Part 21 Report - 1998-570

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.

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