ML20043G179

LER 90-009-00:on 900512,incorrect Wiring in Solid State Protection Sys Discovered.Caused by Inadvertent Installation of Extra Wire by Mfg.Extra Wire Removed & Sys Successfully tested.W/900613 Ltr

ML20043G179
Person / Time
Site:	South Texas
Issue date:	06/13/1990
From:	Ayala C, Vaughn G HOUSTON LIGHTING & POWER CO.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
LER-90-009, LER-90-9, ST-HL-AE-3487, NUDOCS 9006190148
Download: ML20043G179 (6)

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The Light i

compting Houston Lig & Powera ny South Texas Project P. O. BoaElectric Generetlog 289 Wadsworth. Tenni 77483 St I

i June 13, 1990 l ST llL AE*3487 I File No.: G26 1 10CFR50.73 U. S Nuclear Legulatory Commission Attention: Document Control Desk Washington, DC 20555 South Texas Project Electric Generating Station-Unit 2 Docket No. STN 50 499 Voluntary Licensee Event Report 90 009 Regarding Discovery of Incorrect Firint in the Solid State Protection System Pursuant to 10CFR50.73, Houston Lighting & Power Company (lilAP) submits the attached Voluntary Licensee Event Report (LER 90 009) regarding Discovery of Incorrett Wiring in the Solid State Protection System. This event did not have any adverse impact on the health and safety of the public.

If you should have any questions on this matter, please contact Mr. C. /.. Ayala at (512) 972 8628 or myself at (512) 972 7921.

1 Vice President

Nuclear Generation BEM/n1

Attachment:

LER 90 009 (South Texas, Unit 2) 90061901 ADO g [ h 99 PDR FDC 5

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Regional Administrator, Region IV Rufus S. Scott Nuclear Regulatory Commission Associate General Counsel 611 Ryan Plaza Drive, Suite 1000 Houston Lighting & Power Company o

. 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 1100 circle 75 Parkway L J. I. Tapia Atlanta, CA 30339-3064 Senior Resident Inspector c/o U. S. Nuclear Regulatory Dr. Joseph M. Hendrie Commission 50.Be11 port Lane P. O. Box 910 Be11 port, NY 11713 Bay City, TX 77414 D. K. Lacker J. R. Newman, Esquire Bureau 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 78704 l

D. E. Ward /R. P. Verret l Central Power & Light Company '

P. O. Box 2121 Corpus Christi, TX 78403 J. C. Lanier Director of Generation City of Austin Electric Utility i 721 Barton Springs Road l Austin, TX 78704 R. J. CosttLlo/M. T. Hardt l l City Public Service Board l P, O. Box 1771 .

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On May 12, 1990, Unit 2 was in Mode 5 for a forced outage. During the performance of corrective maintenance to investigate a flashing " Train C SI Blocked" status lamp, an extra wire was discovered in the Solid State Protection System (SSPS). Evaluation of this wire determined that it would not have prevented fulfillment of a safety function; however, due to the potential significance, H1AP has chosen to report this event as a voluntary LER. It was subsequently determined that the extra wire was inadvertently installed by Westinghouse during assembly or continuity testing of the SSPS cabinets. The wire was removed and the system successfully tested. The remaining SSPS logic train cabinets on both units have been inspected to verify the absence of this wiring error.

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DESCRIPTION OF EVfdIf on May 12, 1990, Unit 2 was in Mode 5 for a forced outage. During the performance of corrective maintenance to investigate a flashing " Train C S1 Blocked" status lamp, an extra wire was discovered in the Solid State Protection System (SSPS), connected between the output of the logic Train R Steam Generator B high high level trip logic card and an input terminal of the Train C Safety Injection block logic card. This wire, as installed, would have caused a Train C Safety injection block signal when the reactor trip breakers were open and the Steam Generator B water level reached the high high level trip setpoint. The wire did not affect S1 initiation from logic Train S. On May 14, 1990 this condition was conservatively determined to be reportable and the NRC was notified at 1730 hours0.02 days <br />0.481 hours <br />0.00286 weeks <br />6.58265e-4 months <br />. Upon further evaluation, this event was determined to be not reportable; however, due to its potential significance this voluntary LER has been prepared. I An investigation into the source of the extra wire was performed. The wire color and termination match the factory wiring in the bulk of the cabinets.

No records were found which indicated that a design change or repair had been implemented which could have installed the extra wire. It has been concluded l that the wire was inadvertently installed at the Westinghouse factory during i assembly or continuity testing. A review of the manufacturer's quality control records was performed; however, no notations were found which indicated that the extra wire had been found or added. The other SSPS Logic Cabinets were inspected for this same error and were found to be correct.

The SSPS was designed and assembled under the Westinghouse Quality Assurance Program. The preliminary design was defined through functional diagrams. The l

functional logic blocks can be roughly correlated to hardware function cards. l The system logic was configured by placing hardware function cards in the slots and connecting wiring jumpers between pins on the card edge connectors.

The functional diagrams were then translated into schematics which thew signal flow from card to card. The schematics also identify the card slot, eard J type, and interconnecting points. The cabinet wire list was developed from the schematics and is the document which was actually used to wire each cabinet. Each of those steps was independently checked. Once the cabinets were fully assembled, both a functional test and a point to point continuity check were conducted. The continuity check is actually a double test; each connected pin is listed on the wire list with the destination of each wire attached to that pin. The destination pin itself is also listed as having a connection back to the original point. Following system installation on site, another group of functional tests was conducted by the Startup group. During operation, periodic surveillance tests are conducted in accordance with the Technical Specifications. All of these tests demonstrate the operability of required functions; there are no specific tests to verify the absence of additional functions.

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This wiring error is the second such occurrence which was not detectable through the normal testing process of Westinghouse SSPS's, which has been reported to Westinghouse. Westinghouse has installed a total of approximately 296,000 wires in the Solid State Protection Systems. In both instances, the actual errors manifested themselves as unexplained indications and were discovered by troubleshooting.

CAUSE OF EVENT!

The cause of this event was inadvertent installation of an extra wire in the Solid State Protection System by the munufactur-r.

MALYSIS OF EVENT:

Westinghouse has reviewed the safety significance of this extra wire and has concluded that it does not represent a safety concern. The only accident postulated which may affect both Safety Injection and S/G high level trip is a Steam Cenarator Tube Rupture. The analysis indicates that SI would be initiated by low Reactor Coolant System pressure 15 to 20 minutes before water level in the affected S/G would reach the high level trip setpoint. Thus, if S/G B had experienced a tube rupture and SI occurred, the blocking of Train C SI some 15 to 20 minutes later (when S/G B water level reached the high level trip setpoint) would not have affected the course of the event. Actuation of Safety Injection components would already be complete. In addition, the Logic Train S input to SI Train C actuation would still be present until manually reset by the operator.

Due to the potential significance of incorrectly installed SSPS wiring, HiAP has chosen to report this event as a voluntary LER pursuant to 10CFk50.73.

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The following corrective actions have been taken as a result of this event:

1. The extra wire in the SSPS Train R cabinet has been removed and the I system successfully tested. ]

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2. The other SSPS Logic Cabinets on both units have been inspected to insure they did not contain the same wiring error.

3. Past work requests on the STP SSPS were reviewed for indication of I any unexplained anomalies. The only item identified was an Unit 2 j trip caused by the unexplained opening of the Train S Reactor Trip Breaker. Wiring associated with the associated Undervoltage Driver Card was inspected for extra wires or incorrect terminations, and no discrepancies were identified. Shift Supervisors were surveyed to determine if operations personnel had noticed any unexplained  ;

anomalies during operation of the SSPS. None were identified, i ADDITIONAL INFORMATION:

There have been no previous events reported regarding incorrect manufacturer's wiring which resulted in inoperable Engineered Safety Features I equipment.

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