Hot-isostatic pressing of U-10Zr by a coupled grain boundary diffusion and creep cavitation mechanism

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 600°C (α + δ-phase) and 700°C (γ-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 600°C, but occurred readily at 700°C. The driving force dependence at 700°C (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 γ-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.

Hot-isostatic pressing of U-10Zr by a coupled grain boundary diffusion and creep cavitation mechanism Academic Article