Tokaimura nuclear accidents

Nuclear power was an important energy alternative for natural-resource-poor Japan to limit dependence on imported energy, providing about 30% of Japan's electricity up until the Fukushima nuclear disaster of 2011, after which nuclear electricity production fell into sharp decline. Tōkai's location (about 70 miles from Tokyo) and available land space made it ideal for nuclear power production, so a series of experimental nuclear reactors and then the Tōkai Nuclear Power Plant – the country's first commercial nuclear power station – were built there. Over time, dozens of companies and government institutes were established nearby to provide nuclear research, experimentation, manufacturing, fuel fabrication, enrichment and disposal facilities. Nearly one-third of Tōkai's population relied upon nuclear industry-related employment. == 1997 nuclear waste accident ==

On 11 March 1997, Tōkai's first serious nuclear incident occurred at PNC's bituminization facility. It is sometimes called the , 'Dōnen' being an abbreviation of PNC's full Japanese name Dōryokuro Kakunenryō Kaihatsu Jigyōdan. The site encased and solidified low-level liquid waste in molten asphalt (bitumen) for storage, and that day was trialing a new asphalt-waste mix, using 20% less asphalt than normal. A gradual chemical reaction inside one fresh barrel ignited the already-hot contents at 10:00 a.m. and quickly spread to several others nearby. Workers failed to properly extinguish the fire, and smoke and radiation alarms forced all personnel to evacuate the building. At 8 p.m., just as people were preparing to reenter the building, built up flammable gases ignited and exploded, breaking windows and doors, which allowed smoke and radiation to escape into the surrounding area. The incident exposed 37 nearby personnel to trace amounts of radiation in what the government's Science and Technology Agency declared the country's worst-yet nuclear accident, which was rated a 3 on the International Nuclear Event Scale. A week after the event, meteorological officials detected unusually high levels of caesium 40 km (25 miles) southwest of the plant. Aerial views over the nuclear processing plant building showed a damaged roof from the fire and explosion allowing continued external radiation exposure. PNC management mandated two workers to falsely report the chronology of events that led to the facility's evacuation, in order to cover up the lack of proper supervision. Dōnen leadership failed to immediately report the fire to the Science and Technology Agency (STA). This delay was due to their own internal investigation of the fire, which hampered the deployment of emergency response teams and prolonged the radiation exposure. Dōnen facility officials initially reported a 20% increase of radiation levels in the area surrounding the reprocessing plant, but later revealed the true percent was ten times higher than initially published. Tōkai residents demanded criminal prosecution of PNC officials, reorganization of company leadership and closure of the plant itself. Later, Prime Minister Ryutaro Hashimoto criticized the delay that allowed radiation to continue to impact local areas. == 1999 accident ==

}}The second, more serious Tōkai nuclear accident () occurred about four miles away from the PNC facility on 30 September 1999, at a fuel enrichment plant operated by JCO, a subsidiary of Sumitomo Metal Mining Company. It was the worst civilian nuclear radiation accident in Japan prior to Fukushima (2011). This led to delays in informing the nearby public of the accident. In addition, the regulator did not conduct routine inspections to determine that the production process was not being carried out correctly. The second contributing issue was the use of an unapproved procedure. The accident occurred while manufacturing fuel at a different enrichment which was made infrequently. Because of a combination of reduced revenue, layoffs and inexperience, the company felt pressured to make this fuel despite not having the procedure approved. They stated that they did not submit a procedure for making this type of fuel to the regulator because they knew it would not get approved, and they would not be able to make it at all. Enriching nuclear fuel requires precision and has the potential to impose extreme risks to technicians. If done improperly, the process of combining nuclear products can produce a fission reaction which, in turn, produces radiation. In order to enrich the uranium fuel, a specific chemical purification procedure is required. The steps included feeding small batches of uranium oxide powder into a designated dissolving tank in order to produce uranyl nitrate using nitric acid. Next, the mixture is carefully transported to a specially crafted buffer tank. The buffer tank containing the combined ingredients is specially designed to prevent fission activity from reaching criticality. In a precipitation tank, ammonia is added forming a solid product. This tank is meant to capture any remaining nuclear waste contaminants. In the final process, uranium oxide is placed in the dissolving tanks until purified, without enriching the isotopes, in a wet-process technology specialized by Japan. Pressure placed upon JCO to increase efficiency led the company to employ an illegal procedure where they skipped several key steps in the enrichment procedure. The technicians poured the product by hand in stainless-steel buckets directly into a precipitation tank. The worker passed out, then regained consciousness 70 minutes later. The three workers were then transferred to the hospital, which confirmed that they were exposed to high doses of gamma, neutron, and other radiation. In addition to these three workers who immediately felt symptoms, 56 people at the JCO plant were reported to have been exposed to the gamma, neutron, and other irradiation. In addition to the workers at the site, construction workers who were working on a job site nearby, were also reported to have been exposed. The hazardous level was reached after the technicians added a seventh bucket containing aqueous uranyl nitrate, enriched to 18.8% U, to the tank. The solution added to the tank was almost seven times the legal mass limit specified by the STA. The buffer tank's tall, narrow geometry was designed to hold the solution safely and to prevent criticality. In contrast, the precipitation tank had not been designed to hold unlimited quantities of this type of solution. The designed wide cylindrical shape made it favorable to criticality. The workers bypassed the buffer tanks entirely, opting to pour the uranyl nitrate directly into the precipitation tank. Uncontrolled nuclear fission (a self-sustaining chain reaction) began immediately, emitting intense gamma and neutron radiation. Over the next several hours the fission reaction produced continuous chain reactions. Ouchi and Shinohara immediately experienced pain, nausea, and difficulty breathing; both workers went to the decontamination room where Ouchi vomited. Ouchi received the largest radiation exposure, resulting in rapid difficulties with mobility, coherence, and loss of consciousness. Emergency service workers arrived and escorted other plant workers outside of the facility's muster zones. This restriction was lifted the next afternoon. Almost 15 days later, the facility instituted protection methods with sandbags and other shielding to protect from residual gamma radiation. Aftermath Without an emergency plan or public communication from the JCO, confusion and panic followed the event. Sometime after the incident, people in the area were asked to lend any gold they had to help estimate the neutron flux the public was exposed to. Ultimately the incident was classified as an "irradiation" not "contamination" accident under Level 4 on the Nuclear Event Scale. The two technicians who received the higher doses, Ouchi and Shinohara, died several months later. Hisashi Ouchi, 35, was treated at the University of Tokyo Hospital for 83 days. Ouchi suffered serious radiation burns to most of his body, had severe damage to his internal organs, and had a near-zero white blood cell count. Without a functioning immune system, Ouchi was vulnerable to hospital-acquired infection and was placed in a special radiation ward to limit the risk of infection. A micrograph of his chromosomes showed that none of them were identifiable. Doctors tried to restore some functionality to Ouchi's immune system by administering peripheral blood stem cell transplantation, which at the time was a new form of treatment. Although small areas of Ouchi's skin and mucous membranes recovered with treatment, his overall condition continued to deteriorate, and medical personnel privately doubted whether treatment should be continued given the lack of effectiveness and the pain Ouchi was experiencing. Masato Shinohara, 40, was transported to the same facility. He underwent radical cancer treatments, numerous successful skin grafts, and a transfusion from congealed umbilical cord blood (to boost stem cell count). He succumbed to lung and kidney failure on 27 April 2000. Their supervisor, Yutaka Yokokawa, 54, received treatment from the National Institute of Radiological Sciences (NIRS) in Chiba, Japan. He was released three months later with minor radiation sickness. He faced negligence charges in October 2000. Contributors to both accidents According to the International Atomic Energy Agency, the cause of the accidents were "human error and serious breaches of safety principles". == In popular culture ==

The 1999 accident is mentioned, along with a flashback scene of a hospital visit to Hisashi Ouchi, in the 2023 Japanese miniseries The Days, a dramatization of the Fukushima nuclear accident. ==See also==