Group Actinide Extraction Research Articles

Physicochemical properties of extraction solvents for the advanced recycling of spent nuclear fuel

A comprehensive understanding of solvent physicochemical properties is essential to developing advanced solvent extraction processes, such as Advanced PUREX (Plutonium Uranium Reduction Extraction) and GANEX (Group Actinide Extraction), that can safely and efficiently recycle spent nuclear fuel. The densities, viscosities and surface tensions of binary mixtures of tributyl phosphate (TBP) (0.92–3.66 M) in n-dodecane and N,N-di (2-ethyl hexyl)isobutyramide (DEHiBA) (0.69–2.78 M) in n-dodecane were measured at atmospheric pressure from 278.15 to 333.15 K. Through these measurements, empirical expressions to predict the density and viscosity at any molar composition of these solvents within the studied temperature range were constructed and shown to be in good correlation with all experimental data across the studied variables. The relationship between temperature and viscosity of pure TBP and DEHiBA can be described by the Arrhenius equation for viscosity in the temperature range studied. Surface tension measurements (air-liquid interface) were obtained for varying extractant concentrations between 278.15 and 333.15 K, which showed that DEHiBA acts as a surfactant when mixed with n-dodecane whilst TBP exhibits a higher surface tension than n-dodecane.

Solvent Optimization Studies for a New EURO-GANEX Process with 2,2’-Oxybis(N,N-di-n-decylpropanamide) (mTDDGA) and Its Radiolysis Products

ABSTRACT The diglycolamide 2,2’-oxybis(N,N-di-n-decylpropanamide) (mTDDGA) is being studied as an extractant for actinides and lanthanides in the European Grouped Actinide Extraction (EURO-GANEX) process. The aim is the development of a more simplified process using a single extractant instead of a mixture of extractants used in the current EURO-GANEX process. This work presents solvent optimization studies of mTDDGA, with regards to the extraction characteristics of the different diastereomers of mTDGA and of mixed diastereomer solutions. Also radiolysis behavior has been studied by irradiation of solvent extraction systems in a gamma irradiation facility using 60Co. The availability of irradiated organic solutions made it possible to gain valuable insights into the plutonium loading capacity after gamma-irradiation of the solvent up to 445 kGy and to quantify degradation compounds. Solvent extraction characteristic of the major degradation compounds themselves were determined. Like other methylated diglycolamides, we found a remarkable difference in extraction of up to two orders of magnitude between the two diastereomers. High plutonium loading (36 g L−1) is feasible using this single extractant, even after absorbing a dose of 445 kGy. This remarkable observation is possibly promoted by the presence of the main degradation compound which extracts plutonium verywell.

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 spent nuclear 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 explosive red oil reactions. Here, the substitution of TBP by a N,N-dialkyl monoamide, DEHBA, is investigated. The findings suggest that DEHBA can be a suitable extracting agent for use in the CHALMEX solvent, although identified drawbacks need to be further investigated.

Effects of Gamma Irradiation on the Extraction Properties of Innovative Stripping Solvents for i-SANEX/GANEX Processes

Recovery of trivalent minor actinides or of the transuranium elements from highly active raffinate could be industrially achieved by innovative Selective ActiNide EXtraction (i-SANEX) and Grouped ActiNide EXtraction (GANEX) processes, respectively. All chemicals involved in the partitioning of actinides must be resistant to acidic and radioactive environments since hydrolysis and radiolysis can have a huge impact on process safety and performance. In this work, the hydrolytic and radiolytic stabilities of two innovative hydrophilic complexing agents, 2,6-bis[1-(propan-1-ol)-triazolyl]pyridine and 2,6-bis[1-(propan-1,2-diol-triazolyl)]pyridine, have been investigated as they proved to be endowed with high actinide selectivity. In order to simulate the damage experienced under process conditions, the stripping solutions were aged in HNO3 for several weeks and γ-irradiated up to 200 kGy with 60Co sources. Batch liquid–liquid extraction tests were performed on fresh, aged, and irradiated stripping solutions in order to verify whether aging and γ-irradiation affect system performance. Furthermore, nuclear magnetic resonance (NMR) analyses were carried out to ascertain the radiation-induced ligand degradation and subsequent byproduct formation. The stripping solutions manifested exceptional performance and radiochemical stability, even under harsh process conditions, to demonstrate their industrial applicability to i-SANEX and GANEX processes.

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

ABSTRACT 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 mM CyMe4-BTBP in 30% v/v TBP and 70% v/v FS-13), using hydrophilic masking agents (20 mM bimet and 0.2 M mannitol) in the aqueous phase for the complexation of troublesome fission products. Two nitric acid scrub steps (0.5 M HNO3) were efficient in removing co-extracted acid, all molybdenum and the majority of silver. Two stripping stages (0.5 M 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.

Fuel breeding and waste burnup capabilities of an accelerator‐driven system using thorium and reprocessed fuels

Fuel breeding and waste actinide burnup capabilities of a lead-cooled accelerator-driven system were evaluated using thorium and reprocessed fuels. The subcritical core simulated was filled with a hexagonal lattice formed by 232ThO2 rods and reprocessed fuel rods. Four types of reprocessed fuel were studied: Group ActiNide EXtraction (GANEX) fuel spiked with 51% of thorium, GANEX fuel spiked with 51% of depleted uranium, Uranium Extraction Plus (UREX+) fuel spiked with 51% of thorium and UREX+ fuel spiked with 51% of depleted uranium. The results indicated that the use of thorium and reprocessed fuels allows thorium regeneration and reduction of the inventory of high radiotoxicity isotopes. The Monte Carlo code SERPENT 2.1.31 was used for the simulations.

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

ABSTRACT 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 mM 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.

Highly selective extraction of Pu (IV) and Am (III) by N,N′-diethyl-N,N′-ditolyl-2,9-diamide-1,10-phenanthroline ligand: An experimental and theoretical study

The group actinide extraction ligand, N,N′-diethyl-N,N′-ditolyl-2,9-diamide-1,10-phenanthroline (Et-Tol-DAPhen) has been successfully developed in our laboratory recently. In this work, the extraction behaviors of the tetradentate Et-Tol-DAPhen toward Am(III) and Pu(IV) by using 1-(trifluoromethyl)-3-nitrobenzene as the diluent were systematically explored. The effects of HNO3 and ligand concentration as well as temperature were studied in detail. In addition, the selectivity of this ligand towards actinides and the stripping performance of the extraction system were also investigated to assess its potential application for group actinide separation over trivalent lanthanides (Ln(III)). According to our results, Et-Tol-DAPhen exhibits large distribution ratios for both Am(III) and Pu(IV) with high separation factors over Pm(III) in a wide range of acidity. Moreover, Am(III) and Pu(IV) can be efficiently stripped into the aqueous phase via three stages of batch back extraction. In addition, density functional theory (DFT) calculations suggest that the ligand selectivity towards actinides over Ln(III) probably results from the higher covalency of An-N bonds. The consistency between calculated thermodynamic parameters and experimental observations demonstrates the reasonability of the proposed extraction mechanism. Our findings afford insightful extraction parameters of Et-Tol-DAPhen towards actinides with different oxidation states and justify its versatile coordination abilities with respect to group actinide separation over lanthanides.

On the Basic Extraction Properties of a Phenyl Trifluoromethyl Sulfone-Based GANEX System Containing CyMe4-BTBP and TBP

ABSTRACTA Grouped ActiNide EXtraction (GANEX) process for the extraction of actinides from used nuclear fuel for transmutation purposes has been investigated. The studied solvent consists of phenyl trifluoromethyl sulfone (FS-13), CyMe4-BTBP, and TBP, a combination that has previously shown promising results. The time to reach extraction equilibrium for the system has been found to be less than 20 min. A 2:1 complex has been found between CyMe4-BTBP and americium(III) or curium(III), whereas plutonium(IV) and CyMe4-BTBP create a 1:1 complex. The extraction of fission product is low in the system.

Towards understanding the correlation between UO22+ extraction and substitute groups in 2,9-diamide-1,10-phenanthroline

2,9-Diamide-1,10-phenanthroline (DAPhen) ligands represent a new family of tetradentate extractants given their strong affinity to actinides and the CHON principle. Among this family, N,N′-diethyl-N,N′-ditolyl-2,9-diamide-1,10-phenanthroline (Et-Tol-DAPhen), initially reported by us, exhibits excellent selectivity towards actinides (U, Th, Am, Pu) over lanthanides and thus can be potentially applied in the group actinide extraction (GANEX) process for the group separation of actinides. In this article, by tailoring the lengths of alkyl chains, we synthesized other four DAPhen ligands with different substitute groups in the diamide moieties, and characterized the relationship between properties and substitute groups of DAPhen ligand. The extraction results show that three of the ligands exhibit high performance in UO22+ extraction from an acidic solution and the extracted UO22+ can be easily stripped by only using ultrapure water. Spectrophotometry titration confirms that UO22+ combined with all the four ligands in 1:1 mode. The extended X-ray absorption finestructure (EXAFS) study shows that six donor atoms comprise the first equatorial shell of the UO22+ ions bonded by the DAPhen ligands, among which two nitrogen and two oxygen atoms are from the DAPhen ligand, while other two oxygen atoms are from one nitrate ions. This article promises to provide basic data for assessing the feasibility of this kind of DAPhen ligands applied in actinides separation from nuclear wastes.

Various flowsheets of actinides recovery with diamides of heterocyclic dicarboxylic acids

Solvents on the base of diamides of heterocyclic dicarboxylic acids are promising alternatives for studied Grouped ActiNide EXtraction (GANEX) solvents. Advantage of these ligands is the possibility of simultaneous extraction not only of residual uranium and plutonium, but also minor actinides—neptunium, americium and curium. Two flowsheets on the base of diamides of heterocyclic dicarboxylic acids for separation of actinides form acidic solutions were developed, tested in laboratory scale and compared. Both flowsheets allow separation of more than 99.95% of actinides from raffinates with high content of lanthanides.

UxTh1-x(C2O4)2 Solid Characterisation Studies

Many advanced reprocessing schemes under development are aimed at co-processing and co-conversion of actinides, unlike current reprocessing plants that produce separate uranium and plutonium products. The most well developed option for the co-conversion stage is probably oxalate co-precipitation, followed by the thermal co-conversion to a mixed oxide product. It is thus envisaged that future processes will avoid separation of plutonium from uranium and instead allow part of the uranium to flow with the plutonium, resulting in co-precipitation as the oxalate, and finally co-conversion to a mixed uranium-plutonium oxide (MOX), which can be fabricated into recycled nuclear fuel for further energy generation.The co-crystallisation of uranium (IV) and plutonium (III) into a single oxalate structure ensures the homogenous distribution of the two actinides at the molecular scale. The joint conversion of uranium and plutonium to the oxide form makes it possible to remove the complicated step of blending and grinding the two distinct oxide powders, as currently employed for the purposes of MOX fuel fabrication. This concept can also be extended to other actinides, including minor actinides from partitioning processes such as SANEX (Selective Actinide Extraction) and GANEX (Grouped Actinide Extraction) processes or even a thorium containing product from recycle of thorium based fuels.A selection of UxTh1-x(C2O4)2 solids at varying concentrations of uranium and thorium were prepared by oxalate co-precipitation. Uranium (VI) was conditioned electrochemically at -0.7 V to uranium (IV), in the presence of hydrazine. The reduced uranium (IV) in nitric acid was mixed with thorium nitrate solutions at different concentration ratios with oxalic acid. The mixed tetravalent uranium-thorium oxalate solid products have been characterised by Raman and IR spectroscopies. The influence of thorium substituted into the uranium oxalate structure was evaluated. Several vibrational modes were found to be affected by the variation in ionic radius appearing to be metal sensitive and therefore, provide the initial indication in the evaluation of the chemical composition.

The EURO-GANEX Process: Current Status of Flowsheet Development and Process Safety Studies

A new hydrometallurgical grouped actinide extraction process has been developed to separate the transuranic actinide ions from dissolved spent fuel solution (after an initial uranium extraction cycle). This “EURO-GANEX” process is aimed towards the homogeneous recycling of plutonium and minor actinides in a future closed fuel cycle. The separation process is based on the co-extraction of actinides and lanthanides from aqueous nitric acid into an organic phase followed by selective co-stripping of actinides. A suitable organic phase has been formulated and distribution ratios determined for lanthanides, actinides and some problematic fission products under extraction and stripping conditions. The process flowsheet has been proven on surrogate feed solutions as well as with spent fast reactor fuel; excellent recoveries of the actinides and good decontamination factors from the lanthanides and other fission products were obtained. A variation on the EURO-GANEX flowsheet (the “TRU-SANEX” process) has now been designed to produce separate Pu+Np and Am+Cm products for heterogeneous recycling. Progress on underpinning process chemistry and safety studies as well as flowsheet tests are summarized.

Development of the Chalmers Grouped Actinide Extraction Process

Abstract Several solvents for Grouped ActiNide EXtraction (GANEX) processes have been investigated at Chalmers University of Technology in recent years. Four different GANEX solvents; cyclo-GANEX (CyMe4- -BTBP, 30 vol.% tri-butyl phosphate (TBP) and cyclohexanone), DEHBA-GANEX (CyMe4-BTBP, 20 vol.% N,N-di-2(ethylhexyl) butyramide (DEHBA) and cyclohexanone), hexanol-GANEX (CyMe4-BTBP, 30 vol.% TBP and hexanol) and FS-13-GANEX (CyMe4-BTBP, 30 vol.% TBP and phenyl trifluoromethyl sulfone (FS-13)) have been studied and the results are discussed and compared in this work. The cyclohexanone based solvents show fast and high extraction of the actinides but a somewhat poor diluent stability in contact with the acidic aqueous phase. FS-13-GANEX display high separation factors between the actinides and lanthanides and a good radiolytic and hydrolytic stability. However, the distribution ratios of the actinides are lower, compared to the cyclohexanone based solvents. The hexanol-GANEX is a cheap solvent system using a rather stable diluent but the actinide extraction is, however, comparatively low.

Phenyl trifluoromethyl sulfone as diluent in a grouped actinide extraction process: extraction properties of the solvent components TBP and CyMe4-BTBP

The grouped actinide extraction (GANEX) process combines two extractants CyMe4-BTBP and TBP in a diluent, in this study phenyl trifluoromethyl sulfone (FS-13). The extraction of U-235, Np-239, Pu-238, Am-241, Cm-244 and Eu-152 has been investigated in four different systems. System 1: 70 %vol FS-13, 30 %vol TBP and 10 mM CyMe4-BTBP, system 2: 70 %vol FS-13 and 30 %vol TBP, system 3: 100 %vol FS-13 and 10 mM CyMe4-BTBP and system 4: pure FS-13. In all cases 4 M HNO3 was used as aqueous phase. In system 1 all actinides were extracted and separated from the lanthanides. In both system 2 and 3 mainly U and Pu were extracted. In system 4 none of the metals were extracted.

Distribution of plutonium, americium and interfering fission products between nitric acid and a mixed organic phase of TODGA and DMDOHEMA in kerosene, and implications for the design of the “EURO-GANEX” process

For the homogeneous recycling of actinides from spent nuclear fuels, within the future nuclear fuel cycle based on a transition to fast neutron reactors, a new GANEX (Grouped Actinide Extraction) process is under development. This potentially provides a simpler, more proliferation resistant hydrometallurgical process for recycling actinides. The so-called EURO-GANEX process is based on liquid–liquid extraction into an organic phase comprising 0.2mol/L TODGA and 0.5mol/L DMODHEMA in an odourless kerosene diluent. Before testing the EURO-GANEX process with dissolved fast reactor spent fuel, data are required on the distribution ratios of likely problematic fission products (Fe, Sr, Zr, Mo, Tc, Ru, Pd) under typical extraction and scrubbing conditions. Also, suitable conditions must be defined for the selective backwashing of the transuranic actinides (specifically plutonium and americium) in the presence of extracted lanthanide elements.Distribution ratio data obtained indicate that conditions can be defined that prevent iron and strontium break through whilst maintaining actinide extraction across the extract-scrub contactors although some accumulation may occur. Zirconium and palladium extraction can be effectively inhibited by a polycarboxylate ligand: CDTA. However, technetium and molybdenum are likely to be extractable in the first contactor due to high distribution ratios and no significant suppression with CDTA. Ruthenium may be partially extracted but behaviour is complex in nitric acid. It was also shown that plutonium and americium can be efficiently separated from lanthanides by stripping with a combination of a sulphonated bis-triazinyl pyridine (BTP) ligand and acetohydroxamic acid (AHA) for plutonium concentrations ranging from <1mg/L to 10g/L plutonium solvent loading.

Single Centrifugal Contactor Test of a Proposed Group Actinide Extraction Process for Partitioning and Transmutation Purposes

In this work a solvent comprising of tri-butyl phosphate and bis-triazinyl, bi-pyridine in cyclohexanone has been used in a single centrifugal contactor test to evaluate its GANEX process potential. It was found that the density of the aqueous phase had to be increased to facilitate phase separation in the centrifuge. The kinetics of the system was also found to be relatively slow in the equipment of choice, especially regarding the stripping. However, it was still possible to recover more than 87% of all actinides in one extraction step with minor fission product contaminations using a flowrate of 30 mL/h.

Stability of phenyl trifluoromethyl sulfone as diluent in a grouped actinide extraction process

In this work, stability experiments have been performed on a phenyl trifluoromethyl sulfone based solvent containing 6,6′-bis(5,6-dialkyl-[1,2,4-]triazin-3-yl)-2,2′-bipyridine and tri-butyl phosphate. This solvent is intended to be used in a grouped actinide extraction process for partitioning and transmutation purposes. The distribution ratio for americium was determined to approximately 20 and for europium approximately 0.26 giving a separation factor of 77. The solvent maintain good distribution ratios and separation factors during both gamma irradiation of 6.6 kGy h−1 for up to 24 h and acid contact for up to 6 weeks at room temperature.

1,10-Phenanthroline and non-symmetrical 1,3,5-triazine dipicolinamide-based ligands for group actinide extraction.

The synthesis and evaluation of new extractants for spent nuclear fuel reprocessing are described. New bitopic ligands constituted of phenanthroline and 1,3,5-triazine cores functionalized by picolinamide groups were designed. Synthetic routes were investigated and optimized to obtain twelve new polyaza-heterocyclic ligands. In particular, an efficient and versatile methodology was developed to access non-symmetric 2-substituted-4,6-di(6-picolin-2-yl)-1,3,5-triazines from the 1,3,5-triazapentadiene precursor in the presence of anhydride reagents. Extraction studies showed the ability of both ligand series to extract and separate actinides selectively at different oxidation states (U(VI), Np(V,VI), Am(III), Cm(III), and Pu(IV)) from an acidic solution (3 M HNO3). Phenanthroline-based ligands show the most promising efficiency for use in the group actinide extraction (GANEX) process due to a higher number of donor nitrogen atoms and a suitable pre-organization of the dipicolinamide-1,10-phenanthroline architecture.

Development of a New Flowsheet for Co-Separating the Transuranic Actinides: The “EURO-GANEX” Process

A flowsheet for a novel GANEX (Grouped ActiNide EXtraction) process has been tested in a spiked flowsheet trial in a 32 stage plutonium-active centrifugal contactor rig with a simulant feed that contained 10 g/L plutonium as well as some fission products and other transuranic actinides. The solvent system used was a combination of 0.2 mol/L N,N,N’,N’-tetraoctyl diglycolamide (TODGA) and 0.5 mol/L N,N’-(dimethyl-N,N’-dioctylhexylethoxy-malonamide (DMDOHEMA) in a kerosene diluent that co-extracted actinides and lanthanides. Actinides were subsequently selectively co-stripped away from the lanthanides using a sulphonated and, therefore, hydrophilic bis-triazinyl pyridine (BTP) complexant in conjunction with acetohydroxamic acid (AHA). Plutonium and americium recoveries were high with decontamination factors across the strip contactors of ˜14,000 and ˜390, respectively. However, approximately 30% of neptunium was lost to the aqueous raffinate which was due to recycling within the first extract-scrub section causing a large build-up of neptunium. Some accumulation of strontium was also observed but in this case it was fully directed to the raffinate stream. In the stripping section, a small fraction of europium (taken as a model lanthanide ion), ca. 7%, was found in the actinide product stream. Modelling of selected data using the PAREX code has shown that even with a relatively simplistic treatment, reasonable agreement between modelling and experiment can be obtained, giving confidence in the use of modelling to refine the GANEX flowsheet design prior to further testing with irradiated fast reactor fuel.