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

The sol-gel route via internal gelation was applied for the production of Nd- and Ce-doped uraniumdioxide microspheres. Trivalent and tetravalent Ce precursors were used and the influence of the pre-cursors’oxidation state on the fabrication process and thefinal product was studied. The successfulintroduction of the dopant into the 3UO3,2NH3,4H2O matrix of the dried gels, independent of thedopant and the oxidation state of its precursor, was demonstrated forLncontents up to 30 mol%.Densities of the dried gels were determined and the particle volume shrinkage during the thermaltreatment was investigated. X-ray powder diffraction analyses proved the presence of U1yLnyO2±xsinglephase solid solutions for the sintered Nd-doped microspheres and Ce-doped microspheres preparedusing the tetravalent precursor. For Ce-doped compositions prepared with the trivalent precursor, thepresence of two solid solutions was observed for Ce contents>15 mol%. The lattice parameters deter-mined for the single phase solid solutions follow Vegard’s law and show a decreasing lattice parameterwith increasing dopant content. In the case for the Nd-doped material different charge compensationmechanisms, depending on the dopant content, were observed. The conditions applied in this studyallow the usage of a solution containing the gelation agents, resulting in a particle fabrication process forthe production of Pu and/or minor actinide containing UO2transmutation fuel, which has benefits interms of automating and remote handling, leading to a better implementation in glove boxes or hot cells