Event

The nuclear power plant at Chernobyl included four nuclear reactors in four separate buildings.  The model chosen for this plant was the RBMK-1000 (reaktor bolshoy moshchnosti kanalniy) [1, 1] which consisted of a water-cooled system around several graphite rods and natural uranium fuel [7, 1]. Each of these reactors had a capacity of 925 MW.[7, 2]  There were four units, and an experiment was devised to test one of the safety features in Unit 4.[5, 1]  The experiment involved turning off some off the other safety features, and removing some of the graphite rods that were usually in the reactor.

At 12:10 in the morning on April 26, 1886 the experiment began.  The reactor was giving off 720 MW of power, but the output dropped to 30 MW.  At 1:22:30 a warning was sent to the control room instructing the operators to immediately make an emergency shutdown of the reactor, but this warning was ignored.  The reactor was now left with insufficient energy to complete the experiment. [1,2]

The majority of reactors are designed so that the power output is reduced when less coolant is supplied to the reactor, but in the case of the RBKM, the opposite is true.  This would prove to be one of the main causes of the explosion. [1,3]

At 1:23 AM the experiment began and almost immediately the power output of the reactor began to rise rapidly.  There was a problem with the pressurized water coolant which was flowing inadequately to cool the reactor cores sudden increase of temperature.  Pressure built up and a steam explosion tore the reactor apart and devastating its surrounding housing. [1, 2]