Experimental study with DFT validation on the effect of radiation on 1-carboxymethyl-3-methylimidazolium bis(trifluoromethylsulfonyl) imide ([HOOCCH2MIM][NTf2]) as a solvent and extractant in rapid homogeneous extraction of UO22+ was performed for the first time. The radiolytic products of the anions and cations of [HOOCCH2MIM] [NTf2] were identified by F-19 NMR and high-resolution ESI-MS, respectively, and they were attributed to a decrease in UO22+ partitioning. Experimental study with DFT validation for complexing reactions between [HOOCCH2MIM] [NTf2] and radiolytic products proved that F- competition was one of the main reasons for the decrease in UO22+ partitioning. However, UO22+ partitioning in irradiated [HOOCCH2MIM] [NTf2] can largely be recovered after thorough water washing because of the removal of radiolytic products of [NTf2](-).