Partitioning and transmutation (P&T) of minor actinides (MA) is currently studied to reduce the nuclear waste inventory. In this context, the fabrication of MA bearing materials is of great interest to achieve an effective recycling of these highly radioactive elements. To ensure the in-pile behavior, nuclear oxide fuels have to respect several criteria including preservation of the fluorite structure and defined oxygen to metal ratio (O/M). In the case of Am bearing materials, such as U(1-y)Am(y)O(2±x) (y = 0.10, 0.15, 0.20), the O/M determination is quite challenging using conventional methods (TGA, XRD) because of the particular thermodynamic properties of Am. Despite the lack of experimental data in the U-Am-O system, thermodynamical models are currently developed to effectively assess the O/M ratio. In this work, the O/M ratios were calculated for various oxygen potentials using the cation molar fraction determined by XAS measurements. These results are an important addition to the experimental data available for the U-Am-O system. Moreover, XRD and XAS indicated that the fabrication of fluorite U(1-y)Am(y)O(2±x) solid solution was achieved for all Am content and oxygen potentials investigated. On the basis of the molar fraction, a description of the solid solution was proposed depending on the considered sintering conditions. Finally, the occurrence of an unexpected charge compensation mechanism was pointed out.

The GALAXIES beamline at the SOLEIL synchrotron is dedicated to inelastic X-ray scattering (IXS) and photoelectron spectroscopy (HAXPES) in the 2.3-12 keV hard X-ray range. These two techniques offer powerful complementary methods of characterization of materials with bulk sensitivity, chemical and orbital selectivity, resonant enhancement and high resolving power. After a description of the beamline components and endstations, the beamline capabilities are demonstrated through a selection of recent works both in the solid and gas phases and using either IXS or HAXPES approaches. Prospects for studies on liquids are discussed.

No abstract

No abstract

Intrinsic properties of a compound (e.g. electronic structure, crystallographic structure, optical and magnetic properties) define notably its chemical and physical behavior. In the case of nanomaterials, these fundamental properties depend on the occurrence of quantum mechanical size effects and on the considerable increase of the surface to bulk ratio. However, the literature on this size-dependence and on the involved mechanisms is quite elusive and scarce. Here, we explore the size-dependence of both crystal and electronic properties of CeO2 nanoparticles (NPs) with different sizes by state-of-the art spectroscopic techniques. XRD, XPS and HERFD-XANES demonstrate that the as-synthesized NPs crystallize in the fluorite structure and they are predominantly composed of Ce IV ions. The strong dependence of the lattice parameter with the NPs size was attributed to the presence of adsorbed species at the NPs surface thanks to FTIR and TGA measurements. In addition, the size-dependence of the t2g level in the Ce LIII XANES spectra was experimentally observed by HERFD-XANES and confirmed by theoretical calculations.

No abstract

XRD, EXAFS and HR-TEM study reveals a strong correlation between AnO2 (An = Th and Pu) nanoparticle size and An(iv) local structure.

No abstract