verifiedCite
While every effort has been made to follow citation style rules, there may be some discrepancies. Please refer to the appropriate style manual or other sources if you have any questions.
Select Citation Style

What caused the Chernobyl disaster?

The Chernobyl disaster occurred when technicians at nuclear reactor Unit 4 attempted a poorly designed experiment. They shut down the reactor’s power-regulating system and its emergency safety systems, and they removed control rods from its core while allowing the reactor to run at 7 percent power. These mistakes were compounded by others, and at 1:23 am on April 26, 1986, the chain reaction in the core went out of control. Several explosions triggered a large fireball and blew off the heavy steel and concrete lid of the reactor. This and the ensuing fire in the graphite reactor core released large amounts of radioactive material into the atmosphere, where it was carried great distances by air currents. A partial meltdown of the core also occurred.