XANES characterization of UO sub(2)/Mo(Pd) thin films as models for [epsilon]-particles in spent nuclear fuel

X-ray absorption near edge structure (XANES) is recorded for nano- and microparticles formed in Mo doped UO sub(2) thin films (TFs) prepared by in situ sputter co-deposition and 1000[degrees]C tempering. These UO sub(2)/Mo TFs are intended to serve as synthetic models for [epsilon]-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 USi sub(3), which forms at the high temper temperatures. Micron-sized Mo-particles are formed when SiO sub(2) is used as substrate. Using focussed X-ray beams of varying size (500[mu]m, 25[mu]m and 5[mu]m), these particles are characterized to be predominantly hexavalent Mo oxides, potentially with tetrahedral coordinated [Mo(VI)O sub(4)] super(2-) at the surface and a MoO sub(3)-like phase in the bulk. These TFs are poor synthetic models for spent fuel [epsilon]-particles but do offer the opportunity to study changes in surface structures in response to stress/charge as a function of particle size.