XANES characterization of UO2/Mo(Pd) thin films as models for ϵ-particles in spent nuclear fuel

Abstract

X-ray absorption near edge structure (XANES) is recorded for nano- and micro-particles formed in Mo doped UO2 thin films (TFs) prepared by in situ sputter co-deposition and 1000°C tempering. These UO2/Mo TFs are intended to serve as synthetic models for ϵ-particles in spent nuclear fuel. We find that when Si is used as substrate, nano-sized zero-valent Mo particles form as desired. However, these are embedded in USi3, which forms at the high temper temperatures. Micron-sized Mo-particles are formed when SiO2 is used as substrate. Using focussed X-ray beams of varying size (500μm, 25μm and 5μm), these particles are characterized to be predominantly hexavalent Mo oxides, potentially with tetrahedral coordinated [Mo(VI)O4]2− at the surface and a MoO3-like phase in the bulk. These TFs are poor synthetic models for spent fuel ϵ-particles but do offer the opportunity to study changes in surface structures in response to stress/charge as a function of particle size.