The Chernobyl disaster was a nuclear plant accident occurring in 1986 in the Ukraine.  It was the result of a flawed reactor design that was operated with inadequately trained personnel.  The resulting explosion and fires released at least 5% of the radioactive reactor core into the atmosphere and downwind.  Two of the pant workers died directly from the accident, and a further 28 people died within a few weeks as a result of acute radiation poisoning.  Since the accident, the population of people around the area have been relocated out of harms way, although it is unknown exactly how much radiation they were exposed to.