The worst nuclear power accident in history, which occurred at the Chernobyl nuclear power plant in the Ukraine, will affect, in one form or another, 20 percent of the republic’s population (2.2 million people). On April 26, 1986, at 1:23:40A.M., during unauthorized experiments by the operators in which safety systems were deliberately circumvented in order to learn more about the plant’s operation, one of the four reactors rapidly overheated and its water coolant “flashed” into steam. The hydrogen formed from the steam reacted with the graphite moderator to cause two major explosions and a fire. The explosions blew apart the 1,000 ton (907 metric ton) lid of the reactor, and released radioactive debris high into the atmosphere. It is estimated that 50 tons of fuel went into the atmosphere. An additional 70 tons of fuel and 700 tons of radioactive reactor graphite settled in the vicinity of the damaged unit.

Human error and design features (such as a positive void coefficient type of reactor, use of graphite in construction, and lack of a containment building) are generally cited as the causes of the accident. Thirty-one people died from trying to stop the fires. More than 240 others sustained severe radiation sickness. Eventually 150,000 people living near the reactor were relocated; some of whom may never be allowed to return home. Fallout from the explosions, containing radioactive isotope cesium–137, was carried by the winds westward across Europe.

The problems created by the Chernobyl disaster are overwhelming and continue today. Particularly troubling is the fact that by 1990–1991, a five-fold increase had occurred in the rate of thyroid cancers in children in Belarus. A significant rise in general morbidity has also taken place among children in the heaviest-hit areas of Gomel and Mogilev.