What actually caused the accident at Chernobyl?
As is usually the case in any accident, a number of things combined to cause this one at Chernobyl. Unlike power reactors operating in the U.S. and other nations, the Chernobyl RBMK reactor (which is a graphite rather than a light water system) has a built-in instability that occurs at low power, which is how the reactor was operating at the time of the accident. If some of the cooling water in this reactor converts to steam, the RBMK increases in power. This in turn causes more steam to form, which causes _another_ increase in power. (In Western light water reactors, the power decreases.) The power increase feature of the RBMK caused a rupture in the cooling system and a large steam explosion occurred. This caused the cooling system to fail and the outer covering (or cladding) of the fuel elements to increase in temperature. The cladding was hot enough to react with the steam, causing hydrogen to form. The hydrogen then caused a second explosion. The release of this energy set the gra
