  A R&D program is developed at the ALTO facility to provide new beams of
exotic neutron-rich nuclei, as intense as possible. In the framework of
European projects, it has been shown that the use of refractory targets with
nanometric structure allows us to obtain beams of nuclei unreachable until now.
The first parameter to be controlled in the processing to obtain targets with a
homogeneous nanostructure is the grinding of uranium dioxide, down to 100 nm
grain size. In this study, dry and wet grinding routes are studied and the
powders are analyzed in terms of phase stabilization, specific surface area and
grain morphology. It appears that the grinding, as well dry as wet, leads to
the decrease of the particle size. The oxidation of UO2 is observed whatever
the grinding. However, the dry grinding is the most efficient and leads to the
oxidation of UO2 into U4O9 and U3O7 whose quantities increase with the grinding
time while crystallite sizes decrease.
