In 1957 Mayak was the site of the Kyshtym disaster , one of the worst nuclear accidents in history . During this catastrophe , a poorly maintained storage tank exploded , releasing 20 million curies in the form of 50-100 tons of high-level radioactive waste . The resulting radioactive cloud contaminated an expansive territory of more than 750 km2 ( 290 sq mi ) in the eastern Urals with the consequence of sickness and death from radiation poisoning
Kyshtym disaster
Kyshtym disaster
Mayak