05000400/LER-2003-002

LER-2003-002, 1 O OF 3 3

Docket Number
Event date:	05-20-2003
Report date:	07-21-2003
Initial Reporting
4002003002R00 - NRC Website

I. DESCRIPTION OF EVENT

On May 20, 2003 at 0453 with the reactor at approximately 20 percent power in Mode 1, the reactor was manually tripped as directed by plant procedures in response to an automatic trip of the single operating main feedwater pump (MFP) [SJ-P]. The "A" MFP tripped in response to an unplanned trip of the "A" condensate booster pump (CBP) [SG-P]. Both motor-driven auxiliary feedwater (AFW) pumps [BA-P] started due to the trip of the MFP. Safety systems functioned as required. The operations crew responded to the event in accordance with applicable plant procedures. The plant was stabilized at normal operating no-load reactor coolant system (RCS) [AB] temperature and pressure following the reactor trip.

The cause of the unplanned trip of the "A" CBP was due to low oil pressure after a gear [GR] in its variable speed fluid coupling (VSFC) failed following vendor refurbishment. The refurbishment included replacement of the internal oil pump pinion gear that resulted in tighter clearances in the internal oil pump. Without proper "run in" of the pinion gear, the gear teeth did not develop adequate load-carrying capability subsequently causing a mechanical overload of the pinion gear. This overloaded condition damaged the teeth of the pinion gear in the "A" CBP internal oil pump causing a decrease in oil pressure and subsequently resulted in an automatic trip of the "A" CBP.

Energy Industry Identification System (ENS) codes are identified in the text within brackets [ ].

II. CAUSE OF EVENT

The cause of the unplanned trip of the "A" CBP was due to low oil pressure after a gear in its VSFC failed following vendor refurbishment.

III. SAFETY SIGNIFICANCE

Other than the transient induced by the manual reactor trip, no safety significant consequences exist as a result of this event. The plant was manually tripped from approximately 20% power by control room operators as directed by plant procedures. The plant is designed for a loss of main feedwater, and it responded as expected for this condition. The initial plant conditions were within the bounding conditions for the plant design. The plant was promptly stabilized at normal operating no-load RCS temperature and pressure following the manual reactor trip. Plant equipment functioned as required, and no unusual conditions were observed for plant equipment following this event. No additional or compensatory measures were required for this event. The operating staff performed the required actions for the trip.

The potential safety consequences under other alternate conditions, such as operating at higher power, may have increased the severity of the transient, but they would not be expected to challenge the ability to stabilize the plant.

IV. CORRECTIVE ACTIONS

Immediate corrective action was to replace the VSFC. Additional corrective action will be to specify a "run-in" of the gear set following VSFC refurbishment to develop adequate load-carrying capability of the gear teeth.

V. PREVIOUS SIMILAR EVENTS

This failure is similar to the failure of the "A" CBP internal oil pump that occurred during the previous refueling outage in 2001. An apparent cause evaluation was performed at that time and concluded that the test procedure caused the failure by installing jumpers to run the CBP internal oil pump and its auxiliary oil pump simultaneously. The root cause evaluation associated with this LER confirmed that even short simultaneous runs of the two oil pumps can cause damage to the pinion gear of the CBP internal oil pump. However, in the event reported by this LER, no jumpers were installed to run the two oil pumps simultaneously. In this event, the cause of the gear failure was due to improper "run in" of the pinion gear in the CBP VSFC following vendor refurbishment. Therefore, the corrective actions of the previous failure would not have prevented the event reported by this LER.