Selective separation of Am(III) from PUREX raffinate with a TODGA-based solvent using innovative hydrophilic complexing agents

The minor actinides (americium and curium) contribute to less than 0.1% of the initial spent fuel mass, but dominate the long-term radiotoxicity and heat load of the residual high active waste (e.g. vitrified waste) after PUREX. Several solvent extraction processes using different strategies (multi-cycle versus single-cycle) have already been developed for minor actinide separation from PUREX raffinate[1]. Due to the high radioactivity and share of spontaneous fission in the decay of curium isotopes, any fabrication of curium containing nuclear fuel would require special handling and a facility with high level of shielding. Therefore, an effective method for separating Am(III) alone prior to re-fabrication is a major prerequisite for the discussion of further innovative fuel cycle scenarios. This strategy requires separating Am(III) from Cm(III), which is an even more challenging task than the actinide(III)/lanthanide(III) separation. In the framework of the European funded project SACSESS three different approaches have been investigated. They are based on the co-extractiion of lanthanide(III) and actinide(III) cations from a PUREX raffinate into an organic phase containing the diglycolamide TODGA as extractant, and then stripping Am(III) with selectivity towards Cm(III) and lanthanides. Three ligands were studied: H4TPAEN developed at the CEA Marcoule, TS-BTPhen developed at the University of Reading, UK, and SO3-Ph-BTBP developed at KIT. Very promising results were achieved for all systems with a quite high Cm(III)/Am(III) selectivity between 3-4 to carry out the difficult separation at reasonably high process relevant nitric acid acidities. This paper summarizes the work performed to design flowsheets of the Am(III) stripping step in preparation for demonstration tests using centrifugal contactors and is divided in three main sections: Acquisition of batch experimental data for the model, the development of a flow sheet and tests on single centrifugal extractors to get information on the kinetic and hydraulic performance of the systems. [1] Modolo, G.; Geist, A.; Miguirditchian, M. Minor Actinide Separations in the Reprocessing of Spent Nuclear Fuels: Recent Advances in Europe. Chap. 10 In Reprocessing and Recycling of Spent Nuclear Fuel; Taylor R., Ed.; Woodhead Publishing: Oxford, 2015; 245–287