γ-Radiation Effects on the Performance of HCCD-PEG for Cs and Sr Extraction

Cobalt dicarbollide and polyethylene glycol in phenyltrifluoromethyl sulfone (HCCD/PEG in FS-13) is currently under consideration for use in the process-scale selective extraction of fission product cesium and strontium from acidic radioactive solutions. While the Cs and Sr solvent extraction efficiency of this formulation has been previously characterized, this solvent will be exposed to high radiation doses during use, and has not been adequately investigated for radiation stability. Here, HCCD/PEG was γ-irradiated to various absorbed doses, to a maximum of 432 kGy, using 60Co. Irradiations were performed for the neat organic phase, and also for the organic phase in contact with 1M-nitric acid mixed by air sparging. Post-irradiation solvent extraction measurements showed that Cs distribution ratios were unaffected, however, strontium distribution ratios decreased with absorbed dose under both conditions. The decrease in extraction efficiency for strontium was greater when in contact with the aqueous phase. Stripping performance was not affected. A mechanism, based on reaction with the products of direct diluent radiolysis is proposed to explain the decreases in strontium extraction efficiency