Tokaimura nuclear accidents
The Tokaimura nuclear accidents represent a sobering chapter in Japan's nuclear history, exposing severe vulnerabilities in safety protocols and regulatory oversight. These two distinct incidents—a radioactive waste fire in 1997 and a catastrophic criticality accident in 1999—unveiled the profound human cost and the critical importance of a robust safety culture within the nuclear industry. Join us as we explore how these events unfolded and the harrowing, life-altering lessons they taught the world. Both Tokaimura accidents stemmed from critical lapses in regulatory oversight, inadequate worker training, and a dangerous disregard for established safety procedures. The 1999 criticality accident, caused by workers manually mixing uranium fuel in an improper container, led to two agonizing deaths from extreme radiation exposure. These incidents spurred a major overhaul of Japan's nuclear safety laws, emphasizing stringent inspections, enhanced training, and a commitment to preventing future disasters.
AI Summary
The Tokaimura nuclear accidents represent a sobering chapter in Japan's nuclear history, exposing severe vulnerabilities in safety protocols and regulatory oversight. These two distinct incidents—a radioactive waste fire in 1997 and a catastrophic criticality accident in 1999—unveiled the profound human cost and the critical importance of a robust safety culture within the nuclear industry. Join us as we explore how these events unfolded and the harrowing, life-altering lessons they taught the world.
- Both Tokaimura accidents stemmed from critical lapses in regulatory oversight, inadequate worker training, and a dangerous disregard for established safety procedures.
- The 1999 criticality accident, caused by workers manually mixing uranium fuel in an improper container, led to two agonizing deaths from extreme radiation exposure.
- These incidents spurred a major overhaul of Japan's nuclear safety laws, emphasizing stringent inspections, enhanced training, and a commitment to preventing future disasters.
Japan's Nuclear Ambitions
For a nation rich in innovation but poor in natural resources, nuclear power has long been a vital energy source for Japan. It offered a pathway to energy independence, providing a significant portion of the country's electricity and reducing reliance on imported fuels. This ambition led to the development of a sophisticated nuclear industry.
The village of Tokaimura, about 70 miles northeast of Tokyo, became the heart of this endeavor. Its location offered ample space for the construction of experimental reactors, power plants, and a sprawling complex of facilities dedicated to nuclear research, fuel fabrication, and waste disposal. Nearly a third of its population relied on the nuclear industry for employment.
However, this hub of nuclear activity would also become the site of two devastating accidents. In 1997, a fire broke out at a nuclear waste processing plant, exposing workers to radiation. Then, just two years later, a far more severe criticality accident occurred at a different fuel reprocessing facility, leading to agonizing deaths and widespread public alarm. These events would forever change Japan's nuclear landscape.
The 1997 Waste Fire: A Warning Ignored
The first serious incident struck on March 11, 1997, at the Power Reactor and Nuclear Fuel Development Corporation, or PNC, in Tokaimura. This facility was responsible for a process called bituminization, where low-level liquid radioactive waste was encased and solidified in molten asphalt for safe storage. It was a routine procedure, but on this day, something went terribly wrong.
Workers were trialing a new mix, using 20% less asphalt than usual. A gradual chemical reaction inside one of the freshly mixed barrels ignited its hot contents at 10:00 a.m., and the fire quickly spread to several nearby containers. Efforts to extinguish it failed, and smoke and radiation alarms forced a facility-wide evacuation.
But the danger wasn't over. Hours later, as personnel prepared to re-enter, flammable gases that had accumulated inside the building ignited, causing an explosion. Windows shattered, doors broke open, and a plume of radioactive smoke and gases escaped into the surrounding environment. This incident, later rated Level 3 on the International Nuclear Event Scale, exposed 37 workers to trace amounts of radiation.
Adding to the crisis, PNC management initially attempted to cover up the extent of the accident and delayed reporting the incident to the Science and Technology Agency. This critical delay hampered emergency response efforts and prolonged the public's potential exposure to radiation. The true radiation levels were ten times higher than initially reported.
Public outrage was immediate, with demands for criminal prosecution, leadership changes, and the plant's closure. Prime Minister Ryutaro Hashimoto publicly criticized the delays. While the facility eventually reopened years later, this incident served as a stark, though ultimately unheeded, warning of deeper systemic issues.
The 1999 Criticality Catastrophe: Uncontrolled Chain Reaction
Just two and a half years later, on September 30, 1999, a far more devastating accident unfolded about four miles from the PNC facility. This time, it was at a fuel enrichment plant operated by JCO, a subsidiary of Sumitomo Metal Mining Company. It would become Japan's worst civilian nuclear radiation accident prior to Fukushima.
A Recipe for Disaster
The JCO facility converted uranium hexafluoride into enriched uranium dioxide fuel, a crucial step in manufacturing fuel rods for Japan's power and research reactors. This process demands extreme precision, as improperly handled nuclear materials can initiate a fission reaction, unleashing dangerous radiation. The procedure involved carefully feeding uranium oxide powder into a dissolving tank to produce uranyl nitrate, using nitric acid.
However, under pressure to increase efficiency and meet shipping requirements, JCO supervisors allowed technicians to deviate from approved procedures. Instead of using designated equipment, workers manually mixed chemicals in stainless-steel buckets, bypassing several crucial safety steps entirely. This practice was not approved by the regulatory agency, but it had become an unofficial company standard since 1993.
A critical safety design feature was completely circumvented. The official procedure required the uranyl nitrate solution to be stored in a buffer tank with a tall, narrow geometry, specifically engineered to prevent a critical mass from forming. The precipitation tank, where the accident occurred, was wide and cylindrical—a shape highly conducive to criticality if too much fissile material was introduced.
On that fateful morning, technicians Hisashi Ouchi, Masato Shinohara, and Yutaka Yokokawa poured a seventh bucket of aqueous uranyl nitrate solution, enriched to 18.8% uranium-235, directly into the precipitation tank. This brought the total uranium in the tank to about 16 kilograms—almost seven times the legal limit specified by the regulatory agency. At 10:35 a.m., the solution reached critical mass.
An uncontrolled nuclear chain reaction began immediately. A startling blue-white flash—likely Cherenkov radiation, emitted by charged particles moving faster than light in the solution—illuminated the room. Gamma radiation alarms blared, and Ouchi and Shinohara, who were leaning over the tank, instantly felt pain, nausea, and difficulty breathing. Yokokawa, sitting nearby, also saw the flash.
Chronology of a Crisis
Day Time Event/action Affected parties 30 September 1999 10:35 Criticality event occurred, setting off radiation monitors and alarms; evacuation begins and employees exposed to radiation 3 workers: Hisashi Ouchi, Masato Shinohara and Yutaka Yokokawa 30 September Until 23:30 (5 hours later) STA confirms continuing chain reactions; Tokaimura sets up headquarters for the incidents, (12 hours later) broadcasts all surrounding residents to evacuate, informs Japan's leadership and ceased all crop and water usage Tokaimura City and National Leadership 1 October 1999 All day Road blocks implemented; shelter in place lifted but schools closed all day; water drainage initiated to stop chain reaction. All residents 2 October 1999 All day Health checks conducted on all residents, measuring radiation; schools reopened and government press conferences held All residents
The chain reaction continued for nearly 20 hours. To halt the uncontrolled fission, emergency workers had to drain the cooling water from a jacket surrounding the precipitation tank. Water acts as a neutron reflector, essentially bouncing neutrons back into the fuel and sustaining the reaction. Then, a solution of boric acid was added directly to the tank. Boron is an excellent neutron absorber, effectively soaking up the neutrons and stopping the chain reaction, bringing the material back to a sub-critical state.
The Human Cost
The three technicians involved suffered severe radiation exposure. Hisashi Ouchi received an estimated 17 Sieverts (Sv), Masato Shinohara 10 Sv, and Yutaka Yokokawa 3 Sv. To put this in perspective, a dose of just 4-5 Sv is typically considered lethal without aggressive medical intervention. Ouchi and Shinohara had received doses far beyond anything survivable.
Hisashi Ouchi, 35, endured an agonizing 83-day struggle for life at the University of Tokyo Hospital. His body was ravaged by severe radiation burns, his internal organs were critically damaged, and his white blood cell count plummeted to near zero, leaving him with no immune system. Doctors attempted a peripheral blood stem cell transplant from his sister, a pioneering treatment at the time.
Despite a temporary increase in white blood cells, Ouchi's condition relentlessly deteriorated. Multiple organ failure set in, and he suffered cardiac arrest. Though revived, his medical team and family faced the grim reality that survival was impossible. After weeks of unimaginable suffering, his family ultimately agreed to a do-not-resuscitate order, and Ouchi died on December 21, 1999.
Masato Shinohara, 40, also fought for months in the same hospital. He underwent numerous successful skin grafts and received stem cells from umbilical cord blood. However, his lungs and kidneys eventually failed, and he succumbed to his injuries on April 27, 2000, nearly seven months after the accident.
Their supervisor, Yutaka Yokokawa, 54, received treatment for minor radiation sickness and was released three months later. While he survived the physical ordeal, he later faced negligence charges in connection with the accident.
Community Impact and Aftermath
As the crisis unfolded, nearly 161 people from 39 households within a 350-meter radius were evacuated. Later, 300,000 residents in Tokaimura were instructed to shelter indoors and cease agricultural activities. Roadblocks were set up, and a state of uncertainty gripped the community, exacerbated by a lack of clear communication from JCO.
In the chaotic aftermath, authorities conducted over 10,000 medical check-ups for residents and emergency workers. It was discovered that a roof ventilation fan at the plant had been left on, potentially releasing radioactive gas even after the critical reaction was stopped. People in the area were even asked to lend any gold they owned, as gold could be used to estimate neutron flux exposure.
The 1999 incident was classified as a Level 4 accident on the International Nuclear Event Scale, denoting a 'serious accident with local consequences.' In total, at least 667 workers, first responders, and nearby residents were exposed to excess radiation. JCO eventually paid $121 million in compensation to settle thousands of claims, covering affected individuals and businesses.
A Reckoning and Renewal
Both Tokaimura accidents were ultimately attributed to a confluence of human error and serious breaches of safety principles. Careless material handling, inexperienced technicians, inadequate supervision, and outdated safety procedures combined with a company culture of complacency, where the unapproved 'bucket method' had been in use for years to save time.
The fallout was severe. In March 2000, JCO's operating credentials were revoked—a first in Japan's history. Its president resigned, and six company officials, including Yokokawa, were charged with professional negligence. They pleaded guilty, revealing during the trial that a 1995 safety committee had even approved the use of steel buckets, and an unauthorized 1996 manual recommended the shortcut.
In response to the public outcry and the stark lessons learned, Japan implemented sweeping reforms. New laws mandated stringent operational safety procedures, quarterly inspections, and enhanced safety education and training for all nuclear facility personnel. The atomic and nuclear commissions began regular, rigorous investigations, striving to embed a strong safety culture throughout the industry.
The Tokaimura accidents fueled antinuclear movements in Japan, deepening the tension between the nation's critical energy needs and public safety concerns. While Japan continues to pursue nuclear power as part of its 'Strategic Energy Plan,' the legacy of Tokaimura serves as a constant, stark reminder of the devastating consequences when safety is compromised.
Tokaimura in Popular Culture
The harrowing events of the 1999 Tokaimura accident, particularly the suffering of Hisashi Ouchi, gained international attention. The incident is notably referenced in the 2023 Japanese miniseries "The Days," a dramatization of the Fukushima nuclear accident, which includes a flashback scene depicting Ouchi's tragic hospital stay, underscoring the enduring impact of Tokaimura on Japan's collective memory.
Article
Tokaimura nuclear accidents
Tokai Nuclear Plant, Japan's first nuclear power station
The Tokaimura nuclear accidents were two nuclear incidents which occurred near the village of Tōkai, Ibaraki Prefecture, Japan. The first accident occurred on 11 March 1997, producing an explosion after an experimental batch of solidified nuclear waste caught fire at the Power Reactor and Nuclear Fuel Development Corporation (PNC) radioactive waste bituminisation facility. Over twenty people were exposed to radiation.
The second was a criticality accident at a separate fuel reprocessing facility belonging to Japan Nuclear Fuel Conversion Co. (JCO) on 30 September 1999 due to improper handling of liquid uranium fuel for an experimental reactor. The incident spanned approximately 20 hours and resulted in the deaths of two workers; of 436 people whose doses of radiation exposure were evaluated, none of them exceeded annual regulatory dosage limits.
It was determined that the accidents were due to inadequate regulatory oversight, lack of appropriate safety culture and inadequate worker training and qualification. After these two accidents, a series of lawsuits were filed and new safety measures were put into effect.
By March 2000, Japan's atomic and nuclear commissions began regular investigations of facilities, expansive education regarding proper procedures and safety culture regarding handling nuclear chemicals and waste. JCO's credentials were removed, the first Japanese plant operator to be punished by law for mishandling nuclear radiation. This was followed by the company president's resignation and six officials being charged with professional negligence.
Background
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, and fuel fabrication, enrichment and disposal facilities. Nearly one-third of Tōkai's population relied upon nuclear industry-related employment.
1997 nuclear waste accident
Tokaimura nuclear accidents
On 11 March 1997, Tōkai's first serious nuclear incident occurred at PNC's bituminization facility. It is sometimes called the Dōnen accident (動燃事故, Dōnen jiko), '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. Following public outcry, the facility closed until reopening in November 2000 when it was reinstated as a nuclear fuel reprocessing plant.
Later, Prime Minister Ryutaro Hashimoto criticized the delay that allowed radiation to continue to impact local areas.
1999 accident
Tokaimura nuclear accidents
The second, more serious Tōkai nuclear accident (Japanese: 東海村JCO臨界事故, romanized: Tōkai-mura JCO-rinkai-jiko) 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). The incident exposed the surrounding population to hazardous radiation after the uranium mixture reached criticality. Two of the three technicians mixing fuel were killed. The incident was caused by lack of regulatory supervision, inadequate safety culture and improper technician training and education.
The first issue contributing to the accident was the lack of regulatory oversight. There was no criticality accident alarm (because the licensing board incorrectly concluded that a criticality accident could not happen) and the site was not included in the National Plan for the Prevention of Nuclear Disasters. 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.
The JCO facility converted uranium hexafluoride into enriched uranium dioxide fuel. This served as the first step in producing fuel rods for Japan's power plants and research reactors. 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. This process inadvertently contributed to a critical mass level incident triggering uncontrolled nuclear chain reactions over the next several hours.
Victim report
Two of the workers were working on the tank at the time of the accident; the third was in a nearby room. All three immediately reported seeing blue-white flashes. They evacuated immediately upon hearing the gamma alarms sound. After evacuating, one of the workers that was at the tank began experiencing symptoms of radiation exposure. 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.
Nuclear criticality event chronology
JCO facility technicians Hisashi Ouchi, Masato Shinohara, and Yutaka Yokokawa were speeding up the last few steps of the fuel/conversion process to meet shipping requirements. It was JCO's first batch of fuel for the Jōyō experimental fast breeder reactor in three years; no proper qualification and training requirements were established to prepare for the process. To save processing time, and for convenience, the team mixed the chemicals in stainless-steel buckets. The workers followed JCO operating manual guidance in this process but were unaware it was not approved by the STA. Under correct operating procedure, uranyl nitrate would be stored inside a buffer tank and gradually pumped into the precipitation tank in 2.4 kg (5.3 lb) increments.
At around 10:35, the precipitation tank reached critical mass with its fill level at about 16 kg (35 lb) of uranium. The hazardous level was reached after the technicians added a seventh bucket containing aqueous uranyl nitrate, enriched to 18.8% 235U, to the tank. The solution added to the tank was almost seven times the legal mass limit specified by the STA.
The nuclear fuel conversion standards specified in the 1996 JCO Operating Manual dictated the proper procedures regarding dissolution of uranium oxide powder in a designated dissolution tank. 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. At the time of the event, Ouchi had his body draped over the tank while Shinohara stood on a platform to assist in pouring the solution. Yokokawa was sitting at a desk four metres away. All three technicians observed a blue flash (possibly Cherenkov radiation) and gamma radiation alarms sounded. 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. Upon the point of critical mass, large amounts of high-level gamma radiation set off alarms in the building, prompting the three technicians to evacuate. All three of the workers were unaware of the impact of the accident or reporting criteria. A worker in the next building became aware of the injured employees and contacted emergency medical assistance; an ambulance escorted them to the nearest hospital. The fission products contaminated the fuel reprocessing building and immediate surroundings of the nuclear facility. Emergency service workers arrived and escorted other plant workers outside of the facility's muster zones.
The next morning, workers ended the chain reaction by draining water from the surrounding cooling jacket installed on the precipitation tank. The water served as a neutron reflector. A boric acid solution was added to the precipitation tank to reduce all contents to sub-critical levels; boron was selected for its neutron absorption properties.
<table><thead><tr><th>Timeline of 1999 accident</th></tr></thead><tbody><tr><td>Day</td><td>Time</td><td>Event/action</td><td>Affected parties</td></tr><tr><td>30 September 1999</td><td>10:35</td><td>Criticality event occurred, setting off radiation monitors and alarms; evacuation begins and employees exposed to radiation</td><td>3 workers: Hisashi Ouchi, Masato Shinohara and Yutaka Yokokawa</td></tr><tr><td>30 September</td><td>Until 23:30</td><td>(5 hours later) STA confirms continuing chain reactions; Tokaimura sets up headquarters for the incidents, (12 hours later) broadcasts all surrounding residents to evacuate, informs Japan's leadership and ceased all crop and water usage</td><td>Tokaimura City and National Leadership</td></tr><tr><td>1 October 1999</td><td>All day</td><td>Road blocks implemented; shelter in place lifted but schools closed all day; water drainage initiated to stop chain reaction.</td><td>All residents</td></tr><tr><td>2 October 1999</td><td>All day</td><td>Health checks conducted on all residents, measuring radiation; schools reopened and government press conferences held</td><td>All residents</td></tr></tbody></table>
Tōkaimura evacuation
By mid-afternoon, the plant workers and surrounding residents were asked to evacuate. Five hours after the start of criticality, evacuation began of some 161 people from 39 households within a 350-metre radius from the conversion building. Twelve hours after the incident, 300,000 surrounding residents of the nuclear facility were told to stay indoors and cease all agricultural production. 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. Authorities warned locals not to harvest crops or drink well water. To ease public concerns, officials began radiation testing of residents living about 10 kilometres (6 mi) from the facility. Over the next 10 days, about 10,000 medical check-ups were conducted. Dozens of emergency workers and residents who lived nearby were hospitalized and hundreds of thousands of others were forced to remain indoors for 24 hours. Testing confirmed 39 of the workers were exposed to the radiation. At least 667 workers, first-responders, and nearby residents were exposed to excess radiation as a result of the accident. Radioactive gas levels stayed high in the area even after the plant was sealed. Finally, on October 12, it was discovered that a roof ventilation fan had been left on and it was shut down. 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. This determination labeled the situation low risk outside of the facility. The technicians and workers in the facility were measured for radiation contamination. The three technicians measured significantly higher levels of radiation than the measurement designated the maximum allowable dose (50 mSv) for Japanese nuclear workers. Many employees of the company and local population suffered accidental radiation exposure exceeding safe levels. Over fifty plant workers tested up to 23 mSv and local residents up to 15 mSv. The incident was fatal to two of the technicians, Ouchi and Shinohara.
Environmental impact
STA and Ibaraki Prefecture began monitoring the levels of gamma immediately after they were notified of the accident. They collected samples of tap water, well water and precipitation within 10 kilometres of the site. They also took samples of vegetation, sea water, dairy products and sea products for testing. They found low levels of radioactivity in some of the vegetation, but they did not find any in the dairy products, water or sea.
Impact on technicians
According to the radiation testing by the STA, Ouchi was exposed to 17 Sv of radiation, Shinohara 10 Sv, and Yokokawa received 3 Sv. 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.
After receiving the transplant from his sister, Ouchi's white blood cell counts temporarily increased, but he soon began to succumb to his other injuries. Many other interventions were conducted in an attempt to arrest further decline of his badly damaged body, including repeated use of cultured skin grafts and pharmacological interventions with painkillers, broad-spectrum antibiotics and granulocyte colony-stimulating factor, without any measurable success. 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.
Two months after the accident, Ouchi suffered cardiac arrest; although he was revived, he became unresponsive. At the wishes of his family, doctors continued to treat him, even though it was clear he could not survive. On December 19th, the family agreed to a do-not-resuscitate order. His wife had hoped that Ouchi would at least survive until 1 January, since it was the arrival of the 2000s. But his condition deteriorated into multiple organ failure, and he died on 21 December 1999.
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". Several human errors caused the incident, including careless material handling procedures, inexperienced technicians, inadequate supervision and obsolete safety procedures on the operating floor. The company had not had any incidents for over 15 years, making company employees complacent in their daily responsibilities.
The 1999 incident resulted from poor management of operation manuals, failure to qualify technicians and engineers, and improper procedures associated with handling nuclear chemicals. The lack of communication between the engineers and workers contributed to lack of reporting when the incident arose. Had the company corrected the errors after the 1997 incident, the 1999 incident would have been considerably less devastating or may not have happened.
Comments within the 2012 Report by the National Diet of Japan Fukushima Nuclear Accident Independent Investigation Commission notice regulatory and nuclear industry overconfidence, and governance failures may equally apply to the Tokaimura nuclear accident.
Victim compensation and plant closure
Over 600 plant workers, firefighters, emergency personnel and local residents were exposed to radioactivity following the incident. In October 1999, JCO set up advisory booths to process compensation claims and inquiries of those affected. By July 2000, over 7,000 compensation claims were filed and settled. In September 2000, JCO agreed to pay $121 million in compensation to settle 6,875 claims from people exposed to radiation and affected agricultural and service businesses. All residents within 350 metres of the incident and those forced to evacuate received compensation if they agreed to not sue the company in the future.
In late March 2000, the STA cancelled JCO's credentials for operation serving as the first Japanese plant operator to be punished by law for mishandling nuclear radiation. This suit was followed by the company president's resignation. In October, six officials from JCO were charged with professional negligence derived from failure to properly train technicians and knowingly subverting safety procedures.
Resulting legal suits
In April 2001, six employees, including the chief of production department at the time, pleaded guilty to a charge of negligence resulting in death. Among those arrested was Yokokawa for his failure to supervise proper procedures. The JCO President also pleaded guilty on behalf of the company. During the trial, the jury learned that a 1995 JCO safety committee had approved the use of steel buckets in the procedure. Furthermore, a widely distributed but unauthorized 1996 manual recommended the use of buckets in making the solution. A STA report indicated JCO management had permitted these hazardous practices beginning in 1993 to shortcut the conversion process, even though it was contrary to approved nuclear chemical handling procedures.
As a response to the incidents, special laws were put in place stipulating operational safety procedures and quarterly inspection requirements. These inspections focused on the proper conduct of workers and leadership. This change mandated both safety education and quality assurance of all facilities and activities associated with nuclear power generation. Starting in 2000, Japan's atomic and nuclear commissions began regular investigations of facilities, expansive education regarding proper procedures and safety culture regarding handling nuclear chemicals and waste.
Efforts to comply with emergency preparedness procedures and international guideline requirements continued. New systems were put in place for handling a similar incident with governing legislature and institutions in an effort to prevent further situations from occurring.
Japan imports 80% of its energy; so mounting pressures to produce self-sustaining energy sources remain. In 2014, Japan's government decided to establish the "Strategic Energy Plan" naming nuclear as an important power source that can safely stabilize and produce the energy supply and demand of the country. This event contributed to antinuclear activist movements against nuclear power in Japan. To this day, the tensions between the need for produced power outside of nonexistent natural resources and the safety of the country's population remain. Advocacy for acute nuclear disease victims and eradication of nuclear related incidents has led to several movements across the globe promoting human welfare and environmental conservation.
In popular culture
Tokaimura nuclear accidents
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.