Synthesis and characterization of homogeneous (U,Am)O(2) and (U,Pu,Am)O(2) nanopowders

This paper details the first dedicated production of homogeneous nanocrystalline particles of mixed actinide oxide solid solutions containing americium. The target compositions were U(0.75)Pu(0.20)Am(0.05)O(2), U(0.90)Am(0.10)O(2) and U(0.80)Am(0.20)O(2). After successful hydrothermal synthesis and chemical characterisation, the nanocrystals were sintered and their structure and behaviour under self-irradiation were studied by powder XRD. Cationic charge distribution of the as-prepared nanocrystalline and sintered U(0.80)Am(0.20)O(2) materials was investigated applying U M(4) and Am M(5) edge high energy resolution XANES (HR-XANES). Typical oxidation states detected for the cations are U(iv)/U(v) and Am(iii)/Am(iv). The measured crystallographic swelling was systematically smaller for the as-synthesised nanoparticles than the sintered products. For sintered pellets, the maximal volumetric swelling was about 0.8% at saturation, in line with literature data for PuO(2), AmO(2), (U,Pu)O(2) or (U,Am)O(2).