Feedback of operational experience from the Westinghouse Owners Group emergency procedures and reactor trip reduction program

Before the accident at Three Mile Island (TMI), Westinghouse Owners Group (WOG) utilities used emergency guidelines based on events. For example, one procedure was written for a loss of coolant event, another and separate procedure was written for a steam generator tube rupture and a third independent procedure was written for a secondary break. After the TMI accident, however, it became apparent that additional guidance had to be provided to the control room operators and, thus, the WOG embarked on a three year effort to develop symptom based guidelines for responding to emergency events. The WOG Emergency Response Guidelines (ERGs) were the basis of the emergency procedures in place at the time of Virginia Power's North Anna Unit 1 steam generator tube rupture on 15 July 1987. The North Anna emergency procedures closely resembled the WOG ERGs and their use during the steam generator tube rupture event can be considered to be a representative test of the ERG steam generator tube rupture recovery technique. The operators used their emergency procedures and had no major difficulties in responding to the event. In the area of reactor trip reduction, the WOG established a two part programme to reduce reactor trips. The efforts of the WOG Reactor Trip Reduction Program has resulted in tangible benefits. The rate of unplanned reactor trips at WOG utilities has decreased from an average of nearly eight per year per plant in 1980 to just over four per year in the first half of 1987. The contribution of the feedwater system as a trip initiator has decreased from 34% of all trips prior to 1985 to only 17% in 1987. The improvements can be attributed to both the increased awareness of the problem, brought about in part by WOG efforts, and to hardware changes independently initiated by utilities. (author). 7 figs