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.





*** END OF DOCUMENT ***