On the morning of September 30, 1999, a nuclear fuel-processing facility in Tokaimura, Japan, became the site of a tragic accident.
Hisashi Ouchi, 35, along with two colleagues, was involved in purifying uranium oxide to produce fuel rods for a research reactor.
The Washington Post said that Ouchi was standing next to a tank. He was holding a funnel. His co-worker, Shinohara, was pouring uranium oxide into the tank from a bucket. Suddenly, a bright blue light flashed, and they knew something was wrong.
The workers, unfamiliar with the enriched uranium they were handling, accidentally added too much into the tank.
This resulted in a criticality accident, where an uncontrolled nuclear chain reaction released harmful radiation, as explained in a 2000 article in Bulletin of the Atomic Scientists.
The Level of Radiation Exposure
Ouchi, positioned closest to the nuclear reaction, was exposed to one of the highest levels of radiation ever recorded in such accidents. Experts have estimated the radiation dose he received ranged between 16 to 25 gray equivalents (GyEq).
His co-worker Shinohara, standing about 18 inches away, received a significantly lower but still dangerous dose of approximately 6 to 9 GyEq. The third worker, further from the reaction, was exposed to a lesser amount.
Many articles have labeled Ouchi as “the most radioactive man in history,” though nuclear expert Edwin Lyman notes that while the radiation doses Ouchi experienced were among the highest ever recorded, it is unclear if they represent the absolute highest.
How High Radiation Levels Affect the Body
Criticality accidents can be more dangerous than the radiation from catastrophic nuclear plant accidents, such as the 1986 Chernobyl explosion.
Lyman explains that a criticality accident can release a huge burst of radiation in a very short period, potentially delivering a lethal dose within seconds to anyone close enough.
High radiation doses damage the body’s cells, particularly those responsible for producing red and white blood cells, which are crucial for carrying oxygen and fighting infection. Without these cells, the body can’t function, and death becomes inevitable.
Ouchi and his colleagues were quickly transported to the National Institute of Radiological Sciences in Chiba, where their blood cell counts dropped to dangerously low levels.
They exhibited severe symptoms like nausea, dehydration, and diarrhea.
Three days later, they were transferred to the University of Tokyo Hospital, where doctors struggled to save their lives.
Ouchi’s Slow Deterioration
When Ouchi first arrived at the hospital, he appeared relatively normal despite the high radiation exposure.
His face was slightly red, his eyes bloodshot, and he complained of pain in his ears and hand, but there were no visible burns or blisters. Initially, doctors thought there was a chance of saving him.
But Ouchi got very sick quickly. The next day, he needed oxygen, and his stomach got bigger. Six days later, doctors saw that his bone marrow cells were badly damaged.
This meant his body could not make new cells. A week later, he got a stem cell transplant from his sister.
Despite this, Ouchi’s health continued to decline. He developed intense thirst, and his skin started to peel off as medical tape was removed.
Eventually, blisters formed, and tests confirmed the radiation had destroyed the chromosomes needed for skin regeneration. His skin, the body’s protective outer layer, began to disappear.
The pain was unbearable, and he struggled to breathe. Two weeks after the incident, he could no longer eat and had to be fed intravenously.
Ouchi’s Final Days
Two months into his ordeal, Ouchi’s heart stopped, but doctors managed to revive him. Ultimately, on December 21, at 11:21 p.m., Ouchi succumbed to multiple organ failure.
His passing was met with grief, and Japan’s then-Prime Minister Keizo Obuchi expressed condolences, vowing to improve nuclear safety standards in response to the tragedy.
Shinohara, Ouchi’s co-worker, also died in April 2000 from multiple organ failure as a result of the radiation exposure.
Consequences and Responsibility
An investigation by the Japanese government found that the accident was primarily caused by inadequate regulatory oversight, lack of safety culture, and insufficient training.
Six officials from the company responsible for the plant were charged with professional negligence and violations of nuclear safety laws.
In 2003, the court handed down suspended prison sentences to the officials, and fines were imposed on both the company and at least one of the individuals involved.
Important Facts
Radiation exposure can be measured in different ways. Rads and grays show how much radiation was absorbed. Rems and sieverts show how much damage the radiation did to the body.