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 UN 2 matrix. The thermodynamic properties and bonding nature of Ba and Zr atoms in different incorporation configurations indicate that Zr is more soluble in UN 2 matrix than Ba. With increasing the concentration of the impurity atoms, Zr-doped UN 2 exhibits a slight tendency to contract, while Ba-doped UN 2 tends to swell. Based on the competition between steric effect and chemical interaction, various incorporation trends for Ba and Zr in UN 2 as well as in UN have been understood.