On September 29, 1957, at 4:20 p.m., an enormous explosion in a tank containing highly radioactive waste occurred in the Mayak nuclear weapons plant in the southern Ural mountains of the Soviet Union. The fallout plume spread strontium-90 and other dangerous radionuclides over more than 15,000 square kilometers, which remain contaminated to this day. …

Read the full article at http://www.armscontrol.org/act/2005_07-08/Makhijani