Evaluation of melting behavior in the system UO₂-ZrO₂: Molecular dynamics simulation

Melting point of UO₂ was evaluated by four calculation methods of molecular dynamics simulation. Comparing with the one-phase simulation, the melting point obtained by the two-phase simulation was closer to the experimental value and was almost constant with respect to the size of supercell. In the surface melting simulation, the melting points of supercells with (100) and (110) surfaces were the almost same, however, that obtained for the supercell with (111) surface was higher than others. Using the nanocrystal UO₂ with Wulff shape, the volume dependence of melting point was evaluated. As a result, the melting point increased with the volume of nanocrystal and was lower than those obtained by other simulation methods. Two-phase simulation technique was applied to the evaluation of melting points of UO₂-ZrO₂ solid solutions. The mixing UO₂ and ZrO₂ caused a small instability of a crystal phase, therefore, the fusion enthalpy and melting point of solid solution decreased with an increase of ZrO₂ content up to 60-80 mol%. Above that content, the melting point increased again.