Fabrication of Nd- and Ce-doped uranium dioxide microspheres via internal gelation

Abstract

The sol-gel route via internal gelation was applied for the production of Nd- and Ce-doped uranium dioxide microspheres. Trivalent and tetravalent Ce precursors were used and the influence of the precursors’ oxidation state on the fabrication process and the final product was studied. The successful introduction of the dopant into the 3UO3⋅2NH3⋅4H2O matrix of the dried gels, independent of the dopant and the oxidation state of its precursor, was demonstrated for Ln contents up to 30 mol%. Densities of the dried gels were determined and the particle volume shrinkage during the thermal treatment was investigated. X-ray powder diffraction analyses proved the presence of U1−yLnyO2±x single phase solid solutions for the sintered Nd-doped microspheres and Ce-doped microspheres prepared using the tetravalent precursor. For Ce-doped compositions prepared with the trivalent precursor, the presence of two solid solutions was observed for Ce contents > 15 mol%. The lattice parameters determined for the single phase solid solutions follow Vegard’s law and show a decreasing lattice parameter with increasing dopant content. In the case for the Nd-doped material different charge compensation mechanisms, depending on the dopant content, were observed. The conditions applied in this study allow the usage of a solution containing the gelation agents, resulting in a particle fabrication process for the production of Pu and/or minor actinide containing UO2 transmutation fuel, which has benefits in terms of automating and remote handling, leading to a better implementation in glove boxes or hot cells.