Infiltration of porous uranium oxide microspheres prepared by internal gelation

Process conditions for the fabrication of porous uranium oxide microspheres prepared via internal gelation were assessed. To improve conditions for the application of infiltration, microstructural parameters such as density, porosity and specific surface area were assessed. Specifically, the effect of calcination temperature and the use of pore-formers was studied. Accessible porosity levels around 20% were obtained after calcination at 773 K or 823 K, without the use of a pore-former. As a novel application, starch was used as a low-temperature, burnable pore-former, and its effect was compared to that of graphite. Accessible porosity levels increased to 34% after calcination due to the use of starch, whereas the application of graphite was discarded because it requires too elevated calcination temperatures. A subset of porous uranium oxide microspheres was infiltrated with neodymium nitrate solution as a surrogate for americium nitrate. Very good agreement between targeted and actual Nd content was observed after sintering of the microspheres, and a maximum concentration of y = 25 mol% (U1-yNdyO2-x) could be reached.