Codecontamination is a solvent extraction process that uses tributyl phosphate (TBP) to co-extract U, Pu, and Np from spent fuel dissolved in nitric acid, followed by selective stripping to recover U/Pu/Np in a single product stream, and the remaining U in a second effluent. For successful separation, the process requires predictable control of the behavior of the key species involved in the separations. In terms of flowsheet design, the major factors include controlling the U:TRU ratio in the U/Pu/Np product, directing the majority of the Np to the U/Pu/Np product, minimizing the extraction of fission products (specifically Mo, Ru, and Zr), and controlling Tc behavior. To that end, lab-scale flowsheet testing has been divided into three components: (1) demonstrating that extraction of the key fission products, Ru, Mo and Zr is controlled as predicted by the Argonne Model for Universal Solvent Extraction (AMUSE) code, (2) characterizing the extraction of Np as a function of redox chemistry, and (3) demonstrating the partial stripping of U in the second segment of the process. Multistage tests of the first and second segments of the Codecontamination flowsheet were run with a lab-scale 2-cm contactor to validate the design criteria used to develop the flowsheet. A number of small-scale tests were also conducted using a microfluidic extraction device. By varying flow rates and capillary lengths, mass transfer and kinetics data can be elucidated for U and Np in the TBP/alkane-nitric acid system. The behavior of U in the extraction is well-understood, which allows us to characterize the microfluidics device. Since Np demonstrates complicated redox chemistry that is difficult to regulate at large scales in this process, the microfluidic device was used to elucidate the Np extraction kinetics for different processing conditions.
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