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Hisashi Ouchi: Earth’s Most Radioactive Man

The saying that every job comes with its hazard couldn’t have been truer for Hisashi Ouchi. On September 30, 1999, Hisashi was exposed to the highest amount of radiation any human has ever been exposed to in documented history.

Effect of radiation on the human body.

Hisashi Ouchi was a 35-year-old technician who worked at a nuclear facility owned by the Japanese Nuclear Fuel Conversion Company known as Tokaimura. And he would go on to become the most radioactive man ever recorded to date. The level of radiation Ouchi was exposed was said to be almost the same as at the blast centers in the 1945 nuclear bombings of Hiroshima and Nagasaki. It was also reported to be at about 17,000 times the maximum annual permissible exposure in Japan.

Nuclear power has become an integral energy alternative for natural-resource starved Japan to limit dependence on imported energy. Tokaimura’s location and available land space made it an ideal investment for nuclear power production. Nuclear power provides approximately 30% of Japan’s electricity today.

In this article, we would rewind the hands of time to learn in detail, the unfortunate series of events that led to the disaster, its impact on humans, the environment and lessons learned from it.

How much radiation was Hisashi Ouchi exposed to?

Hisashi Ouchi was exposed to about 17 Sieverts of radiation, according to the Science and Technology Agency’s National Institute of Radiological Sciences in Chiba, near Tokyo.

How many Sieverts (the unit measurement of radiation) is lethal?

One Sievert, the unit measurement for a dose of radiation, will cause illness if absorbed all at once, and 8 Sieverts will result in death, even with treatment.

How nuclear plants operate

Nuclear power stations rely on fission, a process that involves splitting large heavy uranium atoms (U235) into smaller atoms. When they split, the atoms release large amounts of energy which is captured as heat, used to power boilers and steam turbines to generate electricity.

Large amounts of fuel are then loaded into a nuclear reactor as the fission reaction is allowed to get underway. The U235 is split by a particle called a neutron, and each time a U235 atom splits it releases energy and another neutron. This particle is then free to split another atom and there follows a growing cascade of splitting atoms called a chain reaction.

The reaction is controlled in the reactor to help keep the energy release under moderate proportions. Unimpeded, the chain reaction occurs almost instantaneously in an atomic explosion very much like the A-bombs exploded over Japan at the height of the Second World War.

JCO’s Function

JCO’s role was to provide the uranium fuel used by these stations. Ordinary uranium does not have enough uranium 235 (U235), a particular isotope that splits easily under the right conditions.

The company, and others like it, take more and enrich it, raising the level of U235 to between 2 and 4 percent of the total fuel weight. This is “rich” enough to make the power stations work and drive the turbines.

Does radiation melt skin?

Radiation is just energy being deposited in your body. However, a radiation dose high enough to melt your skin is going to cause unconsciousness well before that happens and acute death as well. It won’t really melt, but a high radiation dose can cause severe burns.

Nuclear power production process at Tokaimura

Tokaimura is an average-sized town in the Ibaraki prefecture (county), which sits on a crossroads of the Japanese nuclear energy industry. The region is populated with nuclear facilities, including power plants, fuel manufacturing facilities and service companies, all committed to the maintenance of the nuclear ethic.

Handling nuclear materials imposes extreme risks to technicians; it requires precision and seasoned employees to safely conduct procedures. The process of combining nuclear products involves a fission process with the potential to produce radiation and explosive energy.

In order to produce the necessary uranium fuel, a purified chemical procedure with three crucial steps is required:

  1. Feeding of small batches of uranium oxide powder into a designated dissolving tank in order to produce uranyl nitrate using nitric acid.
  2. 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.
  3. 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.

The JCO uranium processing plant disaster

It’s also important to state that Tokaimura was the site of Japan’s first nuclear plant, completed in 1966, and is home to no fewer than 17 nuclear facilities. It has also previously experienced a nuclear accident in March 1997 when a plutonium reprocessing plant suddenly caught fire, leaving 37 people exposed to radiation.

How does radiation kill?

Radiation damages your stomach and intestines, blood vessels, and bone marrow, which makes blood cells. Damage to bone marrow lowers the number of disease-fighting white blood cells in your body. As such, most people who die from radiation sickness are killed by infections or internal bleeding.

Chronology of events leading to nuclear criticality

Hisashi Ouchi and Masato Shinohara weren’t involved in ordinary fuel production at the JCO plant. They were formulating super-enriched fuel, which experts now believe was destined for an experimental new nuclear reactor. They were enriching the uranium to 19-20 percent. And as such, they worked in a “conversion experiment building”, one of the many large buildings on the JCO complex.

The production of uranium fuel pellets process involves relatively conventional industrial chemistry, but the risks involved were most certainly higher since the men were working with radioactive materials. Hisashi Ouchi and Masato Shinohara most likely resumed work much the same as they had the day before without any inkling of the disaster ahead of them.

30 September 1999

In an attempt to speed up the last few stages of the fuel-conversion process to meet shipping requirements, JCO facility technicians Hisashi Ouchi, Masato Shinohara, and Yutaka Yokokawa 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 standard STA operating procedure, uranyl nitrate should be stored inside a buffer tank and gradually pumped into the precipitation tank in 2.4 kg increments.

With the workers manually transferring the solution, they had no way of measuring how much solution had been transferred and at around 10:35 am, the precipitation tank reached critical mass when its fill level, containing about 16 kilograms (35 pounds) of uranium, reached criticality in the tall and narrow buffer tank.

The hazardous level was reached after the technicians added a seventh bucket containing aqueous uranyl nitrate, enriched to 18.8% U235 to the tank. The solution added to the tank was more than seven times the legal mass limit specified by the STA.

The nuclear fuel conversion standards specified in the 1996 JCO Operating Manual outlined the proper procedures regarding the 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.

The workers bypassed the buffer tanks entirely, opting to pour the uranyl nitrate directly into the precipitation tank. Uncontrolled nuclear fission began immediately. The resulting nuclear fission chain became self-sustaining emitting intense gamma and neutron radiation in the nuclear facility.

At the time of the event, Hisashi Ouchi had his body over the tank while Shinohara stood on a platform to assist in pouring the solution. Yokokawa was sitting at a desk four meters away. All three technicians observed a blue flame which is believed to be Cherenkov radiation.

Hisashi Ouchi been transported to the hospital after suffering massive radiation exposure.

Technicians Ouchi and Shinohara immediately experienced pain, nausea, and difficulty breathing.  Hisashi Ouchi received the largest radiation exposure resulting in problems 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 triggering evacuation.


By mid-afternoon, the plant workers and surrounding residents were asked to evacuate. Five hours after the start of the criticality, evacuation of about 161 people from 39 households within a 350-meter radius from the conversion building commenced.

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 following afternoon. Almost 15 days later, the facility instituted protection methods with sandbags and other shielding to protect from residual gamma radiation.


The lack of concrete and steel shielding around the building was considered a factor that helped the spread of radiation quickly. It was hitherto thought of as unnecessary because this type of accident was not supposed to be possible. Over the next several hours the fission reaction produced continuous chain reactions.

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.

Aftermath of the Disaster

With JCO lacking an emergency plan and no public communication from them, confusion and panic followed the event. Authorities warned not to harvest crops or drink well water. In order to ease public concerns, officials began radiation testing of residents living approximately 6 miles from the facility.

Consequently, the incident was classified as an “irradiation” and not a “contamination” accident under Level 4 on the Nuclear Event Scale. This determination labelled the situation low risk outside of the facility. Even with its low-risk classification, at least 667 workers, first-responders, and nearby residents were exposed to excess radiation as a result of the accident, resulting in two deaths.

In his remark, Jan Rispens, an energy specialist with Greenpeace said the plant “had the safety standards of a bakery and not a nuclear facility. It was just a normal building.

Effect of Radiation on Hisashi Ouchi and Others

According to the radiation testing done 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.

An alleged image of Ouchi in hospital with skin falling off

Hisashi Ouchi

Hisashi Ouchi was transported and treated at the University of Tokyo Hospital. Ouchi suffered serious radiation burns to most of his body, experiencing severe damage to his internal organs. When Doctors did a micrograph of his bone marrow, they discovered that his chromosomes were destroyed and he had a near-zero white blood cell count. Without a functioning immune system, Hisashi Ouchi was vulnerable to hospital-borne pathogens and was placed in a special radiation ward to limit the risk of contracting an infection.

Doctors attempted to treat him with novel cancer treatment, peripheral blood stem cell transplantation. He initially experienced increased white blood cell counts temporarily but succumbed to his other injuries shortly thereafter. The leukocytes being produced by transplanted tissues were found to have mutated by the residual radiation present in his body triggering autoimmune responses that fast-tracked his rapidly deteriorating condition.

Other interventions were conducted in an attempt to stop the further decline of Ouchi’s severely damaged body, including repeated use of cultured skin grafts and pharmacological intervention with painkillers, broad-spectrum antibiotics and granulocyte colony-stimulating factor, though each of these attempts at intervention failed.

At the requests of his family, doctors repeatedly revived Ouchi when his heart stopped, even as it became clear the damage his body had sustained through radiation was untreatable. Despite their efforts, his condition deteriorated into multiple organ failures 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.

Masato Shinohara

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

Yutaka Yokokawa

Their supervisor, Yutaka Yokokawa, 54, received treatment from the National Institute of Radiological Sciences (NIRS) in Chiba. He was released three months later with minor radiation sickness. He faced negligence charges in October 2000.

How many nuclear accidents have there been?

As of 2014, there have been more than 100 serious nuclear accidents and incidents from the use of nuclear power. Fifty-seven accidents or severe incidents have occurred since the Chernobyl disaster, and about 60% of all nuclear-related accidents/severe incidents have occurred in the USA.

Legal suits

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 meters of the incident and those forced to evacuate received compensation if they agreed to not sue the company in the future.

By April 2001 six employees, including the chief of the production department at the time, pleaded guilty to the charge of negligence resulting in death. Among those arrested was Yokokawa for his failure to supervise proper procedures. A year before that, in late March 2000, the STA withdrew JCO’s credentials for operation thereby becoming the first Japanese plant operator to be punished by law for mishandling nuclear radiation.

This suit was followed by the company president’s resignation. 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. An STA report indicated JCO management had permitted these hazardous practices beginning in 1993 to hasten the conversion process, even though it was contrary to approved nuclear chemical handling procedures.

Response by government

As a response to the incidents, special laws were enacted 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.

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Conspiracy theory on the treatment of Hisashi Ouchi

While the doctors claim that Ouchi’s family was a source of support to the medical team, quite a few believed that he had been used as a test subject for unapproved medical treatment plans.

According to Kazuhiko Maekawa, a professor at the University of Tokyo Hospital, the kind of treatment given to Hisashi Ouchi, was completely new to him. In his words, ”It was the first time I experienced such a case in my 30-plus years as a doctor,” Maekawa, 58, told Kyodo News.

Almost every day, we came across situations that were not covered in medical textbooks, and there were tough moments in continuing treatment without any sign of a way out,” he added.

Hisashi Ouchi was resuscitated 3 times despite begging for his suffering to end. While at the University of Tokyo Hospital, he underwent the world’s first transfusion of peripheral stem cells. According to reports, before losing consciousness Hisashi managed to say, “I can’t take it any more… I am not a guinea pig.” But doctors kept treating him to keep him alive.

On November 27, Hisashi’s heart failed for 70 minutes, but the medical team treating him kept him alive with blood transfusions and various drugs to keep his blood pressure and pulse stable. Finally, on December 21, his heart failed and the doctors did not resuscitate him because his family wanted him to finally have a peaceful death.

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After enduring 83 days of pain and agony, the doctors allowed Hisashi Ouchi to die. Following His death, physicians were criticized for their treatment of him. It was believed that he was kept alive so that the effects of radiation poisoning on a human body could be observed. The quality of his life seemed to matter less to them.

Comparison to Other Major Nuclear Disasters

The Tokaimura incident was classified as an “irradiation” under Level 4 on the Nuclear Event Scale and so pales in comparison to other more popular nuclear disasters such as the Chernobyl disaster of 1986 or the Three Mile Island disaster of 1979 or the more recent Fukushima Daiichi Nuclear Power Plant disaster of 2011 in Japan.


The accident was caused by bringing together excess uranium enriched to a relatively high level, causing a ‘criticality’ (a limited uncontrolled nuclear chain reaction), which continued intermittently for 20 hours. The incident resulted from poor management of operation manuals, failure to qualify technicians and engineers, and improper procedures associated with handling nuclear chemicals.

While the Tokaimura nuclear disaster had numerous victims albeit mildly, none was more prominent like Hisashi Ouchi. He lived for 83 days with excruciating pain and massive organ failures including numerous cardiac arrests and near-zero white blood cell count.

Had the company corrected the errors after the 1997 incident; the 1999 incident may not have happened and Hisashi Ouchi would probably still be alive today.


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