Tokaimura nuclear accidents

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.[16] The worker passed out, then regained consciousness 70 minutes later. The three workers were then transferred to the hospital, who confirmed that they were exposed to high doses of gamma, neutron, and other irradiation.

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.[16]

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.[1] 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.[15] 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.[12]

At around 10:35, the precipitation tank reached critical mass when its fill level, containing about 16 kg (35 lb) of uranium, reached criticality.[14] The hazardous level was reached after the technicians added a seventh bucket containing aqueous uranyl nitrate, enriched to 18.8% ²³⁵U, to the tank.[17] The solution added to the tank was almost seven times the legal mass limit specified by the STA.[17]

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.[18] 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. An uncontrolled nuclear fission began immediately. The resulting nuclear fission chain became self-sustaining, emitting intense gamma and neutron radiation.[1] 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 meters away.[15] All three technicians observed a blue flash (possibly Cherenkov radiation) and gamma radiation alarms sounded.[3] 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.[15] 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.[17] 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 immediately outside the nuclear facility.[19] Emergency service workers arrived and escorted other plant workers outside of the facility's muster zones.[1]

The next morning, workers ended the nuclear 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.[19]

By mid-afternoon the plant workers and surrounding residents were asked to evacuate. Five hours after the start of the criticality, evacuation commenced of some 161 people from 39 households within a 350-meter 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.[21] This restriction was lifted the following afternoon. Almost 15 days later, the facility instituted protection methods with sandbags and other shielding to protect from residual gamma radiation.

Without an emergency plan or public communication from the JCO, confusion and panic followed the event.[21] Authorities warned locals not to harvest crops or drink well water.[21] In order to ease public concerns, officials began radiation testing of residents living approximately 6 miles from the facility. Over the next 10 days, approximately 10,000 medical check-ups were conducted.[21] 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.[19] At least 667 workers, first-responders, and nearby residents were exposed to excess radiation as a result of the accident.[12] 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. [22] Sometime after the incident, people in the area were asked to lend any gold they had to allow calculations of the size and range of the gamma ray burst. [23]

Ultimately the incident was classified as an “irradiation” not “contamination” accident under Level 4 on the Nuclear Event Scale.[1] This determination labeled the situation low risk outside of the facility.[1] 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.[19] 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.[1] Fatal doses of radiation ended the lives of two technicians, Ouchi and Shinohara.

STA and Ibaraki Prefecture began monitoring the levels of gamma immediately after they were notified of the accident. They collected samples, within 10 km of the site, of the water from the tap, well, and percipitation. They also took samples of vegetation in surrounding areas, sea water, dairy products, and sea products were all measure for radioactivity following the accident. [16] They found low levels of radioactivity in some of the vegetation that was within close proximity of the nuclear facility, but they did not find any in any of the dairy products. They also did not find any in the water or sea.

According to the radiation testing by the STA, Ouchi was exposed to 17 Sv of radiation, Shinohara 10 Sv, and Yokokawa received 3 Sv.[21] The two technicians who received the higher doses, Ouchi and Shinohara, died several months later.

Hisashi Ouchi, 35, was transported and treated at the University of Tokyo Hospital for 83 days.[24] Ouchi suffered serious radiation burns to most of his body, experienced 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-borne pathogens and was placed in a special radiation ward to limit the risk of contracting an infection.[25] Doctors attempted 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.[12] After receiving the transplant from his sister, Ouchi initially experienced increased white blood cell counts temporarily but succumbed to his other injuries shortly thereafter.[24] The leukocytes being produced by the transplanted tissue were found to have been mutated by the residual radiation present in his body, triggering autoimmune responses that exacerbated his rapidly deteriorating condition, and white blood cell counts began to decrease.[12] Numerous other interventions were conducted in an attempt to arrest further decline of Ouchi's severely 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.[12]

At the wishes of his family, doctors repeatedly revived Ouchi when his heart stopped, even as it became clear the damage his body had sustained through radiation exposure was untreatable. After one such cardiac arrest rendered Ouchi completely unresponsive, the family deliberated that if his heart stopped again, they would not force the situation again. His wife hoped that he would at least survive until 1 January since it was the arrival of the 2000s. Despite their efforts, his condition deteriorated into multiple organ failure resulting from extensive radiation damage, exacerbated by the repeated incidents where Ouchi's heart stopped. He died on 21 December 1999 following an unrecoverable cardiac arrest.[26][27] According to Japanese law, the doctors were legally obligated to proceed with treatment until nothing more could be done, with the exception of express permission from Ouchi to suspend treatment, permission that was not granted during the period in which he was still able to communicate.[28]

Masato Shinohara, 40, was transported to the same facility where he died on 27 April 2000 of multiple organ failure. He endured radical cancer treatment, numerous successful skin grafts, and a transfusion from congealed umbilical cord blood (to boost stem cell count). Despite his seven month battle, he was unable to fight radiation-exacerbated infections and internal bleeding, resulting in fatal lung and kidney failure.

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.[29]

According to the International Atomic Energy Agency, the cause of the accidents were "human error and serious breaches of safety principles".[19] Several human errors caused the incident, including careless material handling procedures, inexperienced technicians, inadequate supervision and obsolete safety procedures on the operating floor.[12] 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.[15] 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.

Over 600 plant workers, firefighters, emergency personnel and local residents were exposed to radioactivity following the incident.[21] In October 1999, JCO set up advisory booths to process compensation claims and inquiries of those affected.[21] 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.[20] All residents within 350 meters of the incident and those forced to evacuate received compensation if they agreed to not sue the company in the future.[21]

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.[3] 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.[26]

In April 2001 six employees, including the chief of production department at the time, pleaded guilty to a charge of negligence resulting in death.[20] Among those arrested was Yokokawa for his failure to supervise proper procedures.[3] The JCO President also pleaded guilty on behalf of the company.[20] 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.[12]

As a response to the incidents, special laws were put in place stipulating operational safety procedures and quarterly inspection requirements.[12] 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.[12]

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.[12]

Japan relies heavily on imports for 80% of all energy requirements, due to this shortage, mounting pressures to produce self-sustaining energy sources remain. In 2014, the Japanese government decided to establish the "Strategic Energy Plan" naming nuclear power as an important power source that can safely stabilize and produce the energy supply and demand of the country.[4] This event contributed to antinuclear activist movements against production of nuclear energy in Japan.[1] 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.[30]