Abstract : After spent nuclear fuel processing, the Zircaloy-4 cladding tubes are compacted in a wafer form, placed into a steel container, and then into a concrete over-pack with a view to being disposed of in geological repository. These wastes are mostly composed of activated oxidized metal pieces which also contain traces of fission, activation products and actinides. In the repository, they are exposed to radioactivity in presence of resaturation water. The water radiolysis may accelerate the oxidised metal corrosion processes. By the way, the wastes degradation is mainly due to corrosion process. A fundamental study has thus been defined on the effects of vapour and liquid water radiolysis on Zircaloy-4 corrosion. Various water vapour pressures have been studied with proton irradiation and an aqueous solution simulating resaturated waste water was used with gamma irradiation. The results obtained on samples irradiated or not have been compared to determine the effect of water radiolysis on the stability of the oxide layer.