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On April 26, 1986, explains the International Atomic Energy Agency (IAEA), the Number Four RBMK reactor at the nuclear power plant at Chernobyl, Ukraine, went out of control during a test at low-power, leading to an explosion and fire that demolished the reactor building and released large amounts of radiation into the atmosphere.

According to HowStuffWorks, "Chernobyl was poorly designed and improperly operated, but it dramatically shows the worst-case scenario. Chernobyl scattered tons of radioactive dust into the atmosphere." Prypiat, the city of 44,000 people located less than 3 miles from the site of the disaster, is where most of the Chernobyl lived. Prypiat was evacuated within 60 hours of the accident and likely will remain abandoned for perhaps hundreds of years due to radiation.

Official Chernobyl death counts are relatively low, but a 2006 Greenpeace report revealed that the "full consequences of the Chernobyl disaster could top a quarter of a million cancer cases and nearly 100,000 fatal cancers."