Researchers at the Savannah River Site (SRS) and Oak Ridge National Laboratory (ORNL) examined the performance and stability to irradiation of an improved calix[4]arene-based paraffin extraction solvent consisting of a calix[4]arene chelator, 1-(2,2,3,3-tetrafluoropropoxy)-3-(4-sec-butylphenoxy)-2-propanol (Cs-7SB modifier) and trioctylamine (TOA) for the removal of cesium from high-level waste. As a result of testing performed in 1998, modifications to the solvent system were made to improve chemical stability. The robustness to irradiation of the current calix[4]arene-based solvent system was examined by exposing agitated solvent in contact with aqueous phases representing the composition on the stages of extraction (alkaline waste simulant), scrub (0.05-M nitric acid), and strip (0.001-M nitric acid) to a dose up to 50 Mrad by a Co-60 gamma source. The solvent was also agitated for 101 days with high-level liquid waste from the Savannah River Site (SRS) tanks. After irradiation, the concentration of the components in the solvent system and the identification of degradation products were determined primarily using gas chromatography (GC) and high-performance liquid chromatography (HPLC). The expected yearly dose the solvent will receive is 100 krad/year. An approximately 10% concentration drop in trioctylamine was observed at a 2-Mrad dose of gamma radiation, an estimate 20-year radiation dose. At gamma-radiation doses as high as 16 Mrad, or an estimated 160-year-radiation dose, there was not a significant loss of the calix[4]arene chelator (less than 10%), and there was only a minor loss (less than 2%) of Cs-7SB modifier that yields the degradation product 4-sec-butylphenol. Additional testing indicated that this phenol is readily removed by a caustic wash. Distribution coefficients for Cs between the phases (D-Cs) were also determined using inductively coupled plasma mass spectroscopy (ICP-MS) and gamma-counting methods. Relative to unirradiated solvent, extraction, scrubbing, and stripping performance were not significantly affected by external gamma-radiation doses as high as 8 Mrad, an estimated 80-year dose. These findings indicate that the solvent is stable and retains its expected extraction, scrubbing, and stripping properties after exposure to relatively high-gamma-radiation doses (up to 8 Mrad).