Infiltration of porous uranium oxide microspheres for transmutation target preparation

A major challenge in the utilization of nuclear energy is the management of spent nuclear fuel. While uranium and plutonium can be recycled, the long-term radiotoxicity remains dominated by a group of elements known as the minor actinides (Am, Np, Cm). To reduce the footprint of spent fuel, sustainable methods for partitioning and transmutation of minor actinides are being investigated. We have examined a hybrid route combining internal gelation and infiltration to prepare U1-yNdyO2-x microspheres as a surrogate for U1-yAmyO2-x transmutation targets. The fabrication of porous uranium oxide microspheres, showing efficient infiltration of a dopant solution into the host matrix, was studied by using starch or graphite as a pore-former in the internal gelation process. In particular, the effects of a change in calcination temperature prior to infiltration were investigated. By using starch as pore former and applying a calcination temperature between 823 K and 923 K, high accessible porosity levels (∼30%) were obtained, and average dopant levels up to y = 30 mol% after sintering could be achieved. The evolution of microstructural properties such as phase composition, porosity distribution, grain size and dopant homogeneity throughout the hybrid fabrication route are discussed in more detail.