Speaker
Description
Closing the nuclear fuel cycle through advanced reprocessing of spent nuclear fuel is a key strategy to improve resource utilization, reduce the long-term radiotoxicity of high-level waste, and minimize the volume destined for deep geological disposal. A wide range of partitioning and separation approaches has therefore been investigated to recover fissile and fertile materials, particularly uranium, plutonium, and minor actinides. The mission is focused on recycling these nuclides as energy resources for Generation IV reactor systems, since in fast-neutron spectra, heavy nuclides exhibit more favorable fission and transmutation behavior.
Within this framework, the CHALMEX process is a solvent-extraction-based partitioning concept developed at Chalmers University of Technology. The process is designed to achieve the quantitative recovery of actinides from spent nuclear fuel using dedicated solvent extraction equipment, including mixer-settlers and centrifugal contactors. In this process, two extractants, tri-n-butyl phosphate (TBP) and 6,6’-bis-(5,5,8,8-tetramethyl-5,6,7,8-tetrahydro-benzol-[1,2,4]-triazin-3-yl)-[2,2’]-bipyridine (CyMe4-BTBP), are combined and dissolved in phenyl trifluoromethyl sulfone (FS-13), enabling the direct separation and quantitative recovery of actinides.
From an industrial implementation perspective, centrifugal contactors are attractive and under investigation due to their compact design, rapid phase separation, and high mass-transfer rates. Consequently, kinetic performance and phase stability under operational conditions become crucial parameters for reliable extraction efficiency and process robustness. In parallel, nuclear criticality safety considerations remain central for the handling of fissile materials. In this case, mixer-settlers are of particular interest because the settler compartment operates without mechanical agitation and relies on gravity-driven phase disengagement, which can promote phase holdup gradients, stratification, and localized accumulation of fissile nuclides (e.g., 239-Pu). Such phenomena may create unfavorable reactivity configurations and therefore require careful evaluation in accordance with OECD/NEA and IAEA nuclear criticality safety guidance.
So far, the work is addressing two complementary aspects of the CHALMEX recycling system: kinetic and phase-behavior requirements for the process scale-up, and criticality safety considerations, relevant when mixer-settlers are selected. Together, these elements allow technology choice and operating conditions for robust actinides recovery.