Hisashi Ouchi- Tokaimura Nuclear Accident Full History


Energy is used in the generation of electricity that powers most of our infrastructure. There are two categories of energy sources namely renewable and non-renewable energy sources. Nuclear energy is a non-renewable energy source. It is obtained by the fusion of nuclei atoms. This complex process is performed in a special facility known as a Nuclear Power Plant. Read further about Tokaimura nuclear accident.

Tokai or Tokai-mura is a coastal village in Naka District, Ibaraki, Japan. It lies along the Pacific Ocean. It is home to one of the nuclear power plants that were owned by the Japan Nuclear Fuel Conversion Company (JCO). A nuclear accident occurred at this facility on September 30, 1999. Mr. Hisashi Ouchi was one of the three employees who were exposed to massive radiation doses during this accident. Let’s revisit this catastrophic event to establish the significance of this particular victim.

Company Background

JCO was a subsidiary of Sumitomo Metal Mining Company, Japan. It was established in 1979 as a Japanese nuclear fuel cycle company. This company was responsible for the supply of enriched Uranyl Nitrate for research institutions and local experimental nuclear reactors. It successfully did this at the Tokai facility from 1988 up until the occurrence of the accident.

The Tokai facility was Japan’s first commercial nuclear power plant commissioned in 1966. For some reason, it stopped operations until its re-opening in 1979 by JCO. It was established as a small-scale fuel preparation plant. The main economic activity in Tokai village is employment from nuclear power industries. Companies like JCO were a welcomed break in this region. 

In 1997, three years before the nuclear accident, the company illegally modified its nuclear reactor. First and foremost, they introduced the use of stainless steel buckets instead of a dissolution tank in mixing uranium oxide with nitric acid. Secondly, the solution was tipped directly into the precipitation tank instead of first passing through a storage column. Thirdly, there was no measuring of the amount to be added into the precipitation tank due to the lack of a storage column. Instead, they worked with estimated quantities which were highly dangerous. Fourthly, mixing was done mechanically instead of within the storage column since it was not in use. 

JCO management had permitted these hazardous methods since 1993 to shorten the conversion process. They even included these unlawful policies and procedures in their official operation manuals given to employees. These policies and procedures were contrary to regulatory compliance in nuclear chemical handling procedures and JCO was fully aware of this. However, they made informed decisions to operate the Tokai nuclear power plant with unlawful standards.

The company had breached several protocols in terms of safety and process controls. This was an extremely high-risk working environment and a disaster waiting to happen. Surprisingly, they managed to keep this poor state of affairs under wraps and avoided scrutiny from government officials. This was probably because they were not directly involved in supplying electricity to the national grid. Hence were perceived as insignificant and small players in the nuclear industry.

Cause of Tokaimura Nuclear Accident 

The management of JCO wanted the production of Uranyl Nitrate within a short period of time in September 1999. The process involved mixing Uranium Oxide with Nitric Acid.

Ordinarily, this is a basic process for experts. The problem arises when enriched levels of the components are used. This requires advanced training, hi-tech equipment, and strict controls to ensure that the process is safe and successful. In this case, the employees had to work under pressure and use production methods that were both illegal and unsafe.

The main team tasked with this dangerous responsibility of mixing enriched levels of the components to produce the Uranyl Nitrate was Hisashi Ouchi (35 years), Masato Shinohara (40 years), and Yutaka Yokokawa (54 years). Unfortunately, this three-man team lacked the advanced expertise and technology needed to handle the enriched levels of the nuclear components.

Ouchi’s team used inaccurate ratios of the components, inappropriate equipment, and overlooked control measures. They bypassed the buffer tanks and worked directly on the precipitation tank. They also poured excess amounts of the highly enriched uranyl nitrate directly into the precipitation tank all at once instead of doing it in specified time intervals with correct quantities.

While performing this hazardous task, Ouchi was leaning over the precipitation tank. Shinohara was standing next to him on a platform to assist in pouring the solution over the edge of the precipitation tank. Yokokawa was sitting at a desk a few meters away from the two and the precipitation tank.

When Ouchi and Shinohara finished pouring the seventh and last steel bucket of enriched uranyl nitrate (which was in excess as per engineering standards), a blue flash of light was observed in the precipitation tank.

The three-man team tried to run in vain. How do you outrun gaseous poison? It instantaneously becomes one with the air you breathe and equally flows quickly in the atmosphere. It is almost impossible to overcome its speed. The radiation doses were too high and they collapsed a few meters from the precipitation tank.

Nuclear chain reactions started immediately after the blue flash of light and continued for the next seven hours. This led to the continuous leakage of fission products within the nuclear power plant exposing all its occupants and surroundings to radioactive doses in varying degrees.

The plant’s contamination alarms went off and one of the workers in the adjacent building called the emergency teams to help their colleagues. On arrival, the emergency medical teams started evacuating all the workers including the three-man team.

The Tokai-mura nuclear accident was stopped the next day by workers. They drained the water surrounding the precipitation tank since the water was a sustaining catalyst. They also added boric acid in the precipitation tank to neutralize its contents.

Ouchi being the nearest to the precipitation tank received massive doses of up to 17 Sieverts (Sv) during this accident. This was almost double the non-fatal range of below 04 Sv. Shinohara registered 10 Sv of radiation doses. Yokokawa registered 03 Sv of radiation doses.

The injured three-man team was first taken to a nearby local hospital. They were later transferred to the National Institute of Radiological Sciences, Chiba. Yokokawa continued recuperating at this facility for three months and he survived to tell the story. The worst affected of the three, Ouchi and Shinohara, were later moved to the University of Tokyo Hospital, Japan for advanced medical treatment.

Controversial Medical Treatment for the Tokaimura Nuclear Accident

The medical treatment administered on Ouchi made him hit the headlines other than the fact that he was part of the main team working on the nuclear reactor at the JCO Tokai facility at the time of the nuclear accident. This specifically refers to the interventions given by the medical team at the University of Tokyo Hospital, Japan.

As stated earlier, Ouchi received the largest dose of radiation at the Tokai nuclear power plant. The non-fatal exposure rate is below 04 Sv. When someone is exposed to more than this, their survival rate is extremely low. In addition, the level of injury is extremely severe and the pain, unimaginable. Yet Ouchi was exposed to 17 Sv at the time of his admission, almost five times the non-fatal range. His intensity was related to that of the epicenter of the Hiroshima nuclear bomb.

For some strange reason, the doctors at the University of Tokyo Hospital, Japan decided to keep him alive despite the knowledge that he was in unbearable pain and he could no longer survive. In some quarters, it is said he was kept alive due to government restrictions on euthanasia. In other quarters, it is said that his family insisted that everything is done to keep him alive because they were ignorant of the hopeless situation that Ouchi was experiencing.

Ouchi had received serious damage to his body. It was practically impossible to save him. His immune system was destroyed, he had the worst radiation burns, his skin was falling off, all his organs were failing, his digestive system was destroyed, he had no white blood cell count, he was barely conscious, he was breathing with assistance, his lungs retained water and he experienced three heart attacks as the last blow to his survival efforts. 

The medical facility attempted to give him cancer treatment to reverse the radiation effects. They harvested stem cells from his sister and administered them to him. The white blood cell count started increasing upon receiving the stem cell transplant. Unfortunately, the transplant leukocytes started mutating after coming into contact with the contaminated cell residue in his system. This caused an autoimmune response in his body and the white blood cells generated started to deteriorate. Several other medical intervention methods were introduced in a bid to save him but they were all in vain. He later died on December 21, 1999, following an unrecoverable cardiac arrest.

Ouchi was admitted and kept alive at the University of Tokyo Hospital, Japan for a total of 83 days. His treatment remains controversial since many believe that there was no logical reason to keep any patient in this state alive no matter the government or family restrictions. The argument is that the doctors ought to have clearly communicated to relevant authorities and family members the true picture of his medical status. This would have helped both the government and family members make informed decisions.

Shinohara endured radical cancer treatment, skin grafting, and blood transfusions. He was admitted to the medical facility for a period of seven months. Unfortunately, he succumbed to radiation infections and internal bleeding. This led to multiple organ failures. He died on April 27, 2000.

Impact of the Tokaimura Nuclear Accident

The Tokai facility accident was the worst civilian Tokaimura nuclear accident in Japan recorded by authorities at the time. The surrounding populations were exposed to poisonous nuclear radiation. Just a few hours after the accident, over fifty plant workers and one hundred and sixty-one residents near the nuclear power plant were evacuated. Those further away were told to stay indoors, cease all agricultural production and stop consumption of local groundwater. This restriction was lifted the next day.

The technicians and workers in the facility were measured for radiation contamination. The three-man team measured significantly higher levels of radiation than the permissible quantity due to proximity to the mixing area. This exposure ended the lives of two of them. The other six hundred and sixty-seven JCO employees, emergency workers, and residents also suffered accidental radiation exposure exceeding safe levels. This led to the large-scale hospitalization of workers and residents.

Without an emergency plan or public communication from JCO, confusion and panic surrounded the event. Lack of communication between engineers and workers contributed to this poor reporting when the accident happened.

The public made protests concerning health and safety issues. This forced the government officials to start radiation tests within 6 miles of proximity from the facility. Within two weeks, almost ten thousand medical checks were conducted in the area. The JCO management also initiated protection methods within fifteen days. They used sandbags and other shielding materials to protect the environment from residual gamma radiation in the exposed areas. 

The Tokai facility accident was classified by nuclear energy authorities as a criticality accident. This is also referred to as critical excursion, critical power excursion, or divergent chain reaction. This meant that it was an accidental and uncontrolled nuclear fission chain reaction. These types of accidents are an unintended accumulation of critical mass arrangement of fissile material.

However, the accident was later classified as an “irradiation” and not a “contamination” accident under Level 4 on the Nuclear Event Scale. This rendered the accident to be “low risk” for the surrounding environment and its inhabitants. It was concluded by relevant authorities that the Tokai nuclear accident was caused by a lack of regulatory compliance, poor safety protocols, and the use of unqualified personnel.

Compensation and Litigation Cases 

JCO started processing inquiries and insurance claims of those affected by the Tokai nuclear accident in October 1999. This included their own workers, emergency workers, first responders, evacuates, and residents within 350 meters radius from the accident point who were exposed to radioactivity.

The Science and Technology Agency (STA) officially closed the operations of JCO in March 2000. However, compensation payments continued and related lawsuits ensued. 

Almost seven thousand compensation claims were filed and settled in the preceding ten months up to July 2000. Over six thousand claims from people exposed to radiation received payments from JCO in September 2000. This included agricultural and service business owners. These amounts came to a total of hundred and twenty-one million dollars.

In October 2000, an initial six JCO officials were charged with professional negligence for failing to adequately train personnel and alteration of safety procedures. A few months later in April 2001, six more JCO employees, including Yutaka Yokokawa (the surviving technician from the three-man team that caused the accident) and his chief of production department at the time, pleaded guilty to a charge of negligence resulting in death. The JCO president also pleaded guilty on behalf of the company.

Japan has since implemented better policies and procedures to regulate nuclear power companies. Special legislations were passed for the safety and inspection of the nuclear power industry. As a result, Japan’s atomic and nuclear commissions started regular facility inspections. They also embarked on initiating education programs on a large scale. These were aimed at imparting knowledge and skills on proper procedures and safety culture while working with nuclear chemicals and waste. 


Nuclear energy is a preferred source of energy since it can be produced artificially, generates more electricity, and has minimal pollution impact on the environment. However, risks arise during its production and manufacture. As a result, the production processes must be carefully and painstakingly managed to prevent these life-changing risks.

We have observed the negative impact of nuclear energy since it was first discovered in the 1930s. From catastrophic wars that affect countries like the Hiroshima and Nagasaki bombings to industrial incidences in various parts of the world like Tokai, Japan, and Chernobyl, Ukraine. We have also read reports citing leakage of nuclear waste in our international water bodies such as those dumped under seas and oceans.

These are just a few of the disastrous examples officially documented. The results are devastating and communities rarely fully recover from the impact. This involves lifelong genetic mutation and sudden physical pain once exposed to the radioactivity associated with nuclear energy. The physical environment is also polluted to very high degrees and all living things cannot thrive in this toxicity whether plants or animals.

Stakeholders in this very complex and hazardous industry must take full responsibility for the production and use of this form of energy. They must remain accountable and transparent to the community and regulatory bodies. This is the only way that we can save mankind from grandiose suffering that arises from the mismanagement of nuclear energy.

Frequently Asked Questions 

  1. Who were the three technicians working on the Tokai nuclear power plant at the time of the tokaimura nuclear accident?

They were Hisashi Ouchi, Mashato Shinohara and Yutaka Yokokawa.

  1. Which was the parent company of JCO?

This was known as Sumitomo Metal Mining Company.

  1. Where is Tokai located?

Tokai or Tokai-mura is a village in Naka District, Ibaraki, Japan.

Hisashi Ouchi- Tokaimura Nuclear Accident Full History

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