[en] Nuclear fission reactions occurred 2000 Ma ago in the uraninites of the Oklo-Okelobondo and Bangombe uranium deposits (Gabon). These uraninites contain actinides and fission products and therefore are considered as natural analogues for artificial nuclear spent fuel of PWR type nuclear plant. Mineralogical, chemical and oxygen isotopic analyses have been performed in order to determine the stability of the uraninites in weathering conditions. Results show that the alteration of uraninites by meteoric waters affects the cell parameters and the chemistry of the uraninites but not the oxygen isotopic composition. Radiolysis of water is invoked as a possible mechanism for the very low values of δ¹⁸O (-22.0 0/00 SMOW) measured in the uraninites. (authors)