United States Nuclear Regulatory Commission - Protecting People and the Environment

ACCESSION #: 9807290284


SIEMENS

July 22, 1998
NRC:98:051

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. 98-004 "Gap Conductance Analyses for Co-Resident BWR Fuel"

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

/jak

Enclosure

cc: Mr. J. L. Birmingham (USNRC) OWFN 10 H5
Mr. E. Y. Wang (USNRC) OWFN 10 H5
Project No. 702
Siemens Power Corporation
Nuclear Division
Engineering & Manufacturing
2101 Horn Rapids Road
P.O. Box 130
Richland, WA 99352-0130
Tel: (509) 375-8100
Fax: (509) 375-8402


Interim Report (98-004)

Subject: Interim report of evaluation of a deviation pursuant to 10 CFR 21.21 (a)(2)
Title: Gap Conductance Analyses for Co-Resident BWR Fuel
Identification of Basic Activity: Calculation of co-resident BWR fuel rod gap conductance for input to MCPR transient analyses.
Basic Activity Supplied by: Siemens Power Corporation - Nuclear Division
Nature of Deviation: For BWR reactors where SPC provides reload fuel, postulated transient events are analyzed each cycle to establish MCPR operating limits. During transition cycles, SPC establishes limits for SPC fuel and also for co-resident fuel manufactured by other fuel vendors. Transient analyses are required to address co-resident fuel as well as SPC fuel because previous co-resident fuel transient analyses and limits may no longer be valid due to changes in core neutronic characteristics. Inputs to the transient analyses include the fuel pellet to cladding gap heat transfer coefficient for both SPC fuel and co-resident fuel. The gap heat transfer coefficient is calculated using the RODEX2 computer code.
An SPC internal licensing methodology review was recently performed and concerns were identified relative to the values for several fuel rod characteristics used in the RODEX2 analyses to calculate gap conductance values for input to the transient analyses for co-resident fuel. An evaluation of whether these deviations represent reportable defects under 1 0 CFR 21 has been initiated. A schedule for completing the evaluation is provided below.
Discovery Date: May 26, 1998
Corrective Actions to Date: Condition Report (CR) 6565 was initiated on May 26, 1998.
As part of CR 6565, an operability evaluation was performed. Two plants are potentially impacted; LaSalle Unit 2 Cycle 8 (LS2C8) and Quad Cities Unit 2 Cycle 15 (QC2C15). LS2C8 will not begin operation until early 1999. Reanalyses to determine LS2C8 operating limits will be performed prior to startup to address other changes that have occurred since the original analyses. These reanalyses will incorporate any changes required to calculate co-resident fuel gap conductance. QC2C15 is currently operating and is at a cycle exposure of 2.7 GWd/MTU as of mid-July 1998. Because transient analyses are performed using the limiting (largest delta CPR) cycle exposure conditions that occur at end of cycle (EOC), significant MCPR margin exists for transients early in cycle operation. The QC transient analyses were performed for a EOC exposure of 13.7 Gwd/MTU. Any increase in ACPR due to changes in co-resident fuel rod gap conductance will be less than existing margin until operation approaches EOC. Preliminary evaluations indicate that MCPR margin existing prior to mid-cycle (February 1999 at the earliest) is more than sufficient to offset any increase in delta due to changes in gap conductance for co-resident fuel.
An evaluation is in progress to determine fuel rod characteristics for the co-resident fuel that are appropriate for RODEX2 gap conductance calculations. Revised fuel gap conductance values will be calculated based on the fuel characteristics determined. Following determination of appropriate gap conductance values for the co-resident fuel, the impact on LS and QC MCPR operating limits will be determined and new limits will be established if necessary.
Evaluation Completion Schedule Date: October 1, 1998.


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