Impacts of Am Aggregation on the Bulk Properties of Mixed Oxides (U, Am)O2 from First Principles

Abstract

We present a first-principles density functional theory with the Coulomb interaction U (DFT + U) investigation of the bulk properties, including structural, energetic, electronic, and mechanical properties for uranium–americium mixed oxides (U, Am)O2. The various Am aggregation contents were investigated to better understand the impact of Am on the nuclear fuel UO2. The supercell defect models at different scales were used to describe the solid solution (U, Am)O2. The obtained results show that different contents of Am aggregation have a significant impact on the volume and energy of the formation of mixed oxide systems. The results of the electronic structure calculations exhibit no bandgap owing to the mixing of UO2 and AmO2. The mixing enthalpy of the Am aggregation systems is used to describe the phase stability of the solid solution. In particular, the mixing enthalpy of (U, Am)O2 is significantly reduced as the Am content increases. The elastic properties of the (U, Am)O2 mixed oxides have also been compared as a function of the Am content. Moreover, the impacts of the whole Pu aggregation content range on the bulk properties for the (U, Pu)O2 mixed oxides are also discussed.