[en] The behaviour of the spent nuclear fuel in the conditions expected in a deep geological repository depends on some basic processes such as the formation of oxidizing species due to the radiolysis of water, the effect of these species on the spent nuclear fuel matrix oxidation and dissolution, and the precipitation of secondary solid phases. In this work, some of those processes have been studied in detail. In particular, both uranium dioxide oxidation and dissolution rates have been determined in the presence of oxygen an hydrogen per-oxide (the most important molecular species formed in the radiolysis of water). In addition, the precipitation of secondary phases on the UO₂ surfaces in the presence of hydrogen peroxide has also been fool owed by means of the Atomic Force Microscope allowing the identification of studies (UO₄.H₂O). On the other hand, the radiolytical models of the dissolution of spent nuclear fuel need to estimate the surface site densities of the solid. In this sense, we have studied surface site densities of three different uranium oxides: UO₂, U₃O₈, and UO₃.4H₂O. (Author) 42 refs