The development of Generation IV sodium-cooled fast reactors (SFR) is currently studied by several countries, France in particular. To manufacture the UO2-PuO2 fuels for these new types of reactors, new innovative wet colloidal processing routes are investigated. Among these wet colloidal processes, some involve at first the preparation of high solid content water-based suspensions. This key step needs to be investigated in order to obtain highly and easily processable suspensions, featuring optimal viscosity and dispersion state. The structures and properties for all intermediate and final products involved in such ceramic manufacturing processes are heavily affected by these suspension characteristics. Therefore, they are critical to ensure a compliant final product (i.e. fuel pellets) with the required density, homogeneity, mechanical strength and absence of defects. In this scope, preparation process of such suspensions was developed by the use of UO2 and PuO2 surrogating (i.e. mimicking) powders, TiO2 and Y2O3 respectively.