Hisashi Ouchi, 35 years old, Masato Shinohara, 39 years old, and Yutaka Yokokawa, 54 years old, were working at the JCO nuclear fuel processing plant located inside the Tōkai-Mura Nuclear Power Plant. 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 (just over 13 feet) away. Suddenly, there was a blue flash as the mixture experienced a nuclear reaction emitting neutron radiation and gamma-rays.
The mixture was able to reach critical mass due to a number of factors. First, the maximum amount of uranium allowed in the mixture was 2.4 kilograms. When the reaction occurred, there were 16 kilograms of uranium in the mixture. Second, these men had no training in this level of enrichment of uranium for fuel as this was the first time this process had been attempted in this factory in three years. Also, the plant was only inspected two times a year by the state regulator. It had never been inspected while the plant was in operation.
Ouchi, being nearest to the tank, was blasted with 17 sieverts of radiation. This is possibly the highest dose of radiation any human has ever experienced. Shinohara received 10 sieverts while Yokokawa received 3 sieverts.
At the time, Japan limited workers’ exposure to radiation to 50 millisieverts a year. 8 sieverts is considered a lethal dose of radiation.
Nuclear Radiation 101: Nuclear radiation affects the atoms in our bodies by removing the electrons. This breaks the bonds between atoms, including DNA and water in our bodies, damaging them. If your DNA gets damaged enough, cells can’t replicate and they die. Those that can still replicate, create more damaged cells. When damaged cells multiply, it creates cancer.
The effects of the radiation on Ouchi were immediate. He was in pain and couldn’t breathe. He vomited into the tank and lost consciousness in the decontamination chamber.
Shinohara turned to run but only made it about 3 steps before he collapsed.
Upon arrival at the Mito hospital, Ouchi’s skin was red and puffy but he showed few other outward signs of his condition. Then doctors began tested his chromosomes. They had “shattered like glass.” They could not be identified or arranged. Without chromosomes, his cells could not regenerate and his body could not heal. His white blood cell count was 0.
It was estimated that the amount of radiation Ouchi’s body experienced was similar to that at the epicenter of the atomic bomb dropped on Hiroshima. The radiation destroyed his DNA and immune system.
The plant was still in criticality. Radiation creates heat so the steel tank used to mix the fuel was soaking in cool water. This cooling of the tank helped to prolong the nuclear reaction which lasted intermittently for 20 hours. Eventually, workers were able to drain the water, allowing the mixture to heat up and the reaction to cease. Then a solution of boric acid was added to the fuel mixture. Boric acid acts as a neutron absorber. 27 workers were exposed to additional radioactivity in this process. A shield had to be put in place around the tank to keep gamma radiation from affecting people outside of the plant.
119 people in the plant received doses of radiation around 50 millisieverts. Approximately 300 residents living in the area of the plant were exposed to levels less than 50 millisieverts.
310,000 people within 6 miles of the plant were ordered to stay indoors and people living within 350 meters (just under a 1/4 mile) were evacuated. Although it would take 5 hours before this evacuation was ordered. They were allowed to return after 2 days.
There was no critical accident alarm at the facility. When the accident first occurred, other workers were unaware of the emergency. After they were made aware, there was confusion as to whether or not the danger had passed. This led to three members of emergency personnel being unexpectedly exposed while trying to rescue the workers inside.
Because the plant was not included in the National Plan for the Prevention of Nuclear Disasters, immediate protocols for the protection of individuals outside of the plant were not in place. Workers at a lumber yard very near the plant were not evacuated until 3pm, 4 1/2 hours after the reaction.
Yokokawa, Ouchi and Shinohara remained in the hospital.
On day 6, Ouchi was placed in a sterile room at the University of Tokyo Hospital. He needed a peripheral cell transplant (this had never been done before) so that he could begin generating white blood cells again. His sister was a match and donated the cells for transplant.
After one week in the hospital, he began to show outward signs of radiation sickness. His skin began sloughing off. Because his cells couldn’t regenerate, no new skin formed to replace it. He again began to have difficulty breathing. Ouchi said, “I can’t take it anymore. I am not a guinea pig.” He was in extreme pain despite medication. At this time, he was put on a ventilator and kept in a medically induced coma.
On day 18, Ouchi’s white blood count returned to normal. It appeared that the transplant had been a success, but a week later tests showed that the radiation was attacking the transplanted cells as well.
On day 27, Ouchi’s intestines started “to melt.” Three weeks later, he started hemorrhaging. He began receiving blood transfusions, sometimes as many as 10 in 12 hours. He began losing a significant amount of fluids (10 liters, or over 2 1/2 gallons, a day) through his skin so they wrapped him completely in gauze. He was bleeding from his eyes. His wife said that it looked like he was crying blood. Ouchi started receiving daily skin transplants using artificial skin, but they wouldn’t stick. His muscles began falling off the bone.
On his 59th day in the hospital, his heart stopped three times in just 49 minutes. He was resuscitated. This severely damaged his brain and kidneys. At this point, Ouchi was on life support.
Doctors continued life saving measures but Ouchi died of multi-organ failure on December 21, 1999 after 83 days in the hospital.
Shinohara seemed to be getting better. On New Year’s Day 2000, he was taken in his wheelchair to visit the hospital gardens.
However, in late February 2000, Shinohara contracted pneumonia and the damage to his lungs from the radiation meant that he needed to be put on a ventilator. This prevented him from speaking, so he had to write messages to nurses and family. Some of the last words written by Shinohara were “Mommy, please.”
Shinohara died April 27, 2000 of multi-organ failure.
Yokokawa stayed in the hospital for six months. He was then released to recover at home.
In reaction to the accident, which was found to be completely the result of human error, the Tōkai-Mura power plant was fully automated and fitted with neutron monitoring equipment. Tōkai-Mura had a history of taking shortcuts and putting their employees at risk to speed up production. The deaths of Ouchi and Shinohara were the ultimate penalty for their carelessness.
One year after the devastating accident, 6 employees were arrested and charged with negligence. One of the 6 was Yokokawa who claimed he “forgot” or was not aware of the dangers in the plant. He pled guilty.
At the time, Japan generated approximately 1/3 of its electricity from nuclear power.
The first Tokaimura nuclear accident occurred in a nuclear reprocessing plant of the Dōnen (Power Reactor and Nuclear Fuel Development Corporation) on 11 March 1997. It is sometimes referred to as the Dōnen accident (動燃事故 Dōnen jiko).
In the evening hours of Tuesday, 11 March 1997, a small explosion occurred in a nuclear reprocessing plant of the Dōnen. Windows broke, allowing smoke to escape into the atmosphere.[1] On the following Thursday, workers used duct tape to perform repairs on thirty broken windows and three doors that sustained damaged from the blast. At least 37 of the workers were exposed to elevated levels of radiation during the incident.[2]
A week after the event, meteorological officials detected unusually high levels of caesium 40 kilometers (25 miles) south-west of the plant.[3]
In 1999
The second, more serious Tokaimura nuclear accident (Japanese: 東海村JCO臨界事故 Tōkai-mura JCO-rinkai-jiko) occurred on 30 September 1999,[4][5][6] and resulted in two deaths.[7] It was the worst civilian nuclear radiation accident in Japan prior to the Fukushima Daiichi nuclear disaster of 2011.
The criticality accident occurred in a uranium reprocessing facility operated by JCO (formerly Japan Nuclear Fuel Conversion Co.), a subsidiary of Sumitomo Metal Mining Co. in the village of Tōkai, Naka District, Ibaraki Prefecture.[8]
The accident occurred as three workers, Hisashi Ouchi, Masato Shinohara, and Yutaka Yokokawa,[9] were preparing a small batch of fuel for the Jōyō experimental fast breeder reactor, using uranium enriched to 18.8% with the fissile radionuclide (radioisotope) U‑235 (with the remainder being the fissionable-only U‑238). It was JCO's first batch of fuel for that reactor in three years, and no proper qualification and training requirements appear to have been established to prepare those workers for the job. At around 10:35, a precipitation tank reached critical mass when its fill level, containing about 16 kilograms (35 pounds) of uranium, reached about 40 liters (11 U.S. gallons).[8]
Details
Criticality was reached upon the technicians adding a seventh bucket of an aqueous uranyl nitrate solution to the tank. The nuclear fission chain reaction became self-sustaining and began 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 pour the solution into it; Yokokawa was sitting at a desk four meters away. All three technicians observed a blue flash (possibly Cherenkov radiation) and gamma-radiation alarms sounded.[7] [10]
Technicians Ouchi and Shinohara immediately experienced pain, nausea, difficulty breathing, and other symptoms. Ouchi then began to vomit in the decontamination room a few minutes later and lost consciousness shortly after.[11] Fission products such as yttrium‑94 and barium‑140 began contaminating the building.
Being a wet process with an intended liquid result, the water sustained the chain reaction by serving as a neutron moderator, whereby neutrons emitted from fissioned nuclei are slowed so they are more readily absorbed by neighboring nuclei, inducing them to fission in turn. The criticality continued intermittently for about 20 hours. As the solution boiled vigorously, steam bubbles attenuated the liquid water's action as a neutron moderator (see Void coefficient) and the solution lost criticality. However, the reaction resumed as the solution cooled and the voids disappeared.
The following morning, workers permanently stopped the reaction by draining water from a cooling jacket surrounding the precipitation tank. The water was serving as a neutron reflector. A boric acid solution (boron selected for its neutron absorption properties) was then added to the tank to ensure that the contents remained subcritical.[8]
Cause
Under correct operating procedure, uranyl nitrate would be stored inside a buffer tank and gradually pumped into the precipitation tank in 2.4 kg increments. 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 with a stainless steel bucket. The additional solution contained 16 kg of uranium, thus exceeding the tank's uranium limit of 2.4 kg. An uncontrolled nuclear fission began immediately.
The precipitation tank, in contrast to the buffer tank, had not been designed to hold this type of solution and was not configured to prevent criticality.[9]
Evacuation
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. Residents were allowed home two days later with sandbags and other shielding to protect from residual gamma radiation. Twelve hours after the start of the incident residents within 10 km were asked to stay indoors as a precautionary measure, and this restriction was lifted the following afternoon.[8]
Aftermath
Dozens of emergency workers and nearby residents were hospitalized and hundreds of thousands of others were forced to remain indoors for 24 hours; 39 of the workers were exposed to the radiation.[12] At least 667 workers, emergency responders, and nearby residents were exposed to excess radiation as a result of the accident.[7]
By measuring the concentration of sodium-24, created by a neutron activation whereby sodium-23 nuclei were rendered radioactive by absorbing neutrons from the accident, it was possible to deduce the dose received by the technicians. According to the STA, Hisashi Ouchi was exposed to 17 sieverts (Sv) of radiation, Masato Shinohara received 10 Sv, and Yutaka Yokokawa 3 Sv.[7][9] By comparison, a dose of .05 sieverts is the maximum allowable annual dose for Japanese nuclear workers.[8] A dose of 8 Sv (800 rem) is normally fatal and more than 10 Sv almost invariably so.[9] Normal background radiation amounts to an annual exposure of about 3 mSv (millisieverts).[7] There were 56 plant workers whose exposures ranged up to 23 mSv and a further 21 workers received elevated doses when draining the precipitation tank. Seven workers immediately outside the plant received doses estimated at 6–15 mSv (combined neutron and gamma effects).[8]
The two technicians who received the higher doses, Ouchi and Shinohara, died several months later. 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.[7] Shinohara received numerous skin grafts, which were successful, but he ultimately succumbed to infection due to the damage his immune system sustained in the incident. Ouchi died on 21 December 1999, while Shinohara died on 27 April 2000.
The cause of the accident was said to be "human error and serious breaches of safety principles", according to the International Atomic Energy Agency.[8]
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.[13]
In April 2001 six employees, including the plant administrator and accident survivor Yutaka Yokokawa, plead guilty to a charge of negligence resulting in death. The JCO President also plead guilty on behalf of the company. The court heard that a 1995 safety committee had approved the use of buckets in the procedure, and a widely distributed but unauthorised 1996 manual recommended the use of buckets in making the solution. A Science and Technology Agency report indicated JCO management had since 1993 permitted the use of a stainless steel bucket as a shortcut in the process, even though it was contrary to written procedures.[13]
icantbelieveitsnonfiction.com/2018/02/14/hisashi-ouchi-and-masato-shinohara/
en.wikipedia.org/wiki/Tokaimura_nuclear_accident
www.youtube.com/watch?v=YUrKTHJ-4P0
www.youtube.com/watch?v=Mik8j5w8Q2w&list=UUveNNxBuwG_DaJSzp6iPE-Q&index=2
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