ST-HL-AE-3901, Forwards Response to Generic Ltr 91-06, Resolution of Generic Issue A-30, 'Adequacy of Safety-Related DC Power Supplies.' Facilities Do Not Have Battery Charger Failure Alarms

Forwards Response to Generic Ltr 91-06, Resolution of Generic Issue A-30, 'Adequacy of Safety-Related DC Power Supplies.' Facilities Do Not Have Battery Charger Failure Alarms

ML20085L549
Person / Time
Site:	South Texas
Issue date:	10/28/1991
From:	Rosen S HOUSTON LIGHTING & POWER CO.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
REF-GTECI-A-30, REF-GTECI-EL, TASK-A-30, TASK-OR GL-91-06, GL-91-6, ST-HL-AE-3901, NUDOCS 9111040224
Download: ML20085L549 (5)

Text

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The Light c o m p a ny '""d' l " "'I"' I I""i' """I"" *'"" "'I'"'# * * 'I ' " "' d " I " * ' * " '

licuston 1.ighting A Power October _8, 1991 ST-llL- AE- 3901 Fila l;o . G03.08 10.TR50. 54 U. S. Nuclear Regulatory Commission Attention: Docuraent Control Desk Washington, DC 20555 _

South Texas Project Elect ric Generating Station Units 1 and 2 Dockets No. STN 50 498 and 50 499 Bupans e t o Gene r ic Le t t e r 91 - 06 ,

Houston Lighting & Power Company (IllAP) has cottpleted the requestec' response to questions concerning adequacy of safety-related DC power supplies as directed in NRC Ceneric Letter 91-06. Attached is lilAls response to Generic Letter 91-06.

If you should have any questions concerning this matter, please contact Mr . W . J . J ump a t (512) 972-7205.

S. L. Rosen _

Vice President, Nuclear Engineering AMR/sgs

Attachment:

Response to Generic Letter 91-06

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South Teus Project Electric Generating Station Page 2 of 4 cC; Regional Administrator, Region IV Rufus S. Scott Nuclear Regulatory Commission Associate General Counsel 611 Ryan Plaza Drive, Suite 400 llouston Lighting & Power Company Arlington, TX 76011 P. O. Box 61667 llouston, TX 77208 George Dick, Project Manager U.S. Nuclear Regulatory Commission INPO Washington, DC 20555 Records Center 1100 circle 75 Parkway J. 1. Tapia Atlanta, CA 30339-3064 Senior Residant inspector c/o U. S. Nucitar Regulatory Dr. Joseph M. llendrie Commission 50 Bellport 1;ute P. O. Box 910 Bellport, NY 11713 Bay City, TX 77414 D. K Lacker J. R. Newman, Esquire Bureau of Raulation Control Newman & lloltzinger, P.C. Texas Department of llealth 1615 L Street, N.W. 1100 West 49th Street Washington, DC 20036- Austin, TX 78756-3189 D. E. Ward /T. M. Puckett Central Power anC Light Company P, O. Box 2121 Corpus Christi, TX 78403 J. C. Lanier/M. B. Lee City of Austin Electric Utility Department P.O. Box 1088 Austin, TX 78767 K. J. Fiedler/M. T. liardt City P"blic Service Board P. O. box 1771 San Antonio, TX 78296 Revised 10/11/91 L4/NRC/

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Attachment

• ST-llL AE 3901 Page 3 of 4 RESPONSE TO GENERIC LETTER 91-06 As directed in Generic Letter 9106, South Texas Project Electric Generating Station (STPEGS) is responding to the questions presented concerning resolution of Generic lasue A-30, " Adequacy of Safety Related DC Power Supplies." STPEGS is a two unit plant and the responses to the provided 1 questions are the same for each unit, l i

There are four independent redundant divisions of Class IE or safety related DC power for each unit at STPEGS. Two functional safety related divisions of DC power are necessary to attain safe shutdown of ]

each unit. The control rooms of each unit have the following separate, '

independently annunciated alarms for each division of DC power:

e Battery disconnect or circuit breaker open,

• Battery charger disconnect or circuit breaker open (both input AC and output DC),

• DC system ground,

= DC bus undervoltage, ano overvoltage There are also the following separate, independently annunciatad indications in the control rooms of each unit for each division of DC power:

• Battery float charge current,

• Battery circuit output current, and

• Bus voltage.

Each unit at STPEGS has written procedures for response to the above alarms and indications.

STPECS does not have battery charger failure alarms. The shared load by the '

battery chargers results in a very low normal current compared to the rated current. An alarm provided in the original design was overly sensitive to l small fluctuations in this current, which resulted in a high rate of spurious L alarms. The alarm was consequently taken out of service in 1987. Weekly i surveillances are performed that require charger current to he checked to assure charger operability. Other system failure alarms also provide adequate-indication of problems.

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.Th ere are no al arms or indications for battery discharge as noted in the response to Question 430.35N of the STPEGS Updated Final Safety Analysis Report. Briefly, the response to Question 430.35N states that the discharge rate of the battery varies with time, so an overcurrent setting on the sensing device cannot be provided without generating nuisance alarms. The DC bus voltage indicator in the control room, supplemented by the DC bus undervoitage alarm, provides adeque ce information to the operator regarding battery status.

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• ST -llL- AE- 3901 Page 4 of 4 RESPONSE TO GENERIC LETTER 91-06 Both units at STPEC3 have indication of bypassed and inoperable status of circuit breakers or other devices that can be used to disconnect the battery and battery charger from its DC bus and the battery charger from its AC power source during maintenance or testing. A review of maintenance and terting activities to minimize the potential for human error causing more than one DC division to be unavailable is not necessary. Plant Operations Department utilizen an Operabilit, i>seking 1.og (governed by plant procedure) which pros: des guidelines for the - mking of activities that could render any safety related components or equipment inoperable. Also, plant procedures prohibit maintenance or testing on redundant DC 61vlsions at the same time.

The STPEGS Units 1 and 2 Technical Specificati ins have provisto is equivalent to those found in the Vestinghouse Str.ndard Technical Specifications for maintenance and surveillance. Therefore, no response is necessary to the questicus conce rning survel) lance and testing inter, als, STPEGS docs bave operatiotal features such that following le a= cf one safety-tolated DC potier supply >r bus, capa#111ty t is maintained for ensuring continued and adequate reacter cooling, and toactor coolant system integrity and isolatien capabi' ' y sre maintained. Also, operating procedures, instrumentation (including indicators and annunciators), and control functions are adequate t r. Initiate systems as required to maintain adequate core cooling.

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• File No.: 003,08 i

NUCLEAR REGULATORY COMMISSION In the Matter )

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llouston Lighting & Power ) Docket Nos. 50-498 Company, et al., ) 50-499

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South Texas Project )

Units 1 and 2 )

AFFIDAVII S. L. Rosen being duly sworn, hereby deposes and says that he is Vice President, Nuclear Ensincering, of Houston Lighting & Power Company; that he is duly authorized to sign and file with the Nuclear Regulatory Commission the attached response to NRC Ceneric Letter 91-06; is familiar with the content thereof; and that the matters set forth therein are true and correct to the best of his knowledge and belief, b M S. L. Rosen Vice President Nuclear Engineering Subscribed and sworn to before me, a Notary Public in and for The State of Texas this M'ZA day of CF 1991.

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