Application of density functional theory in assessing properties of thoria and recycled fuels

The application of the Density Functional Theory (DFT) approximation to assess the mechanical and structural properties of recycled urania and thoria fuel is presented. The total energy technique based on the local density approximation plus Hubbard U as implemented in the CASTEP code is used. The calculated values of the lattice constants and mechanical moduli of ThO2 and UO2 agree with the experimental data. However only non-local hybrid functional (B3LYP) leads to a larger band gap (6.9 eV) of thoria, in better agreement with experiment (6 eV) than value (4.7 eV) calculated using the LDA + U (6 eV) scheme. The calculations are further expanded to study lattice constants of (Pu, U) oxides and U3O8 for which we currently do not have experimental data. The elastic moduli of ThO2, UO2 and (Pu, U) oxides are compared.