Uranium Nitride (UN) Doped with Niobium (Nb) as a New Nuclear Fuel

Abstract

Uranium nitride (UN) has emerged as a strong candidate for advanced nuclear fuels owing to its high uranium density, excellent thermal conductivity, and favourable neutronic characteristics relative to conventional UO2. A key limitation of UN, however, is its susceptibility to oxidation. This drawback can be alleviated through doping strategies, which facilitate the formation of more stable oxides and thereby improve the fuel’s overall performance. The study employed sputtering deposition to synthesise uranium nitride (UN) thin films doped with niobium (Nb) under varying sputtering conditions. The samples were characterised using X-ray diffraction (XRD), X-ray reflectivity (XRR), and X-ray photoelectron spectroscopy (XPS). Data analysis and fitting were carried out using GenX for XRR and CasaXPS for XPS. The findings reveal a shift in the diffraction peaks toward higher 2θ values, observed as a movement to the right, was noted, which typically indicates a reduction in the lattice parameter and hence lattice contraction. This effect arises because niobium atoms substitute for uranium within the UN lattice; owing to its smaller atomic radius relative to uranium, niobium incorporation reduces the interatomic spacing. XRR analysis confirmed differences in layer thickness, density, and interface roughness, while XPS indicated similar U 4f peak positions across the tested samples with minor variations in chemical states. These results demonstrate the significant influence of niobium incorporation on the structural and chemical properties of UN, providing insights for optimising doped nitride fuels for advanced reactor applications.