NOC-AE-000683, Forwards 30-day Rept Concerning Significant Changes to Accepted Large Break Loss of Coolant Accident ECCS Evaluation Model for South Tx Project,Units 1 & 2,IAW 10CFR50.46(a)(3)(ii)

Forwards 30-day Rept Concerning Significant Changes to Accepted Large Break Loss of Coolant Accident ECCS Evaluation Model for South Tx Project,Units 1 & 2,IAW 10CFR50.46(a)(3)(ii)

ML20217N871
Person / Time
Site:	South Texas
Issue date:	10/19/1999
From:	Leazar D HOUSTON LIGHTING & POWER CO.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
NOC-AE-000683, NUDOCS 9910290148
Download: ML20217N871 (5)

Text

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, South Tees thyrtEkvincGemntmgStatkm PO Bar189 5%dsmvth. Tcus77483 w October 19, 1999 NOC-AE-000683 File No.: G02, M33.02 STI: 30973519 )

10CFR50.46(a)(3)(ii) {

U. S. Nuclear Regulatory Commission

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Attention: Document Control Desk I Washington, DC 20555-0001 South Texas Project l Units 1 and 2 Docket Nos. STN 50-498, STN 50-499 10CFR50.46 Thirty Day Report of Sinnificant Chances to the Accepted Emercency Core Cooline System Model I

References:

1) Correspondence from D. A. Leazar to NRC Document Control Desk, "10CFR50.46 Annual Report of Emergency Core Cooling System Model Revisions," dated December 17,1998 (NOC-AE-000390).

2) WCAP 13451 " Westinghouse Methodology For Implementation of 10 CFR I 50.46 Reporting," October 1992.

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3) WCAP 10484-P-A," Spacer Grid Heat Transfer Effects During Reflood", M.Y.  !

Young et. al., March 1991.

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Pursuant to 10CFR50.46(a)(3)(ii), the STP Nuclear Operating Company (STPNOC) is )

submitting this 30 day report concerning significant changes to the accepted Large Break Loss of Coolant Accident Emergency Core Cooling System (ECCS) evaluation model for the South Texas Project Units 1 and 2. Following their investigation of code errors in the LOCBART code, Westinghouse reanalyzed the limiting case with the corrected LOCBART code. The result of the new analysis was a 76 F increase in the Large Break Loss of Coolant Accident peak clad temperature for the South Texas Project.

The revised Large Break Loss of Coolant Accident peak clad temperature, including all peak clad temperature assessments,is 2192 F. Since the limiting case was reanalyzed and peak clad temperature, including all assessments,is below the regulatory limit of 2200 F, a schedule for \7/.

reanalysis is not being provided. ji Backcround In late 1998, Westinghouse discovered a potential issue related to a logic error in the ,J \ j LOCB ART code, which causes the cladding zirc-water oxidation calculations to be performed three times per time step. Initial indications were that correcting the error would lead to an l I

increase in the calculated peak cladding temperature. In accordance with WCAP-13451 (Reference 2), Westinghouse identified the error as a Potential Issue.

l 9910290148 991019 PDR ADOCK 05000498 P PDR

. NOC-AE-000683 Page 2 Prior to the completion of their investigation of the logic error in the LOCBART code, ,

Westinghouse discovered a second error in the LOCB ART code related to the correlation used to 1 compute the single-phase heat transfer enhancement for axial elevations located downstream of spacer grids. The Safety Evaluation Report for WCAP 10484-P-A, " Spacer Grid IIcat Transfer ,

Effects During Reflood"(Reference 3) requires that a length-averaged value be used to specify j the heat transfer coefficient for a given cell, since the use of a local value, corresponding to the i forward edge or the rear edge of the cell, could be non-conservative. Westinghouse determined  !

that the length averaging in the LOCBART code was not being done correctly in all cases.

1 Westinghouse recently completed their investigation of these issues. As part of the )

investigation, Westinghouse reanalyzed the limiting Large Break Loss of Coolant Accident case )

for the South Texas Project. The new analysis resulted in a 76 F increase in the limiting case I peak cladding temperature. The new South Texas Project Large Break 5 oss of Coolant Accident peak cladding temperature is 2192*F.

If you should have any questions concerning this matter, please contact Mr. Charles R.

Albury at (361) 972-8901 or me at (361) 972-7795.

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. 0-D.A.leaz' Director, Nuclear Fuel and Analysis kaw/jmw

Attachment:

LARGE BREAK LOCA ECCS EVALUATION MODEL PEAK CLADDING TEMPERATURE l

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L- NOC-AE-000683 File No.: G02, M33.02 l Page 3

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-cc: ,

Ellis W. Merschoff a. Jon C. Wood  !

l Regional Administrator, Region IV

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Matthews & Branscomb L ' U.- S. Nuclear Regulatory Commission One Alamo Center 611 Ryan Plaza Drive, Suite 400 , 106 S. St. Mary's Street, Suite 700 l Arlington, TX 76011-8064 San Antonio,TX 78205-3692 l

l- Thomas W. Alexion - Institute of Nuclear Power Project Manager, Mail Code 0-4D3 Operations - Records Center U.- S. Nuclear Regulatory Commission 700 Galleria Parkway Washington, DC 20555-0001- Atlanta, GA. 30339-5957 Cornelius F. O'Keefe ~ Richard A. Ratliff l

.Sr. Resident Inspector Bureau of Radiation Control c/o U. S. Nuclear Regulatory Commission . Texas Department of Health P. O. Box 910 1100 West 49th Street Bay City, TX 77404-0910 Austin, TX 78756-3189 J. R. Newman, Esquire D. G. Tees /R. L. Balcom Morgan, I2wis & Bockius Houston Lighting & Power Co.

1800 M. Street, N.W. P. O. Box 1700  ;

Washington, DC 20036-5869 Houston,TX 77251 M. T. Hardt/W.' C. Gunst Central Power and Light Company

. City Public Service ATTN: G. E. Vaughn/C. A. Johnson P. O. Box 1771 P. O. Box 289, Mail Code: N5012 San Antonio,TX 78296 Wadsworth,TX 77483

- A. Ramirez/C. M. Canady U. S. Nuclear Regulatory Commission Cityof Austin Attention: Document Control Desk Electric Utility Depanment Washington, D.C. 20555-0001 721 Barton Springs Road Austin,TX 78704 i

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NOC-AE-000683 Attachment ATTACHMENT LARGE BREAK LOCA ECCS EVALUATION MODEL PEAK CLADDING TEMPERATURE 1

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. NOC-AE-000683 Attachment i

LARGE HREAK LOCA ECCS EVALUATION MODEL PEAK CLADDING TEMPERATURE l

l The Large Break Loss of Coolant Accident (L.BLOCA) Emergency Core Cooling System evaluation model peak cladding temperature (PCT) and peak cladding temperature assessments are summarized below.

Current Licensing Basis PCT (LBLOCA Reanalysis PCT, Ref.1) 2090 F Assessment to account for Accumulator Water Temperature greater than 90 F (Ref.1) + 26 F Change in LBLOCA PCT as a result of the limiting case reanalysis. + 76 F New Large Break Loss of Coolant Accident peak cladding temperature 2192 F 1

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