Root cause analysis of the June 9, 1985, Davis-Besse event

Equipment failures and human errors have not been designed out of nuclear power plants. Although the tolerance of plants to accept multiple failures and errors without direct harm to the public has been demonstrated repeatedly around the nation, they must find the root causes of failures and errors to assure optimum nuclear safety and protection of their investment and generating facilities. This paper addresses the root causes analysis techniques used following a loss-of-auxiliary-feedwater event on June 9, 1985, at the Davis-Besse Nuclear Power Station. The event started with a capacitor failure causing loss of main feedwater. This was followed by an operator pushing the wrong buttons during the transient. This error was multiplied in impact by steam feedwater rupture control system and auxiliary feedwater pump design deficiencies, equipment failures, and human factors problems. Other equipment failed to perform properly or was damaged as a result of the transient.