United States Nuclear Regulatory Commission - Protecting People and the Environment

ACCESSION #: 9907120103


Westinghouse Electric Company LLC
Box 355
Pittsburgh Pennsylvania 15230-0355


June 29, 1999

U.S. Nuclear Regulatory Commission
Attn: Document Control Desk
Washington, DC 20555

Subject: Update and Schedule Revision Regarding Westinghouse Interim Report No. 98-029.

Reference: 1. NSD-NRC-98-5819, "Interim Report of an Evaluation of a Deviation or Failure to Comply Pursuant to 10CFR21.21(a)(2)", dated December 22, 1998.

On December 22, 1998 Westinghouse submitted an Interim Report (Reference 1), pursuant to the requirements of 10CFR Part 21, regarding an evaluation of reportability which could not be completed within 60 days from the discovery of the deviation or failure to comply. The issue being evaluated by Westinghouse concerns a LOCBART Computer Code Error and was designated Interim Report No. 98-029.

The purpose of this letter is to provide the NRC staff with an update of Interim Report No. 98-029.

If you have any questions regarding this matter, please contact me at 412-374-5036.


J. S. Galembush, Acting Manager
Regulatory and Licensing Engineering



NSD-NRC-99-5838 June 29, 1999

Westinghouse Electric Company
P.O. Box 355
Pittsburgh, PA 15230-0355

Interim Report No. 98-029 (Update)

Date: 6/29/99

SUBJECT: Update to Interim Report 98-029 regarding an Evaluation of a Deviation or Failure to Comply Pursuant to 10CFR21.21 (a)(2).
TITLE: LOCBART Computer Code Error
BASIC COMPONENT SUPPLIED BY: Westinghouse Electric Company
NATURE OF DEVIATION: Westinghouse identified a potential issue related to a logic error discovered in the LOCBART code. The 1981 Evaluation Model with BASH uses the LOCBART computer code to calculate the thermal and hydraulic response of the hot assembly and hot rod to a postulated large break loss of coolant accident. Consistent with Appendix K requirements, the Baker-Just model is used to calculate the cladding metal-water reaction rate. A logic error was discovered in LOCBART which caused the Baker-Just metal-water reaction calculations to be performed three times per timestep. Correcting the error reduces the total cladding oxidation, while increasing the heat deposition in the cladding. This could potentially affect the 10CFR50.46 acceptance criterion for peak cladding temperature.
EVALUATION STATUS: LOCBART calculations, with a corrected code version, have been performed for a number of typical large break LOCA transients. Based on these results and plant-specific information currently available to Westinghouse, it has been determined that this situation does not represent a substantial safety hazard and all affected plants are believed to be operating in a manner that would result in calculated ECCS performance which would satisfy 10 CFR 50.46 acceptance criteria. In a very limited number of cases this conclusion requires taking credit for available plant specific peaking factor margins or cycle burnup effects. Additional time is required for Westinghouse to validate and verify this conclusion for these plants on a plant-specific basis and to work with the individual affected licensees and the Westinghouse Owners' Group in connection with our verification and validation efforts. Upon final validation and verification, the NRC will be notified of the evaluation results


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