ST-HL-AE-4258, Special Rept:On 921007,SDG Tripped on Turbocharger Thrust Bearing Failure.Caused by Improper Installation of New Eutectic or Degradation of Turbocharger.Turbocharger Replaced.Vendor Manual,Drawings & Procedures Revised

Special Rept:On 921007,SDG Tripped on Turbocharger Thrust Bearing Failure.Caused by Improper Installation of New Eutectic or Degradation of Turbocharger.Turbocharger Replaced.Vendor Manual,Drawings & Procedures Revised

ML20116L160
Person / Time
Site:	South Texas
Issue date:	11/13/1992
From:	Jump W HOUSTON LIGHTING & POWER CO.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
ST-HL-AE-4258, NUDOCS 9211180191
Download: ML20116L160 (4)

Text

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a l'ower 33"""""'"aung Stadon l' a Uus W Kadsw o"EI'na* 77m Noveraber 12, 1992 ST-HL-AE-4258 File No.: G02 10CFR50 U. S. Nuclear Regulhtory Commission Attention: Document Control Desk Washington, DC 20555 South Texas Project Unit 1 Docket No. STN 50-498 Special Report Regarding A Non-Valid Failure qf Standby Diesel Generator #12 on October 16, 1992 r Pursuant to the South T( '

. Project (STP) Technical Specifications 4.8.1.1.3 and 6.9.2, Houston Lighting & Power (HL&P) submits the attached Special Report regarding a Standby Diesel Generator #12 non-valid failure which occurred on October 16, 1992.

If you should have any questions on this matter, please contact Mr. C. A. Ayala at (512) 972-8626 rT me at (512) 972-~<205.

j nt. .

William J. Jump General Manager, Nuclear Licensing MKJ/sr

Attachment:

1. Special Re port Regarding A Non-Valid Failure of SDG

1. 12 on October 16, 1992 17~10G 1

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9 11 utton L!ghting & Power Company ST-HL-AE-4258 South Texas Project F.lectric Genciating Station File-No.t 002 Page 2 Cet Regional Administrator, Region IV Rufus S. Scott Nuclear hogulatory Commission Ase >ciato General Counsel 611 Ryan Plaza Drive, Suite 400 Houston Lighting & PoWor Company Arlington, TX 76011 P. O. Box 61867 i Houston, TX 77208 George Dick, Project Manager U.S. Nuclear Regulatory Commission INPO Washington, DC 20555 Records Centar 1100 circle 75 Parkway J. I. Tapia Atlanta, GA- 39339-3064 Senior Resident Inspector j c/o U. S. Nuclear Regulatory Dr. Joseph H. Hondric  !

Commission 50 bellport Lane P. O. Box 910 Bollport, NY 11713 Bay City, TX 77414 D. K. Lacker l J. R. Newman, Esquire Bureau of Radiation Control i

' Nowman & Holtzinger, P.C. Texas Department of Health -

1615 L Stroct, N.W. 1100 West 49th Street -1

- Washington, DC 20036 Austin, TX 78756-3189 D. E. Ward /T. M. Puckett l Contral Power and Ljght Company .

P. O. Box 2121 Corpus Christi, TX 78403 J. C. Lanicr/M. B. Leo '

City of ,,ustin Electr4c Utility Department P.O. Box 1088 .;

Austin, TX 78767

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K. J. Fiodler/M. T. Hardt City Public Service Board P. O. Box 1771  :

San Antonio, TX 78296 t

Povised- 10/11/91 L4/NRC/

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ST-HL-AE-4258 page 1 of 2 l South Texas project l Unit 1  ;

Docket No. STN 50-498 i Special Report Hegarding A Non-Valid l Failure of Standby Diesel Gerlplator #12 on October 16< 1992 DMOHEHON OF EVENT:

l On October 7, 1992 at 0057 hours6.597222e-4 days <br />0.0158 hours <br />9.424603e-5 weeks <br />2.16885e-5 months <br />, Standby Diesel Generator (SDG) ]

/12 had been st- ed for a fivo hour maintenance run. The SDG was l loaded incremently to 100 percent. The SDG tripped at 0456 hours0.00528 days <br />0.127 hours <br />7.539683e-4 weeks <br />1.73508e-4 months <br /> -

on a turbochargue thre. bearing failure. The actual thrust l clearance was verified und found to be acceptable However, during troubleshooting the eutectic was found to be tripped and was subsequently replaced in accordance with procedural guidsnce.

On October 16, 1992, Unit 1 was in no modo during a refueling outage. SDG #12 was started in the emergency mode at 0156 hours0.00181 days <br />0.0433 hours <br />2.579365e-4 weeks <br />5.9358e-5 months <br /> and loaded to perform the surveillance procedure for the 24 hour2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> load test. After being released from the emergency mode SDG #12 tripped at 0205 hours0.00237 days <br />0.0569 hours <br />3.38955e-4 weeks <br />7.80025e-5 months <br />. The locsl annunciator indicated a failed >

turbocharger thrust bearing. The cutoctic was again identified as a problem. The instructions for catting the eutectic were modified to add a tolerance to the clearance by 1/8 turn with the on-site Cooper-Bessemer representative concurrence. The catectic was then i replaced utilizing the modified clearance. This event wan l classified as a non-valid failure.

The turbo thrust bearing failure trip is actuated by a entectic installed in the turbocharger air inlet end bearir.g cap. If the turbo thruct bearing clearance is excessive, then the' impeller nut i

will induce friction on the end of the outectic, heating and l melting the alloy. The molting alloy allows control air to be l dumped from the uafety trip valve, tripping the engine thus providing protection for the turbocharger.

i On October 17, 1992, at 0420 hours0.00486 days <br />0.117 hours <br />6.944444e-4 weeks <br />1.5981e-4 months <br /> SDG #12 was started in the non-l emargency modo to verify proper function prior to'the 24 hour2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> run.

i The SDG was taken to 110 percent full load for a load test on the turbo thrust bearing trip. At 0642 hours0.00743 days <br />0.178 hours <br />0.00106 weeks <br />2.44281e-4 months <br /> SDG #12 was placed in the cooldown cycle. Approximately two minutes into the cooldown cycle,

! the SDG tripped on turbo thrust bearing failure. 'The ff-site Cooper-Bessemer factory expert was contacMd ann he d wied a request for any further increase in the outectic setting. In order

.to assure resolution of the ongoing problems with the turb> charger thrust bearing and to allow continued progress on the SDG work, a-management decision was made to replace the turbocharger. The l

turbocharger has been sent off-site for a failure analysis.

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ST-HL-AE-42Sd Page 2 of 2 Cit %E 0F.12L1L :

The cause of tuo trips that occurred on October 7, 1992 and October 36, 1992, is suspected to be due tc improper installation of the new outectic or degradation in the turbocharger allowing the rotor to actuate the trip por design. The October 17, 1992, trip l j

may be due to a defective eutectic. Inspection of the eatectic indicated a small pinhole leak. Since there is minimal thrust on-the turbocharger rotor during the cooldown cycle and the leak was so omall, a defective eutectic was suspected. Further failure analysis of the turbocharger will be conducted to determine if a-.

degradation of the turbocharger contributed to this event.

MMLYSIS.0F EVENT:

This incident is classified as a non-valid failure since the SDG operated satinf actorily in the emergency mode Lnd if challonged would have perf ormed its safety function. The turbo thrust bearing failure trip is bypassed in the emergency mode.

CQ@ECTIVE ACTIONS:

1. The vendor manual, appropriate drawings and procedures will be revised to reflect tolerances associated with setting the outmtic clearance. Copper-Bessemer has agreed to allow P. toed tolarances for the eutectic setting. This will be r" 1a ted by December 15, 1992.

2. 'o? . owing the third trip on October li, the turbocharger was

Aace.d. A failure analysis will be conducted on the turbocharger and will be completed by January 28,_1993.

ADDITIONAL INFORMATIOll:

Per STPEGS Technical Specificatica 4.8.1.1', there has been 1 valids >

failure in the last 20 valid tests of SDG 12.- The number of valid.

failures:within the_last 100 valid tests.is less than or equal to -

4. Therefore, the testing frequency for SDG 12 re.nains at once per 31 days.

SKEP\97-306,001

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