Preparation and oxidation of (U_1-yZr_y)O_2+x

(U_1−yZr_y)O_2−x has gained recent interest following the Fukushima Daiichi nuclear power plant disaster in 2011, where extreme temperatures in the core led to melting between the fuel-cladding layers and the formation new UO₂–ZrO₂ phases. Mixed reports from literature indicate improved U and fission product retention in (U_1−yZr_y)O_2−x compared to UO₂, while others show accelerated oxidation in (U_1−yZr_y)O_2−x. A series of (U_1−yZr_y)O_2−x materials (y from 0 to 0.2) was synthesized by coprecipitation of doped ammonium diuranate (ADU) from nitrate stock solutions. Doped U₃O₈ was produced by calcining the precipitate in air, while UO₂ pellets were made by sintering in a reducing atmosphere of 4% H₂/Ar. Infrared absorption, Raman spectroscopy, and powder X-ray diffraction (pXRD) indicate a single phase, and thus both UO₂ and U₃O₈ are able to accommodate at least 20-at.% Zr. In situ pXRD shows a significant decrease in oxidation resistance of UO₂ to U₃O₈ with the addition of 0.1-at.% Zr.