Theoretical investigation on the solution behaviors of Ba and Zr in uranium dinitride

The in-pile performance of ceramic fuels is significantly affected by the fission products. In this work, we have performed first-principles density functional theoretical calculations to study the interaction between metallic fission products（barium and zirconium） and the uranium dinitride UN2 matrix. The thermodynamic properties and bonding nature of Ba and Zr atoms in different incorporation configurations indicate that Zr is more soluble in UN2 matrix than Ba. With increasing the concentration of the impurity atoms, Zr-doped UN2 exhibits a slight tendency to contract, while Ba-doped UN2 tends to swell. Based on the competition between steric effect and chemical interaction, various incorporation trends for Ba and Zr in UN2 as well as in UN have been understood.