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    Impact of Hydrogen on Dimensional Stability of ZIRLO Fuel Assemblies

    Published: 01 January 2002

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    The high-operating-temperature fuel duty, 18-month and longer-cycle lengths, and higher burnups have put increased demands on PWR fuel during recent years. As a result of these demanding operating conditions, the corrosion and dimensional stability of PWR fuel assembly skeletons are being challenged. To understand the in-reactor performance of fuel assembly skeletons, two hot cell programs were initiated on high duty fuel. Specifically, two Zircaloy-4 skeletons and one ZIRLO skeleton were dimensionally characterized and destructively examined to understand the effect of corrosion on the dimensional stability of guide tubes and grids.

    While previous papers have dealt with the effects of fluence and crystallographic texture on the irradiation growth of zirconium alloys, this paper focuses on the effect of corrosion (oxidation and hydrogen uptake) on the dimensional stability of ZIRLO and Zircaloy-4. Laboratory tests were performed to quantify potential dimensional changes resulting from corrosion. Accelerated autoclave tests of ZIRLO and Zircaloy-4 in 589 K water containing 700-ppm lithium revealed that dimensional changes were well correlated to hydrogen content, not oxide thickness. In addition, the dimensional changes for both guide tube and strip (grid) autoclave specimens showed similar dependency upon hydrogen content and no significant dependency on crystallographic texture.

    The hot cell evaluation of the irradiated ZIRLO and Zircaloy-4 structural components revealed increasing dimensional changes of grids and guide tubes from the bottom to the top of the assembly. This variation was strongly correlated with increasing hydrogen content as suggested by the autoclave tests. For a given alloy (i.e., ZIRLO or Zircaloy-4), the grid dimensional change is similar to the guide tube diameter change, suggesting that the effects of hydrogen are generic and not related to processing or starting material geometry. Comparison of ZIRLO and Zircaloy-4 dimensional data reveals greater stability of ZIRLO as a result of lower hydrogen uptake, a lower fluence component to growth, and a lower hydrogen component to growth. ZIRLO structural components, thimbles and grids, show an enhanced degree of dimensional stability with the combined effects of irradiation and corrosion/hydriding.


    ZIRLO, Zircaloy-4, in-reactor performance, corrosion, hydrogen, hydrogen growth, hydrides, irradiation growth, grids, guide thimble tubes

    Author Information:

    King, SJ
    Advanced technical engineer, fellow engineer, senior design engineer, Westinghouse Electric Co., Columbia, SC

    Kesterson, RL
    Advanced technical engineer, fellow engineer, senior design engineer, Westinghouse Electric Co., Columbia, SC

    Yueh, KH
    Advanced technical engineer, fellow engineer, senior design engineer, Westinghouse Electric Co., Columbia, SC

    Comstock, RJ
    Program manager, Westinghouse Electric Company, Pittsburgh, PA

    Herwig, WM
    Supervisor, Reactor Engineering/Nuclear Fuel Management, South Carolina Electric and Gas, Jenkinsville, SC

    Ferguson, SD
    Principal engineer, Wolf Creek Nuclear Operating Corporation, Burlington, KS

    Committee/Subcommittee: B10.02

    DOI: 10.1520/STP11402S