ML20079D685

Special Rept:On 910625,Unit 1 Diesel Generator a Invalid Failure Occurred During Maint Testing.Temporary Instrumentation Installed Observing Various Pneumatic Pressures & Troubleshooting Start Conducted

ML20079D685
Person / Time
Site:	Catawba
Issue date:	07/18/1991
From:	Tuckman M DUKE POWER CO.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
NUDOCS 9107240074
Download: ML20079D685 (3)

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{) ountpowen July 18,1991 U. S. Nuclear Regulatory Commission A1TN: Document Control Desk Washington, DC 20555

Subject:

Catawba Nuclear Station, Unit 1 Docket No. 50-413 Special Report invalid Failure of Diesel Generator l A Pursuant to Technical Specification 4.8.1.1.3 and 6.9.2, find attached a Special Report concerning the Unit 1 Diesel Generator A (D/G 1 A) invalid failure that occurred on June 25, 1991.

Very truly yours,

, S' W M. S, Tuckman CRIJSR71691 Attachment xc: S. D. Ebneter Regional Administrator, Region 11 W. T Orders Senior Resident inspector R. E, Martin, ONRR 9107240074 910710 PDR fiDOCr. OnOO v

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SPECIAL RiiPORT [

CATAW11A NUCLEAR STATION Dil!SEL GENERATOR l A INVALID FAILURE DUli TO FAILURil OF PNEUM ATIC COMPONiiNTS An invalid failure occurred on diesel generator (D/0) 1 A on June 25, 1991 during the investigation of an intermittent actuation of non emergency trip annunciators !! 7 (high  ;

pressure crank case) and 118 (vibration). At the time of the invalid failure, start No. 906, i Unit I was in a plant status of Mode 1. The invalid failure occurred during Maintenance testing. D/O 1A was on a monthly operability test schedule at the time of this invalid failure. There have been 0 valid failures in the past 20 valid starts and 0 valid failures in the past 100 valid starts for D/G 1A. Diesel generator I A was unavailable for approximately 7 hours8.101852e-5 days <br />0.00194 hours <br />1.157407e-5 weeks <br />2.6635e-6 months <br />,  !

While completing the functional nm after maintenance, several non-cmergency inp annunciators alarmed and immediately cleared. A work request was written to investigate the sporadic annunciator actuations.

Temporary instrumentation was installed to observe various pneumatic pressures and a troubleshooting start (#906) was conducted. The test indicated that the pneumatic control devices were not fully charging. Approximately 1 minute into the start, the diesel generator shut down when control air pressure was not established at the normal value of F 60 psi.

IAE inspected and tested the non cmergency pneumatic shutdown sensors in scarch of a possible fault that would have caused the engine to shutdown. They found the No. 4 main bearing sensor slowly leaking, The engine mounted left bank vibration sensor was also found slowly leaking. These leaking sensors prevented the system from pressurizing L because they were continually venting.

No other abnormal system configurations were found.

l The No. 4 main bearing sensor was inspected, it had not tripped but it had drifted and was l

causing the air to leak out to atmosphere. A new bearing sensor was drawn from spares, tested and installed into the main bearing.

Because of previous bearing sensor problems with creep (drifting) caused by aging and temperature, and some factory mis set sensors, all Unit I and Unit 2 main bearing sensors l were changed out with new sensors during IEOC4 and 2EOC3, All new sensors were l tested by IAU prior to their instaliation. This replacement of all main bearing sensors was done to provide better availability and reliability for non-emergency operations. During an emergency operation or demand, these sensors are bypassed and the diesel generator will support all Tech Spec required loads. ,

The engine mounted left bank vibration sensor was replaced with a new one from spares.

The replaced sensor was inspected and evidence of internal debris was present. This was an original installation sensor having more than 900 start pressure cycles and more than

, 1530 operating hours. The leakage is attributed to internal contamination with foreign debris. The vibration sensor trips are also bypassed on an emergency start.

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After maintenance, the diesel generator was started for testing and successfully completed the test run.

Operations then performed the Operability irr and declared the diesel generator ,

" Operable".  ;

During IEOC6 and 21IOC5 the non emergency trip functions will be replaced with an electronic system.

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