The Chernobyl nuclear disaster

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In April 1986 a reactor exploded at the Chernobyl nuclear power plant in Ukraine, in the USSR, causing the worst nuclear accident ever. Sergii Mirnyi was in charge of a monitoring unit which measured radiation levels in the 30 km exclusion zone around the plant. (Photo: The Chernobyl plant shortly after the explosion in 1986. Credit: Getty Images)