How It Happened
Reactor 4 at the Chernobyl Nuclear Power Plant was scheduled for a shutdown to perform routine maintenance on April 25th, the day before the disaster. This shutdown was to take place, in part, so an experiment could be undertaken. The engineers at the plant intended to test the turbines running the generators in the reactor to see if they would continue to run even if there was an external power outage. This would be an important safety component, as the reactor type used at Chernobyl requires a constant spray of water in order to remain cool. Of course, the turbines could not turn forever under their own momentum (or else there would be no need for a nuclear power plant). There was a forty second delay between the shutdown of the electricity and the initiation of the backup generators. The engineers needed to test if the turbines could continue to turn for a minimum of forty seconds, thus producing a seamless transition in the event of a power outage.
In a twist of fate, the grid controller in the area requested that the reactor stay online, however, rather than decreasing power output. This was due to a regional power station gong offline that day, and the controller anticipating the need for the electricity during the peak hours of the day. Chernobyl agreed, and the power decrease did not start until nearly 11:00 that night. Thus, the safety test was put into the hands of the less experienced and understaffed night shift. The new crew was not made aware of the fact that they had postponed the power decrease, and thus followed the plan for shutdown as if it had been decreasing throughout the day.
Without getting into the scientific aspects of the disaster, suffice to say that this lack of knowledge (and the plant’s unacceptable safety systems), led directly to the meltdown. While trying to complete the experiment, the staff removed the manual control rods for the reactor, since they were not getting the desired results from their shutdown. The reactor, set inexorably towards a runaway reaction, was left without anything to prevent it. By the time systems began to show…