First-principles study of elastic and thermodynamic properties of UO2, gamma-UO3 and alpha-U3O8

A detailed solid-state density functional theory study of uranium dioxide (UO2), gamma uranium trioxide (gamma-UO3), and alpha triuranium octoxide (alpha-U3O8), which are very common materials throughout the nu-clear fuel cycle, was carried out. DFT simulations of these three oxides were presented using both PBE + U and LDA + U functionals to examine their mechanical and thermodynamic properties. The computed lat-tice parameters were found to be in very good agreement with previous experimental results. The values of elastic properties like bulk, shear, and Young's modulus, as well as Poisson's ratio, were predicted, and the calculated Debye temperature was reported. The elastic anisotropy of UO2, gamma-UO3, and alpha-U3O8 was calculated for the first time, from which the anisotropic degrees of these oxides were revealed by the values of anisotropic parameters and three-dimensional surface constructions of elastic properties. In ad-dition, thermodynamic properties of UO2, gamma-UO3, and alpha-U3O8, including heat capacity, entropy, enthalpy, phonon free energy, and Gibbs free energy, were determined as a function of temperature in the range of 0 -20 0 0 K. The computed thermodynamic values show an overall good agreement with available experi-ments, especially at low temperatures. The obtained physical parameters can provide meaningful data for further experimental investigations and promote the development of nuclear fuel cycles.(c) 2022 Elsevier B.V. All rights reserved.

Automated summary

A detailed solid-state density functional theory study was conducted on uranium dioxide, gamma uranium trioxide, and alpha triuranium octoxide. The calculated results were in good agreement with experimental results, providing meaningful data for further experimental investigations.