ST-HL-AE-1651, Final Part 21 & Deficiency Rept Re Potential Error in Westinghouse Core Exit Temp Measurement Sys.Initially Reported on 850509.Item Not Reportable Per Part 21 or 10CFR50.55(e)

Final Part 21 & Deficiency Rept Re Potential Error in Westinghouse Core Exit Temp Measurement Sys.Initially Reported on 850509.Item Not Reportable Per Part 21 or 10CFR50.55(e)

ML20205N993
Person / Time
Site:	South Texas
Issue date:	05/07/1986
From:	Goldberg J HOUSTON LIGHTING & POWER CO.
To:	Martin R NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION IV)
References
CON-#286-168, REF-PT21-86, REF-PT21-86-175-000 OL, PT21-86-175, PT21-86-175-000, ST-HL-AE-1651, NUDOCS 8605210056
Download: ML20205N993 (5)

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My iiousion tigniing & eower eo. nox i7oo iiousion.rexas 72ve, o i.o 22s-92ii May 7, 1986 ST-HL-AE-1651 File No. G12.239 Mr. Robert D. Martin Regional Administrator, Region IV U. S. Nuclear Regulatory Commission 611 Ryan Plaza Drive, Suite 1000 Arlington, Texas 76011 South Texas Project Units 1 & 2 Docket Nos. STN 50-498, STN 50-499 Final Report Concerning Core Exit Temperature Measurement System

Dear Mr. Martin:

On May 9, 1985, pursuant to 10CFR50.55(e), Houston Lighting & Power Company (HL&P) notified your office of a reportable item concerning the safety grade Westinghouse core exit temperature measurement system. This-item has been reported pursuant to 10CFR21 by Westinghouse. HL&P has determined that for the South Texas Project this deficiency does not meet the criteria for reportability pursuant to 10CFR50.55(e). Attached is the final report concerning this item.

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

Very truly yours, J. H. Goldberg Group Vice President, Nuclear THC/yd

Attachment:

Final Report Concerning Core Exit Temperature Measurement System l

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Ilouston Lighting & Power Company ST-HL-AE-1651 File No.: G12.239 Page 2-cc:

Hugh L. Thompson, Jr. , Director Brian E. Berwick, Esquire Division of PWR Licensing - A Assistant Attorney General for Office of Nuclear Reactor Regulation the State of Texas U.S. Nuclear Regulatory Commission P.O. Box 12548, Capitol Station Washington, DC 20555 Austin, TX 78711 N. Prasad Kadambi, Project Manager Lanny A. Sinkin U.S. Nuclear Regulatory Commission Christic Institute 7920 Norfolk Avenue 1324 North Capitol Street Bethesda, MD 20814 Washington, DC 20002 Claude E. Johnson Oreste R. Pirfo, Esquire Senior Resident Inspector /STP Hearing Attorney c/o U.S. Nuclear Regulatory Office of the Executive Legal Director Comaission U.S. Nuclear Regulatory Commission P.O. Box 910 Washington, DC 20555 Bay City, TX 77414 Charles Bechhoefer, Esquire M.D. Schwarz, Jr. , Esquire Chairman, Atomic Safety &

Baker & Botts Licensing Board One Shell Plaza U.S. Nuclear Regulatory Commission Houston, TX 77002 Washington, DC 20555 J.R. Newman, Esquire Dr. James C. Lamb, III Newman & Holtzinger, P.C. 313 Woodhaven Road 1615 L Street, N.W. Chapel Hill, NC 27514 Washington, DC 20036 Judge Frederick J. Shon Director, Office of Inspection Atomic Safety and Licensing Board and Enforcement U.S. Nuclear Regulatory Commission U.S. Nuclear Regulatory Commission Washington, DC 20555 Washington, DC 20555 Mr. Ray Goldstein, Esquire T.V. Shockley/R.L. Range 1001 Vaughn Building Central Power & Light Company 807 Brazos P.O. Box 2121 Austin, TX 78701 Corpus Christi, TX 78403 Citizens for Equitable Utilities, Inc.

H.L. Peterson/G. Pokorny c/o Ms. Peggy Buchorn City of Austin Route 1, Box 1684 P.O. Box 1088 Brazoria, TX 77422 Austin, TX 78767 Docketing & Service Section J.B. Poston/A, vonRosenberg Office of the Secretary City Public Service Board U.S. Nuclear Regulatory Commission P.O. Box 1771 Washington, DC 20555 San Antonio, TX 78296 (3 Copies)

Advisory Committee on Reactor Safeguards U.S. Nuclear Regulatory Commission i 1717 H Street Washington, DC 20555 Revised 12/2/85 L1/NRC/tc

ST-HL-AE-1651 File No.: G12.239 Page 1 of 3 South Texas Project Units 1 & 2 Docket Nos. STN 50-498, STN 50-499 Final Report Concerning Core Exit Temperature Measurement System I. Summary Environmental qualification test results on components in the reactor core exit temperature measurement system (thermocouples, connectors, splices, etc.) indicate the potential for a total system error greater than anticipated. The error may be greater than the error assumed for fixing the Westinghouse Owner's Group Emergency Response Guideline (ERG) setpoints for operator actions. While the error cannot be completely eliminated,_it can be quantified and compensated for.

HL&P has determined that this item does not meet the criteria for reportability pursuant to 10CFR50.55(e).

II. Description of Deficiency During the Westinghouse environmental qualification testing of the safety grade core exit temperature measurements system (consisting of thermocouples, connectors potting adaptors, splices, and the reference junction box), it was determined that the potential total error of the system is greater than the error that was assumed for fixing the Generic ERG setpoints for operator actions. The ERG's are the basis for plant specific Emergency Operating Procedures (EOPs).

The safety grade core exit temperature measurement system will remain functional throughout a design basis event. The sum of the individual component errors however, is approximately 60 F as opposed to the 30 F total system error assumed. The individual component errors are the result of moisture ingression and thermal expansion. These errors can be compensated for by adjusting the E0P operator action setpoints. Core exit temperature is used to determine RCS subcooling margin and onset of inadequate core cooling (ICC).

RCS Subcooling Margin ThegenericERGsrecommendedtheuseofcoreexittemperaturefnthe calculation of RCS subcooling margin and assume less than a 30 F uncertainty allowance. For STP, actions that are taken in the ERGS based wholly or in part on the subcooling margin include safety injection (SI) termination and reinitiation. Plant specific application of the generic ERGS requires determination of the plant specific temperature uncertainty

,ntribution to the RCS subcooling calculation based on the specific system configuration.

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ST-HL-AE-1651 File No. G12.239, G2.2.

Page 2 of 3 The potential consequences of exceeding the assumed temperature channel error include the following: (1) delay in terminating SI following a secondary high energy line rupture or small-break LOCA, which could result in water relief through the pressurizer safety and/or relief valves; and (2) inappropriate SI termination following a small LOCA.

Inadequate Core Cooling Detection The generic ERG's utilize core exit temperature for the detection of the onset of ICC. In particular, for the Core Cooling Critical Safety Function Status Tree, the two decision points are core exit temperature greater than 1200 F and core exit temperature greater than 700 F in conjunction with low reactor vessel water level.

III. Corrective Action The Westinghouse recommendations which are being implemented for STP are as follows:

.RCS Subcooling Margin The RCS subcooling margin channel inaccuracies based upon core exit temperature input have been calculated. The subcooling margin calculation on South Texas is based upon the maximum quadrant thermocouple average temperature. Conservatively, 10 thermocouples were assumed to be operable in computing the quadrant thermocouple average temperature. The errors associated with the thermocouple input to the subcooling margin calculations are within the assumed tolerance for a normal environment, but not for an adverse environment. The inaccuracies in subcooled margin during a design basis event are being used in the STP Emergency Operating Procedures.

Inadequate Core Cooling Detection An uncertainty of up to 200 F is acceptable in the 1200 F setpoint on the core cooling status tree, i.e., the actual core exit temperature could be between 1000 F and 1400 F. The safety grade core exit temperature system meets acceptable channel accuracy requirements for the 1200 F Core Cooling Status Tree setpoint, therefore no corrective action is required.

The 700 F setpoint was intended to ensure that there is superheating of the steam at the core outlet. The core exit temperature channel inaccuracy is within the assumed tolerance for a normal environment, but not for an adverse environment. The 700 F setpoint in the ERGS assumed a maximum core exit temperature error of approximately 30 F. The actual error, under adverse containment conditions, is approximately 60 F. Assuming the RCS is at a maximum pressure corresponding to the relief setpoint of the pressurizer safety valves (approximately 2500 psia), the 700 F setpoint minus the temperature L1/NRC/tc

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. ST-HL-AE-1651 File No.: G12.239 Page 3 of 3 5

uncertainty is intended to ensure that the core exit temperature (670 F) isindicativeofsugerheatedsteampriortoenteringanICCmitigatgng guideline. The 700 F setpoint will be changed to approximately 730 F in the-STP E0Ps to reflect the greater system error.

The Qualified Display Processing System (QDPS) displays and alarm

. setpoints are being revised to reflect these conservative values.

IV. Recurrence Control No recurrence control is required. This deficiency was discovered during the equipment qualification process, which is in place specifically to identify problems such as this. This deficiency is being corrected through the normal process -for finalization of calculations.

V. Safety Analysis The potential consequences of exceeding the assumed temperature channel error for RCS subcooling margin have been listed above. These situations could result in events more severe than currently described in the FSAR.

Although the safety grade core exit temperature system has been received at the jobsite, the EOP Setpoint Study for STP being performed by Westinghouse, was not finalized at the time this deficiency was 1

identified. .The corrective actions identified by Westinghouse have been incorporated in the EOP Setpoint Study. Since the deficiency was identified and is being corrected within the normal design processes, i HL&P has determined that this deficiency does not meet the criteria for

reportability pursuant to'10CFR50.55(e) for STP.

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