Protecting People and the EnvironmentUNITED STATES NUCLEAR REGULATORY COMMISSION
LICENSEE: NORTHEAST UTILITIES
SITE: MILLSTONE 1 EN NUMBER:34615
DOCKET: 05000245 EVENT DATE: 08-07-98
RX TYPE: BWR EVENT TIME: 12:00
VENDORS: GE-3 NOTIFY DATE: 08-07-98
EMERGENCY CLASS: N/A REGION: 1 STATE: CT TIME: 16:16
OPS OFFICER: DICK JOLLIFFE
10 CFR SECTION: CDEG 21.21(c)(3)(i) DEFECTS/NONCOMPLIANCE
UNIT SCRAM RX INIT INITIAL MODE CURR CURRENT MODE
CODE CRIT PWR PWR
1 N N 0 REFUELING 0 REFUELING
- 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 (TTs) TO PROVIDE THE GOVERNOR WITH THE SPEED SIGNALS
FROM THE GTG AND THE DIESEL 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 LOSS OF
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. 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.
