United States Nuclear Regulatory Commission - Protecting People and the Environment

ACCESSION #: 9809240275


September 18, 1998


Document Control Desk
ATTN: Chief, Planning, Program and Management Support Branch
U. S. Nuclear Regulatory Commission
Washington, D. C. 20555

10 CFR 21 Evaluation and Notification for Gap Conductance Analyses for Co-Resident BWR Fuel

Ref.: 1. Letter, James F. Mallay to Document Control Desk, "Interim Report of Evaluation of a Deviation Pursuant to 10 CFR 21.21(a)(2)," NRC:98:051, July 22, 1998.

This letter is written notification of a reportable defect per 10 CFR Part 21 reported to the NRC Operations Center by facsimile on September 17, 1998.

The reportable defect was determined during the Part 21 evaluation of the deviation identified in Interim Report No. 98-004 provided to the NRC by Reference 1. Based on the Part 21 evaluation, SPC has concluded the deviation represents a defect as defined in 10 CFR 21.3, "A condition ... that could contribute to the exceeding of a safety limit..."

The affected BWR utility has been kept informed, and the actions taken and to be taken to address the defect are provided in the attachment to this letter.

Very truly yours,

James F. Mallay, Director
Regulatory Affairs



cc: E. Y. Wang (NRC, MS O-11F1)
E. R. Merschott, Administrator, NRC Region IV

Page A-1


(i.) Name and address of the individual informing the Commission H. D. Curet, Manager, Product Licensing, Siemens Power Corporation, 2101 Horn Rapids Rd., Richland, WA 99352
(ii.) Identification of the facility, the activity, or the basic component supplied for such facility or such activity within the United States which fails to comply or contains a defect. The defects are non-conservative MCPR operating limits previously provided to ComEd for LaSalle Unit 2 Cycle 8 and Quad Cities Unit 2 Cycle 15.
(iii.) Identification of the firm constructing the facility or supplying the basic component which fails to comply or contains a defect. Siemens Power Corporation, Richland, WA.
(iv.) Nature of the defect or failure to comply and the safety hazard which is created or could be created by such a defect or failure to comply.
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 the 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 (referred to as "gap conductance") for both SPC fuel and co-resident fuel.
SPC had assumed that the cladding for co-resident fuel was similar to SPC cold-worked cladding and used the same cladding creep coefficients to model the fuel performance. The co-resident fuel cladding was found to be annealed which creeps differently than cold-worked cladding. The change from cold-worked cladding to annealed cladding decreased the gap conductance for the co-resident fuel.
Transient analyses use gap conductance data in both the core average gap conductance and in the hot channel assembly average gap conductance. For fast pressurization transients, decreasing the core average gap conductance increases ACPR because of the reduction in void reactivity feedback in the neutronic response of the core during the transient.
(v.) The date on which the information of such defect or failure to comply was obtained. On May 26, 1998 a deviation was identified. When it was apparent the evaluation of the deviation could not be completed in 60 days Interim Report No. 98-004 was sent to the NRC on July 22, 1998.
(vi.) In the case of a basic component which fails to comply, the number and the location of all such components in use at, supplied for, or being supplied for one or more facilities or activities subject to the regulations in this part. ComEd - LaSalle Unit 2 Cycle 8 and Quad Cities Unit 2 Cycle 15
(vii.) The corrective action which has been, is being, or will be taken; the name of the individual or organization responsible for the action; and the length of time that has been or will be taken to complete the action.
The previously calculated and reported operating limits for LaSalle Unit 2 Cycle 8 will be revised before the reactor starts up (anticipated startup in March 1999). The previously calculated and reported operating limits for Quad Cities Unit 2 Cycle 15 were determined at the limiting EOC exposure conditions. Corrected analyses have been performed which demonstrate that the current operating limits are bounding from BOC to a cycle exposure of 8 GWd/MTU. The Quad Cities Unit 2 operating limits will be revised before the cycle reaches 8 GWd/MTU (Early 1999).
(viii.) Any advice related to the defect or failure to comply about the facility, activity, or basic component that has been, is being, or will be given to purchasers or licensees.
ComEd has been advised that the MCPR operating limits for LaSalle Unit 2 Cycle 8 and Quad Cities Unit 2 Cycle 15 are to be revised.

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