ST-HL-AE-3070, Ro:On 890329,standby Diesel Generator 13 Tripped.Caused by non-emergency Mode Shutdown Circuit.Test Mode Control Valve Will Be Replaced During Next Train Outage Currently Scheduled for 890522

Ro:On 890329,standby Diesel Generator 13 Tripped.Caused by non-emergency Mode Shutdown Circuit.Test Mode Control Valve Will Be Replaced During Next Train Outage Currently Scheduled for 890522

ML20245J672
Person / Time
Site:	South Texas
Issue date:	04/28/1989
From:	Vaughn G HOUSTON LIGHTING & POWER CO.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
ST-HL-AE-3070, NUDOCS 8905040218
Download: ML20245J672 (3)

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The Light company' P.O. Box 1700 liouston, Texas 77001 (713) 228 9211 Ilouston Lighta.ng8e Power _ - - - . _ . . . _ _ - . r m April 28,1989 ST-HL-AE-3070 File No.: G02 10CFR50.36(c)(5) r U. S. Nuclear Regulatory Commission Attention: Document Control Desk Washington, DC 20555 ,

South Texas Project Electric Generating Station Unit i Docket No. STN 50-498 Special Report Regarding A Nonvalid Failure of #13 Standby Diesel Generator on March 29, 1989 Pursuant to the South Texas Project Electric Generating Station Technical Specifications 4.8.1.1.3 and 6.9.2, Houston Lighting & Power submits the attached Special Report regarding a nonvalid failure of the #13 Standby Diesel Generator on March 29, 1989.

If you should have any questions on this matter, please contact l Mr. C. A. Ayala at (512) 972-8628.

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G. E. Vaughn Vice President Nuclear Operations GEV/BEM/n1

Attachment:

Special Report Regarding A donvalid Failure of #13 Standby Diesel Generator on March 29, 1989

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8905040218 890428 PDR ADOCK 05000498 1 g PDC QY NL.89.075.01 A Subsidiary of Houston Industries incorporated ,

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, llouen Lighting & Power Company Attachment ST-HL-AE-3070 Page 1 of 2 South Texas Project Electric Generating Station Unit 1 Docket No. STN 50-498 Special Report Regarding A Nonvalid Failure of #13 Standby Diesel Generator on March 29, 1989 DESCRIPTION OF EVENT:

On March 29, 1989, Unit 1 was in Mode 1 at 100% Reactor Power. At 2119 hours0.0245 days <br />0.589 hours <br />0.0035 weeks <br />8.062795e-4 months <br /> Standby Diesel Generator (SDG) #13 was started t- demonstrate operability as required by Technical Specification 4.8.1.1.a.2 because SDG #11 was inoperable. It attained rated speed and voltage within ten seconds as required. Approximately one minute later it tripped when released from the

" emergency mode". No alarms were present which would have indicated an emergency mode trip.

Troubleshooting was performed to identify the cause of the trip. Since the

" Master Trip Circuit" light was on at the local control pane 1< the trip was determined to have been caused by the non-emergency mode shutdown circuit. In the emergency mode, non-emergency trips are bypassed. Operations personnel conducted checks on engine systems and verified that there were no abnormal conditions present which could have caused the trip. The engine was started again at 2134 hours0.0247 days <br />0.593 hours <br />0.00353 weeks <br />8.11987e-4 months <br /> on March 29, 1989 for further troubleshooting. The SDG started normally and did not trip when released from the " emergency mode".

There have been three previous non-valid failures of SDG 13 which had no obvious cause. As a result of the first two failures, three valves in the control air system were replaced in an attempt to prevent recurrence. These three valves belong to a group of four valves whose misoperation could result in the symptoms observed during this event. The remaining " Test Mode Fuel Control Valve" has not been replaced since this group of non-valid failures began to occur. A review of non-valid failures on other SDG's identified that a similar valvs was the source of a previous trip on SDG 12. The three previous non-va?.id failures on SDG 13 have also occurred on the first attempt to release the SDC from the " emergency mode". Subsequent transfers have been successful. Therefore, it is believed that the " Test Mode Fuel Control Valve" may be sticking and freeing up after the initial attempt to transfer the SDG to the " Emergency Mode". At the time of this event, corrective action identified from the third non-valid failure had not yet been implemented.

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l NL.89.075.01

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lipuston Lighting & Power Company Attachment ST-HL-AE-3070 Page 2 of 2 CAUSE OF OCCURREliCE:

T! a most probable cause of this nonvalid failure is sticking of the " Test Mode

. "ontrol Valve".

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ANALYSIS OF EVENT:

This event occurred as a result of a trip which is bypassed in the emergency mode. Per the criteria in Regulatory Guide 1.108, this event has been classified as a non-valid failure. In the event of an actual challenge of the SDG, it would have performed its safety function without tripping.

CORRECTIVE ACTION:

As identified in letter ST-HL-AE-3032, dated March 29, 1989, the " Test Mode Fuel Control Valve" will be replaced during the next train outage which is currently scheduled for May 22, 1989.

ADDITIONAL INFORMATION:

Per the criteria of Regulatory Guide 1.108, the failure described in this report has been classified as a nonvalid failure. As such, the test interval for SDG 13 remains at 31 days. There have been 32 valid tests performed on SDG 13 since receipt of the Unit 1 Operating License. There have been no valid failures.

NL.89.075.01.

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