Optimization of new ligands for the complexation of Ru and Tc for future spent fuel recycling processes

This thesis is anchored in the framework of the spent nuclear fuel reprocessing by a liquid liquid extraction process with the TBP molecule or a monoamide as an extractant molecule. The aim of this process is to recover uranium and plutonium in the organic phase. However, some fission products, like ruthenium and technetium, are also extracted. The studied way in this work is to add a masking agent in the aqueous phase to avoid the extraction of ruthenium and technetium, or to back extract these elements during a scrubbing stage. For the ruthenium, two different molecules were studied with OH group or nitrogen donor atoms. However, the ruthenium speciation in nitric acid medium is changing with the experimental conditions, so finding a selective masking agent is difficult. The best results obtained in this work is to heat the scrubbing stage as it allows the selective back extraction of ruthenium. For technetium, some polyammonium cage ligands were tested to maintain this element in the aqueous phase during the extraction step or during the back extraction. The first studied molecule, whose solubility is weak in nitric acid medium, was optimized by adding hydrophilic groups. For the most soluble ligand, some outstanding results were obtained for technetium back extraction: it is selective towards uranium and plutonium and the equilibrium is reached very quickly. Masking agent stability regarding γ radiolysis has also been studied and results show similar complexation strength than before irradiation. (author)