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Plutonium(IV) oxalate hexahydrate (Pu(C2O4)2 ⋅ 6 H2O; PuOx) is an important intermediate in the recovery of plutonium from used nuclear fuel. Its formation by precipitation is well studied, yet its crystal structure remains unknown. Instead, the crystal structure of PuOx is assumed to be isostructural with neptunium(IV) oxalate hexahydrate (Np(C2O4)2 ⋅ 6 H2O; NpOx) and uranium(IV) oxalate hexahydrate (U(C2O4)2 ⋅ 6 H2O; UOx) despite the high degree of unresolved disorder that exists when determining water positions in the crystal structures of the latter two compounds. Such assumptions regarding the isostructural behavior of the actinide elements have been used to predict the structure of PuOx for use in a wide range of studies. Herein, we report the first crystal structures for PuOx and Th(C2O4)2 ⋅ 6 H2O (ThOx). These data, along with new characterization of UOx and NpOx, have resulted in the full determination of the structures and resolution of the disorder around the water molecules. Specifically, we have identified the coordination of two water molecules with each metal center, which necessitates a change in oxalate coordination mode from axial to equatorial that has not been reported in the literature. The results of this work exemplify the need to revisit previous assumptions regarding fundamental actinide chemistry, which are heavily relied upon within the current nuclear field. [ABSTRACT FROM AUTHOR]

High pressure high temperature (HP/HT) studies of actinide compounds allow the chemistry and bonding of among the most exotic elements in the periodic table to be examined under the conditions often only found in the severest environments of nature. Peering into this realm of physical extremity, chemists have extracted detailed knowledge of the fundamental chemistry of actinide elements and how they contribute to bonding, structure formation and intricate properties in compounds under such conditions. The last decade has resulted in some of the most significant contributions to actinide chemical science and this holds true for ex situ chemical studies of actinides resulting from HP/HT conditions of over 1 GPa and elevated temperature. Often conducted in tandem with ab initio calculations, HP/HT studies of actinides have further helped guide and develop theoretical modelling approaches and uncovered associated difficulties. Accordingly, this perspective article is devoted to reviewing the latest advancements made in actinide HP/HT ex situ chemical studies over the last decade, the state-of-the-art, challenges and discussing potential future directions of the science. The discussion is given with emphasis on thorium and uranium compounds due to the prevalence of their investigation but also highlights some of the latest advancements in high pressure chemical studies of transuranium compounds. The perspective also describes technical aspects involved in HP/HT investigation of actinide compounds. [ABSTRACT FROM AUTHOR]

Uranium chlorides are important in actinide chemistry and nuclear industries, but their chemical bonding and many physical and chemical properties are not well understood yet. Here, we report the first experimental observation of two gaseous uranium hexachloride anions, UCl6- and UCl62-, which are probed by photoelectron spectroscopy in conjunction with quantum chemistry calculations. The electron affinity of UCl6 is measured for the first time as +5.3 eV; its second electron affinity is measured to be +0.60 eV from the photoelectron spectra of UCl62-. We observe that the detachment cross sections of the 5f electrons are extremely weak in the visible and UV energy ranges. It is found that the one-electron one-determinental molecular orbital picture and Koopmans' theorem break down for the strongly internally correlated U-5f2 valence shell of tetravalent U+4 in UCl62-. The calculated adiabatic and vertical electron detachment energies from ab initio calculations agree well with the experimental observations. Electronic structure and chemical bonding in the uranium hexachloride species UCl62- to UCl6 are discussed as a function of the oxidation state of U. [ABSTRACT FROM AUTHOR]

Recently reported 3,3'‐dimethoxy‐phenyl‐bis‐1,2,4‐triazinyl‐2,6‐pyridine (DMOP‐ BTP) ligand is recognized as an efficient candidate for the stripping of actinides (An) from lanthanides (Ln) in nuclear wastes in nitric acid medium. However, the complexation behaviour and selectivity of this DMOP‐BTP ligand towards AnIII/LnIII is still unclear. In order to understand the origin of complexation of this ligand, a series of metal ions (M3+=Ce, Nd, Eu, U, Am, Cm) have been chosen and its binding ability to form ML(NO3)3 (L=DMOP‐ BTP) complex is studied using scalar relativistic ZORA/DFT calculations. Metal ‐Nitrogen bond lengths obtained from optimized geometries reveal that AnIII prefer binding to DMOP‐BTP ligand compared to LnIII. To elucidate the metal‐ligand bonding nature, Mayer and Nalewajsk‐ Mrozek (NM) bond order analyses have been carried out. Quantum Theory of Atoms In Molecules (QTAIM) and Energy Decomposition Analysis (EDA) have been done using the optimized geometries to comprehend the bonding situation in these ML(NO3)3 complexes. Results reveal that the bonds of AnIII ions tend to have a higher covalency compared to that of their lanthanide ions. Furthermore, it is understood that the NO3 ions around the metal ion also take part in interaction with the ligand and help in the stabilization of the metal complex. Thus, this work throws light on the preferential selectivity of the DMOP‐ BTP ligand for AnIII ions over LnIII ions. [ABSTRACT FROM AUTHOR]

The π coordination of arene and anionic heteroarene ligands is a ubiquitous bonding motif in the organometallic chemistry of d‐block and f‐block elements. By contrast, related π interactions of neutral heteroarenes including neutral bora‐π‐aromatics are less prevalent particularly for the f‐block, due to less effective metal‐to‐ligand backbonding. In fact, π complexes with neutral heteroarene ligands are essentially unknown for the actinides. We have now overcome these limitations by exploiting the exceptionally strong π donor capabilities of a neutral 1,4‐diborabenzene. A series of remarkably robust, π‐coordinated thorium(IV) and uranium(IV) half‐sandwich complexes were synthesized by simply combining the bora‐π‐aromatic with ThCl4(dme)2 or UCl4, representing the first examples of actinide complexes with a neutral boracycle as sandwich‐type ligand. Experimental and computational studies showed that the strong actinide–heteroarene interactions are predominately electrostatic in nature with distinct ligand‐to‐metal π donation and without significant π/δ backbonding contributions. [ABSTRACT FROM AUTHOR]

A novel polyfunctional neutral organophosphorus ligand 1,2,4,5-tetra(diphenylphosphihyl)-benzene I containing four Ph2P(O)- groups fixed on the benzene platform was synthesized and studied as an extractant for U(VI), Th(IV) and lanthanides(III) ions from HNO3 solutions. The influence of aqueous and organic phases on the extraction efficiency was elucidated. Stoichiometry of the extracted complexes was determined, and the equilibrium constants were calculated. The extraction efficiency of compound I towards U(VI)), Th(IV) and lanthanides(III) ions is significantly higher than that of its analogue V with methylene spacers between P(O) groups and a benzene ring. Compound I extracts U(VI) more effectively than tetraphenylmethylenediphosphine dioxide VIa, one of the most effective extractants of actinides and lanthanides from nitric acid solutions, but ranks below in the extraction of Th(IV) and Ln(III). [ABSTRACT FROM AUTHOR]

A series of novel structurally related glutaramides (GAs) were synthesized and applied to the extraction and separation of selected actinides and lanthanides from nitric acid medium. The influence of the nature of the alkyl chain on the distribution ratio of U(VI) and Th(IV) was examined. N,N′-Dimethyl-N, N′-dioctylglutaramide (DMDOGA) and N, N′-dihexyl-N, N′-dioctylglutaramide (DHDOGA) were chosen and applied to the selective extraction and separation of U(VI), Th(IV), and selected lanthanides Ln(III) [Nd(III), Eu(III), Gd(III), Sm(III), and Dy(III)]. The distribution ratios of U(VI) and Th(IV) were determined in relation to the diluent type, shaking time, nitric acid concentration, salting-out agents, concentration of substituted glutaramide, and temperature. The extraction of lanthanides is negligible in the entire studied range of HNO3 concentrations (0.1–7 M). With an increase in the HNO3 concentration, the extraction of U(VI) increased up to 5 M HNO3 and then decreased on further increase in the acidity, whereas the extraction of Th(IV) slowly increased with the HNO3 concentration in the entire range studied. The stoichiometry of the U(VI) and Th(IV) extractable species was determined to be UO2(NO3)2·2GA and Th(NO3)4·GA, respectively. The IR spectra of the extracted species were recorded. Both DMDOGA and DHDOGA are more selective to U(VI) compared to Th(IV) in HNO3 solutions. Good separation of U(VI) from Th(IV) can be achieved at 0.1–0.5 M HNO3. The back-extraction of U(VI) and Th(IV) from the organic phase was also studied. [ABSTRACT FROM AUTHOR]

The octacarbonyl cation and anion complexes of actinide metals [An(CO)8]+/− (An=Th, U) are prepared in the gas phase and are studied by mass‐selected infrared photodissociation spectroscopy. Both the octacarbonyl cations and anions have been characterized to be saturated coordinated complexes. Quantum chemical calculations by using density functional theory show that the [Th(CO)8]+ and [Th(CO)8]− complexes have a distorted octahedral (D4h) equilibrium geometry and a doublet electronic ground state. Both the [U(CO)8]+ cation and the [U(CO)8]− anion exhibit cubic structures (Oh) with a 6A1g ground state for the cation and a 4A1g ground state for the anion. The neutral species [Th(CO)8] (Oh; 1A1g) and [U(CO)8] (D4h; 5B1u) have also been calculated. Analysis of their electronic structures with the help on an energy decomposition method reveals that, along with the dominating 6d valence orbitals, there are significant 5f orbital participation in both the [An]←CO σ donation and [An]→CO π back donation interactions in the cations and anions, for which the electronic reference state of An has both occupied and vacant 5f AOs. The trend of the valence orbital contribution to the metal–CO bonds has the order of 6d≫5f>7s≈7p, with the 5f orbitals of uranium being more important than the 5f orbitals of thorium. [ABSTRACT FROM AUTHOR]

Abstract A disposal method for radioactive waste should be carefully chosen on a case-by-case basis, taking into consideration, chemical and radiological properties of the waste, acceptance criteria required for disposal site, and circumstance of the country where the waste is generated. A large volume of uranium-bearing waste (UO 2 -Sb 2 O 3 -Fe 2 O 3 -SiO 2 mixture oxide) from to be finally disposed will be generated from a process to treat spent uranium catalyst in South Korea. This worked studied a glass-ceramic composite wasteform tailor-made for the final uranium-bearing generated from the process. The physicochemical properties of the prepared glass-ceramic wasteform were evaluated to ensure that the waste acceptance criteria for a disposal site in South Korea could be met. The mechanism of forming the glass-ceramic matrix and its final structure were investigated by using TG-DSC, SEM-EDS and XRD. The optimal sintering temperature and content of B 2 O 3 to be added were 1100 °C and approximately 2–3 wt % in the total uranium-bearing waste, respectively. The SiO 2 , Fe 2 O 3 and Sb 2 O 3 in the target uranium-bearing waste formed a glass phase with help of B 2 O 3 , and SbFeO 4 oxide phase, respectively. Both UO 2 and Al 2 O 3 , which exhibit high melting points, remained as refractory phases in the sintered body. Conversion of the uranium-bearing waste into a glass-ceramic composite matrix wasteform was confirmed to be an effective way to deal with the uranium-bearing waste in terms of volume reduction of the waste and waste acceptance criteria for the disposal site in Korea. Graphical abstract Image 1 Highlights • Development of glass-ceramic wasteform for immobilization of uranium-bearing waste. • Uranium-bearing waste generated from a process to treat spent uranium catalyst. • High volume reduction of uranium-bearing waste to be disposed with meeting waste acceptance criteria for disposal. • Evaluation of glass-ceramic wasteform structure and formation mechanism of glass-encapsulated ceramic wasteform. • Formation of glass-ceramic wasteform by using powder metallurgy. [ABSTRACT FROM AUTHOR]

Abstract Uranium nitride-silicide composites are being considered as a high-density and high thermal conductivity fuel option for light water reactors. During development, chemical interactions were observed near the silicide melting point which resulted in formation of an unknown U Si N ternary phase. In the present work, U Si N composite samples were produced by arc-melting U 3 Si 2 under an argon-nitrogen atmosphere to form the ternary phase. The resulting samples were characterized by SEM/EDS-EPMA and XRD, and demonstrated an equilibrium between U 3 Si 2 , UN, USi and a U Si N phase with a distinct crystallographic structure. Rietveld refinement of the ternary structure was performed, considering the ternary structures existent in the analogue U Si C system, and a good fit was obtained for the hexagonal U 20 Si 16 N 3 phase. DFT + U calculations were performed in parallel to evaluate the thermodynamic and dynamic stability of the ternaries U 20 Si 16 N 3 and U 3 Si 2 N 2. The calculated enthalpy of formation and phonon dispersion support the existence of stable U 20 Si 16 N 3 and U 3 Si 2 N 2 , although some soft modes in the U 20 Si 16 N 3 phase phonons are observed. The results presented here thus demonstrate the occurrence of at least one ternary phase in the U Si N system. [ABSTRACT FROM AUTHOR]

Abstract A UO 4 and A 3 UO 6 uranates (A = Ca, Sr, Ba or Pb) have been synthesized by solid state reaction. Their crystallographic structures have been studied combining Powder X-ray Diffraction (PXRD) and Extended X-ray Absorption Fine Structure (EXAFS). Depending on the nature of the alkali earth metal, the uranates compounds crystallize in different structures, in which the uranium local environment around the atoms have been identified. The U geometry has been compared to the oxidation states determined from X-ray Absorption Near Edge Spectroscopy (XANES). [ABSTRACT FROM AUTHOR]

Uranium-containing samples of magnesium potassium phosphate (MPP) compound were synthesized using a nitric acid uranium solution. Uranium is incorporated in the MPP compound in the form of potassium uranyl phosphate with the structure of metaankoleite natural mineral, K(UO2)PO4·3H2O. The differential and integral uranium leach rates, determined in accordance with GOST (State Standard) R 52 126-2003 on the 28th day of contact of the compound with water, are 1.7 × 10-6 and 2.7 × 10-6 g cm-2 day-1, respectively, and the degree of leaching is 0.014%. High hydrolytic durability of the compound with respect to uranium leaching reduces the risk of release of uranium isotopes from radioactive waste into the environment. [ABSTRACT FROM AUTHOR]

An intermediate neglect of differential overlap method for examining the electronic structure of actinide complexes is developed. It is characterized by a basis set obtained from relativistic Dirac–Fock atomic calculations, the inclusion of all one-center two-electron integrals, and a parameter set based on molecular geometry and ionization spectra. The model is successful in reproducing the geometries of many small test molecules, especially the hexahalides and tetrahalides of the early actinides. We also investigate the bonding in actinocenes and the photoelectron spectra of pentavalent uranium amide/imide complexes as two diverse examples in which this model can be used to help in understanding and prediction. [ABSTRACT FROM AUTHOR]

As representatives of actinyl and bare actinide ions, U(VI) and Th(IV) show different solvent extraction performance and complexation mechanisms with phenanthroline phosphonate (POPhen) ligands. [Display omitted] • Phenanthroline phosphonate extractants show strong extraction ability toward U(VI) and Th(IV) in high acidity. • The complexation mechanism of phenanthroline phosphate with U(VI) and Th(IV) has been thoroughly studied. • Increasing carbon chain substituents can enhance the extraction capacity for tetravalent and hexavalent actinides. The extraction and separation of actinide over lanthanide elements is a key step in the spent fuel reprocessing process, which involves a variety of actinides with different valence states. The phenanthroline phosphonate (POPhen) extractants have a strong ability to extract trivalent actinides over lanthanides from highly acidic HNO 3 solution with good separation ability of An(III) over Ln(III). However, the extraction properties and complexation mechanism of POPhen extractants for high-valence actinides have yet to be studied. In this work, U(VI) and Th(IV) were selected as representatives of high-valence actinides to systematically study the extraction effect and complexation mechanism of C2-POPhen and C4-POPhen with them. The results showed that POPhen extractants had excellent coordination and extraction ability for U(VI) and Th(IV) under highly acidic nitrate conditions. The extraction capacity of C4-POPhen was stronger than that of C2-POPhen, and both ligands hold a stronger extraction capacity for Th(IV) than U(VI) under the same experimental conditions. Both the slope analysis and spectroscopic studies indicated that POPhen extractants could form the sole 1:1 complexes with U(VI) and both 1:1 and 1:2 metal-to-ligand complexes with Th(IV). The structures of the 1:1 and 1:2 Th(IV) complexes with POPhen-type extractants were first elucidated by X-ray crystallography. This study will be helpful to deepen the understanding of the extraction effect and complexation mechanism of POPhen with high-valence actinide elements, providing a fundamental data basis and theoretical reference for the development of the advanced subsequent actinides separation process. [ABSTRACT FROM AUTHOR]

Meso-Cenozoic intracontinental orogenic processes in the Tian Shan orogenic belt have significant effect on the sandstone-hosted uranium deposits in the intramontane basins and those adjacent to the orogen. The Sawafuqi uranium deposit, which is located in the South Tian Shan orogenic belt, is investigated to reveal the relationships between uranium mineralization and orogenies. Recent exploration results show that the Sawafuqi uranium deposit has tabular, stratiform, quasi-stratiform, and lens-like orebodies and various geological characteristics different from typical interlayer oxidation zone sandstone-hosted uranium deposits. Systematic studies of ore samples from the Sawafuqi uranium deposit using a variety of techniques, including thin section observation, α-track radiograph, electron microprobe and scanning electron microscope, suggest that uranium mineralization is closely related to pyrite and organic matter. Mineralization-related alterations in the host rocks are mainly silicification and argillation including kaolinite, illite (and illite-smectite mixed layer) and chlorite. Tree stages of mineralization were identified in the Sawafuqi uranium deposit: (i) uranium-bearing detritus and synsedimentary initial pre-enrichment; (ii) interlayer oxidization zone uranium mineralization; and (iii) vein-type uranium mineralization. The synsedimentary uranium pre-enrichment represents an early uranium enrichment in the Sawafuqi uranium deposit, and interlayer oxidation zone uranium mineralization formed the main orebodies, which are superimposed by the vein-type uranium mineralization. Combining the results of this study with previous studies on the Meso-Cenozoic orogenies of South Tian Shan, it is proposed that the synsedimentary uranium pre-enrichment of the Sawafuqi uranium deposit was caused by Triassic Tian Shan uplift, and the interlayer oxidation zone uranium mineralization occurred during the Eocence-Oligocene period, when tectonism was relatively quiet, whereas the vein-type uranium mineralization took place in relation to the strong orogeny of South Tian Shan since Miocene. [ABSTRACT FROM AUTHOR]

Extraction of microamounts of U(VI), Th(IV), and REE(III) from HNO and HClO solutions with solutions of (α-pyridyl)tetraphenylmethylenediphosphine N,P,P'-trioxide in dichloroethane was studied. The stoichiometry of the extractable complexes was determined, and the influence of the extraction structure and aqueous phase composition on the efficiency and selectivity of the extraction of U(VI), Th(IV), and REE(III) into the organic phase was studied. Introduction of the pyridine N-oxide fragment into the methylene bridge of the tetraphenylmethylenediphosphine dioxide molecule to obtain (α-pyridyl)tetraphenylmethylenediphosphine N,P,P'-trioxide leads to a decrease in its ability to extract U(VI), Th(IV), and REE(III) from nitric acid solutions, whereas the U/REE separation factors increase. The REE(III) extraction efficiency considerably increases in going from nitric acid to perchloric acid solutions. [ABSTRACT FROM AUTHOR]

Actinide chemistry is very interesting not from scientific perspective but also from technological importance. Elucidating the valence state and coordinating environment of actinide ion like uranium in technologically important magnesium aluminate spinel (MAS) is important to fully understand its hazardous and other harmful effect in human as well as environment. Magnesium aluminate spinel doped with 1.0 mol % of Uranium ion has been synthesized using citric acid assisted gel-combustion route at 800 °C. The as prepared powder is characterised using X-ray diffraction (XRD), time resolved photoluminescence spectroscopy (TRPLS) and density functional theory (DFT) calculations. Uranium is an interesting element because it exhibits multiple oxidation state and each one of them is having characteristics fluorescence behavior. TRPLS is used to investigate the oxidation state and coordination behavior of uranium in MgAl 2 O 4 . Indeed in our earlier work on undoped and lanthanide ion doped MAS; it was oberved that in undoped sample itself defect induced emission could be seen in visible region which was probed using DFT. Here on doping uranium in MAS; complete energy of host is transferred to uranium ion which is explained using DFT. From excitation and emission spectroscopy it was observed that uranium stabilizes in +6 oxidation state in the form of UO 2 2 + ion. Based on luminescence lifetime and its comparison with the emission profile of uranyl fluoride crystal it was inferred that majority of uranium is occupying relatively asymmetric MgO 4 polyhedra and minority substitutes AlO 6 . The site stability of the uranyl ion in MAS was also validated using DFT based first principle calculations. Time resolved emission shows the uranyl at Mg 2+ site differs from the one at Al 3+ site in terms of peak position and intensity. [ABSTRACT FROM AUTHOR]

[Display omitted] • Two novel asymmetrical tetra-alkylcarbamides were developed, which showed stronger affinity to U(VI) than other actinides. • The ligands complexed with U(VI) in the form of UO 2 (NO 3) 2 ·2 L . • The interactions between ligands and U(VI) show mainly ionic characteristics. • This study enriches the coordination chemistry of actinides by tetra-alkylcarbamides. In this work, the solvent extraction and complexation behaviors of U(VI) by two novel asymmetrical tetra-alkylcarbamides, N,N'-butyl-N,N'-hexylurea ( L1 : SBHU) and N,N'-butyl-N,N'-pentylurea ( L2 : SBPU) in HNO 3 media were systematically investigated. Both two ligands extract U(VI) more effectively than other metals such as Pu(IV), Np(IV), and Th(IV) in a wide range of acidity. Under 5 mol/L HNO 3 , D U reached 5.25, while D Pu = 1.08, D Np = 0.11, D Th = 0.13.. Additionally, no third-phase was present by the extraction of highly uranium concentration solution with SBHU even under 7 mol/L HNO 3 after four cycles demonstrating good acid resistance and resistance to the formation of the third phase. Slope analyses and FT-IR indicate that the U(VI) complexes are a form of UO 2 (NO 3) 2 ·2 L for the two ligands during the extraction. Additionally, based on the DFT calculations, the NBO analysis, and topological analysis were analyzed in detail. The results demonstrate that the interactions between ligands and U(VI) are shown mainly as ionic characteristics, and the ligand-to-metal charge transfer was also observed. This study enriches the coordination chemistry of actinides: Th(IV), U(VI), Np(IV), Am(III), and Pu(IV) by tetra-alkylcarbamides, which may shed light on the design and synthesis of novel U(VI) selective ligands. [ABSTRACT FROM AUTHOR]

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 U x Th 1-x (C 2 O 4 ) 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. [ABSTRACT FROM AUTHOR]

Describes the discovered compounds of the U[sub2]T[sub2]X type, which contribute to heavy fermion research due to a systematic occurrence of gamma enhancement. Factor that affects the magnetic and electronic properties of light actinides in intermetallic compounds; Examples of nonmagnetic compounds that exhibit spin-fluctuation features; Characteristics of the obtained spectra of the compounds.

Eighteen actinyl complexes of a Schiff-base polypyrrolic macrocycle (H4L), [(Sol)(AnmO2)(H2L)]n− (Sol = Vacant, pyridine (py) and tetrahydrofuran (THF); An=U, Np and Pu; m = VI and n = 0, m = V and n = 1) were investigated using relativistic density functional theory. Comparison of complexes with and without the explicit solvent coordination to the metal center, and changes in actinide element and metal oxidation state provide insight into their effects on structural and energetic properties of the complexes. Compared with those of the solvent-free complexes, the An=O bond lengths of the solvated complexes differ within 0.01 Å, and the deviation of the O=An=O angles is less than 1°. The H···Oendo bonds are relatively sensitive to the explicit solvent coordination, showing the largest discrepancy of 0.05 Å. Charges and electron-spin densities of actinides are only slightly affected by the inclusion of the explicit solvent. Reduction potentials of actinyl complexes have been addressed, and their dependence on the bulk solvent polarity is being discussed, using a simple model based on the Born equation. [ABSTRACT FROM AUTHOR]

A Mamdani-type fuzzy inference system for prospectivity modeling of mineral systems is described. The system is a type of knowledge-driven symbolic artificial intelligence that is transparent, intuitive and is easy to construct by geologists because they are built in natural language and use linguistic values. No examples are used for training the system and expert-opinions are incorporated indirectly in terms of objective mathematical functions, which reduce the possibility of over-emphasizing the known deposits usually used as training data. The cognitive reasoning of the exploration geologist is captured in explicit if–then type of statements written in natural language using linguistic values. Conditional dependencies in the exploration data sets are managed through the use of fuzzy operators. A case study for surficial uranium prospectivity modeling in the Yeelirrie area, Western Australia, is used to demonstrate the approach. In the output prospectivity map, the SE-NW trending Yeelirrie and E-W trending Hinkler's Well palaeochannels show high prospectivity, while other channels show very low prospectivity ranges. The known surficial uranium deposits fall in high prospectivity areas, although minor showings and anomalies in the southern part of the study area fall in low prospectivity areas. A comparison of the prospectivity model with the radiometric image shows that several channels showing high surface uranium concentrations in the NW and NE quadrants may not be prospective. [ABSTRACT FROM AUTHOR]

We report the synthesis and structural determination of three uranium(IV) complexes bearing two, four, and six salicylaldiminate ligands. Reaction of UI4(1,4-dioxane)2with two, four, and six equivalents of K[OC6H4C(H)=N(2,6-iPr2C6H3)],1, yielded [(2,6-iPr2C6H3)N=C(H)C6H4O-κ2(O,N)]2UI2(NCCH3),2, [(2,6-iPr2C6H3)N=C(H)C6H4O-κ1(O)]2[(2,6-iPr2C6H3)N=C(H)C6H4O-κ2(O,N)]2U(THF),3, and {[2,6-iPr2C6H3)N=C(H)C6H4O-κ1(O)]6U}2−,4. While2shows normalκ2-coordination through both oxygen and nitrogen donors,3has two salicylaldiminate ligands bound only through oxygen and4has all six ligands bound only through oxygen. This is an exceedingly rare example of a chelating ligand not completing its chelation in f-element chemistry. In addition,4is the first report of a homoleptic octahedral actinide complex with a Schiff base ligand. [ABSTRACT FROM AUTHOR]

[Display omitted] • An efficient and reliable method for the synthesis of crack-free hierarchically porous functionalized silica monolith was demonstrated. • Tetravalent actinides can be selectively separated with high efficiency and ultra-fast kinetics. • High-performance solid-phase extraction of thorium from monazite was firstly achieved by diglycolamic acid-functionalized silica monolith column. Separation of actinides is of great concern from the perspective of nuclear energy development and environmental issues, and the development of a highly efficient solid-phase extraction (SPE) process holds significant promise for actinide separation. However, the slow mass transfer kinetics in the currently available SPE separation media limited the throughput and efficiency, rendering the separation process more challenging. Hierarchically porous structures with well-organized and highly interconnected pore systems have been shown to provide efficient mass transfer and enhanced performance in nature. Herein, this paper reports the synthesis of a crack-free diglycolamic acid-functionalized silica monolith with hierarchical macro and meso porous structure for SPE. The hierarchically porous structures were retained upon mild modifications, which favored the convective mass transport and provided more binding sites, resulting in fast kinetics and high throughput. The separation ability was evaluated based on the separation and recovery of Th(IV) from a complex matrix. A superior Th(IV) separation performance (K d > 2.6 × 104 mL/g) was achieved in the presence of alkaline earth metals, rare earth elements, and uranium within 1 min by batch sorption, and the maximum separation coefficients of Th(IV)/Ln(III) and Th(IV)/U(VI) exceed 1000 and 140, respectively. Particularly, the synthesized material allowed the separation of Th from monazite leachates with highly efficient recovery (> 96%) at a high flow rate (5 mL/min) by column study. Investigation of the binding mechanism revealed the formation of a stable coordination complex (Th(NO 3)L 3) via Th−O bonds. The material was also employed for the extraction of Pu(IV), and satisfactory sorption was achieved. Thus, this new functionalized material has potential application prospects for an improved actinide separation process. [ABSTRACT FROM AUTHOR]

Valence-to-core resonant inelastic X-ray scattering (RIXS) and high energy resolution fluorescence detection (HERFD) X-ray absorption measurements were performed at the U L3 edges of UO2 and UO2(NO3)2(H2O)6. The results are compared with model calculations based on the local-density-approximation formalism, taking into account Coulomb interaction U (LDA + U). We show that despite strong 5f-5f electronic correlations in the studied systems and the use of core-level excitations in the intermediate stage of the spectroscopic process, the RIXS technique probes a convolution of the single-particle densities of states in the valence and conduction bands. For UO2, the detected crystal-field splitting between the U 6d eg and t2g orbitals from the RIXS spectra (~3.5 eV) is larger than that previously derived from optical spectroscopy. Furthermore, by using an example of the U0.75Pu0.25O2 mixed oxide, we show that the RIXS technique at the U L3 edges is sensitive to the substitution of U with other actinide, in contrast to conventional X-ray absorption methods. That is, due to changes in the occupied part rather than in the unoccupied part of the U 6d states caused by the substitution. [ABSTRACT FROM AUTHOR]

To further our fundamental understanding of the nature and extent of covalency in uranium-ligand bonding, and the benefits that this may have for the design of new ligands for nuclear waste separation, there is burgeoning interest in the nature of uranium complexes with soft- and multiple-bond-donor ligands. Despite this, there have so far been no examples of structurally authenticated molecular uranium-arsenic bonds under ambient conditions. Here, we report molecular uranium(IV)-arsenic complexes featuring formal single, double and triple U-As bonding interactions. Compound formulations are supported by a range of characterization techniques, and theoretical calculations suggest the presence of polarized covalent one-, two- and threefold bonding interactions between uranium and arsenic in parent arsenide [U-AsH2], terminal arsinidene [U=AsH] and arsenido [U≡AsK2] complexes, respectively. These studies inform our understanding of the bonding of actinides with soft donor ligands and may be of use in future ligand design in this area. [ABSTRACT FROM AUTHOR]

The synthesis of the rnono(imidazolin-2-iminato) actinide(IV) complexes [(ImRN)An(N{SiMe3)2}3] (3-8) was accomplished by the protonolysis reaction between the respective imidazolin-2-imine (ImRNH, R = tBu, Mes, Dipp) and the actinide metallacycles [{(Me3Si)N}2An{κ²C,N-CH2SiMe2N(SiMe3)}] (1, An = U; 2, M = Th). The thorium and uranium complexes were obtained in high yields, and their structures were established by single-crystal X-ray diffraction analysis. The mono(imidazolin-2-iminato) actinide complexes 3-8 display short An-N bonds together with large An-N-C angles, indicating strong electron donation from the imidazolin-2-iminato moiety to the metal, corroborating a substantial π-character to the An-N bond. The reactivity of complexes 3-8 toward benzaldehyde was studied in the catalytic dimerization of aldehydes (Tishchenko reaction), displaying low to moderate catalytic activities for the uranium complexes 3-5 and moderate to high catalytic activities for the thorium analogues 6-8, among which 8 exhibited the highest catalytic activity. In addition, actinide coordination compounds showed unprecedented reactivity toward cyclic and branched aliphatic aldehydes in the catalytic Tishchenko reaction mediated by the thorium complex [(ImDippN)Th{N(SiMe3)2}3] (8), exhibiting high activity even at room temperature. Moreover, complex 8 was successfully applied in the crossed Tishchenko reaction between an aromatic or polyaromatic and an aliphatic cyclic and branched aldehyde, yielding selectively the asymmetrically substituted ester in high yields (80-100%). [ABSTRACT FROM AUTHOR]

Assessment of flux rates and concentrations of potentially toxic elements in sediment cores from 5 lakes adjacent to the McClean Lake uranium mines in northern Saskatchewan (impact lakes) compared to results from a set of 5 upwind and distant lakes (reference lakes) clearly indicated enrichment of several elements in lakes close to the mining operations. The flux of uranium to the sediments of the 5 impact lakes was significantly higher post-1960 from the mean pre-1960 background conditions by 1.5 to 23 times. Flux rates of arsenic, molybdenum, and selenium also indicated significant enrichment from background conditions in the majority of the impact lakes. In contrast, large and significant increases in flux only occurred in 1 of the 5 reference lakes for arsenic. The highest levels of enrichment were found in the 3 lakes either in closest proximity to the tailings management facility, waste-rock piles, or downstream from the treated effluent management system. High flux rates and concentrations of elements such as arsenic and vanadium in both the reference lakes and in pre-mining samples of the impact lakes indicated that potentially toxic elements can occur naturally in this region. Sediment core analyses of elemental flux and concentration in both reference lakes and pre-1960 conditions in the impact lakes provided an estimate of natural background conditions. Our data suggest that the McClean Lake mine may be a source for the enrichments of toxic elements in the lakes in close proximity to the mining operations. [ABSTRACT FROM AUTHOR]

The terminal imido complexes U(NDipp)Cl 2 (tppo) 3 (tppo = triphenylphosphine oxide) and U(NDipp)Cl 2 (R 2 bpy) 2 (Dipp = 2,6- i Pr 2 -C 6 H 3 ; R 2 bpy = 4,4′-R 2 -2,2′-bipyridyl; R = Me, t Bu) contain reactive U N bonds, which undergo [2 + 2] cycloaddition reactions with the N–C multiple bonds of isocyanates and benzonitrile. These low valent imido complexes display a preference for forming cycloaddition products, in contrast to high valent bis (imido) complexes, which undergo imido group exchange when treated with isocyanates. This disparity suggests that the U(IV) NR linkage, already known to be more ionic than U(VI) NR bonds, is also weaker than its U(VI) congener. The cycloaddition products that were used in this qualitative bond strength analysis have been characterized by X-ray crystallography and NMR spectroscopy. Most importantly, U(NDipp)Cl 2 (tppo) 3 and U(NDipp)Cl 2 (R 2 bpy) appear to be excellent synthetic precursors to new and intriguing organometallic uranium complexes. [ABSTRACT FROM AUTHOR]

Biological Mn oxidation is responsible for producing highly reactive and abundant Mn oxide phases in the environment that can mitigate metal contamination. However, little is known about Mn oxidation in low-pH environments, where metal contamination often is a problem as the result of mining activities. We isolated two Mn(II)-oxidizing bacteria (MOB) at pH 5.5 (Duganella isolate AB-14 and Albidiferax isolate TB-2) and nine strains at pH 7 from a former uranium mining site. Isolate TB-2 may contribute to Mn oxidation in the acidic Mn-rich subsoil, as a closely related clone represented 16% of the total community. All isolates oxidized Mn over a small pH range, and isolates from low-pH samples only oxidized Mn below pH 6. Two strains with different pH optima differed in their Fe requirements for Mn oxidation, suggesting that Mn oxidation by the strain found at neutral pH was linked to Fe oxidation. Isolates tolerated Ni, Cu, and Cd and produced Mn oxides with similarities to todorokite and birnessite, with the latter being present in subsurface layers where metal enrichment was associated with Mn oxides. This demonstrates that MOB can be involved in the formation of biogenic Mn oxides in both moderately acidic and neutral pH environments. [ABSTRACT FROM AUTHOR]

We present here an overview of the properties of transuranium superconductors, but also of the (non-superconducting) transuranium analogues of uranium superconductors. We briefly review superconductivity in actinide elements and uranium compounds and focus in particular on the PuTX 5 ( T = Co , Rh ; X = Ga , In ) series, the largest superconducting system in actinides and NpPd 5 Al 2 , the so far unique neptunium superconductor. The effects of chemical substitution, ageing and pressure on the properties of transuranium superconductors are also discussed. [ABSTRACT FROM AUTHOR]

Understanding the effect of soil parameters (pH, Eh and organic and inorganic ligands availability) on uranium mobility under different geochemical conditions is fundamental for reliable prediction of its behaviour and fate in the environment. In this study, the impact of total and available phosphorus content, humus and acidity of Serbian agricultural soils on the content of total and available uranium were evaluated by Response Surface Methodology (RSM), second order polynomial regression models (SOPs) and artificial neural networks (ANNs). The performance of ANNs was compared with the performance of SOPs and experimental results. SOPs showed high coefficients of determination (0.785-0.956), while ANN model performed high prediction accuracy: 0.8893-0.904. According to the results, total and available uranium content in the soil were mostly affected by pH, statistically significant at p < 0.05 level. For the same responses the total phosphorus was found to be also very influential, statistically significant at p < 0.05 and p < 0.10 levels. The impact of available phosphourus and humus was much more influential on total and available uranium content, compared to total phosphorus content. Proposed chemometric approach will be very helpful in preserving the natural resources and practical application for risk assessment modeling of uranium environmental pathways. [ABSTRACT FROM AUTHOR]

A series of actinide-transition metal hetero-bimetallics has been prepared, featuring thorium, uranium, and cobalt. Complexes incorporating the binucleating ligand N[?-(NHCH2PiPr2)C6H4]3 with either Th(IV) (4) or U(IV) (5) and a carbonyl bridged [Co(CO)4]- unit were synthesized from the corresponding actinide chlorides (Th: 2; U: 3) and Na[Co(CO)4]. Irradiation of the resulting isocarbonyls with ultraviolet light resulted in the formation of new species containing actinide-metal bonds in good yields (Th: 6; U: 7); this photolysis method provides a new approach to a relatively unusual class of complexes. Characterization by single-crystal X-ray diffraction revealed that elimination of the bridging carbonyl and formation of the metal-metal bond is accompanied by coordination of a phosphine arm from the N4P3 ligand to the cobalt center. Additionally, actinide-cobalt bonds of 3.0771(5) Å and 3.0319(7) Å for the thorium and uranium complexes, respectively, were observed. The solution-state behavior of the thorium complexes was evaluated using 1H, 1H-1H COSY, 31P, and variable-temperature NMR spectroscopy. IR, UV-vis/NIR, and variable-temperature magnetic susceptibility measurements are also reported. [ABSTRACT FROM AUTHOR]

Single-chain magnets (SCMs) are materials composed of magnetically isolated one-dimensional (1D) units exhibiting slow relaxation of magnetization. The occurrence of SCM behavior requires the fulfillment of stringent conditions for exchange and anisotropy interactions. Herein, we report the synthesis, the structure, and the magnetic characterization of the first actinide-containing SCM. The 5f-3d heterometallic 1D chains [{[UO2(salen)(py)][M(py)4](NO3)}] n, (M=Cd ( 1) and M=Mn ( 2); py=pyridine) are assembled trough cation-cation interaction from the reaction of the uranyl(V) complex [UO2(salen)py][Cp*2Co] (Cp*=pentamethylcyclopentadienyl) with Cd(NO3)2 or Mn(NO3)2 in pyridine. The infinite UMn chain displays a high relaxation barrier of 134±0.8 K (93±0.5 cm−1), probably as a result of strong intra-chain magnetic interactions combined with the high Ising anisotropy of the uranyl(V) dioxo group. It also exhibits an open magnetic hysteresis loop at T<6 K, with an impressive coercive field of 3.4 T at 2 K. [ABSTRACT FROM AUTHOR]

To advance the understanding of the chemical behavior of actinides, a series of trans-bis(imido) uranium(VI) complexes, U(NR)2(THF)2(cis-I2) (2R; R = H, Me, 'Bu, Cy, and Ph), U(NR)2(THF)3(trans-I2) (3R; R = H, Me, 'Bu, Cy, and Ph) and U(N'Bu)2(THF)3(cis-I2) (3'Bu'), were investigated using relativistic density functional theory. The axial Uâ•N bonds in these complexes have partial triple bonding character. The calculated bond lengths, bond orders, and stretching vibrational frequencies reveal that the Uâ•N bonds of the bis-imido complexes can be tuned by the variation of their axial substituents. This has been evidenced by the analysis of electronic structures. 2H, for instance, was calculated to show iodine-based high-lying occupied orbitals and U(f)-type low-lying unoccupied orbitals. Its Uâ•N bonding orbitals, formed by U(f) and N(p), occur in a region of the relatively low energy. Upon varying the axial substituent from H to 'Bu and Ph, the Uâ•N bonding orbitals of 2'Bu and 2Ph are greatly destabilized. We further compared the Uâ•E (E = N and O) bonds of 2H with 3H and their uranyl analogues, to address effects of the equatorial tetrahydrofuran (THF) ligand and the E group. It is found that the Uâ•N bonds are slightly weaker than the Uâ•O bonds of their uranyl analogues. This is in line with the finding that cis-UNR2 isomers, although energetically unfavorable, are more accessible than cis-UO2 would be. It is also evident that 2H and 3H display lower Uâ•(NH) stretching vibrations at 740 cm-1 than the Uâ•O at 820 cm-1 of uranyl complexes. With the inclusion of both solvation and spin-orbit coupling, the free energies of the formation reactions of the bis-imido uranium complexes were calculated. The formation of the experimentally synthesized 3Me, 3Ph, and 2'Bu are found to be thermodynamically favorable. Finally, the absorption bands previously obtained from experimental studies were well reproduced by time-dependent density functional theory calculations. [ABSTRACT FROM AUTHOR]

In stark contrast to uranocene, (Cot)2Th reacts with neutral mono- or bidentate Lewis bases to give the bent sandwich complexes (Cot)2Th(L) (L = py, 4,4'-bipy, tBuNC, phen, Me4phen). DFT calculations in the gas phase show that, for both U and Th, formation of the bent compound (Cot)2An(L) should be facile, the linear and bent forms being close in energy. [ABSTRACT FROM AUTHOR]

Abstract: Diffusion of actinides in uranium dioxide plays an important role in determining thermodynamic and mechanic properties of the material. Activation energies of Th, U, Np, and Pu diffusion in uranium dioxide were systematically studied using first-principles calculations. The generalized gradient approximation and projector-augmented wave methods with on-site Coulomb repulsive interaction were applied within Density Functional Theory and Plane Wave framework. Two diffusion paths, one along the lattice 〈110〉 direction and the other along the lattice 〈100〉 direction, were examined in the face-centered cubic UO2 structure. The results show that the 〈110〉 path has lower migration energy than the 〈100〉 path. Under the assumption of a vacancy-assisted jump diffusion mechanism, the major contribution to the activation energy is the migration energy, followed by the vacancy formation energy and vacancy binding energy, where the last has the lowest contribution. However, differences in the activation energies among different actinides stem from both the migration and vacancy binding energies, both of which decrease with atomic number. While discrepancies between the absolute values of the calculated and experimentally observed activation energies remain, this study shows a correlation between activation energy and atomic number and an asymptotic relation between activation energy and ionic radius of the actinides. The present study suggests that the migration of the actinides through the uranium dioxide lattice is closely correlated to the number of 5f electrons and the size of the diffusing atoms. [Copyright &y& Elsevier]

The sodetal importance of uranium complexes containing the uranyl moiety [ 0=U=0 ]n+ continues to grow with the ongoing international nuclear enterprise and associated accumulating legacy waste. Further studies of the electronic structure of uranyl and its analogues are imperative for the development of crucial technologies, including lanthanide/actinide extractants and chemical and environmental remediation methodologies. Actinide oxo halides are a subset of the growing class of actinyl (uranyl) analogues. The understanding of their electronic structures links the detailed spectroscopic studies of uranyl, indicating the role of die pseudocore 6p orbitals in U--O bonding, to hypotheses about the 6p orbitals' role in the chemical bonding of uranyl analogues. These actinide oxo halides are a very small class of actinide compounds that present the inverse trans influence (IT1). This class of complexes was, until recently, limited to two crystallographically characterized compounds, namely, [UCl50][PPh4] and [PaCl5O][NEt4]2. These complexes are important because tfiey give a readily and clearly defined experimental observable: the difference between the M--Xtrans and M--Xcis (here X = CI) bond lengths in tiie solid state. This bond metric is a sensitive probe for the role of 6p, 6d, and 5f orbitals, as well as electrostatic interactions, in determining their electronic structure. This Viewpoint Article reviews the theoretical, experimental, and synthetic work on the ITÏ in actinide complexes and contextualizes it within broader studies on the electronic structure of uranyl and its analogues. Furthermore, our recent work on the ITI in high-valent uranium(V/VI) oxo and imido complexes is described as a whole. This work builds on the extant synthetic literature on tiie ITI and provides design parameters for the synthesis and characterization of high-valent uranium--ligand multiple bonds. [ABSTRACT FROM AUTHOR]

Chemical trends within the periodic table are frequently used as guides for predicting reactivity, structure, and electronic properties of the elements. While these trends have been rigorously investigated for the transition metals, the understanding of trends within the actinide series is elementary in comparison. Herein, we report the synthesis and characterization of five new U(IV) sulfate compounds and discuss their relationship to previously reported An(IV) sulfate species, an analysis that allows for the elucidation of solid state trends across the actinides. One such trend suggests the increase in Lewis acidity that occurs when traversing the actinides from thorium to plutonium promotes bidentate binding of the sulfate ligand as long as complexation can outcompete the resulting increase in steric pressure. This hypothesis correlates well with the experimental results previously reported for the solution phase speciation in An(lV) sulfate systems. [ABSTRACT FROM AUTHOR]

Abstract: Oxalic precipitation is usually applied to process radioactive wastes or to recover actinides from a multicomponent solution. Due to their later handling and use, actinide precipitates have to satisfy strict requirements. In nuclear environment where experiments are limited, simulation may be the only way to test different industrial configurations in order to adjust industrial campaigns. In this manuscript, the modelling of the tetravalent uranium oxalate precipitation in an unbaffled reactor is achieved using a hybrid multizonal/CFD model. The population balance is solved according to the moment method in a multizonal model entirely parameterised through computational fluid dynamics calculations based on large-eddy simulation (LES) and a sub-grid model of micromixing. The modelling is applied to show how the specificity of flow field in an unbaffled reactor can have a noticeable effect on the uranium oxalate properties. [Copyright &y& Elsevier]

Abstract: In the frame of the heterogeneous transmutation of minor actinides in MABB (Minor Actinides Bearing-Blanket) fuels, the CEA program DIAMINO aims to assess the influence of americium content and microstructure on helium release and fuel swelling. For DIAMINO experiment, four sets of U1-xAmxO2±δ ceramic fuels, namely two compositions (x = 0.075, 0.15) and two microstructures (highly dense: > 95%TD, and highly porous: < 85%TD), were produced in the ATALANTE facility following innovative preparation methods. Pellets were further characterized by several techniques and were all found to be in full compliance with the strict specifications required for such irradiation programs. [Copyright &y& Elsevier]

Abstract: A brief status of the development of actinide separation in china is presented. The activities on actinide separation include: 1) Neptunium chemistry and its separation in Purex Process; 2) actinide separation from HLLW; 3) separation of actinides from rare earth; and 4) preliminary studies on uranium cathode deposit by pyrochemical process. [Copyright &y& Elsevier]

Uranyl(VI) 5,5'-azobis[tetrazolide] pentahydrate was synthesized and characterized using X-ray crystallography, elemental analysis, UV/vis, MIR, FIR, and Raman spectroscopy. It is the second-most nitrogen rich compound of uranium (26.72 wt % N) and only the second structurally characterized uranium complex with a tetrazole ligand described in the literature. The compound's structure is characterized by an exceptionally small uranyl angle of 172.4(1)°, which provides information on the coordination properties of tetrazole ligands as they afiect the donor's environment by strong steric and perhaps electrostatic repulsion. The compound showed luminescence under excitation with a near UV laser. The mean lifetime of its exdted state was shorter than in the case of U02(N03)2-6H20, indicating quenching by the ligand. Despite its high nitrogen content (and thus potentially explosive character), the title compound proved to be stable even under neutron radiation causing induced fission processes. [ABSTRACT FROM AUTHOR]

The soft X-ray beamline BL23SU at SPring-8 has undergone an upgrade with a twin-helical undulator of in-vacuum type to enhance the experimental capabilities of the endstations. The new light source with a fast helicity-switching operation allows not only the data throughput but also the sensitivity in X-ray magnetic circular dichroism (XMCD) to be improved. The operational performance and potential are described by presenting XMCD results of paramagnetic β-US2 measured with a 10 T superconducting magnet. [ABSTRACT FROM AUTHOR]

The complexes [NpO(DMSO)](ClO) ( 1) and [PuO(DMSO)](ClO) ( 2), isostructural to the known uranyl complex, were synthesized in the form of single crystals. Their crystallographic characteristics were determined by single crystal X-ray diffraction. The IR and electronic absorption spectra of the crystalline U(VI), Np(VI), and Pu(VI) complexes were measured and analyzed. [ABSTRACT FROM AUTHOR]

Abstract: A method for the assessment of intrinsic proliferation resistance (PR) in a variety of nuclear fuel cycle systems as a dynamic quantity is described in this paper. This method is based upon the direct coupling of a code for nuclear fuel isotopic characterization (ORIGEN-S) to a model for proliferation resistance, based upon a generalized fuel cycle model. The resulting coupled model is applied to evaluate PR as a dynamic system property as a function of three fuel cycle categories: open cycles, a “modified open cycle” (MOC) consisting of limited actinide recycle, and a fully closed cycle. Proliferation resistance is evaluated along several key operational parameters of the chosen fuel cycles, including fuel burnup and actinide separation strategies (including uranium and minor actinide co-extraction). For purposes of demonstration, a PR model developed at NC State shall be used for fuel cycle PR evaluation; the mechanics of this model will be presented in brief. [Copyright &y& Elsevier]

Abstract: Uranium(VI) complex with silicoundecatungstate, K7H6[K(UO2)(H2O)(α-SiW11O39)2]·21H2O, has been obtained and its structure has been determined using X-ray single crystal diffractometry and confirmed by electron and IR absorption spectroscopy. The stability of An(VI) complexes with monolacunary heteropolyanions in solution is discussed from the structural point of view. [Copyright &y& Elsevier]

Dispersed fuel composites consisting of uranium carbide particles (microspheres) in a zirconium carbide (inert) matrix were fabricated and characterized. Advanced fuels including refractory inert matrix fuels are being considered for gas fast reactors, which can accommodate a variety of feed materials including recycled transuranics that include minor actinides for incineration and high-level waste reduction. The particles for this effort were fabricated by employing a custom built rotating electrode machine. This process employed a uranium carbide electrode manufactured by combustion synthesis of uranium hydride and graphite powders. Two process parameters, namely, arc intensity and rotational speed, were varied to assess their effects on the size of the particles produced. The particles were characterized for microstructure, density, and composition (homogeneity). These particles were mixed with pure zirconium and graphite powders in different matrix to particle volumetric ratios of 90/10, 80/20, and 70/30 and inductively heated to 1850°C to initiate combustion synthesis to produce composites of zirconium carbide with the embedded uranium carbide particles. The aim was to limit process temperature and in particular process time, bearing in mind the possible future extensions of these processes to minor actinide-bearing fuels and also to avoid any changes in the structural integrity of the particles and large-scale diffusion of uranium into the matrix. The composites were characterized for microstructure, phase composition, density, and porosity distribution. The results are presented. [ABSTRACT FROM AUTHOR]