Comparative XRPD and XAS study of the impact of the synthesis process on the electronic and structural environments of uranium–americium mixed oxides

Melting behaviour of americium-doped uranium dioxide

“…It was shown that the compounds are fluorite solid solutions for all Am contents. Regarding the charge distribution, equimolar proportions of Am +III and U +V have been measured in U 0.85 Am 0.15 O 2±d [17,18,20] meaning that the O/M ratio is close to 2.00. On the contrary, only U(IV) has been reported for the U 0.90 Am 0.10 O 2±d and U 0.80 Am 0.20 O 2±d compounds used in this work, suggesting the hypo-stoichiometry of these materials [5].…”

“…The chemical compositions are presented in table 1 20 mol.%-Am samples were synthesized at Joint Research CentreInstitute for Transuranium Elements (JRC-ITU) using a process based on combination of (sol + gel) and infiltration methods to produce non-contaminant beads used as precursors for sintering [5,28]. The 15 mol.%-Am samples were prepared at Commissariat à ĺEnergie Atomique et aux énergies alternatives (CEA) from UO 2+d and AmO 2Àe starting powders (similar to those described in [7,8]) following the UMACS process based on two successive thermal treatments separated by a grinding step [7].…”

“…Before conducting the laser heating experiment, the materials have been characterised by XRD and XAS, those results have been already published [5,41]. It was shown that the compounds are fluorite solid solutions for all Am contents.…”

“…The radiotoxicity and heat load of ultimate nuclear waste would thus be decreased as well as the ecological footprint of deep geological repositories [2,3]. In this context, several studies have been dedicated to U 1Àx Am x O 2±d compounds, not only to investigate synthesis methods [4][5][6][7][8][9][10][11] and assess their behaviour under irradiation in reactors [4,7,12,13], but also to determine their structural and thermophysical properties, the latter remaining scarcely known [14][15][16][17][18][19][20]. Among them, no data regarding the U 1Àx Am x O 2±d melting behaviour has been reported, despite the importance of such information with respect to safety margins during irradiation, notably in accidental conditions.…”

“…The samples were also characterised after melting using powder X-ray Diffraction (XRD) and X-ray Absorption Spectroscopy (XAS). A comparison between pre and postmelting structure (local and long-range) and cationic charge distribution can thus be proposed, based on XRD/XAS characterisation of the same compounds already published in the literature [5,17,18,20].…”