Picture a monster. Fangs, claws, fire, something you could at least see coming. The men in this story had a monster too, and they had a name for it. They called it the dragon. But this dragon was the size of a grapefruit. It sat perfectly still on a laboratory bench, cold and silent and ordinary to the eye. And it killed two men with something no eye can see, no ear can hear, and no hand can feel. Until it is far too late.

This is the story of the Demon Core. One ball of plutonium, two dead men, and a laboratory that watched the same experiment kill once, changed nothing, and watched it kill again.

January 21, 1969. Lucens, Switzerland. An experimental reactor buried in a mountain cavern — built to prove the Swiss could go nuclear on their own — overheated, melted, and blew apart its pressure tube. No one died. The reactor was the only casualty.

The killer was invisible and months old: water from a blower seal had leaked into the coolant circuit, corroding the fuel cladding from the inside. No instrument caught it. By restart day, one fuel assembly was already doomed.

The twist: the accident did NOT end Switzerland's secret A-bomb program. That ran until 1988.

They were told the plant needed no inspection. Then three men carried buckets into it, and poured them through a funnel, one after another, until the uranium did what uranium does.

On September 30, 1999, at a fuel-processing plant in Tokaimura, Japan, a routine procedure went catastrophically wrong — and a nuclear chain reaction started in a steel tank. It burned for twenty hours. Two years earlier, a fire at a nearby plant had been shrugged off. This is the story of what happened when nobody looked twice.

Nuclear Shadows is the true, unsettling history of nuclear accidents, told straight. No screaming, no sound effects. New episodes every Monday and Thursday.

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