Hello and thank you for downloading witness on the BBC World Service with me

Dina Newman. Today we go back to September 1957

and a major nuclear accident in Soviet Russia

nearly 2,000 kilometers to the east of Moscow.

It resulted in a huge radioactive cloud spreading over hundreds of

kilometers and affecting a quarter of a million people.

On Sunday, September 29, 1957, technicians at Mayak, a nuclear plant in the Soviet Union, started their shift as usual.

Myak was a secret facility which had produced the first Soviet nuclear bomb.

Anna Sharava, a chemical engineer, remembered the day of the accident in a documentary produced decades later.

We were on shift from 1 PM until 7. We worked in the lab and being a Sunday there was less work than usual.

And suddenly we heard a kind of thunder. Windows were blown out, glass doors were shattered. We looked

outside and saw a huge cloud. What Anna had heard was an explosion caused by the overheating of tons of highly concentrated nuclear waste

stored without adequate safety procedures.

This highly concentrated nuclear waste was accumulated in big tanks made of steel and underground.

Jares Medvedev is the scientist who studied the fallout from the blast and revealed to the world how it came about.

There were not enough regulation of temperature and so on.

At the certain stage in one of the tanks the system of regulation of

temperature stopped to operate and when temperature reached certain stage the tank explodes.

This blast caused one of the worst nuclear disasters in history.

It's ranked third after Chernobyl and Fukushima. In 1957 it was the worst ever, but such was the secrecy around the plant that no warnings over the high levels of radiation were issued.

At the same time, the accident couldn't go entirely unnoticed.

Over the next few days, local hospitals and clinics could barely cope with the new arrivals. An estimated 200 people died within 10 days.

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