Twenty-five years ago today, disaster rocked Ukraine when a systems test at the Chernobyl nuclear power plant led to a series of explosions, releasing nuclear fallout into the atmosphere. It was the beginning of a months-long struggle by Soviet authorities to contain the spread of deadly radiation. Thousands of workers joined this fight. Sergei Belyakov was one of them. He's the author of a forthcoming book about his experience called "The Liquidator."