Advances in the Application and Understanding of the CHALMEX FS-13 Process

During the last year, the European demand for electricity has increased and at the same time, the production of planned electricity generation has decreased due to unexpected weather conditions and war. Combined with a limited capability to store energy, low-carbon energy producers such as nuclear power is getting renewed attention in many countries. While having benefits such as reliable, clean, affordable and safe electricity production, the main concerns regarding nuclear power usually refer to the extremely long-lived and radiotoxic final waste. The main contributor to the long-lived radiotoxicity of the spent fuel is Pu and the minor actinides (Np, Am, Cm). The Chalmers Grouped ActiNide EXtraction (CHALMEX) process is a solvent extraction process for the recycling of minor and major actinides as a group, from spent nuclear fuel. By recycling the actinides, and using them as fuel in fast reactors, one can significantly reduce both the overall environmental impact of the nuclear fuel cycle, the lifetime- and the radiotoxicity of the final waste. By combining the extractants TBP with CyMe4-BTBP in the diluent FS-13, the CHALMEX solvent has been shown to have preferential physical properties for use in industrial processes. Separation of the actinides from a spent fuel solution is achieved in only 8 process stages. The co-separation of specific fission products is reduced by the use of masking agents and scrubbing stages. Overall, low degrees of fission product contamination is found in the actinide product stream (<1.5%).The kinetics of the system has also been shown to be compatible with contacting in centrifugal contactors. Despite observation of phase entrainment under certain conditions in a centrifugal contactor, the CHALMEX process is a promising process for the actinide separation from spent nuclear fuels

CHALMEX FS-13 investigations for process implementation

From successive neutron absorption by uranium in nuclear reactors, transuranic elements such as neptunium, plutonium, americium and curium are produced. These elements are the main reason for the long-lived, highly radiotoxic and heat-producing nature of spent nuclear fuel. To reduce the strain on a final repository, the concept of partitioning and transmutation (P&T) has been developed. In P&T, the transuranic elements are partitioned from the nuclear fuel prior to final storage and transmuted into shorter-lived and far less radiotoxic elements. If the transmutation is facilitated in a nuclear reactor, as compared to in an accelerator driven system, further benefits include a more sustainable nuclear fuel cycle due to a reduced need for mining. One partitioning option being developed is the Grouped ActiNide EXtraction (GANEX) process, which is a liquid-liquid extraction concept. In the Chalmers GANEX (CHALMEX) version, 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 for the direct separation of the transuranic elements from a spent nuclear fuel solution. The extractants are dissolved in phenyl trifluoromethyl sulfone (FS-13). The focus of the work presented in this thesis has been the optimisation and evaluation of the CHALMEX system for scaled up operations. Knowledge required for later process simulations, such as distribution ratios of all relevant elements over a range of acid concentrations, has been established. A fission product handling strategy using bimet and mannitol as masking agents has been suggested, although an efficient nickel and cadmium handling strategy is still required

Batch flowsheet test for a GANEX-type process: the CHALMEX FS-13 process

The Chalmers grouped actinide extraction (CHALMEX) process is focused on the co-separation of actinides from all other elements in spent nuclear fuel solution, with the ultimate purpose of transmuting the actinides into shorter-lived and less radiotoxic elements. Based on solvent extraction equilibrium distribution data of actinides and fission products, a preliminary flowsheet was developed and tested in batch mode. The flowsheet consists of one extraction step with the CHALMEX FS-13 solvent (25\ua0mM CyMe4-BTBP in 30% v/v TBP and 70% v/v FS-13), using hydrophilic masking agents (20\ua0mM bimet and 0.2\ua0M mannitol) in the aqueous phase for the complexation of troublesome fission products. Two nitric acid scrub steps (0.5\ua0M HNO3) were efficient in removing co-extracted acid, all molybdenum and the majority of silver. Two stripping stages (0.5\ua0M glycolic acid at pH 4) were efficient in recovery of the actinides from the organic phase. The need for a solvent clean-up stage for the removal of nickel, cadmium, iron and the remaining silver from the organic phase was demonstrated. Based on the distribution data, it was calculated that a 99.9% recovery of americium is possible using only 3 ideal extraction stages, 3 ideal scrubbing stages and 2 ideal stripping stages

Batch Tests for Optimisation of Solvent Composition and Process Flexibility of the CHALMEX FS-13 Process

Studies have been performed with the purpose of determining the optimal solvent composition of a Chalmers grouped actinide extraction (CHALMEX) solvent for the selective co-extraction of transuranic elements in a novel Grouped ActiNide EXtraction (GANEX) process. The solvent is composed of 6,6’-bis(5,5,8,8-tetramethyl-5,6,7,8-tetrahydro-benzo-[1,2,4]-triazin-3-yl)-[2,2’]-bipyridine (CyMe4-BTBP) and tri-n-butyl phosphate (TBP) in phenyl trifluoromethyl sulfone (FS-13). The performance of the system has been shown to significantly depend on the ratios of the two extracting agents and the diluent to one another. Furthermore, the performance of the determined optimal solvent (10\ua0mM CyMe4-BTBP in 30% v/v TBP and 70% v/v FS-13) on various simulated PUREX raffinate solutions was tested. It was found that the solvent extracts all transuranic elements with high efficiency and good selectivity with regard to most other elements (fission products/activation products) present in the simulated PUREX raffinate solutions. Moreover, the solvent was found to extract a significant amount of acid. Palladium, silver, and cadmium were co-extracted along with the TRU-radionuclides, which has also been observed in other similar CHALMEX systems. The extraction of plutonium and uranium was preserved for all tested simulated PUREX raffinate solutions compared to experiments using trace amounts

A comparison on the use of DEHBA or TBP as extracting agent for tetra- and hexavalent actinides in the CHALMEX Process

The Chalmers Grouped ActiNide EXtraction process is a solvent extraction process for the homogeneous recycling of spentnuclear fuel. The use of TBP for the extraction of tetra- and hexavalent actinides can be problematic for several reasons,including troublesome degradation products causing crud formation, decreased extraction yield and the possibility of explosivered oil reactions. Here, the substitution of TBP by a N,N-dialkyl monoamide, DEHBA, is investigated. The findingssuggest that DEHBA can be a suitable extracting agent for use in the CHALMEX solvent, although identified drawbacksneed to be further investigated

An Overview of Solvent Extraction Processes Developed in Europe for Advanced Nuclear Fuel Recycling, Part 2 — Homogeneous Recycling

The hydrometallurgical separation concepts for the recycling of irradiated nuclear fuels developed in Europe are presented and discussed. Whilst Part 1 of the review focused on concepts for heterogeneous recycling of minor actinides, this article focuses on group recycling of transuranic actinides, which would support homogeneous recycling scenarios. Most of these concepts were developed within European collaborative projects and involve solvent extraction processes separating all the actinides (U-Cm) in two cycles. The first cycle uses a monoamide extractant to recover uranium leaving all the transuranic actinides in the aqueous raffinate with the fission products. The second cycle aims for a group recovery of the transuranium elements and several strategies have been proposed for this stage. In this review article, the various solvent extraction processes are summarised and the key features of the process schemes are compared