Part 21 Report - 1998-420

ACCESSION #: 9805190359 SIEMENS May 11, 1998 NRC:98:029 Document Control Desk ATTN: Chief, Planning, Program and Management Support Branch U.S. Nuclear Regulatory Commission Washington, D.C. 20555-0001 Interim Report of Evaluation of a Deviation Pursuant to 10 CFR 21.21(a)(2) The following information is provided pursuant to the requirements of 10 CFR 21 to submit an interim report on issues that will not be completed within 60 days of discovery. An interim report for an issue under evaluation by Siemens Power Corporation is enclosed: Interim Report No. 98-002 "TOODEE2 Axial Nodalization" Those SPC customers potentially impacted by this issue will be provided a copy of this interim report. If you have any questions or if I can be of further assistance, please call me at (509)375-8757. Very truly yours, James F. Mallay, Director Regulatory Affairs /arn Enclosure cc: Mr. E. Y. Wang (USNRC) Project No. 702 Siemens Power Corporation Nuclear Division 2101 Horn Rapids Road Tel: (509) 375-8100 Engineering & Manufacturing P.O. Box 130 Fax: (509) 375-8402 Richland, WA 99352-0130 Interim Report (98-002) Subject: Interim report of evaluation of a deviation pursuant,to 10 CFR 21.21(a)(2) Title: TOODEE2 Axial Nodalization Identification of Basic Activity: PWR Large Break LOCA Analysis Basic Activity Supplied by: Siemens Power Corporation - Nuclear Division Nature of Deviation: The axial nodalization in TOODEE2 (part of the NRC-approved EXEM/PWR LBLOCA evaluation model) consists of 3 inch nodes near the peak power node, where rupture and peak cladding temperature are expected to occur, and larger nodes in other regions. The methodology requires that rupture be calculated to occur in a 3 inch node, and standard practice at SPC has been that PCT should also be calculated on a 3 inch node. Larger axial node "illegible print" of between 6 inches and one foot are commonly used at the top of the core where the power is lower than the axial peak value. With this nodalization, the peak cladding temperature for an axial power shape skewed toward the top of the core generally occurs at or slightly above the peak power node which is between 9 and 10.5 feet for a 12 foot core. If the larger nodes at the top of the core are replaced by 3 inch nodes. the EXEM/PWR model may calculate an even higher peak cladding temperature near the top of the fuel (above 10.5 feet) even though power is somewhat lower at this elevation. The prediction of the peak cladding temperature at reduced power nodes near the top of the core is considered unrealistic. Reflood cooling is by steam and entrained liquid flowing from the quench front in the core. Once this mechanism is established and calculated to be sufficient to cool the maximum power nodes and the high power nodes immediately downstream, higher elevations at reduced power should also be cooled. An evaluation of whether this behavior represents a reportable defect under 10 CFR 21 has been initiated. A schedule for completing the evaluation is provided below. Discovery Date: March 12, 1998 Corrective Actions to Date: Condition Report (CR) 6580 was issued in March 1998. The cause of the unrealistic calculations is being investigated. There is no indication at this time that the TOODEE2 axial nodalization problem, after correction, will result in peak cladding temperatures which violate 10 CFR 50.46 limits. Evaluation Completion Schedule Date: September 30, 1998 References: N/A *** END OF DOCUMENT ***

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