United States Nuclear Regulatory Commission - Protecting People and the Environment

ACCESSION #: 9901060170


ABB

1 December, 1998

LD-98-038

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

Subject: Potential Manufacturing Deviation Identified in Fuel Assembly Guide Tube Wear Sleeves

The purpose of this letter, which is provided for information only, is to make the Nuclear Regulatory Commission (NRC) staff aware of a potential manufacturing deviation that has been identified by ABB Combustion Engineering (ABB-CE) with fuel assembly Control Element Assembly Guide Tube Wear Sleeves. Specifically, the potential exists for local regions on some guide tube wear sleeves, in delivered ABB-CE PWR fuel, to have less than the minimum specified chrome plating thickness on the inside diameter. The impact of the potential for thinner chrome plating on operating fuel has been determined not to create a substantial safety hazard, and, therefore, is not reportable pursuant to the provisions of 10CFR21. However, since the guide tube wear sleeve is an NRC approved design, this potential deviation, and the conclusions of the ABB-CE evaluation, are being provided to the NRC for information. The enclosure provides a discussion of the condition and actions taken by ABB-CE. All affected ABB-CE fuel customers have been informed of this potential deviation and our actions and conclusions.

If you have any questions concerning this matter, please do not hesitate to call me or Chuck Molnar of my staff at (860) 285-5205.

Very truly yours,

COMBUSTION ENGINEERING, INC.

Ian. C. Rickard, Director
Nuclear Licensing

Enclosure: As stated

xc: T. E. Collins (NRC)
       S. L. Magruder (NRC)


ABB Combustion Engineering Nuclear Power
Combustion Engineering, Inc.
P.O. Box 500
2000 Day Hill Rd.
Windsor, CT 06095-0500
Telephone (860) 285-9678
Fax (860) 285-3253

Enclosure to LD-98-038

ABB Combustion Engineering Nuclear Power

Discussion of Potential Manufacturing Deviation Identified in Fuel Assembly Guide Tube Wear Sleeves

Introduction & Summary:

The purpose of this enclosure, which is provided for information only, is to make the Nuclear Regulatory Commission (NRC) staff aware of a potential manufacturing deviation that has been identified by ABB Combustion Engineering (ABB-CE) with fuel assembly guide tube wear sleeves. Specifically, the potential exists for local regions on some guide tube wear sleeves in delivered ABB-CE PWR fuel to have less than the minimum specified chrome plating thickness on the inside diameter. This potential arose because the accuracy of the Eddy Current Testing (ECT) device used to measure the chrome plating thickness has been called into question. This device has been in use since the late 1980s. The impact of the potential for thinner chrome plating on operating fuel has been determined not to create a substantial safety hazard, and, therefore, is not reportable pursuant to the provisions of 10CFR21. However, since the guide tube wear sleeve is an NRC approved design, this potential deviation, and the conclusions of the ABB-CE evaluation, are being provided to the NRC for information.

Discussion:

The chrome plated, shop-installed, guide tube wear sleeve that is currently in use in ABB-CE non-System 80 fuel evolved from an interim field-installed guide tube wear sleeve retro-fit for 14x14 fuel assemblies. The guide tube wear sleeves were developed and first used in the late 1970s, when evidence of wear between the guide tube and Control Element Assembly (CEA) rods was observed. This condition was reported to the NRC (Reference 1), and the NRC reviewed and approved the guide tube wear sleeve design (Reference 2). After ABB-CE determined that the guide tube wear sleeve would be retained as a permanent feature of its fuel design to prevent guide tube wear concerns, the design was modified for installation in the shop as part of the fuel fabrication process. This design modification was also submitted to the NRC (Reference 3) and approved (Reference 4). Further design information was provided in References 5 and 6.

When originally conceived, the field-installed sleeve design was intended to perform a structural function in some cases (since it was inserted in guide tubes that had worn due to CEA rod vibration), and in other cases to protect unworn guide tubes from wear during future operation in CEA locations. The function of the shop-installed sleeve is only to protect the unworn guide tube from wear; it no longer serves a structural function. The same minimum chrome plate thickness specification has been maintained on the shop-installed sleeve as on the original field-installed design. However, only a small fraction of the specified minimum chrome plating is actually required for the sleeve to meet its functional requirement of protecting the CEA guide tube from wear.

ABB-CE has obtained plating services from the same vendor prior to, and throughout, the time period that the ECT measuring device has been in use. This vendor has indicated that no significant changes have been made to the plating process. Extensive metallographic measurements made on a wide range of guide tube wear sleeves, including both 14x14 and 16x16 geometries procured over the past three years, have confirmed that adequate chrome plating is present for the sleeve to meet its functional requirement of protecting the guide tube from wear. Therefore, the chrome plating thickness in previously delivered fuel is adequate for the fuel to continue to meet the scrammability and coolability requirements of the General Design Criteria; which was the basis for NRC acceptance of the original sleeve design in Reference 2.

Metallographic measurements have also been used as an overcheck on chrome plating thickness to verify the presence of adequate chrome plating on sleeves of fuel in production. Although ABB-CE has concluded that substantial margin exists between the specified minimum chrome plating thickness and the thickness needed to meet functional requirements, ABB-CE is not proposing to change the sleeve design for the future. That is, there is no plan to reduce the minimum specified chrome plating thickness. Rather, the plating process has been modified to use an alternate, highly reliable measurement technique to assure that future guide tube wear sleeves meet or exceed the specified minimum chrome plating thickness.

Conclusion:

ABB-CE's conclusions regarding this issue can be summarized as follows:

1. A potential for local regions on some CEA guide tube wear sleeves in delivered ABB-CE PWR fuel to have less than the minimum specified chrome plating thickness on the inside diameter has been identified. However,
  • the chrome plating thickness in previously delivered fuel is adequate for the fuel to continue to meet the scrammability and coolability requirements of the General Design Criteria, and
  • the impact of the potential for thinner chrome plating on operating fuel has been determined not to create a substantial safety hazard, and, therefore, is not reportable pursuant to the provisions of 10CFR21.
2. ABB-CE has concluded that substantial margin exists between the specified minimum chrome plating thickness and the thickness needed to meet functional requirements. However, ABB-CE is not proposing to change the sleeve design for the future. That is, there is no plan to reduce the minimum specified chrome plating thickness.
3. The plating process has been modified to use an alternate, highly reliable measurement technique to assure that future guide tube wear sleeves meet or exceed the specified minimum chrome plating thickness.

References:

(1) "Calvert Cliffs Unit #1 Reactor Operation with Modified CEA Guide Tubes", CEN-83(B)-P, February 8, 1978.
(2) "Control Rod Guide Tube Wear in Operating Reactors, Operating Experience Report", NUREG-0641, April 1980.
(3) A. E. Scherer (C-E) letter LD-84-043 to C. O. Thomas (NRC) on "CEA Guide Tube Wear Sleeve Modification", August 3, 1984.
(4) C. O. Thomas (NRC) letter to A. E. Scherer (C-E) on "Acceptance for Referencing of Licensing Special Report LD-84-043 'CEA Guide Tube Wear Sleeve Modification'", September 7, 1984.
(5) "Additional Information on Guide Tube Wear", Amendment 2-P to CEN-79-P, CEN-80(N)-P, CEN-82-P, CEN-83(B)-P, March 8, 1978.
(6) "Arkansas Nuclear One - Unit 2 Reactor Operation with Modified CEA Guide Tubes and Lengthened Upper Guide Structure Flow Channels", CEN 96(A)-P Revision 1, July 12, 1978.

*** END OF DOCUMENT ***


Page Last Reviewed/Updated Thursday, March 29, 2012