The mechanical properties of advanced U–Si compounds using first principles method

Due to high thermal conductivity and higher fissile density, one of the most options being pursued for accident-tolerant fuels is U–Si fuels. Unfortunately, the data available for U–Si fuels are rather limited now. Based on a few assumptions regarding geometry structures, electronic properties, elastic constants and hardness are predicted systematically for U–Si compounds using density functional theory (DFT) in this work. The calculation results show that the U₃Si₂, β-U₃Si and γ-U₃Si compounds are metallic and brittle, which is in good agreement with the previous experimental results. The Si-rich USi_1.84 compound presents the ductile. By analyzing shear anisotropy factors, it is found that the U₃Si₂, β-U₃Si and Si-rich USi_1.84 have the anisotropic characteristics, while the γ-U₃Si is isotropic. Moreover, among the U₃Si₂, β-U₃Si, γ-U₃Si and Si-rich USi_1.84 compounds, the γ-U₃Si is hardest and Si-rich USi_1.84 is softest, then U₃Si₂ is much harder than that of β-U₃Si by the Voigt hardness calculations. The hardness value of U₃Si₂ is overestimated in our calculation than experimental data, mainly because the model may be ideal without considering defects and microstructure. The theoretical investigation of this work will be expected to provide parameters for the physical models in the advanced fuel rod performance analysis.

Graphical abstract

The relationship between crystal structures and three dimensions elastic constants