Christian Schreinemachers

Direct Selective Extraction of Actinides (III) from PUREX Raffinate using a Mixture of CyMe4BTBP and TODGA as 1-cycle SANEX Solvent

Abstract Within the framework of our research activities related to the partitioning of spent nuclear-fuel solutions, the direct selective extraction of trivalent actinides from a simulated PUREX raffinate was studied using a mixture of CyMe4BTBP and TODGA (1-cycle SANEX). The solvent showed a high selectivity for trivalent actinides with a high lanthanide separation factor. However, the coextraction of some fission product elements (Cu, Ni, Zr, Mo, Pd, Ag, and Cd) from a simulated PUREX raffinate was observed, with distribution ratios up to 30 (Cu). The extraction of Zr and Mo could be suppressed using oxalic acid but the use of the well-known Pd complexant N-(2-Hydroxyethyl)-ethylendiamin-N,N′,N′-triacetic acid (HEDTA) was unsuccessful. During screening experiments with different amino acids and derivatives, the sulfur-bearing amino acid L-Cysteine showed good complexation of Pd and prevented its extraction into the organic phase without influencing the extraction of the trivalent actinides Am (III) and Cm (III). The optimization studies included the influence of the L-Cysteine and HNO3 concentration and the kinetics of the extraction. The development of a process-like extraction series showed very promising results in view of further optimizing the process. A strategy for a single-cycle process is proposed within this article.

Direct Selective Extraction of Actinides (III) from PUREX Raffinate using a Mixture of CyMe4BTBP and TODGA as 1-cycle SANEX Solvent Part III: Demonstration of a Laboratory-Scale Counter-Current Centrifugal Contactor Process

The direct selective separation of the trivalent actinides americium and curium from a simulated Plutonium Uranium Refining by EXtraction (PUREX) raffinate solution by a continuous counter-current solvent extraction process using miniature annular centrifugal contactors was demonstrated on a laboratory scale. In a 32-stage spiked test (12 stages for extraction, 16 stages for scrubbing, and 4 stages for Am/Cm stripping), an extractant mixture of CyMe4BTBP and TODGA in a TPH/1-octanol mixture was used. The co-extraction of some fission and corrosion product elements, such as zirconium and molybdenum, was prevented by using oxalic acid. Co-extracted palladium was selectively stripped using an L-cysteine scrubbing solution and the trivalent actinides were selectively stripped using a glycolic acid-based stripping solution. It was demonstrated that a selective extraction and high recovery of > 99.4% of the trivalent minor actinides was achieved with low contamination by fission and corrosion products. The product contained 99.8% of the initial americium and 99.4% of the initial curium content. The spent solvent still contained high concentrations of Cu, Cd, and Ni. The experimental steady-state concentration profiles of important solutes were determined and compared with those from computer-code calculations.

Use of Polyaminocarboxylic Acids as Hydrophilic Masking Agents for Fission Products in Actinide Partitioning Processes

During the partitioning of trivalent actinides from High Active Raffinate (HAR) solutions, most processes have to cope with an undesirable co-extraction of some of the fission products. Four hydrophilic complexing agents of the group of polyaminocarboxylic acids, namely EDTA, HEDTA, DTPA, and CTDA were tested and compared for their ability to complex fission products in a simulated PUREX raffinate solution, thereby preventing their extraction into an organic solvent. Several solvents, based on TODGA and the DIAMEX reference molecule DMDOHEMA, that are commonly known to show quite high Zr and Pd co-extraction, were studied. Our investigations ultimately resulted in a substitution of oxalic acid and HEDTA by cyclohexanediaminetetraacetic acid (CDTA). A small addition of this hydrophilic complexing agent to the feed decreased the distribution ratios of Zr from 100 to <0.01. The suppression of Pd was also very effective, resulting in >90% of the metal retained in the feed solution. The extraction of trivalent actinides and lanthanides was not negatively affected by the presence of CDTA. Furthermore, experiments with high concentrations of Zr proved the applicability of this new masking agent. The suppression of Zr and Pd extraction was also verified at a high Pu loading which makes CDTA as a masking agent attractive for grouped actinide extraction processes (GANEX) as well as DIAMEX-SANEX type separations.