On the morning of September 30, 1999, 35-year-old Hisashi Ouchi and two colleagues were working at a nuclear fuel-processing plant in Tokaimura, Japan. They were purifying uranium oxide to create fuel rods for a research reactor.
Ouchi and his coworker, Shinohara, were transferring a uranium oxide mixture at a processing facility. Ouchi held a funnel near a tank while Shinohara poured the mixture from a container.
Suddenly, a blue light startled them, indicating that something disastrous was imminent.
As detailed in a 2000 article in the Bulletin of the Atomic Scientists, the workers, lacking experience with uranium of that enrichment level, had inadvertently added too much to the tank.
This mistake triggered a criticality accident in the nuclear industry — an uncontrolled nuclear chain reaction that released radiation.
Radiation Exposure: Hisashi Ouchi’s Fate
Hisashi Ouchi positioned closest to the nuclear reaction, endured what likely stands as one of the most significant exposures to radiation in the history of nuclear accidents. His impending fate would serve as a stark reminder of the dangers inherent in 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 report from the U.S. Nuclear Regulatory Commission, the Tokaimura incident was not isolated, with 21 previous criticality accidents occurring between 1953 and 1997.
The two workers promptly exited the room after the incident, detailed in The Washington Post. However, the damage had already been inflicted. Hisashi Ouchi, in closest proximity to the reaction, received a massive radiation dose.
While estimates vary, 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, approximately 18 inches (46 centimeters) away, received a lower but still highly harmful dose of about 6 to 9 GyEq. Another worker, positioned farther away, received a lesser amount of radiation.
Various internet sources often refer to Ouchi as ‘the most radioactive man in history,’ or similar phrases, although nuclear expert Lyman suggests 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.”
Effects of High Radiation Exposure on the Body
In a criticality accident, the radiation dose inflicted can be more severe than that in a catastrophic incident at a nuclear power plant, such as the 1986 reactor explosion at Chornobyl in Ukraine (then part of the Soviet Union), where radiation spread widely.
Despite this, 28 people ultimately perished 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.”
High radiation levels cause significant damage to the body, disrupting its ability to produce new cells.
For instance, radiation can impair the bone marrow’s capacity to generate red blood cells, which transport oxygen, and white blood cells, which are essential for combating infections, as explained 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 an account published in the medical journal BMJ in October 1999, the irradiated workers were transported to the National Institute of Radiological Sciences in Chiba, located east of Tokyo.
Medical assessments revealed that their lymphocyte counts had plummeted nearly to zero. They experienced symptoms such as nausea, dehydration, and diarrhea.
Three days later, they were transferred to the University of Tokyo Hospital, where doctors employed various treatments in a desperate attempt to preserve their lives.
Ouchi’s Health Declined Steadily
Upon arriving at the hospital, Hisashi Ouchi, a robust former high school rugby player with a wife and young son, didn’t initially appear as a victim of severe radiation exposure, as recounted in “A Slow Death: 83 Days of Radiation Sickness,” a 2002 book by journalists from Japan’s NHK-TV, later translated by Maho Harada.
His face showed slight redness and swelling, and his eyes were bloodshot, but he had no blisters or burns, despite complaining of ear and hand pain. The examining doctor initially held hope for his recovery.
However, within a day, Ouchi’s condition deteriorated. He required oxygen, and his abdomen began to swell, as detailed in the book. His condition worsened after his transfer to the University of Tokyo Hospital.
Six days post-accident, a specialist examining images of Ouchi’s bone marrow chromosomes observed only scattered black dots, indicating severe fragmentation.
Ouchi’s body was unable to produce new cells. A week later, he underwent a peripheral blood stem cell transplant, with his sister as the donor.
Despite efforts documented in the book, Ouchi’s condition deteriorated further. He began experiencing intense thirst, and removing medical tape from his chest caused his skin to peel off.
Blisters started appearing as radiation destroyed the chromosomes responsible for skin regeneration.
His epidermis, crucial for protecting his body, gradually disappeared, causing excruciating pain. Breathing problems also emerged.
Within two weeks of the accident, Ouchi could no longer eat and relied on intravenous feeding. Two months later, his heart stopped, though doctors managed to resuscitate him.
Ouchi’s fight for life ended on December 21st at 11:21 pm. Doctors reported his death as a result of multiple organ failure, according to Lyman and Dolley.
This tragedy prompted Japan’s Prime Minister, Keizo Obuchi, to offer his condolences to Ouchi’s family and promise stricter nuclear safety regulations, as reported by the Japan Times.
His co-worker, Shinohara, also passed away in April 2000 from multiple organ failure, as reported by The Guardian.
The Japanese government’s investigation into the incident determined that key factors contributing to the accident included insufficient regulatory oversight, a deficient safety culture, and inadequate training and qualifications for workers, as detailed in an April 2000 report by the U.S. Nuclear Regulatory Commission.
Following the investigation, six officials from the plant’s operating company faced charges of professional negligence and breaching nuclear safety regulations.
In 2003, a court issued suspended prison sentences to these officials, and the company, along with at least one individual, received fines, according to the Sydney Morning Herald.