ST-HL-AE-4262, Special Rept:On 921014,Standby Diesel Generater 12 Shed Load to 0 Kw Due to Failure of Swing Disk Check Valve in Fuel Supply Line.Damaged Check Valve Replaced & Internals Removed.Remaining Check Valves Inspected

Special Rept:On 921014,Standby Diesel Generater 12 Shed Load to 0 Kw Due to Failure of Swing Disk Check Valve in Fuel Supply Line.Damaged Check Valve Replaced & Internals Removed.Remaining Check Valves Inspected

ML20116K566
Person / Time
Site:	South Texas
Issue date:	11/12/1992
From:	Jump W HOUSTON LIGHTING & POWER CO.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
ST-HL-AE-4262, NUDOCS 9211170256
Download: ML20116K566 (5)

Text

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O The Light company llouston Lighting & Power yout WetaiProintI ntric GenuadngStadon P.Ofos289 -Wadywonh,]cxn 77{83 November 12, 1992 ST-IIL-AE-4262 File No.: G02 10CFR50 U. S. Nuclear Regulatory Commission r Attention: Document Control Desk Washington, DC 20555 South Texas Project Unit 1 Docket No. STN 50-498

-Special Report Regarding a Valid Failure of Standbv Diesel Generator 12 on October 14, 1292 Pursuant to the South Texas Project Electric Generating Station (STPEGS) Technical Specifications 4.8.1.1.J and 6.9.2, Houston Lighting & Power submits the attached Special Report regarding a valid failure of Standby Diesel Generator 12 which occurred on October 14, 1992.

If you should have any questions on this matter, please L contact Mr. C. A. Ayala at (S12) 972-8628 or me at

(512) 972-7205.

h William J. Jum General Manager, Nuclear Licensitig MAC/ag

Attachment:

Special Report Regarding a Valid Failure of SDG 12 on October 14, 1992 l

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• Houston Lighting & Power Company .. ST-HL-AE-4262 South Texas Project Electric Generating Station - pile.No. G02 Page- 2 L cc Regional Administrator, Region IV Rufus'S. Scott Nuclear Regulatory Commission Associate General Counsel 611 Ryan Plaza Drive, Suite 400 Houston Lighting & Power Company Arlington, TX 76011 P. O. Box 61867 Houston, TX 77208 George Dick, Project Manager.

U.S. Nuclear Regulatory Commission INPO

Washington, DC 20555 Records Center l 1100 Circle 75 Parkway Tapia J. I. Atlanta, GA 30339-3064 Senior Resident Inspecter c/o U. S. Nuclear Regulatory Dr. Joseph M. Hendrie Commission- 50 Bellport Lane P. O. Box 910 Bellport, NY 11713 Bay City, TX 77414 D. K. Lacker J. R. Newman, Esquire Burea11 of Radiation Control Newman & Holtzinger, P.C. Texas Department of Health 1615 L Street, N.W. 1100 West-49th Street Washington, DC 20036 Austin, TX 78756-3189 D. E. Ward /T. M. Puckett Central Power and Light Company P. O. Box 2121 Corpus Christi, TX 78403 J. C. Lanier/M. B. Lee City of Austin 4 Electric Utility Department l P.O. Box 1088 Austin, TX 78767 K. J. - Fiedler/M. T. Hardt City Public Service Board-P. O.-Box 1771 San Antonio, TX 78296 s

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i Revised 10/11/91- ,

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Attachment ST-HL-AE-4262' Page 1 of 3 South Texas Project Unit 1 Docket No. STN 50-498 Special Report Regarding a Valid Failure of Standby Diesel Generator 12 on October 14. 1992 DESCRIPTION OF EVENT:

On October 8, 1992, prior to the October 14, 1992 event, Standby Diesel Generator (SDG) 12 was operating in steady state at 5500 kW for a post-maintenance run, when the diesel shed approximately a 3500 kW load. After operating several minutes at reduced load, the operators tripped the engine since they were unable to reduce'the speed. It was observed that the governor called for full fuel and that the exhaust temperatures were unbalanced. Initial troubleshooting was conducted finding no apparent problem. The engine ran satisfactorily on October 12.

On October 14, 1992, at 0138 SDG 12 was loaded to 2000 kW in accordance with procedure 1 PSP 03-DG-0020, Standby Diesel 12 Test Mode Override Verification. After a few seconds, SDG 12 shed its load to 0 kW.- The output breaker was opened. Engine speed became erratic with frequency increasing to 61.5 hertz then decreasing to 58.5 hertz. The SDG was then emergency-stopped from the control room since the speed could not be controlled.

After the failed surveillance test, the SDG 12 was instrumented with test equipment to monitor various parameters.

The engine was started and again shed its load from 2000 kW to 0 kW without operator action. Personnel monitoring the performance-noted that the governor drove the fuel rack to the maximum fuel position. Based on monitoring the fuel oil pressure in the manifolds, the test pressure transducers indicated an abrupt increase in pressure upstream of check valve DO-3292 in the fuel oil feed line, simultaneously with a rapid (but not instantaneous) decrease in_the right and left bank header-pressures. It was concluded that check valve DO-3292 which' supplies fuel oil may have degraded and blocked the fuel oil

-flow.

The check valve DO-3292 was removed and disassembled revealing that the nut which secures the disk to the swing hinge had backed completely off. The disk was loose in the valve body.

The nut was recovered in the left bank fuel oil manifold piping.

The stud which joins the disc to the hinge is split to allow for l mechanical locking but this locking device had not been utilized,

thus allowing the nut to back-off. The other two similar check l

valves in the fuel oil piping on this engine were also disassembled and determined to be in the as-designed condition.

SRIP\92-307.001

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.7 s-Attachment ST-;IL-AE-4262 Page.2.of 3-

- CAUSE OF EVENT:

The cause of this event was due to the failure'of a swing disk check valve in the fuel supply line. A contributing'cause' was the bolt locking device which was not1 utilized to secure 1the disk in place. The SDGs were apparently supplied'by the' vendor without these check valve disk locking mechanisms utilized.

ANALYSIS OF EVENT:

In the subject failure, it is concluded that the. load-  !

shedding in all three cases was due to partial or complete fuel:

oil blockage caused by the loose check valve disk in the valve' body. Because the disk was loose, it is likely that the flow' interruption was intermittent as evidenced-by periods-of~

satisfactory operation between load shedding events.

This event ic~significant in that if-the DG-were: challenged, it would not have been able to perform its-safety. function since it was unable to carry load. . As such, this event'is reportable-as a valid failure.. .The testing-frequency'for the DGLwillLremain at once every 31 days since the number of failures in the last 20 j valid tests is'1, and the number of failures in the last 100L  !

valid tests is less than'4. 1 CORRECTIVE ACTIONS:

1. The damaged check valve was replaced and-the internals were'-

removed. (Note: .The-check valve. serves no useful function at1 South Texas Project:because-the elevation'of:the fuel. oil tank is sufficient to' ensure a;positiveJhead to the. fuel-injector pump.) -The.-engine started and loaded successfully.

-No anomalies were' observed inl'the fuel' oil system.-

2. 'The remaining SDGs' fuel oil feed 1line-~ check valves . in both units were inspected and the internals were also removed:as a conservative precaution. The inspection' revealed that the check valve studs were not split to lock'the nut.in place',

however, the nuts.were securely-holding,.the. disks.

-3. The other two-similar check valvesLon the fuel' oil' feed-lines on each SDGs1in both units were 1 inspected to verifyl proper: operation. It isinoted that-the retaining nut on-one-of SDG 21 check valves'wasifound cracked-but still intact.

This condition:did=not: adversely impact. operation'of1the:

disk. The nut was replaced. No other problems 1were found' with the remaining check valves that were inspected.

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ST-HL-AE-4262 Page 3 of 3

. CORRECTIVE ACTIONS: (Con't)

4. Cooper Bessemer was notified of the concern related to.the .

check valves. In addition, the check valve issue was placed on Nuclear Network.

ADDITIONAL INFORMATION:

The check valve that failed is Cooper-Bessemer part number 2-01V-418-03 and it was manufactured by Stockham, Model B319.

A search of the NPRDS database for a Stockham model B319 swing check valve was conducted. There were no reported failures for this model number.

SREPiO2-307.001