Theoretical study on stability, mechanical and thermodynamic properties of (Pu, Zr)N

Actinide nitrides possessing the advantages of high burn-up, superior thermophysical properties and easy reprocessing in nitric acid, are currently considered as promising fuels for advanced nuclear reactors. In this work, a systemic study on the stability, mechanical and thermodynamic properties of (Pu, Zr)N was conducted employing the first-principles density functional theory approaches. We found that the ternary compound (Pu, Zr)N tends to exist in the form of single cubic NaCl-type solid solution, confirmed by incorporation and solution energies of Zr in PuN crystals. The calculated elastic constants of the (Pu, Zr)N crystals satisfy the stability criteria of tetragonal structures, proving their mechanical stability. It is revealed that the elastic constants and mechanical properties such as mechanic moduli and Poisson's ratio monotonically change with the concentration of Zr in (Pu, Zr)N crystals. Additionally, the specific heat also changes monotonically with the concentration of Zr derived from phonon-dispersion spectrums. The obtained results can shed light on the understanding of plutonium nitride materials in the nuclear energy cycles.