The durability of concretes under irradiation must be investigated in connection with research on radioactive waste conditioning (matrices, canisters) and disposal (engineered barriers). The weak element of the concrete, the water present in the pores, or in the hydrated compounds, is the source of radiolysis, the chief cause of radiation damage. The emission of associated dihydrogen, or radiolytic breakdown by internal overpressure, are two objective risks for which the many factors involved and the heterogeneous nature of the material make any long-term forecast difficult.