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    Characteristics of Hydride Precipitation and Reorientation in Spent-Fuel Cladding

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    Transmission electron microscopy (TEM) was used to examine Zircaloy fuel ladding, either discharged from several PWRs and a BWR after irradiation to fluence levels of 3.3 to 8.6 × 1021 n cm-2 (E > 1 MeV) or hydrogen-charged and heat-treated under stress to produce radial hydrides; the goal was to determine the microstructural and crystallographic characteristics of hydride precipitation. Morphologies, distributions, and habit planes of various types of hydrides were determined by stereo-TEM. In addition to the normal macroscopic hydrides commonly observed by optical microscopy, small “microscopic” hydrides are present in spent-fuel cladding in number densities at least a few orders of magnitude greater than that of macroscopic hydrides. The microscopic hydrides, observed to be stable at least up to 333°C, precipitate in association with <c>-type dislocations. While the habit plane of macroscopic tangential hydrides in the spent-fuel cladding is essentially the same as that of unirradiated unstressed Zircaloys, i.e., the {107}Zr plane, the habit plane of tangential hydrides that precipitate under high tangential stress is the {104}Zr plane. The habit plane of radial hydrides that precipitate under tangential stress is the {011} Zr pyramidal plane, a naturally preferred plane for a cladding that has 30° basal-pole texture. Effects of texture on the habit plane and the threshold stress for hydride reorientation are also discussed.


    spent-fuel cladding, radial and tangential hydrides, macroscopic and microscopic hydrides, habit plane, texture, <c>-type dislocations

    Author Information:

    Chung, HM
    Argonne National Laboratory, Argonne, IL

    Daum, RS
    Argonne National Laboratory, Argonne, IL

    Hiller, JM
    Argonne National Laboratory, Argonne, IL

    Billone, MC
    Argonne National Laboratory, Argonne, IL

    Committee/Subcommittee: B10.02

    DOI: 10.1520/STP11406S