Laborers work on construction of the Soviet Union's Chernobyl nuclear power plant on July 1, 1975. The Chernobyl accident is the world's worst nuclear accident. The disaster sent a cloud of radioactive fallout over hundreds of thousands of square miles of Russia, Belarus and Ukraine. The radioactive effects of the explosion were about 400 times more potent than the bomb dropped on Hiroshima during World War II.
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