission, but was made public by the United States on the 23rd. Key government meeting records from the crisis were never kept. In August 2011, several top energy officials were dismissed, including the Vice-minister for Economy, Trade and Industry and the heads of both the Nuclear and Industrial Safety Agency and the Agency for Natural Resources and Energy.

• 7. The Long Cleanup

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  By late 2019, roughly 1.17 million cubic meters of contaminated water was being stored in tanks at the plant. Around 400 tonnes of cooling water per day were still being pumped into the damaged reactors as of 2013, with another 400 tonnes of groundwater seeping in daily. TEPCO constructed an underground ice wall to block groundwater, a $300 million facility that freezes the ground to a depth of 30 meters using 7.8 MW of power. By 2019, daily contaminated water generation had dropped to 170 tonnes.

  The water cannot simply be held indefinitely. In 2021, Japan's Nuclear Regulation Authority warned that around 3,373 waste storage containers for radioactive slurry were degrading faster than expected. A government committee concluded in 2020 that purified water should be discharged to the sea or evaporated to atmosphere. Discharging all water to the sea over one year would expose local residents to approximately 0.81 microsieverts - compared with the 2,100 microsieverts Japanese people receive annually from natural background radiation. In August 2023, Japan began discharging treated water into the Pacific Ocean, sparking protests and prompting China to block all seafood imports from Japan. Discharges were planned to continue over the following 30 years.

  Fuel removal is equally slow. TEPCO completed removal of 1,535 fuel assemblies from the unit 4 spent fuel pool in December 2014, and 566 assemblies from the unit 3 pool in February 2021. The company plans to remove all fuel rods from spent fuel pools in units 1, 2, 5, and 6 by 2037, and to extract the molten fuel debris from reactor containments in units 1, 2, and 3 by approximately 2050. Plant management estimated the full cleanup and decommissioning program at 30 to 40 years. Japan's trade ministry estimated the total cost of decontamination and compensation in November 2016 at 20 trillion yen, equivalent to 180 billion US dollars. In September 2020, the Great East Japan Earthquake and Nuclear Disaster Memorial Museum opened in the town of Futaba, offering exhibits in English, Chinese, and Korean - and tours to the accident area itself had been running since 2018.