ST-HL-AE-2512, Special Rept:On 880116 & 880205,two Diesel Generator Nonvalid Failures Occurred.Caused by Failure of Diaphragm in Test Mode Trip Pilot Valve N1DG-PV-5577A.Investigation Into Cause of Failure Being Conducted.Next Rept by 880404

Special Rept:On 880116 & 880205,two Diesel Generator Nonvalid Failures Occurred.Caused by Failure of Diaphragm in Test Mode Trip Pilot Valve N1DG-PV-5577A.Investigation Into Cause of Failure Being Conducted.Next Rept by 880404

ML20149J233
Person / Time
Site:	South Texas
Issue date:	02/16/1988
From:	Vaughn G HOUSTON LIGHTING & POWER CO.
To:	NRC OFFICE OF ADMINISTRATION & RESOURCES MANAGEMENT (ARM)
References
ST-HL-AE-2512, NUDOCS 8802220322
Download: ML20149J233 (4)

Text

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• The Light company P.O. Box 1700 llouston Texas 77001 (713) 228 9211 llouston Lighting & Power -' - - - - -

Februa ry 16, 1988 ST-HL-AE-2512 File No.: G02 10CFR50.36(c)(5)

U. S. Nuclear Regulatory Commission Attention: Document Control Desk Washington, DC 20555 South Texas Eroject Electric Generating Station Unit 1 Docket No. STN 50-498 Spscial Report Regarding Two Diesel Generator Non-Valid Failures 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 two diesel generator non-valid failures.

The cause of the failure has been attributed to failure of a diaphragm in a test mode trip pilot valve. An investigation into the cause of the failure of the diaphragm is being conducted. A follow-up report will be submitted by April 4, 1988.

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

h. b YM G. E. Vaughn M 6r-Vice President, Nuclear Plant Operations GEV/CAA/bs

Attachment:

Special Report Regarding Two Diesel Generator Non-Valid Failures 8802220322 880216 PDR ADOCK 05000498 S PDR Nt.ee.x2.01 a s h m , - n _ n ins e + ,i _ a P*

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Houston Lighting & Power Company ST-HL-AE-2502 File No.: G26 Page 2 CCI Regional Administrator, Region IV Rufus S. Scott Nuclear Regulatory Commission Associate General Counsel 611 Ryan Plaza Drive, Suite 1000 Houston Lighting & Power Company Arlington, TX 76011 P. O. Box 1700 Houston, TX 77001 N. Prasad Kadambi, Project Manager U. S. Nuclear Regulatory Commission INPO 1 White Flint North Records Center 11555 Rockville Pike 1100 Circle 75 Parkway Rockville, MD 20859 Atlanta, Ga. 30339-3064 Dan R. Carpenter Senior Resident Inspector / Operations e/o U. S. Nuclear Regulatory Commission P. O. Box 910 Bay City, TX 77414 J. R. Newman, Esquire Newman & Holtzinger, P.C.

1615 L Street, N.W.

Washington, DC 20036 R. L. Range /R. P. Verret Central Power & Light Company P. O. Box 2121 Corpus Christi, TX 78403  ;

R. John Miner (2 copies)

Chief Operating Officer City of Austin Electric Utility 721 Barton Springs Road Austin, TX 78704 R. J. Costello/M. T. Hardt City Public Service Board P. O. Box 1771 San Antonio, TX 782c6 Revised 02/03/88 NL.LER. DISTR.1 g -. e--- ---.,r- a + g

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Attachment ST-HL-AE-2512 Page 1 of 2 South Texas Project Electric Generating Station Unit 1 Docket No. STN 50-498 Special Report Regarding Two Diesel Generator Non-Valid Failures DESCRIPTION OF EVENTS:

On January 16, 1988, an Engineered Safety Feature (ESF) auto-start test of Standby Diesel Generator (SDG) #12 was being performed per surveillance procedure 1 PSP 03-DG-0011. At 2221 hours0.0257 days <br />0.617 hours <br />0.00367 weeks <br />8.450905e-4 months <br /> CST, the SDG was started in the emergency mode. When the SDG was released from the emergency mode, the engine '

tripped. A Maintenance Work Request (MVR) was written to investigate the problem but the engine vac not declared inoperable because it had successfully started in the emergency mode. However, work on this problem was not initiated until after the second non-valid failure, described below, which occurred 20 days later. This delay occurred because the nature of the failure did not make the SDG inoperable and it was not recognized that the problem needed to be fixod before the next test required to be preformed on the SDG.

On February 5, 1988, plant operators attempted to perform the monthly operability surveillance on SDG #12, per procedure 1 PSP 03-DG-0002. The engine was started in the emergency mode at 0250 hours0.00289 days <br />0.0694 hours <br />4.133598e-4 weeks <br />9.5125e-5 months <br /> CST, was released from the emergency mode and was loaded to approximately 72% of rated load when the engine tripped. The Unit Supervisor stated that there were no local or Control Room alarms prior to the trip. A local lube oil alarm came in after the trip. The engine was re-started in the test mode at 0320 CST to troubleshoot the lube oil system. The engine started and ran for approximately 5 minutes before tripping. Again there were no alarms prior to the trip and local indications of engine lube oil pressure were normal. An MVR was written to investigate the problem. The operator declared the SDG inoperable at 0806 CST.

The system engineers believed that the absence of alarms indicated the control air reset header was not meintaining adequate pressure to operate in the test mode. I&C technicians were instructed to install temporary pressure gages on the control air reset header and on the air line controlling the test mode safety trip valve (N1DG-PV-5576C). At least 20 psig air pressure must be maintained on the control air reset header to operate in the test mode. The engine was re-started in the test mode at 1122 CST with temporary gages i installed in order to determine the actual pressures in the control air l system. Pressure on the reset heador was seen to drop from about 30 psig to 22 psig within one ranu*.e but the ergine did not trip. The test mode safety trip pilot valve (N1DG-PV-5577A) was leaking air past its diaphragm which caused a pressure reduction in the reset header. A replacement part was installed and the engine was re-started at 1825 CST with temporary gages still installed. (The documentation for this work has not yet been completed.) ,

Reset header pressure was ma11.tained at 37.5 psig, equal to the setting of the l pre.ssure regulator upstream of the trip pilot valve. Temporary gages were removed and a successful operability surveillance was performed between 1911 l and 2026 CST. The SDG was returned to service at 2224 CST. I NL.88.042.01 l

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• ST-HL-AE-2512 Page 2 of 2 When the test mode trip pilot' valve was disassembled, an internal diaphragm was found defective such that it leaked. air. This resulted in a reduced pressure in the rest;t header that was near the setpoint of the trip pilot valve. This condition made the trip pilot valve susceptible to initiating an engine trip whenever a slight pressure fluctuation (reduction) occurred in the non-essential control air system.

The engine was declared inoperable from 0806 to 2224 CST on February 5, 1988. In fact, the SDG would have been able to start and load in the emergency mode because the test mode trip pilot valve is not operative in the emergency mode. For this reason and in accordance with paragraph C.2.e.2 of Regulatory Guide 1.108, these f ailures have been determined to be non-valid.

The two non-valid failures described in this report are the first and second non-valid failures of SDG #12 since fuel load licensing at Unit 1. There have been no valid failures and 12 valid tests of SDG #12 since fuel load licensing. The current surveillance test interval remains, therefore, at 31 days.

ROOT CAUSE Both non-valid failures were caused by the failure of the diaphragm in the test mode trip pilot valve, N1DG-PV-5577A. The cause of the failure of the diaphragm has not been determined.

GENERIC IMPLICATION i

Similar non-valid failures due to malfunction of the test mode trip pilot valve are possible on Unit 1 and Unit 2 SDG's.

CORRECTIVE ACTION An investigation to determine the cause of the diaphragm f ailure is being undertaken. Corrective action will be established based on the results of this investigation. A followup report will be provided by April 4, 1988.

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