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On June 27, 2001, at approximately 18:20, … On June 27, 2001, at approximately 18:20, the Point Beach Nuclear Plant (PBNP) Unit 2 reactor was manually tripped with reactor power at approximately 70%. This trip was directed by procedure (AOP-13A) when the water level in the Circulating Water (CW) System pump bay decreased to less than -11 feet (normal pump bay level with four CW pumps in service is about -7 feet). The Service Water (SW) pumps also take a suction from the pump bays and -11 feet is a conservative minimum water level to assure that components serviced by the SW system will remain capable of performing their safety functions. The decrease in pump bay water level was attributed to the influx of a large number of small forage fish (Alewives) on the Unit 2 traveling water screens. This influx caused a high differential water level across the screens and ultimately resulted in the disabling of the traveling screen drive mechanism. Following the trip one of the two running Unit 2 CW pumps was secured. This action; in conjunction, we believe, with a screen failure that permitted increased water flow into the pump bay; resulted in a rapid recovery of the pump bay level. The preliminary root cause report has identified the following causal factors: ineffective implementation of previously identified corrective actions from related events, delays in operator response while in the AOP, and problems with the sequence of action steps within the procedure. With the exception of two minor equipment problems identified in the report, the operator and equipment responses to the transient were as expected and the unit was stabilized in the hot shutdown condition. Unit 2 returned to normal operation on July 1, 2001.urned to normal operation on July 1, 2001. +
On June 27, 2001, at approximately 18:20, … On June 27, 2001, at approximately 18:20, the Point Beach Nuclear Plant (PBNP) Unit 2 reactor was manually tripped with reactor power at approximately 70%. This trip was directed by procedure (AOP-13A) when the water level in the Circulating Water (CW) System pump bay decreased to less than -11 feet (normal pump bay level with four CW pumps in service is about -7 feet). The Service Water (SW) pumps also take a suction from the pump bays and -11 feet is a conservative minimum water level to assure that components serviced by the SW system will remain capable of performing their safety functions. The decrease in pump bay water level was attributed to the influx of a large number of small forage fish (Alewives) on the Unit 2 traveling water screens. This influx caused a high differential water level across the screens and ultimately resulted in the disabling of the traveling screen drive mechanism. Following the trip one of the two running Unit 2 CW pumps was secured. This action; in conjunction, we believe, with a screen failure that permitted increased water flow into the pump bay; resulted in a rapid recovery of the pump bay level. The preliminary root cause report has identified the following causal factors: ineffective implementation of previously identified corrective actions from related events, delays in operator response while in the AOP, and problems with the sequence of action steps within the procedure. With the exception of two minor equipment problems identified in the report, the operator and equipment responses to the transient were as expected and the unit was stabilized in the hot shutdown condition. Unit 2 returned to normal operation on July 1, 2001.urned to normal operation on July 1, 2001. +
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