Today in History - April 26: Three volunteers stepped up for task they were told would kill them

A safety test mistake at the Chernobyl Nuclear Power Plant in modern-day Ukraine caused the worst nuclear accident in history on April 26, 1986.

For days after the explosion, radioactive smoke and steam poured out from the reactor, spreading radiation all over Europe, especially neighbouring Belarus.

Thousands of deaths have been attributed to cancer caused by the leaking radiation.

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But the Soviet Union did not publicise the meltdown until days later.

The Chernobyl accident was announced on the Soviet news with a 20-second announcement on April 28.

"There has been an accident at the Chernobyl Nuclear Power Plant. One of the nuclear reactors was damaged. The effects of the accident are being remedied," the newsreader said.

"Assistance has been provided for any affected people. An investigative commission has been set up."

The announcement only came after radiation alarms were set off in Sweden, more than 1000km away.

Three men were credited with a particular act of courage on May 4.

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Alexei Ananenko, Valeri Bezpalov, and Boris Baranov walked through knee-deep radioactive water under the reactor to drain the flooded water, averting a much worse meltdown.

The three were told there was a good chance they would die in the process.

It was widely reported that Ananenko, Bezpalov and Baranov died soon after their successful mission.

But Baranov lived until 2005, and the other two are still alive.

A 2600 square kilometre exclusion zone remains in place around Chernobyl, where radiation is still so dangerous that staying there could prove fatal.

Since then the area has been reclaimed by nature.

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