The aim of this work was to study the effect of fission fragment damage on the dissolution of UO$2$ thin films in water. For this purpose, thin films of UO$2$ on LSAT (Al$\mathrm{<mrow\; data-mjx-texclass="ORD">10</mrow>}$La$3$O$\mathrm{<mrow\; data-mjx-texclass="ORD">51</mrow>}$Sr$\mathrm{<mrow\; data-mjx-texclass="ORD">14</mrow>}$Ta$7$) substrates were produced and irradiated by 92 MeV $\mathrm{<mrow\; data-mjx-texclass="ORD">129</mrow>}$Xe$\mathrm{<mrow\; data-mjx-texclass="ORD">23+</mrow>}$ ions to a fluence of 4.8 × 10$\mathrm{<mrow\; data-mjx-texclass="ORD">15</mrow>}$ ions/cm$2$ 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 O$2$ ppm in N$2$ ) to study the effect of the induced irradiation damage and mixing on the dissolution of the UO$2$ 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 UO$2$ films with the substrate elements, which resulted in stabilisation of the UO$2$ matrix and increased its aqueous durability. Secondary phases were also observed on the surface of the UO$2$ films after the dissolution experiment.