ML20086D066

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Special Rept:On 911019 & 20,invalid Failures of Diesel Generator 2A Occurred When High Vibration Trip Signal Received.Caused by Hole in Tubing Line to Left Front Engine Vibration Sensor.Pneumatic Control Sys Will Be Replaced
ML20086D066
Person / Time
Site: Catawba Duke Energy icon.png
Issue date: 11/14/1991
From: Tuckman M
DUKE POWER CO.
To:
NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
NUDOCS 9111250229
Download: ML20086D066 (3)


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DUKE POWER November 14, 1991 l

U. S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, DC 20535

Subject:

Catawba Nuclear Station, Unit 2 Docket No. 50-414 Special Report Invalid Failure of Diesel Generator 2A Pursuant to Technical Specification 4.8.1.1.3 and 6.9.2, find attached a Special Report concerning the five Unit 2 Diesel Generator A (D/G 2A) Invalid failures that occurred on October 19 and 20,1991.

Very truly yours, I,S W

M. S. Tuckman Vice President Catawba Nuclear Generation Department CRL/DG2A1114.91 Attachment xc:

S. D. Ebneter Regional Administrator, Region 11 W. T. Orders Senior Resident Inspector R. E. Martin, ONRR 911.1200229 411114 P DF<

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SPECIAL REPORT CATAWBA NUCLEAR STATION DIESEL GENERATOR 2A INVALID FAILURE DUE TO CONTROL AIR TUBING LEAK Five invalid failures (start attempt #'s 679, 680, 684, 685, and 686) of Diesel Generator (D/G) 2A occurred on October 19 and 20,1991. Unit 2 had just started its 2EOC4 refueling outage and D/G 2A was in the process of its Technical Specification required 24 hour2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> run when these invalid failures occurred. D/G 2A was on a weekly test frequency at the time of these failures.

There have been 2 valid failures in the last 20 valid tests and 4 valid failures in the last 100 valid tests on D/G 2A..b the time of these failures, Unit 2 was in Mode 5. Catawba Technical Specifications require that only one D/G be cperable during Mode 5.

Since D/G 2B was operable, the 2A D/G was not required.

Therefore, there is no unavailability time associated with these failures. D/G 2A remains on a weekly test frequency as a result of these invalid failures.

At 0046 hours5.324074e-4 days <br />0.0128 hours <br />7.60582e-5 weeks <br />1.7503e-5 months <br /> on October 19,1991, D/G 2A was approximately 20 hours2.314815e-4 days <br />0.00556 hours <br />3.306878e-5 weeks <br />7.61e-6 months <br /> into the 24 hour2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> run (start attempt #679) when a 111 Vibration trip signal was received.

The fuel oil supply for the D/G had been swapped from tank 2A2 to tank 2A1 shortly before the trip occurred. An inspection of the Day Tank, filters and strainers was performed and small amounts of water were discovered. This lead the personnel present to believe that this could have caused the vibration signal and subsequent engine trip.

Further investigation and maintenance was performed to ensure there was a completely water-free system. After this was completed, the engine was restarted (start attempt # 680) at 1800 hours0.0208 days <br />0.5 hours <br />0.00298 weeks <br />6.849e-4 months <br /> on October 19, 1991. Once again the engine tripped on 111 Vibration. Operations initiated Work Request 495340PS-1 for the Instrumentation And Elec'rical Section (IAE) to investigate.

Several starts were required for IAE's troubleshooting purposes to pinpoint the cause of the trip. Three of these starts resulted in invalid failures (start attempt #'s 684, 685, and 686). IAE discovered that the tubing line to the Left Front Engine Vibration Sensor had a hole worn in it.

This section of tubing was replaced and the engine was restarted without incident.

The D/G pneumatic control system functions to trip the engine when certain engine parameters exceed their normal values. This is accomplished by the individual sensors venting the pressure from their control air tubing lines when their setpoints are reached.

The tubing line to the left front sensor had apparently been in contact with a piece of vibrating piping beneath it. Over a long period of time this caused a section of the tubing line to wear thin and eventually wear through during the 24 hour2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> run. The hole in the tubing was approximately 3/64" in diameter which would allow enough air to escape the tubing line to initiate a trip. Illgh Vibration trip, like all the other pneumatic trips, ate only active on a non-emergency start. The emergency trip functions, 1o-10 lube oil pressure and overspeed, that were originally pneumatic have already been replaced with electronic devices per NSM #'s CN-11104 (Unit 1) and CN-20486 (Un.it 2). There have been no other incidents of tubing lines wearing through on the D/G's because of vibratory contact. W/R's 5074-5077MES were written to inspect the control tubing lines on D/G's 1 A, 1B, 2A and 2B,

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'respectively, to ensure no similar problems are developing. During 1EOC6 and 2EOC5' outages-the entire pneumatic control' system will be replaced with an electronic system per NSM's CN-11149-(Unit 1) and CN-20528 (Unit 2),

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