Exposure may occur from nuclear fallout when nuclear weapons are detonated or nuclear containment systems are compromised . During World War II , the United States Army Air Forces dropped atomic bombs on the Japanese cities of Hiroshima and Nagasaki , leading to extensive contamination of food , land , and water . In the Soviet Union , the Mayak industrial complex ( otherwise known as Chelyabinsk-40 or Chelyabinsk-65 ) exploded in 1957 . The Kyshtym disaster was kept secret for several decades . It is the third most serious nuclear accident ever recorded . At least 22 villages were exposed to radiation and resulted in at least 10,000 displaced persons . In 1992 , the former Soviet Union officially acknowledged the accident . Other Soviet republics of Ukraine and Belarus suffered also when a reactor at the Chernobyl nuclear power plant had a meltdown in 1986 . To this day , several small towns and the city of Chernobyl remain abandoned and uninhabitable due to fallout
Kyshtym disaster
Kyshtym disaster
Anthropogenic hazard