Hot-isostatic pressing of U-1OZr by a coupled grain boundary diffusion and creep cavitation mechanism
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abstract
To investigate the mechanical response of porous and swelling metallic fuel to cladding restraint, specimens of U-10 wt% Zr were prepared from UH3 + ZrH2 and U + Zr powders. Specimens were sintered under argon to entrap gas and simulate fission gas bubbles and contained different amounts of rigid precipitates resulting from impurities in the starting powders. Hot-isostatic pressing (HIP) was performed at 600C ( + -phase) and 700C (-phase). The phenomenon of HIP is related to grain boundary diffusion and creep cavitation mechanisms for cavity growth during creep. Densification was not detected at 600C, but occurred readily at 700C. The driving force dependence at 700C (n = 3.7 0.5) and observed loading/unloading transients are consistent with a creep-controlled HIP mechanism. The activation energy (187 10 kJ/mol) agrees with a reported value for grain boundary diffusion of uranium in -U, consistent with a grain boundary diffusion-controlled mechanism. The overall mechanism thus appears to be coupled grain boundary diffusion and creep cavitation. The relevance to in-reactor densification under external pressure or contact stress is also discussed.
