Study of the stability of BTP extractants under radiolysis

One of the hydrometallurgical options studied by CEA to separate trivalent minor actinides (An(III)) from highly active PUREX raffinates, consisted first in co-extracting An(III) and Ln(III) by a malonamide and, second, in separating An(III) from Ln(III) by a bis-triazinyl-pyridine (BTP). If malonamides have been successfully applied to the treatment of genuine spent fuel dissolution liquors, the various tetra-alkyl substituted BTP molecules studied until 2001 have shown that they were too sensitive to acidic hydrolysis and alpha radiolysis to envisage the development of an An(III)/Ln(III) separation process. That is why, in the framework of FP5 and FP6 European Integrated Projects (PARTNEW and EUROPART), new structures of Nitrogen polydentate extractants have been synthesized at Reading University (UK) and tested at CEA Marcoule, both on the view point of their extraction properties and on their radiolysis stability. These new ligands are (1) BTPs bearing 'annulating' groups on their triazinyl rings (BTPs), (2) bis-triazinyl-bis-pyridines (BTBPs) and (3) annulated BTBPs (BATBPs). This paper presents the basic research carried out at CEA Marcoule for the past three years to strengthen the BTP stability vs radiolysis and to improve their extraction properties and kinetics (both in extraction and stripping steps of An(III)). (author)