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Characteristics of Hydride Precipitation and Reorientation in Spent-Fuel Cladding
Chung HM, Daum RS, Hiller JM, Billone MC


Pages: 22    Published: Jan 2002


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Source: STP1423-EB


Abstract
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 × 10 n cm ( > 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 -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} plane, the habit plane of tangential hydrides that precipitate under high tangential stress is the {104} plane. The habit plane of radial hydrides that precipitate under tangential stress is the {011} 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.


Keywords:
spent-fuel cladding, radial and tangential hydrides, macroscopic and microscopic hydrides, habit plane, texture, -type dislocations

Paper ID: STP11406S
Committee/Subcommittee: B10.02
DOI: 10.1520/STP11406S
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