DNA Fried in a Nanosecond — Tōkaimura Nuclear Accident & World’s “Most Radioactive Man” Explained

How a worker received 20,000 fatal doses of radiation

Col Jung
14 min readJul 31


Hisashi Ouchi’s excruciating ordeal captivated the world in 1999

In a nuclear plant, no worker wants to see a flash of blue light.

This ominous sight indicates a nuclear chain reaction, similar to what happens in a nuclear weapon.

September 30, 1999, marked the fateful day nuclear power plant worker Hisashi Ouchi received such a death sentence.

As he hand-poured uranium into a vat under the pressure of deadlines, a blinding flash of blue light engulfed him and his colleagues, triggering what was then the worst nuclear accident in Japan.

The media dubbed him the ‘most radioactive man’ in history. [Technically, he’s the most irradiated.]

When Ouchi arrived at the University of Tokyo Hospital, physicians were stunned. The 35-year-old technician had almost zero white blood cells, and thus no immune system.

Soon, he would be crying blood as his skin melted.

An army of Japanese and international medical experts toiled relentlessly to save his life. Defying the limits of medical knowledge, they prolonged his excruciating existence for 83 days before his cooked body succumbed to fate.

Japan’s Rush to Nuclear

Born in 1965, Ouchi began working in the Japanese nuclear energy sector at a pivotal time for his country.

Japan, an island nation with limited natural resources and a substantial reliance on imported energy, had turned its gaze to nuclear power production.

Nuclear power is like a supercharged steam engine, except we’re tapping into the astonishing power released by smashing certain atoms apart.

The mechanics behind nuclear energy and nuclear weapons

Here’s how the magic works.

Neutrons are fired at special fissible atoms Uranium-235 or Plutonium-239, causing them to split and release more neutrons, plus a massive burst of energy.