Effect of Ce~(4+) and Th~(4+) Ion Substitution in Uranium Dioxide

摘要

Uranium dioxide is the most common fuel used in commercial light water nuclear reactors. The fission of the fuel generates fission products (FPs) and minor actinides (MAs), which affects the thermo-physical properties of the fuel. The understanding of the physical and chemical properties of the FPs and MAs is still limited. In this study we have used atomic level simulations to estimate the effect of Ce~(4+) and Th~(4+) ions in urania matrix. Our results show that the structural variation depends on the elastic effect, which is guided by the ionic radius of the substituted ion. Ce~(4+) (ionic radius 0.97 A) reduces the overall lattice parameter, while Th~(4+) (ionic radius 1.05 A) increases the overall lattice parameter of the urania matrix (U~(4+) ionic radius 1.00 A). In addition bulk modulus of the U_(1-x)Ce_xO_2 system does not change with substitution while the modulus of U_(1-x)Th_xO_2 reduces with an increase in Th~(4+) ion concentration. This observation is in accordance with Vegard's law prediction based on the modulus values of bulk UO_2, CeO_2 and ThO_2 systems.