ML20078K736

Special Rept on 941021,DG 1A Invalid Failure Occurred Due to Main Bearing High Temp Trip.Operability Performance Test Successfully Completed & Engine Declared Operable on 941022

ML20078K736
Person / Time
Site:	Catawba
Issue date:	11/17/1994
From:	Rehn D DUKE POWER CO.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
NUDOCS 9411250150
Download: ML20078K736 (3)

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. Catawba Nuclear Generation Department \' ace President

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4800 ConcordRoad (803)8313205 Office York,.SC29745 (803)S313426 Fat DUKEPOWER November 17, 1994 U. S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, DC 20555

Subject:

Catawba Nuclear Station, Unit 1 Docket No. 50-413 Special Report Invalid Failure of Diesel Generator 1A Pursuant to Technical Specification 4. 8.1.1. 3 and 6.9.2, find attached a Special Report concerning the Unit 1 Diesel Generator (DG 1A) invalid failure which occurred on October 21, 1994.

Very truly yours, DL Rehn KEN \DGlA1021.94 Attachment xc: SD Ebneter, Regional Administrator RJ Freudenberger, SRI RE Martin, ONRR

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I 9411250150 PDR 941117 ADOCK 0500o413 PDR /

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SPECIAL REPORT CATAWBA NUCLEAR STATION DOCKET NO. 50-413 DIESEL GENERATOR 1A INVALID FAILURE DUE TO MAIN BEARING HIGH TEMPERATURE TRIP PIP 1-C94-1495 An invalid failure of Diesel Generator (DG 1A) occurred on 10/21/94 at 0914 hours0.0106 days <br />0.254 hours <br />0.00151 weeks <br />3.47777e-4 months <br /> due to a main bearing high temperature trip signal. Two subsequent runs for troubleshooting purposes were also classified as invalid failures. It was determined that a failed Resistance Temperature Detector (RTD) was the cause of the trip signal. Unit I was in Mode 1 (power operations) at 99e power when this failure occurred. There has been 1 valid failure in the last 20 valid tests and 2 valid failures in the last 100 valid tests on DG 1A. DG 1A was on a weekly test frequency due to the starting air valve corrective action required per PIP 1-C94-1301. There were 5 hours5.787037e-5 days <br />0.00139 hours <br />8.267196e-6 weeks <br />1.9025e-6 months <br /> of unavailability time associated with this failure.

On 10/21/94, DG 1A was being prepared for an air roll in order to satisfy the corrective action required from the starting air valve failure. The temperature of main bearing #5 indicated ~160 F on the Rosemount Alarm Monitor panel with the engine in standby condition. This was ~15* F higher than the other bearing temperatures. Following the roll on air, the engine was started at 0907 hours0.0105 days <br />0.252 hours <br />0.0015 weeks <br />3.451135e-4 months <br /> (Start #1034). At 0914 hours0.0106 days <br />0.254 hours <br />0.00151 weeks <br />3.47777e-4 months <br />, DG 1A tripped on high bearing temperature. The alarm monitor panel indicated channel #8 (Main Bearing #5/1LDRD5630) was the source of the trip signal.

This channel indicated ~240* F following the trip, whereas the other bearing temperatures still indicated -145* F. The bearing temperature channels are set to trip the engine at a temperature of 228 F.

Work Order (W/0) 94080816-01 was initiated to troubleshoot the problem. ,

The alarm monitor panel was checked for any abnormalities and found to be in good working condition. When a lead wire for the RTD for this channel (1LDRD5630) was lifted and reterminated, temperature indication immediately dropped to the pre-start reading of 160 F. The engine was restarted (start #1035) and temperature for main bearing #5 immediately increased past the trip point and the engine automatically tripped.

In order to isolate the RTD as the source of the problem, the lead wires were disconnected from the alarm monitor and then reconnected to test equipment that indicated RTD temperature. A false signal was place on channel 8 of the alarm monitor with a Decade resistance box. The engine ,

was once more started (start #1036) and the test equipment indication immediately increased. The engine was manually shutdown at this point.

Operations tagged the engine in the " Maintenance Mode" and Mechanical Maintenance removed the crankcase door to allow IAE access to the RTD.

The RTD was removed from the bearing and replaced with a new one from stock. The indication on channel #8 now agreed with the other bearing .

temperatures. DG 1A was ran for functional verification (start #1037) I without any problems. The operability performance test (start #1038) was successfully completed and the engine was declared operable on 10/22/94 at j 0540 hours0.00625 days <br />0.15 hours <br />8.928571e-4 weeks <br />2.0547e-4 months <br />.

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SPECIAL REPORT CATAWBA NUCLEAR STATION DOCKET NO. 50-413 DIESEL GENERATOR 1A INVALID FAILURE i DUE TO MAIN BEARING HIGH TEMPERATURE TRIP  !

PIP 1-C94-1495 l 1

The trip for high temperature on the main bearings is not an emergency trip function and sould have been bypassed had an emergency start signal been received. The failure of this RTD would not have affected the engine's ability to start and accept loads had it been needed for a design basis event. Therefore, this event is classified as an invalid failure.

The faileu RTD is a JMS Southeast Model # 3ESBK8"X10YP360. These RTDs were installed per NSMs CN-lll49 (Ul) and CN-20528 (U2) during lEOC6 and 2EOCS outages, respectively. These mods replaced the pneumatic control system with an electrical system on each diesel. There are 10 of these RTDs installed in each DG. This is the first failure since their installation. The failed RTD was sent to JMS Southeast for their evaluation. Their analysis showed that lube oil had entered the RTD sensor which resulted in a high resistance and erratic behavior. It is not yet known whether this is an isolated case or a generic problem. A survey of the other DG bearing temperatures has been performed. DG 2B had 2 channels that were indicating temperatures that did not appear to be correct. W/Os 94068192-01 and 94081546-01 have been initiated and scheduled to replace these RTDs prior to the next DG 2B run. The RTDs will be sent to JMS Southeast for their further analysis of this prriblem.

All other indications were satisfactory.

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