The Chernobyl Nuclear Power Plant was a RBMK (Reaktor Bolshoy Moshchnosty Kanalny) type reactor, designed to generate electricity for the Soviet grid. The plant had four reactors, with Reactor 4 being the site of the disaster. On the night of April 25, 1986, a safety test was being conducted on Reactor 4 to determine how long the turbines would keep spinning and generating electricity in the event of a loss of power to the main cooling pumps.