Computational Study of Defects Behavior in Ceramics Fuels

It is well known that the performance of ceramics nuclear fuel is quite related to the defects behavior under irradiation. In UO2, one of most widely used fuel materials, a characteristic defective structure is found to be emerged after some complex processes under the high burn-up. This so called “Rim structure” induces swelling of the lattice then influences the burning effect and life of the fuel. To investigate the microscopic mechanism of the defective structure behavior in the ceramics fuel, computational study from first principles approach to molecular dynamics has been performed for . for UO2, as well as CeO2, a simulation materials of UO2 used in the accelerator experiments due to its similar structural and thermodynamic properties. These calculations revealed the origin of similarities and differences between these two systems from electronic structure level, and give an explanation on the nonstoichiometric features manifested in the phase diagrams of U-O and Ce-O based on point defects model. Further calculations on defect clusters clarified the ambiguousness remaining for long in the structure of nonstoichiometric UO2+x, proposed a new model of oxygen cluster stability. Meanwhile, the molecular dynamics is applied to large scale simulation of planer defect included one of main fission products, Xe atoms. It showed that a planar distribution is meta-stable for Xe atoms under thermodynamic perturbations.