Fabian Sadowski

Direct Selective Extraction of Actinides (III) from PUREX Raffinate using a Mixture of CyMe4BTBP and TODGA as 1-cycle SANEX Solvent Part III: Demonstration of a Laboratory-Scale Counter-Current Centrifugal Contactor Process

The direct selective separation of the trivalent actinides americium and curium from a simulated Plutonium Uranium Refining by EXtraction (PUREX) raffinate solution by a continuous counter-current solvent extraction process using miniature annular centrifugal contactors was demonstrated on a laboratory scale. In a 32-stage spiked test (12 stages for extraction, 16 stages for scrubbing, and 4 stages for Am/Cm stripping), an extractant mixture of CyMe4BTBP and TODGA in a TPH/1-octanol mixture was used. The co-extraction of some fission and corrosion product elements, such as zirconium and molybdenum, was prevented by using oxalic acid. Co-extracted palladium was selectively stripped using an L-cysteine scrubbing solution and the trivalent actinides were selectively stripped using a glycolic acid-based stripping solution. It was demonstrated that a selective extraction and high recovery of > 99.4% of the trivalent minor actinides was achieved with low contamination by fission and corrosion products. The product contained 99.8% of the initial americium and 99.4% of the initial curium content. The spent solvent still contained high concentrations of Cu, Cd, and Ni. The experimental steady-state concentration profiles of important solutes were determined and compared with those from computer-code calculations.

Laboratory-Scale Counter-Current Centrifugal Contactor Demonstration of an Innovative-SANEX Process Using a Water Soluble BTP

In this paper the development and laboratory-scale demonstration of a novel “innovative-SANEX” (Selective Actinide Extraction) process using annular centrifugal contactors is presented. In this strategy, a solvent comprising the N,N,N’,N’-tetraoctyldiglycolamide (TODGA) extractant with addition of 5 vol.-% 1-octanol showed very good extraction efficiency of Am(III) and Cm(III) together with the trivalent lanthanides (Ln(III)) from simulated Plutonium Uranium Refining by Extraction (PUREX) raffinate solution without 3rd phase formation. Cyclohexanediaminetetraacetic acid (CDTA) was used as masking agent to prevent the co-extraction of Zr and Pd. An(III) and Ln(III) were co-extracted from simulated PUREX raffinate, and the loaded solvent was subjected to several stripping steps. The An(III) were selectively stripped using the hydrophilic complexing agent SO3-Ph-BTP (2,6-bis(5,6-di(sulfophenyl)-1,2,4-triazin-3-yl)pyridine). For the subsequent stripping of the Ln(III), a citric acid based solution was used. A 32-stage process flow-sheet was designed using computer-code calculations and tested in annular miniature centrifugal contactors in counter-current mode. The innovative SANEX process showed excellent performance for the recovery of An(III) from simulated High Active Raffinate (HAR) solution and separation from the fission and activation products. ≥ 99.8% An(III) were recovered with only low impurities (0.4% Ru, 0.3% Sr, 0.1% Ln(III)). The separation from the Ln(III) was excellent and the Ln(III) were efficiently stripped by the citrate-based stripping solution. The only major contaminant in the spent solvent was Ru, with 14.7% of the initial amount being found in the spent solvent. Solvent cleaning and recycling therefore has to be further investigated. This successful spiked test demonstrated the possibility of separating An(III) directly from HAR solution in a single cycle which is a great improvement over the former multi-cycle strategy. The results of this test are presented and discussed.

Modified diglycolamides for the An(III) + Ln(III) co-separation: evaluation by solvent extraction and time-resoved laser fluorescence spectroscopy

The use of two recently developed diglycolamide-based extractants for the co-separation of trivalent actinides (An(III)) and lanthanides (Ln(III)) is described and compared to the well-known extractant TODGA (N,N,N’,N’-tetraoctyl diglycolamide). The addition of one or two methyl groups to the central methylene carbon atoms of the TODGA molecule leads to a reduction of the extraction efficiency for An(III) and Ln(III). This is attributed to a lower complex formation constant, which was proven by Time-Resolved Laser Fluorescence Spectroscopy (TRLFS). Conditional stability constants were determined by solvent extraction and TRLFS. The reduction in extraction efficiency leads to overall reduced distribution ratios of all tested metal ions, including Sr(II). The reduced Sr(II) extraction is beneficial as a co-extraction in a solvent extraction process could be avoided, while an efficient extraction of the desired An(III) and Ln(III) is still achieved. Furthermore, this might be a benefit, as the stripping behavior might be improved, even at moderate nitric acid concentrations. The slightly higher affinity of the diglycolamides towards Eu(III) over Am(III) is represented by all ligands, although the selectivity is rather low. This results in promising extraction properties of the modified diglycolamides towards the development of continuous solvent extraction processes.

Solvent Extraction and Fluorescence Spectroscopic Investigation of the Selective Am(III) Complexation with TS-BTPhen

ABSTRACT An americium(III) selective separation procedure was developed based on the coextraction of trivalent actinides (An(III)) and lanthanides (Ln(III)) by TODGA (N,N,N′,N′-tetraoctyl-diglycolamide), followed by Am(III) selective stripping using the hydrophilic complexing agent TS-BTPhen (3,3′,3ʺ,3ʺ′-[3-(1,10-phenanthroline-2,9-diyl)-1,2,4-triazine-5,5,6,6-tetrayl]tetrabenzenesulfonic acid). Distribution ratios were found at an acidity of 0.65 mol L−1 nitric acid that allowed for the separation of Am(III) from Cm(III) (DCm > 1; DAm < 1), giving a separation factor between curium and americium of SFCm/Am = 3.6 within the stripping step. Furthermore, Am(III) was readily separated from the lanthanides with the lowest selectivity for the Ln(III)/Am(III) separation being lanthanum with a separation factor of SFLa/Am = 20. The influence of the TS-BTPhen concentration on Am(III) distribution ratios was studied, giving a slope (logD vs. log[TS-BTPhen]) of approximately −1 for the stripping of An(III) with TS-BTPhen from the TODGA-based organic phase. Time-resolved laser fluorescence spectroscopy (TRLFS) measurements of curium(III) were used to analyze the speciation of Cm(III)-TS-BTPhen complexes. Both 1:1 and 1:2 complexes were identified in single-phase experiments. The formation of the 1:1 complex was suppressed in 0.5 mol L−1 nitric acid but it was significantly present in HClO4 at pH 3. Conditional stability constants of the complex species were calculated from the TRLFS experiments.

TS-BTPhen as a promising hydrophilic complexing agent for selective Am(III) separation by solvent extraction

Abstract The novel hydrophilic back-extraction agent TS-BTPhen (3,3ʹ,3ʺ,3ʹʺ-[3-(1,10-phenanthroline-2,9-diyl)-1,2,4-triazine-5,5,6,6-tetrayl]tetrabenzenesulfonic acid) was tested for its selectivity towards Am(III) over Cm(III) and Eu(III) with a TODGA (N,N,Nʹ,Nʹ-tetraoctyldiglycolamide) based solvent. Batch experiments were carried out using TS-BTPhen dissolved in aqueous nitric acid solution with tracers of 152Eu, 241Am and 244Cm. A significant increase of the separation factor for Cm over Am from SFCm/Am = 1.6 up to SFCm/Am = 3.3 was observed compared to the use of a TODGA-nitric acid system alone. Furthermore, stripping was possible at high nitric acid concentrations (0.6-0.7 mol/L) resulting in a low sensitivity to acidity changes. The influence of the TS-BTPhen concentration was analyzed. A slope of -2 was expected taking into account literature stoichiometries of the lipophilic analogue CyMe4BTPhen. However, a slope of -1 was found. Batch stripping kinetics showed fast kinetics for the trivalent actinides. As an alternative organic ligand the methylated TODGA derivate Me-TODGA (2-methyl-N,N,Nʹ,Nʹ-tetraoctyldiglycolamide) was tested in combination with the hydrophilic TS-BTPhen. The Am(III) separation was achieved at even higher nitric acid concentrations compared to TODGA.

An Advanced TALSPEAK Concept for Separating Minor Actinides. Part 2. Flowsheet Test with Actinide-spiked Simulant

ABSTRACT An Advanced TALSPEAK (trivalent actinide–lanthanide separations by phosphorus-reagent extraction from aqueous complexes) counter-current flowsheet test was demonstrated using a simulated feed spiked with radionuclides in annular centrifugal contactors. A solvent comprising 2-ethylhexylphosphonic acid mono-2-ethylhexyl ester (HEH[EHP] or PC88A) in n-dodecane was used to extract trivalent lanthanides away from the trivalent actinides Am3+ and Cm3+, which were preferentially complexed in a citrate-buffered aqueous phase with N-(2-hydroxyethyl)ethylenediamine-N,N´,N´-triacetic acid (HEDTA). In a 24-stage demonstration test, the trivalent actinides were efficiently separated from the trivalent lanthanides with decontamination factors >1000, demonstrating the excellent performance of the chemical system. Clean actinide and lanthanide product fractions and spent solvent with very low contaminations were obtained. The results of the process test are presented and discussed.

Process Development and Laboratory-Scale Demonstration of a Regular-SANEX Process Using C5-BPP (2,6-Bis(5-(2,2-dimethylpropyl)-1H-pyrazol-3-yl)pyridine)

An optimized solvent comprising 0.01 mol/L C5-BPP + 0.5 mol/L 2-bromo-hexanoic acid in TPH with 10% 1-octanol was developed for the selective extraction of trivalent actinides from lanthanides. Equilibrium extraction data and kinetics of the system in extraction, scrubbing and stripping modes were evaluated and a 16-stage flow-sheet was successfully tested in a spiked centrifugal contactor demonstration. It turned out that 16 stages were insufficient for a complete recovery of An(III), although a clean An(III) product was obtained. The high selectivity of C5-BPP for An(III) was shown. The results of the spiked centrifugal contactor test are presented and discussed.

Direct Selective Extraction of Trivalent Americium from PUREX Raffinate Using a Combination of CyMe4BTPhen and TEDGA—A Feasibility Study

ABSTRACT The direct and selective extraction of Am(III) from simulated PUREX raffinate is demonstrated using a novel combination of the lipophilic extractant CyMe4BTPhen (2,9-bis(5,5,8,8-tetramethyl-5,6,7,8-tetrahydrobenzo[e]-[1,2,4]triazin-3-yl)-1,10-phenanthroline) and the hydrophilic complexant TEDGA (N,N,N’,N’-tetraethyl-diglycolamide) to enhance selectivity toward Am(III) extraction. Separation factors (SF) of up to SFAm/Cm = 4.9 were observed in tracer experiments using this combination of CyMe4BTPhen and TEDGA. Distribution ratios of stable isotopes of fission and activation products contained in a simulated PUREX raffinate solution are reported for the first time with CyMe4BTPhen, and some co-extracted metal ions are identified. The metal ions partly co-extracted from the simulated PUREX raffinate solution were Cu, Pd, Cd, Ag, Ni, and to a lesser extent Sn and Mo. The co-extraction of Pd and Ag was successfully suppressed using Bimet ((2S,2’S)-4,4’-(ethane-1,2-diylbis(sulfanediyl))bis(2-aminobutanoic acid)). The extraction was also studied as a function of the TEDGA concentration. The distribution ratios of Am and Cm can be adjusted by variation of the TEDGA concentration to yield DAm values >1 and DCm values <1. Separation factors for Am(III) over Cm(III) of up to SFAm/Cm = 2.4 were observed in these experiments. For Ln(III) + Y(III), distribution ratios below 1 were observed, thus enabling a direct extraction of Am(III) from simulated PUREX raffinate with a sufficient selectivity against trivalent lanthanides and Cm(III).

Reprocessability of molybdenum and magnesia based inert matrix fuels

Abstract This work focuses on the reprocessability of metallic 92Mo and ceramic MgO, which is under investigation for (Pu,MA)-oxide (MA = minor actinide) fuel within a metallic 92Mo matrix (CERMET) and a ceramic MgO matrix (CERCER). Magnesium oxide and molybdenum reference samples have been fabricated by powder metallurgy. The dissolution of the matrices was studied as a function of HNO3 concentration (1-7 mol/L) and temperature (25-90°C). The rate of dissolution of magnesium oxide and metallic molybdenum increased with temperature. While the MgO rate was independent of the acid concentration (1-7 mol/L), the rate of dissolution of Mo increased with acid concentration. However, the dissolution of Mo at high temperatures and nitric acid concentrations was accompanied by precipitation of MoO3. The extraction of uranium, americium, and europium in the presence of macro amounts of Mo and Mg was studied by three different extraction agents: tri-n-butylphosphate (TBP), N,Nʹ-dimethyl-N,Nʹ-dioctylhexylethoxymalonamide (DMDOHEMA), and N,N,N’,N’- -tetraoctyldiglycolamide (TODGA). With TBP no extraction of Mo and Mg occurred. Both matrix materials are partly extracted by DMDOHEMA. Magnesium is not extracted by TODGA (D < 0.1), but a weak extraction of Mo is observed at low Mo concentration.