The development of Generation IV sodium-cooled fast reactors (SFR) is currently studied by several countries. These new type of reactors are intended to use new types of UO$_2$-PuO$_2$ nuclear fuels. In order to produce them, new innovative liquid routes are investigated. Among these liquid route 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 UO$_2$ and PuO$_2$ surrogating (i.e. mimicking) powders, TiO$_2$ and Y$_2$O$_3$ respectively.