What caused the disaster at chernobyl in 1986?

Answer 1

The disaster was caused by multiple flaws in the reactor design and multiple operator errors when running a poorly planned test (that required intentional disabling of the emergency cooling system, a very bad idea forbidden in the official procedures) with improperly documented and unapproved changes to its procedure, on the reactor. It caused the reactor to enter an unstable and difficult to control state (which official procedures forbade operating in). When the operators finally pressed the SCRAM button to initiate a full shutdown design errors in the control rods instead caused a very large power surge. This power surge caused a steam explosion which destroyed the reactor, blasted a hole in the roof exposing the hot graphite to air which caused it to ignite. The people of Russia were not properly informed of the dangers of nuclear radiation the government chose to do this because they believed their reactors were fool proof and decided the less knowledge people had the better for security. Unfortunately that left a whole staff at the reactor very unprepared when the accident happened.