Impact of the next generation solvent on DWPF CPC processing

Abstract

As part of the Actinide Removal Process (ARP)/Modular Caustic-side Solvent Extraction Unit (MCU) Life Extension Project, a next generation solvent (NGS) and new strip acid will be deployed. Processing will begin with a blend of the current solvent and the NGS. Compositional changes in the NGS solvent and blending with the current solvent require review of previously performed work to determine if additional experimental work is required to address any impacts to the Defense Waste Processing Facility (DWPF) Chemical Process Cell (CPC). The composition change involved the substitution of the N,N’-dicyclohexyl-N”-isotridecylguanidine LIX® 79 guanidine suppressor with N,N’,N”-tris (3,7-dimethyloctyl) guanidine (TiDG) guanidine suppressor. The Savannah River National Laboratory (SRNL) was requested by DWPF to evaluate any impacts to offgas generation, solvent buildup or carryover, chemical, thermal, and radiolytic stability of the blended and pure TiDG based NGS. Previous work has been performed by SRNL to evaluate impacts to CPC processing using the next generation solvent containing LIX® 79 suppressor with boric acid strip effluent. Based on previous experimental work and current literature, the following conclusions are made for processing in the CPC: No mechanism for a change in the catalytic hydrogen evolution in the CPC was identified for the NGS TiDG more » based solvent; The transition from the LIX® 79 based suppressor to the TiDG based suppressor is not expected to have any impact on solvent or Isopar® L accumulation; Transitioning from the current solvent to the TiDG based NGS is not expected to have an impact on solvent carryover or partitioning; No changes to the chemical stability of the solvent in the CPC process are expected; No changes to the thermal stability of the solvent in the CPC process are expected; A “worst case” scenario was examined in which all of the hydrogen atoms from the TiDG based NGS and blended solvent form hydrogen gas in the Sludge Receipt and Adjustment Tank (SRAT) as a result of radiolytic degradation. This represented a ~4% increase in the volume percent hydrogen in the SRAT. Given the chemical similarity and very low concentrations of the suppressor, it is not recommended that additional experimental work be performed to qualify any impacts to the DWPF CPC from the change in suppressor or the revised value for partitioning of the suppressor into the strip effluent. « less