What happened to Chernobyl?

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.