Fabrication of (U,Am)O2 pellet with controlled porosity from oxide microspheres

International audience; U$_{1-x}$Am$_x$O$_{2\pm\sigma}$ mixed-oxides are considered as promising compounds for americium heterogeneous transmutation in Sodium Fast Neutron Reactor. Porous microstructure is envisaged in order to facilitate helium and fission gas release and to reduce pellet swelling during irradiation and under self-irradiation. In this study, the porosity is created by reducing (U,Am)$_3$O$_8$ microspheres into (U,Am)O$_2$ during the sintering. This reduction is accompanied by a decrease of the lattice volume that leads to the creation of open porosity. Finally, an (U0.90Am0.10)O2 porous ceramic pellet (D$\sim$89% of the theoretical density TD) with controlled porosity ($\geq$ to 8% open porosity) was obtained from mixed-oxide microspheres obtained by the Weak Acid Resin (WAR) process.