Complexation of Tetravalent Fission Products and Plutonium(IV) with Polyaminopolycarboxylate Ligands
Friend, Mitchell Thomas
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Management of problematic tetravalent fission products and actinides present in the back end of the nuclear fuel cycle presents important scientific and technical challenges concerning the reprocessing and disposal of used nuclear fuel. Zirconium(IV) and technetium(IV) are of particular concern due to their interfering solvent extraction chemistry and behavior in environmental systems, respectively. Zirconium(IV) is one of the major fission product contaminants present in actinide partitioning processes, and polyaminopolycarboxylate ligands are being investigated for sequestering Zr(IV) in reprocessing systems. Technetium 99 will be a long lived component of disposed used nuclear fuel, and the interactions between 99Tc(IV) with polyaminopolycarboxylate ligands is a known factor in increasing its mobility in the environment. The goal of this work was to address these scientific challenges posed in the back end of the nuclear fuel cycle by providing thermodynamic data for some crucial tetravalent fission products, Tc(IV) and Zr(IV), and actinides (Pu(IV)). A series of projects regarding the determination of the stability constants and thermodynamic parameters for Tc(IV), Zr(IV), Hf(IV), and Pu(IV) complexes with polyaminopolycarboxylate ligands was initiated to accomplish this objective. The findings and the thermodynamic data determined in this work generated improved modeling parameters and speciation information for predicting the behavior of these metals in systems pertaining to the back end of the nuclear fuel cycle, which in turn can be used in devising solutions to the associated challenges.