On April 26, 1986, the operating crew planned to test whether the Reactor No. 4 turbines could produce enough energy to keep the coolant pumps running until the emergency diesel generator was activated in case of an external power loss. During the test, power surged unexpectedly, causing an explosion and driving temperatures in the reactor to more than 2,000 degrees Celsius—melting the fuel rods, igniting the reactor’s graphite covering, and releasing a cloud of radiation into the atmosphere.
Causes of the Chernobyl Nuclear Accident:
The precise causes of the accident are still uncertain, but it is generally believed that the series of incidents that led to the explosion, fire and nuclear meltdown at Chernobyl was caused by a combination of reactor design flaws and operator error.
Loss of Life from the Chernobyl Nuclear Accident:
By mid-2005, fewer than 60 deaths could be linked directly to Chernobyl—mostly workers who were exposed to massive radiation during the accident or children who developed thyroid cancer.
Estimates of the eventual death toll from Chernobyl vary widely. A 2005 report by the Chernobyl Forum—eight U.N. organizations—estimated the accident eventually would cause about 4,000 deaths. Greenpeace places the figure at 93,000 deaths, based on information from the Belarus National Academy of Sciences.