Hisashi Ouchi was a Japanese nuclear plant worker who was exposed to the highest level of radiation ever recorded on a human being. He received an estimated 17 sieverts (Sv) of radiation during a criticality accident at the Tokaimura nuclear plant in Japan on September 30, 1999. This was about 17,000 times the maximum annual permissible exposure level set by the government.
In September 1999, Hisashi Ouchi, a 35-year-old former high school rugby player from Japan, faced an unimaginable ordeal at a nuclear fuel-processing plant. Ouchi and two colleagues were working on purifying uranium oxide when a criticality accident occurred, releasing a dangerous amount of radiation.
The workers, lacking experience with such highly enriched uranium, unintentionally overfilled a tank, leading to the uncontrolled release of radiation. Ouchi, being closest to the reaction, received an unprecedented dose of radiation. It makes him one of the most exposed individuals in the history of nuclear accidents.
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Radiation exposure in criticality accidents can be more severe than in catastrophic nuclear power plant incidents. The burst of neutrons and gamma rays in such accidents can deliver a lethal dose in seconds. High radiation doses damage the body, hindering the production of essential cells, and leading to organ failure.
Ouchi and his colleagues were rushed to medical facilities, showing symptoms like nausea, dehydration, and diarrhea. Despite efforts to save their lives, Ouchi’s condition rapidly deteriorated. His body, unable to regenerate cells, suffered from skin problems, blisters, and intense pain. Two months into treatment, Ouchi’s heart stopped, and on December 21, 1999, he succumbed to multiple organ failure.
The incident prompted a government investigation, revealing regulatory oversights, inadequate safety culture, and insufficient worker training as contributing factors. Six officials from the plant’s operating company faced charges, leading to suspended prison terms and fines in 2003.
Ouchi’s death was a tragedy, but it also led to important advances in the understanding and treatment of radiation sickness. His case is still studied today by scientists and doctors who are working to improve the treatment of radiation victims.
This tragic event serves as a stark reminder of the dangers associated with handling fissile materials. Moreover, the critical importance of strict safety measures in the nuclear industry.