Development of a selective Americium Separation Process by Liquid-Liquid Extraction
Résumé
Recycling americium from spent fuels is an important option considered for the future nuclear cycle as americium is the main contributor to the long-term radiotoxicity and heat power of the ultimate waste. The separation of americium alone from a PUREX raffinate can be achieved by co-extracting lanthanide (Ln) and actinide(III) cations in an organic phase containing TODGA diglycolamide extractant, and then strip Am(III) with selectivity towards curium and lanthanides. The water soluble ligand TPAEN (N,N,N',N'-tetrakis[(6-carboxypyridin-2-yl)methyl]-ethylenediamine) was tested to selectively strip Am from the loaded solvent. Used in combination with TODGA, TPAEN shows a quite high Cm/Am selectivity (SFCm/Am = 4 at 0.1M HNO3), which allows to selectively strip Am while Cm and Ln remain extracted in the organic phase. The molecule can be used at pH 1 without addition of nitrate salts.Further batch extraction data were acquired to design a process flowsheet like extraction isotherms to evaluate the influence of parameters such as americium concentration, temperature, pH, ligand concentration, etc. Kinetics experiments in batch contactors (centrifuges or mixer settlers) are also important to characterize times necessary to reach equilibrium.The impact of radiolysis on TPAEN stripping performances was also characterized after irradiating some samples up to 200 kGy showing that the ligand is particularly sensitive. Further studies should be implemented to better characterize degradation products and impact on process performances.Besides these extraction data, spectroscopic studies are in process to provide detailed knowledge about the chemical species formed in the aqueous phase with TPAEN (micro-calorimetry, UV-visible, TRLIFS, ESI-MS). These results show the formation of 11 species especially with Nd and Am.
Origine : Fichiers produits par l'(les) auteur(s)