First Principles Investigations of Alternative Nuclear Fuels

In this work we present a comparison of properties for U₃Si₂, UN and UO₂ using first principles calculation. The local density approximation (LDA) and generalized gradient approximation (GGA/WC) predict that U₃Si₂ is non-magnetic while GGA/PBE predicts that ferromagnetic ordering (not observed experimentally) is more stable by just 0.02 eV per uranium atom. On the other hand, the ground states of Urania and UN are independent of the used functional, with a non-zero magnetic moment on uranium. U₃Si₂ is predicted to have lower binding energy (−14.4 eV) than UN (−20.4 eV) and UO₂ (−32.7 eV) and a lower melting point (1796 K vs. 2932 and 2987 K, respectively). The calculated minimal lattice thermal conductivity in W(m⁻¹ K⁻¹), indicates that phonon contribution to the thermal conductivity is smaller in both UN and U₃Si₂ (0.78 and 0.64 vs. 1.06). However calculations confirm that UN and U₃Si₂ are safer alternative fuels due to their electronic thermal conductivity’s increasing with temperature as also observed experimentally.