Part 21 Report - 1998-571
ACCESSION #: 9808110186
Northeast Utilities
Millstone Unit No. 1
Docket No. 50-245
Part 21 Notification
Vendor: Eitel Manufacturing
Capistrano Beach, CA
Manufacturer: Eitel 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 orientation 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 governor. A trip is initiated if the signal is 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 not 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-25-1 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 governor 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.
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 governor, or
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 governor.
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 requirements
of 10CFR21.
Northeast Utilities: Peter Miner
Manager, Regulatory Compliance-Millstone Unit No 1
860-440-2085
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 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 THE
FEEDBACK TO THE GOVERNOR FOR SPEED CONTROL OF THE ELECTRIC GENERATOR.
(Continued on next page)
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
FAILURE 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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