On the morning of September 30, 1999, Hisashi Ouchi, 35 years old at the time, and two colleagues were purifying uranium oxide at a nuclear fuel-processing plant in Tokaimura, Japan. Their task was to produce fuel rods for a research reactor.
During their work, Ouchi and his coworker Shinohara transferred a uranium oxide mixture within the processing facility. Ouchi held a funnel near a tank while Shinohara poured the mixture from a container.
Unexpectedly, a sudden blue light startled them, signaling an impending disaster.
According to a 2000 article in the Bulletin of the Atomic Scientists, the workers unintentionally added an excessive amount into the tank due to their lack of experience with uranium of that enrichment level.
This error resulted in a criticality accident within the nuclear industry—an uncontrolled chain reaction occurred, releasing radiation.
Hisashi Ouchi’s Radiation Exposure
Hisashi Ouchi positioned nearest to the nuclear reaction, endured what is likely one of the most severe instances of radiation exposure in the annals of nuclear accidents. His impending fate would underscore the inherent dangers of the Atomic Age.
“The most obvious lesson is that when you’re working with [fissile] materials, criticality limits are there for a reason,” explains Edwin Lyman, a physicist and director of nuclear power safety for the Union of Concerned Scientists, and co-author with his colleague Steven Dolley, of the article in Bulletin of the Atomic Scientists.
If safeguards aren’t carefully taught and followed, there’s potential for “a devastating type of accident,” Lyman says.
According to a 2000 U.S. Nuclear Regulatory Commission report, the Tokaimura incident was not an isolated event, with 21 previous criticality accidents recorded between 1953 and 1997.
Following the incident, as detailed in The Washington Post, the two workers swiftly left the room. However, Hisashi Ouchi, closest to the reaction, sustained a massive dose of radiation.
Estimates vary, but a 2010 presentation by Masashi Kanamori of the Japan Atomic Energy Agency indicated Ouchi’s exposure ranged from 16 to 25 gray equivalents (GyEq).
Masato Shinohara, about 18 inches (46 centimeters) away, received a lower but still significantly harmful dose of approximately 6 to 9 GyEq. Another worker, situated farther from the source, received less radiation.
While numerous online sources often depict Ouchi as ‘the most radioactive man in history,’ nuclear expert Lyman advises caution in fully endorsing this characterization.
“The estimated doses for Ouchi were among the highest known, though I’m not sure if it’s the highest,” explains Lyman. “These typically occur in these kinds of criticality accidents.”
Impact of High Radiation Exposure on the Human Body
During a criticality accident, the radiation dose inflicted can be more intense than that of a catastrophic incident at a nuclear power plant, such as the 1986 reactor explosion at Chornobyl in Ukraine (then part of the Soviet Union), which resulted in widespread radiation dispersion.
Nevertheless, 28 individuals tragically lost their lives due to radiation exposure.
“These criticality accidents present the potential for delivery of a large amount of radiation in a short period, though a burst of neutrons and gamma rays,” Lyman says.
“That one burst, if you’re close enough, you can sustain more than a lethal dose of radiation in seconds. So that’s the scary thing about it.”
Elevated radiation levels inflict substantial harm on the body, disrupting its ability to regenerate cells.
This can lead to impaired production of red blood cells in the bone marrow, which are crucial for oxygen transport, and white blood cells, essential for immune defense against infections, as described by Lyman.
“Your fate is predetermined, even though there will be a delay,” he says, “if you have a high enough dose of ionizing radiation that will kill cells to the extent that your organs will not function.”
In October 1999, an article in the medical journal BMJ detailed how the workers exposed to radiation were taken to the National Institute of Radiological Sciences in Chiba, situated east of Tokyo.
Medical evaluations showed their lymphocyte counts had dropped almost to zero, accompanied by symptoms like nausea, dehydration, and diarrhea.
Three days later, they were transferred to the University of Tokyo Hospital, where doctors utilized various treatments in a desperate effort to save their lives.
Hisashi Ouchi’s Declining Health
Hisashi Ouchi, once a robust former high school rugby player with a wife and young son, initially showed no severe signs of radiation exposure upon arrival at the hospital, as chronicled in “A Slow Death: 83 Days of Radiation Sickness,” a 2002 book by journalists from Japan’s NHK-TV, later translated by Maho Harada.
Initially displaying slight redness and swelling on his face and bloodshot eyes, Ouchi complained of ear and hand pain but had no visible blisters or burns. The examining doctor held cautious optimism for his recovery.
However, within 24 hours, Ouchi’s condition began to deteriorate rapidly. He required oxygen, and his abdomen started swelling, as detailed in the book. His health further declined following his transfer to the University of Tokyo Hospital.
Six days after the accident, a specialist examining images of Ouchi’s bone marrow chromosomes observed severe fragmentation, with only scattered black dots visible.
Ouchi’s body lost its ability to produce new cells, leading to a peripheral blood stem cell transplant a week later, with his sister serving as the donor.
Despite documented medical efforts, Ouchi’s condition worsened. He developed intense thirst, and removing medical tape caused his skin to peel off.
Blisters emerged as radiation destroyed skin-regenerating chromosomes, causing his epidermis to vanish and intensify his pain gradually. Breathing difficulties also arose.
Within two weeks of the incident, Ouchi could no longer eat and relied on intravenous feeding. Two months later, despite doctors resuscitating him after his heart stopped, he succumbed.
On December 21, 11:21 pm, Ouchi passed away from multiple organ failure, confirmed by Lyman and Dolley. Japan’s Prime Minister, Keizo Obuchi, expressed condolences to Ouchi’s family and pledged stricter nuclear safety regulations, according to the Japan Times.
Ouchi’s coworker, Shinohara, also died in April 2000 from multiple organ failure, as reported by The Guardian.
Investigation and Legal Actions
An investigation by the Japanese government attributed the accident to inadequate regulatory oversight, a deficient safety culture, and insufficient worker training, as outlined in an April 2000 report by the U.S. Nuclear Regulatory Commission.
Subsequently, six officials from the plant’s operating company faced charges of professional negligence and violating nuclear safety regulations.
In 2003, they received suspended prison sentences, and fines were imposed on the company and at least one individual, as the Sydney Morning Herald reported.
