Hisashi Ouchi, who died an extremely painful death as a result of the Tokaimura Nuclear Incident of 1999

Hisashi Ouchi, who died an extremely painful death as a result of the Tokaimura Nuclear Incident of 1999.

Hisashi Ouchi was a handsome, powerfully built, former high school rugby player with a wife and young son when he was exposed to what was probably the highest dose of accidental radiation in history. 

On the morning of Sept. 30, 1999, at a nuclear fuel-processing plant in Tokaimura, Japan, 35-year-old Hisashi Ouchi and two other workers were purifying uranium oxide to make fuel rods for a research reactor.

As this account published a few months later in The Washington Post details, Ouchi was standing at a tank, holding a funnel, while a co-worker named Masato Shinohara poured a mixture of intermediate-enriched uranium oxide into it from a bucket.

Suddenly, they were startled by a flash of blue light, the first sign that something terrible was about to happen.

The workers, who had no previous experience in handling uranium with that level of enrichment, inadvertently had put too much of it in the tank, as this 2000 article in Bulletin of the Atomic Scientists details. As a result, they inadvertently triggered what's known in the nuclear industry as a criticality accident — a release of radiation from an uncontrolled nuclear chain reaction.

How Much Radiation Did Ouchi Receive?

Ouchi, who was closest to the nuclear reaction, received what probably was one of the biggest exposures to radiation in the history of nuclear accidents. He was about to suffer a horrifying fate that would become a cautionary lesson of the perils 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.

It wasn't the first time it had happened. A 2000 U.S. Nuclear Regulatory Commission report noted that before Tokaimura, 21 previous criticality accidents had occurred between 1953 and 1997.

The two workers quickly left the room, according to The Post's account. But even so, the damage already had been done. Ouchi, who was closest to the reaction, had received a massive dose of radiation. There have been various estimates of the exact amount, but a 2010 presentation by Masashi Kanamori of the Japan Atomic Energy Agency put the amount at 16 to 25 gray equivalents (GyEq), while Shinohara, who was about 18 inches (46 centimeters) away, received a lesser but still extremely harmful dose of about 6 to 9 GyEq and a third man, who was further away, was exposed to less radiation.

Internet articles frequently describe Ouchi as 'the most radioactive man in history,' or words to that effect, but nuclear expert Lyman stops a bit short of that assessment.

"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."

What Does a High Dose of Radiation Do To the Body?

The radiation dose in a criticality accident can be even worse than in a catastrophic accident at a nuclear power plant, such as the 1986 reactor explosion at Chernobyl in Ukraine, then a part of the Soviet Union, where the radiation was dispersed. (Even so, 28 people eventually died from radiation exposure.)

"These criticality accidents present the potential for delivery of a large amount of radiation in a short period of time, 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 doses of radiation damage the body, rendering it unable to make new cells, so that the bone marrow, for example, stops making the red blood cells that carry oxygen and the white blood cells that fight infection, according to 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."

According to an October 1999 account in medical journal BMJ, the irradiated workers were taken to the National Institute of Radiological Sciences in Chiba, just east of Tokyo. There, it was determined that their lymphatic blood count had dropped to almost zero. Their symptoms included nausea, dehydration and diarrhea. Three days later, they were transferred to University of Tokyo Hospital, where doctors tried various measures in a desperate effort to save their lives.

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