What happened to Chernobyl?

Answer 1

To sum up the essentials, the workers at the chernobyl plant were being pushed to operate the new reactor (#4) at above normal levels. Various anomalies were discovered but due to the increased pressure on the teams they were overlooked. While operating the reactor, a pocket of steam built up beneath the injector rods that was not being released. When it was finally discovered emergency procedures went underway, but due to a stuck injector rod the reaction could not be prevented and therefore started a chain of explosive reactions that caused the chemicals in the reactor to spread and a fire to start.

Answer 2

The disaster began during a systems test on Saturday, 26 April 1986 at reactor number four of the Chernobyl plant, which is near the city of Pripyat and in proximity to the administrative border with Belarus and the Dnipier river. There was a sudden and unexpected power surge, and when an emergency shutdown was attempted, an exponentially larger spike in power output occurred, which led to a reactor vessel rupture and a series of steam explosions. These events exposed the Graphite Moderator of the reactor to air, causing it to ignite and meltdown.