ML20236Y123

Part 21 Rept Re Gas & Turbine Generator for Dedicated Emergency Power to Vital AC Buses

ML20236Y123
Person / Time
Site:	Millstone
Issue date:	08/07/1998
From:	Miner P NORTHEAST NUCLEAR ENERGY CO.
To:	NRC
References
REF-PT21-98 NUDOCS 9808110186
Download: ML20236Y123 (3)

Text

4 AUG-07-98 FR104:32 Ptl NUCLEAR LICENSING SVCS, FAX N0, 860 440 2091 Northeast Utihtjes Millstone Unit No.1 Docket No. 50-245 Part 21 Notification Vendor: Eitel Manufacturing Capistrano Beach, CA Manufacturer: Elte! Manufacturing Model Number. Berkeley model 466-120 issue:

Millstone Unit No.1 uses one diesel and one Gas Turbine Generator (GTG) for dedicated emergency power to vital AC buses during an event. The GTG is a GE LM 1500 that utilizes tachometer transducers to provide the governor with the speed signals from the gas generator and the electric generator. One of these tachometer transducers that was accepted from Eitel was later determined to have the finger spring washer installed in the incorrect orien+ation into the tachometer transducer resulting in an improper fit of the bearings. These tachometer transducers are procured commercially and are dedicated for this safety related application by Millstone.

The tachometer transducer with the defect was accepted and installed in ID location TG-25-5.

Note that although this tachometer transducer had been installed, the GTG had not yet been declared operable when the defect had been confirmed. This tachometer transducer provides an overspeed signal to the govemor. A trip is inrtiated if the signalis lost and in the event that the GTG is operating in an emergency, with an accident signal present, the trip is bypassed.

Therefore, it is concluded that the failure of TG-25-5 alone will net result in the loss of a safety function necessary to mitigate the consequences of an accident, However, it should noted that TG-25-5 is coupled together on the same drive mechanism with tachometer transducer TG-251 which is of the same design as TG-25-5. The signal from TG 25-1 provides the feedback to the governor for speed control of the electric generator. Without this speed signal, the 97vemor cannot control the frequency of the generator which would prevent synchronization to the vital AC buses, In this situation, the GTG would not be able to perform its safety function.

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- The possible scenarios for' failure would be as follows:  !

1. Bearing failure would cause the shaft to seize and break resulting in lost speed signal to the govemor, or a

2. Bearing failure would increase the vibration in the assembly of the tachometer transducers )

resulting in early failure of the windings and a lost speed signal to the govemor, in view of the above it is possible to postulate that in the event of an accident, failure of TG 25-5 could have caused the failure of TG-25-1, rendering the GTG unavailable to mitigate the consequences of an accident. Therefore, this condition is considered reportable under the l

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requirements of 10CFR21.

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Northeast Utilities: Peter Miner  ! l Manager, Regulatory Compliance-Millstone Unit No.1

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PDR ADOCK 05000245 l P PDR * \

i POWER REACTOR EVENT NUMBER: 34615 FACILITY: MILLSTONE REGION: 1 NOTIFICATION DATE: 08/07/98 UNIT: [1] [] [] STATE: CT NOTIFICATION TIME: 16:16 [ET]

RX TYPE: [1] GE-3, [2] CE, [3] W-4-LP EVENT DATE: 08/07/98 EVENT TIME: 12:00[EDT]

NRC NOTIFIED BY: MARI JAWORSKY LAST UPDATE DATE: 08/07/98 HQ OPS OFFICER: DICK JOLLIFFE NOTIFICATIONS EMERGENCY CLASS: NOT APPLICABLE 10 CFR SECTION: TOM MOSLAK RDO CDEG 21. 21 (c) (3 ) (i) DEFECTS / NONCOMPLIANCE VERN HODGE NRR UNIT SCRAM CODE RX CRIT INIT PWR INIT RX MODE CURR PWR CURR RX MODE 1 N N 0 REFUELING 0 REFUELING EVENT TEXT

- 10CFR21 REPORT - DEFECTIVE GAS TURBINE GENERATOR TACHOMETER TRANSDUCER MILLSTONE UNIT 1 USES ONE DIESEL GENERATOR AND ONE GAS TURBINE GENERATOR (GTG) FOR DEDICATED EMERGENCY POWER TO VITAL AC BUSES DURING AN EVENT.

THE GTG IS A GE LM-1500 GENERATOR THAT UTILIZES TACHOMETER TRANSDUCERS (TT)

TO PROVIDE THE GOVERNOR WITH THE SPEED SIGNALS FROM THE GAS GENERATOR AND THE ELECTRIC GENERATOR. ONE OF THESE TTs THAT WAS ACCEPTED FROM EITEL MANUFACTURING COMPANY, CAPISTRANO BEACH, CA, (BERKELEY MODEL #466-120)

WAS LATER DETERMINED TO HAVE THE FINGER SPRING WASHER INSTALLED IN THE INCORRECT ORIENTATION IN THE TT RESULTING IN AN IMPROPER FIT OF THE BEARINGS. BEARING FAILURE WOULD INCREASE VIBRATION IN THE TT ASSEMBLY POSSIBLY RESULTING IN EARLY FAILURE OF THE WINDINGS, OR SEIZURE AND BREAKAGE OF THE SHAFT. EITHER FAILURE WOULD RESULT IN A LOST SPEED SIGNAL TO THE GOVERNOR.

THIS TT PROVIDES AN OVERSPEED SIGNAL TO THE GOVERNOR. A TRIP IS INITIATED IF THE SIGNAL IS LOST. IN THE EVENT THAT THE GTG IS OPERATING IN AN EMERGENCY, WITH AN ACCIDENT SIGNAL PRESENT, THE TRIP IS BYPASSED.

THESE TTs ARE PRODUCED COMMERCIALLY AND ARE DEDICATED FOR THIS SAFETY RELATED APPLICATION BY MILLSTONE. THE TT WITH THE DEFECT WAS ACCEPTED I

AND INSTALLED IN ID LOCATION TG-25-5.

THE DEFECTIVE TT INSTALLED IN LOCATION TG-25-5 IS COUPLED TOGETHER ON THE SAME DRIVE MECHANISM WITH A TT OF THE SAME DESIGN INSTALLED IN LOCATION TG-25-1. THE SIGNAL FROM THE TT INSTALLED IN LOCATION TG-25-1 PROVIDES TME FEEDBACK TO THE GOVERNOR FOR SPEED CONTROL OF THE ELECTRIC GENERATOR.

(Continued on next page)

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FACILITY: MILLSTONE PAGE # 2 OF EVENT NUMBER: 34615 WITHOUT THIS SPEED SIGNAL, THE GOVERNOR CANNOT CONTROL THE FREQUENCY OF THE GENERATOR WHICH WOULD PREVENT SYNCHRONIZATION TO THE VITAL AC BUSES.

FAILURE OF THE TT INSTALLED IN LOCATION TG-25-5 COULD HAVE CAUSED THE FAZLURE OF THE TT INSTALLED IN LOCATION TG-25-1, RENDERING THE GTG UNAVAILABLE TO MITIGATE THE CONSEQUENCES OF AN ACCIDENT. IN THIS SITUATION, THE GTG WOULD NOT BE ABLE TO PERFORM ITS SAFETY FUNCTION.

THE LICENSEE IS CONTINUING TO INVESTIGATE THIS CONDITION AND IS DETERMINING CORRECTIVE ACTIONS.

THE LICENSEE INFORMED THE NRC RESIDENT INSPECTOR.

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