PyTri-Diol behavior at conditions relevant for i-SANEX and EURO GANEX processes

The Partitioning and Transmutation of long-term radiotoxic Transuranium elements (TRU) is a valid approach for minimizing the high-level waste and optimizing both natural resources exploitation and final repository environmental footprint. Among several processes developed so far, the i-SANEX (innovative-Selective Actinide Extraction) and EURO-GANEX (European-Grouped Actinide Extraction) concepts target the selective separation of Minor Actinides (MA: Am and Cm) or, more ambitiously, of all TRU from lanthanides (Ln) and fission products. The well-established Tetraoctyl-diglycolamide (TODGA) ligand is typically employed to co-extract Ln and MA from the aqueous feed, in association with Dimethyl-Dioctyl-hexyl-ethoxy-malonamide (DMDOHEMA) if all TRU need to be extracted. Afterwards, a hydrophilic complexing agent is required to achieve the selective actinide separation. To this aim, among several molecules proposed so far, the CHON PyTri-Diol ligand exhibited promising TRU extraction selectivity and efficiency, and unprecedented radiolytic and hydrolytic stability. In view of possible future industrial implementation, PyTri-Diol behavior has been studied in conditions closer to the process ones. The effect of temperature on PyTri-Diol extraction capability has been investigated by means of solvent extraction experiments in the temperature range of interest, namely between 10 and 50 C. Even if the MA/Eu separation factor decreases at increasing temperature, the system remains sufficiently selective for MA. Furthermore, the effects of Am and Pu loading on PyTri-Diol performances have been studied. In order to demonstrate the applicability to i-SANEX and EUROGANEX processes respectively, solvent extraction experiments were performed with synthetic aqueous feeds containing real-waste concentration of ²⁴¹Am(III) and ²³⁹Pu(IV). The tests were performed with fresh, aged (1 month) and irradiated (up to 200 kGy with 2.5 kGy/h ⁶⁰Co source) PyTri-Diol solutions, in some cases containing Acetohydroxamic Acid (AHA) to enhance Pu(IV) back-extraction. Remarkably, whether fresh, aged or irradiated, PyTri-Diol alone efficiently and selectively recovers Am(III) and, synergistically with AHA, Pu(IV) present in macro-concentrations. These results are very encouraging and furtherly support the implementation of i-SANEX and EUROGANEX processes based on PyTri-Diol system. (authors)