Lab-scale pulsed columns trials for a new nuclear fuel recycling process

Overview & Synopsis

CEA is currently developing a new spent nuclear fuel reprocessing process, which is especially effective for fuels with high levels of plutonium. The process uses an N,N-dialkylamide extraction molecule. To validate the process chemistry, complete extraction cycles are performed using synthetic feed solutions (uranium and plutonium) or real spent fuel feed solutions. These tests are performed in mixer-settlers, which have the advantage of being miniaturisable and easy to operate in a nuclear confinement enclosure [1]. However, the pulsed column will be the device selected for a future facility, as in the current ORANO plant at La Hague. This apparatus offers several advantages over the mixer-settler, such as crud management, criticality control, and the absence of moving parts. It is mandatory to ensure that this type of apparatus performs correctly with the new solvent, both in terms of hydrodynamics and mass transfer efficiency. The knowledge and experience of CEA and ORANO in the operation of pulsed columns with the current TBP-based solvent cannot be directly applied to the new solvent due to its higher viscosity when loaded with uranium. Therefore, a new study on the operation of pulsed columns is necessary. The latter involves both experimental work and a modeling and simulation approach to support scaling up to an industrial size. This communication presents the results of the experimental part of this approach. The objective of this experimental work is two-fold: first, to demonstrate the suitability of the new solvent for use in pulsed columns under the conditions specified for the new industrial process (including specific flow rates, flow rate ratios, and uranium load); and second, to collect data to validate the models of the pulsed column hydrodynamics. Initial tests were conducted using the smallest columns available at the CEA (15 mm in diameter), in order to minimize the required quantities of uranium and solvent. These tests allowed us not only to optimize the column packing, taking into account the solvent viscosity, but also to demonstrate the efficiency of these columns for uranium extraction and back-extraction. When scaling up from 15 mm columns, the first larger diameter chosen is 25 mm. This diameter allows for a significant increase in flow rates (by a factor of 2.8, corresponding to the cross-section ratio). Furthermore, it is the smallest diameter suitable for disc and doughnut packing, which is the type of packing used in industrial columns.