Exploring how exposure to radiolysis and harsh chemical reagents impact americium-241 extraction chromatography†

Abstract

Improving control over radiolysis would advance nuclear technologies, spanning from radiotherapeutics to national security. There is therefore a need to better understand the impact from radiolysis on chemical transformations. Unfortunately, it is difficult to distinguish the impact from radiolysis vs. conventional stimuli for many processes that involve radionuclides. This problem was addressed herein by studying how radiolysis and exposure to chemical processing agents impacted a key separation step in the large-scale production of 241Am for industrial use, via ChLoride Extraction And Recovery (CLEAR). To achieve this goal, aliquots of the McKee-carbamoylmethylphosphine oxide (m-CMPOTBP) resin used in active 241Am(aq) CLEAR process columns were obtained and characterized for (1) americium retention/ release, (2) contaminant removal, and (3) resin degradation. The separative performance from these ‘veteran’ resins (having been exposed to 241Am and processing agents) was evaluated against ‘pristine’ (not exposed to 241Am and processing agents) m-CMPOTBP, rare earth (RE), tetraoctyldiglycolamide (TODGA), and tetraethylhexyldiglycolamide (TEHDGA) resins. The separative performances of ‘pristine’ resins were evaluated after systematic exposure to radiation and acid [HCl(aq)]. Our results showed that TODGA and TEHDGA were more resistant to chemical degradation and outperformed m-CMPOTBP and RE for americium binding capacity, recovery, and purification. These studies also demonstrated how two important extractant classes (CMPO and DGA) succumbed to radiolytic and chemical degradation, leading us to conclude that the DGA resins retained separative performance to a larger extent than the CMPO alternatives. In terms of application, the data suggested that CLEAR processing of 241Am(aq) for industrial use would be more robust and effective if TODGA or TEHDGA was used in place of m-CMPOTBP