Over the last decade there has been much interest in the applications of diglycolamide (DGA) ligands for the extraction of the trivalent lanthanide and actinide ions from PUREX high active raffinates ...or dissolved spent nuclear fuel. Of the DGAs, the N,N,N',N'-tetraoctyldiglycolamide (TODGA) is the best known and most widely studied. A number of new actinide separation processes have been proposed based on extraction with TODGA. This review covers TODGA-based processes and extraction data, specifically focusing on how phase modifiers have been used to increase metal loading and thus enhance the operating process envelopes. Effects of third phase formation and the organic phase speciation are reviewed in this context. Relevant aspects of the extraction chemistry of important solvents (TODGA-modifier-diluent combinations) are described and their performances demonstrated by a consideration of the published flowsheet tests. It is seen that modifiers are successfully enabling the use of TODGA in actinide separation processes but to date the identification and testing of suitable modifiers has been rather empirical. There is a growing understanding of the fundamental chemistry occurring in the organic phase and how that affects extractant speciation and metal loading capacity but studies are still needed if TODGA-based flowsheets are to become an industrially deployable option for minor actinide (MA) recovery processes.
Evidence to support the Raman assignments of the 1LO (578cm−1) and 2LO (1158cm−1) lattice vibrations for PuO2 material is presented. The T2g signal is established at 476±2cm−1 in agreement with ...literature values.
An increase of the 1LO band and an increase of the unit cell lattice parameter with ageing in our samples are found not to be a consequence of PuO2+x formation but rather a result of simple lattice defects due to radiation damage. The Raman spectrum of AnO2(OH)2⋅xH2O (An=Np, Pu) and laser induced decomposition products suggest that the transition to AnO2 involves Np2O5 for neptunium but no such analogue could be detected for Pu.
The presence of a band around 1150±10cm−1 for a range of MO2 fluorite structures (CeO2, ThO2, UO2, NpO2 and PuO2) suggests that this band is not derived from crystal field electronic f–f transitions as proposed previously and supports recent suggestions that it is the first overtone of the 1LO lattice vibration.
The spectrum of PuO2 is taken across a wide wavenumber range (200–4000cm−1) and additional signals (2116 and 2611cm−1) not previously reported have been observed but are not yet assigned with confidence.
Treatment of the thf adduct UO2(NCN)thf (NCN = (Me3SiN)CPh(NSiMe3)) (1) with 2 equiv of B(C6F5)3 provides UO{OB(C6F5)3}(NCN)2 (2) the first example of a neutral uranyl complex exhibiting Lewis basic ...behavior. The crystal structure of 2 shows a UO−B interaction with an elongated UO bond (1.898(3) Å). Raman spectroscopy suggests weakening of the OUO bonding, giving the lowest reported symmetric stretching frequency for a monomeric uranyl complex, ν1 = 780 cm-1. The borane can be selectively removed using PMe3 to give the coordinatively unsaturated UO2(NCN)2 (3) or using tBuNC to provide UO2(CNBut)(NCN)2 (4), the first example of an isonitrile coordinated to uranium.
A flowsheet for a novel GANEX (
G
rouped
A
cti
N
ide
EX
traction) 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.
Trimethylaluminum reacts with CPh3B(C6F5)4 at elevated temperatures to give a mixture of AlMe3-x(C6F5)x compounds, depending on the Al/B ratio. AlBui 3 reacts significantly faster under β-hydride ...abstraction. The Al−C6F5 species rapidly react with Cp2ZrMe2 or Cp2ZrMe+ under C6F5 transfer to give poorly active Cp2ZrMe(C6F5); this reaction may have implications for the deactivation of Cp2ZrMe2/AlR3/CPh3B(C6F5)4 olefin polymerization catalysts.
Spent Magnox fuel corroding in-situ in storage ponds forms sludges comprised of brucite and other Mg based phases with uranium oxide particles.
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► Caracterization study of highly ...radioactive corroded Magnox sludges. ► Unique data from samples of actual corroded nuclear fuel. ► Combined electron microscopy and vibrational spectroscopy study. ► Analysis of particles from legacy spent fuel storage pond at Sellafield. ► Supports major UK decommissioning and nuclear clean up challenge.
Samples of filtered particulates and sludges, formed from corroding magnesium alloy clad uranium metal (“Magnox”) fuel elements, collected from one of the legacy nuclear fuel storage ponds located at Sellafield (UK) were investigated by Environmental Scanning Electron Microscopy with Energy Dispersive X-Ray analysis (ESEM/EDX), micro-Raman spectroscopy and Fourier transform infra-red spectroscopy (FT-IR). ESEM imaging confirmed the dominant morphology to be clusters of interlocking platelets typical of brucite (Mg(OH)
2). EDX analysis was suggestive of some conversion to the related phase, hydrotalcite (Mg
6Al
2(CO
3)(OH)
16·4H
2O), due to elevated levels of Al associated with Mg. Other apparent morphologies were less commonly observed including flaky sheets, consistent with earlier stages of Magnox alloy corrosion. In a few specific cases, rods were also observed suggestive of some conversion to Mg-hydroxycarbonate phases. Discrete phases rich in U were also identified. Fluorescence in the Raman spectroscopy also indicated surface coatings of organic macromolecules and iron sulphide on hematite containing particles, attributed to microbial activity within the open air pond. Some specific differences in the solid phases between pond areas with differing conditions were apparent.
Treatment of UO2Cl2(thf)3 in thf with 2 equiv of NaPhC(NSiMe3)2 (NaNCN) or NaPh2P(NSiMe3)2 (NaNPN) gives uranyl complex UO2(NCN)2(thf) (1) or UO2(NPN)2 (3), respectively. Each complex is a rare ...example of out-of-plane equatorial nitrogen ligand coordination; the latter contains a significantly bent OUO unit and represents the first example of a uranyl ion within a quadrilateral-faced monocapped trigonal prismatic geometry. Removal of the thf in 1 gives UO2(NCN)2 (2) with in-plane N donor ligands. Addition of 3 equiv of NaNCN gives the tris complex Na(thf)2PhCNUO2(NCN)3 (4·PhCN) with elongation and weakening of one UO bond through coordination to Na+. Hydrolysis of 4 provides the oxo-bridged dimer Na(thf)UO2(NCN)22(μ2-O) (6), a complex with the lowest reported OUO symmetrical stretching frequency (ν1 = 757 cm-1) for a dinuclear uranyl complex. The anion in complex 4 is unstable in solution but can be stabilized by the introduction of 18-crown-6 to give Na(18-crown-6)UO2(NCN)3 (5). The structures of 1 − 4 and 6 have been determined by crystallography, and all except 2 show significant deviations of the N ligand atoms from the equatorial plane, driven by the steric bulk of the NCN and NPN ligands. Despite the unusual geometries, these distortions in structure do not appear to have any direct effect on the bonding and electronic structure of the uranyl ion. The main influences toward lowering the UO bond stretching frequency (ν1) are the donating ability of the equatorial ligands, overall charge of the complex, and UO···Na-type interactions. The intense orange/red colors of these compounds are because of low-energy ligand-to-metal charge-transfer electronic transitions.
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.
The ASGARD project (2012–2016) was designed to tackle the challenge the multi-dimensional questions dealing with the recyclability of novel nuclear fuels. These dimensions are: the scientific ...achievements, investigating how to increase the industrial applicability of the fabrication of these novel fuels, the bridging of the often separate physics and chemical communities in connection with nuclear fuel cycles and finally to create an ambitious education and training platform. This will be offered to younger scientists and will include a broadening of their experience by international exchange with relevant facilities. At the end of the project 27 papers in peer reviewed journals were published and it is expected that the real number will be the double. The training and integration success was evidenced by the fruitful implementation of the Travel Fund as well as the unique schools, e.g. practical and theoretical handling of plutonium.
Formo- and aceto-hydroxamic acids are very effective reagents for stripping tetravalent actinide ions from a tri-butyl phosphate phase into nitric acid. A model describing the partitioning of ...actinide (IV) ions has been derived accounting for reactions in the aqueous and solvent phases, including complex formation with nitrate and hydroxamate ions. Predicted distribution ratios for Np(IV) are compared with experimental data in the presence of aceto-hydroxamate ions. Additionally, a value of 0.473 (±0.004) kgmol
−1
for the Np(IV) ion interaction coefficient with nitrate ions (ε
Np4+-NO3−
) was determined.
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