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The Story of Hisashi Ouchi (+Details of the Tokaimura incident)

In this brief guide, we will discuss the story of Hisashi Ouchi, and some details of the Tokaimura incident.

Who was Hisashi Ouchi?

Hisashi Ouchi was a lab technician at the Tokaimura nuclear power plant in Japan, and people know him because he was in a radiation accident that caused him to take in as much radiation as the epicenter of the Hiroshima atom incendiary device.

A book was also written about the ordeal that Hisashi Ouchi went through after he had been in the accident because he was in the hospital for about 83 days after being exposed to radiation, and it is called “A Slow Death: 83 Days of Radiation Sickness”.

Hisashi Ouchi’s name is also sometimes reported as ‘Hiroshi’, though it was definitely Hisashi, and the pronunciation of Ouchi is “Aochi”, and he was 35 years old at the time of the incident.

Hisashi  Ouchi was a native of Ibaraki and he had a younger sister, a wife, and a young son, and he also smoked a pack a day and had played rugby in high school.

By 1999, Hisashi  Ouchi had been employed as a technician at the JCO Tokaimura Plant, where he and his colleagues were responsible for creating fuel for a fast reactor called Joyo, and this is where the accident occured, and while this is a very technical job not much information is available about Hisashi ’s education.

There have been some reports that he and his colleagues were relatively “unqualified” for the work, and the place where the accident happened, which was the conversion test building, was a place that Hisashi  Ouchi had never worked in before.

When the incident at Tokaimura power plant occured, Hisashi  Ouchi was not by himself, there were two other individuals with him, namely Masato Shinohara, 39 years old, and Yutaka Yokokawa, 54 years old.

What happened to Hisashi Ouchi?

Hisashi  Ouchi was working at the Tokaimura Nuclear power plant when a major accident occured and he absorbed more radiation than any man ever had before, and he was then alive for 83 days after which he succumbed to multi organ failure and died.

Hisashi  Ouchi and his colleagues Masato Shinohara and Yakato Yokokawa were working at the JCO nuclear fuel processing plant located inside the Tōkai-Mura Nuclear Power Plant, where Ouchi and Shinohara were mixing a batch of fuel containing uranium in a stainless steel tank while Yokokawa was sitting at a desk 4 meters, or just over 13 feet, away. 

An accident involving the uranium and exothermic chemical reaction involved in the process of creating energy from it led to a major radiation blast which affected a total of 114 people, but while 110 received much lower doses and were fine, these three people, including Hisashi  Ouchi received doses that were extremely high and therefore resulted in 2 deaths, that of Masato and Hisashi .

There is some background needed for this incident, and that is to know how the Tokaimura power plant functioned even before this accident happened, because there were safety issues there to begin with.

Tokaimura Nuclear Incident

The particular JCO (Known previously as the Japan Nuclear Plant) plant at Tokai was commissioned in 1988 and processed up to 3 tonnes per year of uranium enriched up to 20% U-235, which is very enriched uranium, more than what is usually permissible.

Furthermore, the kind of enriched uranium that was in use at this power plant was also a much higher enrichment level than for ordinary power reactors, and it uses a wet process.

The approved nuclear fuel preparation procedure for this particular plant involved dissolving uranium oxide (U3O8) powder in nitric acid in a dissolution tank, then its transfer as pure uranyl nitrate solution to a storage column for mixing, followed by transfer to a precipitation tank, and this is the process that Hisashi  Ouchi and his colleague Masato were involved in on the fateful day.

The precipitation tank in which the mixture was to be transferred was surrounded by a water cooling jacket to remove excess heat generated by the exothermic chemical reaction and any prevention of criticality was based upon the general licensing requirements for mass and volume limitation and the design of the process. 

A big part of this design was the storage column with a criticality-safe geometry and allowing careful control of the amount of material transferred to the precipitation tank.

The problem at this plant was that there were serious breaches in the process involved throughout, and there were 3 main problems that possibly led to the accident that took place.

The company had modified their work procedure three years earlier, without permission from the regulatory authorities and this new type allowed the uranium oxide to be dissolved in stainless steel buckets rather than the dissolution tank. 

Additionally, the operators were allowed to speed the process up by tipping the solution directly into the precipitation tank, which was also something that is against the rules and regulations, which are in place for the safety of everyone involved.

Also, the mixing of chemicals was meant to occur in the storage column but was undertaken by mechanical stirring in the precipitation tank instead and this measure bypassed criticality controls. 

The last straw that broke the camel’s back was the fact that there was no proper control of the amount tipped into the 100-litre precipitation tank, and its shape enhanced the likelihood of criticality within it, and that is also exactly what happened as well.

On September 30, 1999, Shinohara was pouring a uranyl nitrate solution into the mixing tank straight from a steel bucket, and it was the seventh such bucket of the solution to be added. 

Yokokawa started out holding the funnel through which Shinohara poured the liquid, but eventually Hisashi  Ouchi took over while Yokokawa went to sit at a desk in an adjoining room.

Eventually the criticality occurred in the mixing tank, leading to the exothermic reaction, and all three men witnessed a blue flash of light (Cherenkov Radiation) and in that instant they all realised that something horrible had happened and tried to flee immediately, but none of them got too far.

Hisashi  Ouchi made it to the nearby changing room, where he vomited and fainted and the other two also made it a little father but Masato had trouble running too far and Yokokawa got just a little bit farther before losing consciousness.

All three technicians were taken first to the local hospital, then transferred to the National Institute of Radiological Sciences, located in Chiba, and finally, Hisashi  Ouchi was moved to the University of Tokyo Hospital.

Hisashi Ouchi: 83 days in the hospital

Perhaps the most horrific thing about the entire incident is what the 3 men went through, in particular Hisashi  Ouchi, who had been right above the container when the event occurred and absorbed most of the radiation.

According to the reports, Hisashi  Ouchi absorbed a total of about 17 sieverts of radiation, whereas Masato absorbed about 10 sieverts, whereas Yokokawa, being the furthest one, got about 3 sieverts.

The amount of radiation that Hisashi  Ouch received is said to be the maximum radiation any one person has ever gotten, so much so that it has been likened with being at the epicenter of the Hiroshima atom incendiary device , and as expected, it completely destroyed his body.

By the time Hisashi  Ouchi was taken to the Tokyo Hospital it seemed like he was doing somewhat alright, fine, even, and over the next few days, he appeared so normal that physicians were shocked. 

Hisashi  Ouchi had somewhat normal skin which did not seem visibly burned, and only his right arm appeared swollen and slightly red and most importantly, he was fully conscious and able to hold a conversation, which might not be what you would expect from someone who had taken 17 sieverts of radiation when the fatal number is 8 sieverts.

The truth that experts now seem to agree on is that Hisashi  Ouchi was actually in the “Walking Ghost Phase” and the radiation had ruined his chromosomes completely, meaning that his body no longer had any blueprint from which to reproduce cells. 

The only reason Hisashi  Ouchi was living and talking and seemed normal right after the exposure was likely because the cells his body had already made prior to irradiation would still be used to depletion, but even then the blood tests showed that his levels of white blood cells and lymphocytes were dangerously low which meant that he had no immune system.

After being placed in a specially constructed ‘clean room’ in the ICU, he also became the world’s first recipient of peripheral blood stem cells, a radical cancer treatment that was meant to give him some chance of recreating the white blood cells he needed.

These were harvested from his sister’s blood they did help for a while but the radiation sickness was so severe that it started to damage them too eventually.

It is also reported that Hisashi Ouchi was quite unaware of his true condition at this time, and a nurse recalls him saying, “I thought I’d be able to leave the hospital in a month or so, but it’s going to take longer, isn’t it?” and “When you’re exposed to radiation like this, is there a risk of contracting leukemia or something?” 

The true outward symptoms of radiation sickness in Hisashi Ouchi started with his skin falling off, as the cells of the epidermis are some of the most rapidly reproducing in the body and this meant that medical tape couldn’t be used on him, neither could the typical gauze, and a special type had to be used.

Hisashi Ouchi also started suffering from his lungs getting filled with fluid, and a breathing tube was installed, which also means that the reports of him begging for death are not exactly true.

While it is true that he did at some point say that “I am not your guinea pig”, there was never any repeated proclamation of wanting to die because he was almost consistently on assisted respiration from that point on.

It is also true that Hisashi Ouchi was kept alive and the doctors tried so many things to save him because his family had expressed their desire that every test and procedure that had the slightest possibility of working needed to be tried, and since Hisashi himself was not in a state to make any wishes or commands, the family’s wishes were kept.

It is also said that Hisashi Ouchi’s family were never truly informed of the hopelessness of his situation, or how he had received more than twice the dose of radiation that is fatal to human beings.

Hisashi Ouchi’s body was so far gone that when his gauze was changed, it took 3 hours and the room had to be heated because his body could not maintain its own heat and the bandage that was taken off was weighed to measure how much fluid he lost through the tissues so they would know how much to give him.

A common effect of radiation sickness most people are aware of is hair falling out, which is seen with a lot of Chemotherapy patients, but because Hisashi Ouchi had suffered massive radiation, his nails had fallen off and his eyelids could no longer close. 

While he also received skin grafts were performed none of it took and eventually an endoscopy showed that the membrane of his intestines had died and was pulling away from the intestinal wall. 

On day 59 of Hisashi Ouchi’s stay in the hospital, he was pretty out of awareness due to being on Fentanyl, a more potent painkiller than morphine, which meant that he couldn’t have been very aware of his condition or the fact that he was dying.

On the same day, Hisashi Ouchi suffered a series of three heart attacks, and because he did not have a DNR yet, he was revived all three times, but despite this, it was eventually calculated that by the third time, his heart had stopped for a total of forty nine minutes and his breathing for one hour and thirty five minute.

While his brain waves were still somewhat present, his pupillary responses were gone and he had stopped responding to any stimulus, which meant that his cortex had very nearly stopped working, and he was hanging on by a thread.

By this time he was also completely on the ventilator, with the machine breathing for him, and his liver and kidneys had begun to shut down completely, and it seemed mostly clear that he was not going to pull through.

Finally, after 83 days of suffering, Hisashi Ouchi succumbed to multi-organ failure on December 21st, 1997.

A picture of Hisashi Ouchi’s Chromosomes, which had gotten totally damaged and stuck together.


In this brief guide, we discussed the story of Hisashi Ouchi, and some details of the Tokaimura incident.

Nuclear accidents of any type are very chilling, and when there are the sort of details involved that happened with Hishahi Ouchi, it can become a downright horror story.

The hope is simply that people who run places like Tokaimura and those who were in charge in the case of Hisashi Ouchi have learned from the mistakes from the first time around and something like this will never happen again, or if it does, it’s handled better.

If you have any more questions or comments about Hishashi Ouchi, please feel free to reach out to us at any time.

Frequently Asked Questions (FAQs): Hisashi Ouchi

Why did they keep Hisashi Ouchi alive?

Hisashi Ouchi was kept alive possibly because Japan has laws about treating people even if they would not want to be treated, and since Hisashi was barely in any condition to talk too much or complain against the treatment it is possible that he was kept alive because of that.

Another possibility is that Hisashi Ouchi was kept alive because no one had survived that kind of dose of radiation before, and it was something that needed to be studied, or perhaps because the doctors thought they could save him.

Did Hisashi Ouchi die?

Yes, Hisashi Ouchi died, although he was alive for about 83 days after he received a fatal dose of radiation from the nuclear power plant where he worked.

Hisashi Ouchi died of multi organ failure from the radiation he had suffered at the nuclear power plant accident.

What happened to Hisashi Ouchi?

Hisashi Ouchi was critically injured during an accident Sept. 30 at the JCO uranium processing plant in the village of Tokai, Ibaraki Prefecture in Japan, and he was one of the workers who were right at the epicenter of the radiation poisoning, which caused him to take in more radiation than anyone ever has before.

After he had been exposed to so much radiation, Hisashi Ouchi was kept alive through multiple life-threatening problems because of various reasons, none of which seem totally clear.

What caused the Tokaimura nuclear accident?

The tokaimura nuclear accident was caused by too much uranium, enriched to a relatively high level, coming together which caused ‘criticality’, or a limited uncontrolled nuclear chain reaction, which continued intermittently for 20 hours.


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