[en] The aim of this work was to study the effect of fission fragment damage on the dissolution of UO₂ thin films in water. For this purpose, thin films of UO₂ on LSAT (Al₁₀La₃O₅₁Sr₁₄Ta₇) substrates were produced and irradiated by 92 MeV ¹²⁹Xe²³⁺ ions to a fluence of 4.8 × 10¹⁵ ions/cm² to simulate the fission damage and induce chemical mixing that occur within nuclear fuels. The dissolution experiment was conducted under a nitrogen atmosphere (200–900 O₂ ppm in N₂) to study the effect of the induced irradiation damage and mixing on the dissolution of the UO₂ matrix. The irradiated samples showed a decrease in the amount of dissolved uranium, as compared to the corresponding unirradiated samples. This was ascribed to the irradiation-induced chemical mixing of the UO₂ films with the substrate elements, which resulted in stabilisation of the UO₂ matrix and increased its aqueous durability. Secondary phases were also observed on the surface of the UO₂ films after the dissolution experiment. - Highlights: • Stabilisation of the UO₂ matrix by irradiation-induced chemical mixing. • Greater dissolution resistance of single crystal UO₂ versus polycrystalline. • Secondary phases observed from dissolution of UO₂ films on LSAT in deionised water.