FPEX γ-radiolysis in the presence of nitric acid

The solvent formulation known as FPEX (Fission Product Extraction) contains calix[4]arene-bis-(tert-octylbenzo-crown-6) (BOBCalixC6) for Cs extraction; 4,4 ',(5 ')-di-(t-butyidicyclohexano)-18-crown-6 (DtBuCH18C6) for Sr extraction; 1-(2,2,3,3,-tetrafluoropropoxy)-3-(4-sec-butylphenoxy)-2-propanol (Cs-7SB) modifier and trioctylamine (TOA) to aid in Cs stripping, all in an Isopar L diluent. This formulation has favorable extraction efficiency for Cs and Sr from acidic solution, and was investigated here for gamma-radiation stability. When FPEX was irradiated in contact with aqueous nitric acid, the extraction efficiency decreased only slightly when irradiated to absorbed doses as high as 200 kGy. The color of the organic phase changed to a deep yellow-orange, and several new peaks related to radiolysis of the Cs-7SB modifier were detected by GC-ECD analysis. This had little effect on the solvent extraction distribution ratios. Possible reasons for this unexpected robustness under conditions of high radiation and acidity are discussed.