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Only two events have ever reached the maximum level 7 on the International Nuclear Event Scale: the Chernobyl meltdown in 1986 and the Fukushima disaster of 2011. But the causes and effects of the two were quite different. Chernobyl released more radioactive material but cost much less to clean up, principally because almost no compensation was paid to the people affected by the fallout. LV
*One becquerel is a unit of radiation equivalent to one nucleus decay per second. One petabecquerel is 1015 becquerels.
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