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Pyroprocessing holds the key to unlocking a more sustainable future for nuclear energy by handling various types of spent nuclear fuel (SNFs) and reducing radioactive waste volumes. This review examines the role of electrochemical monitoring in molten salt pyroprocessing of SNFs, emphasizing its importance in enhancing process efficiency and nonproliferation. Challenges associated with the monitoring of multi-element environments, flow environments, and sensor stability are discussed. The review suggests that integrating sensor technology with artificial intelligence could lead to significant advancements in the field. [ABSTRACT FROM AUTHOR]

The first example of circularly polarized luminescence (CPL) from a molecular americium (Am) complex is reported. Coordination of Am(III) by a combination of thenoyltrifluoroacetonate and a chiral diphosphine oxide ligand yielded a complex with strong sensitized metal‐centered luminescence. The energy transfer process for sensitization appears to occur via a unique resonant pathway, which results in the removal of the overlap between ligand phosphorescence and sensitized Am luminescence that has often been observed. Owing to this feature, and despite the limited amount of material that could be used due to the radioactivity of 241Am, CPL could be measured. The collected luminescence and CPL spectra provide insight into the crystal field splitting of the 5D1→7F1 transition. These results pave the way for future studies of Am(III) luminescence to investigate electronic structure effects in this and other 5 f elements. [ABSTRACT FROM AUTHOR]

Partial least squares regression (PLSR) and support vector regression (SVR) models were optimized for the quantification of U(VI) (10-320 g L-1) and HNO3 (0.6-6 M) by Raman spectroscopy with optimized calibration sets chosen by optimal design of experiments. The designed approach effectively minimized the number of samples in the calibration set for PLSR and SVR by selecting sample concentrations with a quadratic process model, despite complex confounding and covarying spectral features in the spectra. The top PLS2 model resulted in percent root mean square errors of prediction for U(VI), HNO3, and NO3 - of 3.7%, 3.6%, and 2.9%, respectively. PLS1models performed similarly despitemodeling an analyte with a majority linear response (i.e., uranyl symmetric stretch) and another with more covarying vibrational modes (i.e., HNO3). Partial least squares (PLS) model loadings and regression coefficients were evaluated to better understand the relationship between weaker Raman bands and covarying spectral features. Support vector machine models outperformed PLS1 models, resulting in percent root mean square error of prediction values for U(VI) and HNO3 of 1.5% and 3.1%, respectively. The optimal nonlinear SVR model was trained using a similar number of samples (11) compared with the PLSR model, even though PLS is a linear modeling approach. The generic D-optimal design presented in this work provides a robust statistical framework for selecting training set samples in disparate two-factor systems. This approach reinforces Raman spectroscopy for the quantification of species relevant to the nuclear fuel cycle and provides a robust chemometric modeling approach to bolster online monitoring in challenging process environments. [ABSTRACT FROM AUTHOR]

To validate the nuclear data in JENDL-4.0 and obtain information to improve their accuracy, the analysis of the measured nuclide inventories of the high-burnup PWR UO2 and BWR MOX fuels in the REBUS program was performed by using MVP-BURN with the nuclear library and burnup chain based on JENDL-4.0, and the ratios of the calculated and measured inventories (C/Es) were compared with the previous results obtained with JENDL-3.2 or JENDL-3.3. As a result, an improvement in the accuracy of the neutron cross-sections and cumulative fission yields (CFYs) in JENDL-4.0 was confirmed for the inventories of 236U, 238Pu, 239Pu, 241Pu, 242Pu, 241Am, 243Cm, 244Cm, 133Cs, 145Nd, 148Sm, 149Sm, 151Sm, and 153Eu of the PWR UO2 fuel and 239Pu, 241Pu, 242Pu, 241Am, 243Am, 243Cm, 244Cm, 246Cm, 134Cs, 144Ce, 145Nd, 147Sm, and 154Eu of the BWR MOX fuel. Based on the C/Es obtained with JENDL-4.0, the directions to improve the neutron cross-sections and CFYs were tentatively proposed. They included the neutron capture cross-sections of 234U, 236U, 237Np, 238Pu, 241Am, 242Cm, 245Cm, 143Nd, 147Pm, 154Eu, and 155Eu, the fission cross-sections of 243Cm and 245Cm, and the CFYs of 144Nd, 147Pm, and 155Eu. [ABSTRACT FROM AUTHOR]

As a quick and affordable experimental technique, the heavy ion irradiation method may quickly learn about the correlation between the degree of amorphization and structural modification of samples with varying ion implantation. Using the heavy ion irradiation technique, the irradiation stability of multiphase ceramic waste made of Ln 2 Zr 2 O 7 /SrZrO 3 was assessed. Here, we found that multiphase ceramic waste forms still exhibit excellent radiation resistance while achieving high capacity and weak selectivity for immobilization of actinide nuclides (simulated by lanthanide elements) and fission products 90Sr (replaced by 89Sr). The analysis of grazing incidence and Raman spectroscopy provides evidence for explaining the radiation damage mechanism caused by 84Kr15+ heavy ions. Analysis of grazing incidence offers proof of the manner and extent of radiation damage brought on by 84Kr15+ ions. The impact and mechanism of crystal structure on radiation resistance in multiphase ceramics are discussed. [ABSTRACT FROM AUTHOR]

Partial least squares regression (PLSR) and support vector regression (SVR) models were optimized for the quantification of U(VI) (10–320 g L−1) and HNO3 (0.6–6 M) by Raman spectroscopy with optimized calibration sets chosen by optimal design of experiments. The designed approach effectively minimized the number of samples in the calibration set for PLSR and SVR by selecting sample concentrations with a quadratic process model, despite complex confounding and covarying spectral features in the spectra. The top PLS2 model resulted in percent root mean square errors of prediction for U(VI), HNO3, and NO3− of 3.7%, 3.6%, and 2.9%, respectively. PLS1 models performed similarly despite modeling an analyte with a majority linear response (i.e., uranyl symmetric stretch) and another with more covarying vibrational modes (i.e., HNO3). Partial least squares (PLS) model loadings and regression coefficients were evaluated to better understand the relationship between weaker Raman bands and covarying spectral features. Support vector machine models outperformed PLS1 models, resulting in percent root mean square error of prediction values for U(VI) and HNO3 of 1.5% and 3.1%, respectively. The optimal nonlinear SVR model was trained using a similar number of samples (11) compared with the PLSR model, even though PLS is a linear modeling approach. The generic D-optimal design presented in this work provides a robust statistical framework for selecting training set samples in disparate two-factor systems. This approach reinforces Raman spectroscopy for the quantification of species relevant to the nuclear fuel cycle and provides a robust chemometric modeling approach to bolster online monitoring in challenging process environments.

A series of compounds of the form [HAr]2[UO2X4] is reported here, wherein Ar is systematically varied between pyridine (1‐X), quinoline (2‐X), acridine (3‐X), 2,5‐dimethylpyrazine (4‐X), quinoxaline (5‐X), and phenazine (6‐X), and X=Cl or Br. With greater conjugation in the organic cation, a larger quenching in uranyl luminescence is observed in the solid state. Supporting our luminescence experiments with computation, we map out the potential energy diagrams for the singlet and triplet states of both the [HAr]+ cations and [UO2Cl4]2− anion in the crystalline state, and of the assembly. The distinct energy transfer pathways in each compound are discussed. [ABSTRACT FROM AUTHOR]

Reactions of atomic uranium cations with carbon disulfide form US+ in an efficient exothermic reaction and UCS+ in an inefficient endothermic process. The subsequent reaction of US+ with CS2 forms US2+ in an endothermic process having a low energy threshold. At much higher energies, UCS2+ and UCS+ are also formed. Collision-induced dissociation of US+ with Xe yields U+ + S exclusively in an endothermic reaction. Analysis of the kinetic energy dependent cross sections of the endothermic processes yields the 0 K bond dissociation energies of 5.73 ± 0.15 eV for U+ – S, 3.89 ± 0.08 eV for SU+ – S, 1.69 ± 0.17 eV for U+ – CS, 2.78 ± 0.33 eV for U+ – CS2, 1.53 ± 0.30 eV for SU+ – CS, and 5.65 ± 0.39 eV for S – UCS+. Theory is used to explore the structures and electron configurations of US+, US2+, UCS+, and UCS2+. The thermochemistry measured in this study is further compared to analogous values previously determined for select group 3 metals, lanthanides, and actinides. [ABSTRACT FROM AUTHOR]

Reactions of atomic uranium cations with carbon disulfide form US+ in an efficient exothermic reaction and UCS+ in an inefficient endothermic process. The subsequent reaction of US+ with CS2 forms US2+ in an endothermic process having a low energy threshold. At much higher energies, UCS2+ and UCS+ are also formed. Collision-induced dissociation of US+ with Xe yields U+ + S exclusively in an endothermic reaction. Analysis of the kinetic energy dependent cross sections of the endothermic processes yields the 0 K bond dissociation energies of 5.73 ± 0.15 eV for U+ – S, 3.89 ± 0.08 eV for SU+ – S, 1.69 ± 0.17 eV for U+ – CS, 2.78 ± 0.33 eV for U+ – CS2, 1.53 ± 0.30 eV for SU+ – CS, and 5.65 ± 0.39 eV for S – UCS+. Theory is used to explore the structures and electron configurations of US+, US2+, UCS+, and UCS2+. The thermochemistry measured in this study is further compared to analogous values previously determined for select group 3 metals, lanthanides, and actinides. [ABSTRACT FROM AUTHOR]

We report the formation of a NpIV complex from the complexation of NpVIO22+ with the redox‐active ligand tBu‐pdiop2−=2,6‐bis[N‐(3,5‐di‐tert‐butyl‐2‐hydroxyphenyl)iminomethyl]pyridine. To the best of our knowledge, this is the first example of the direct complexation‐induced chemical reduction of NpVIO22+ to NpIV. In contrast, the complexation of UVIO22+ with tBu‐pdiop2− did not induce the reduction of UVIO22+, not even after the two‐electron electrochemical reduction of [UVIO2(tBu‐pdiop)]. This contrast between the Np and U systems may be ascribed to the decrease of the energy of the 5 f orbitals in Np compared to those in U. The present findings indicate that the redox chemistry between UVIO22+ and NpVIO22+ should be clearly differentiated in redox‐active ligand systems. [ABSTRACT FROM AUTHOR]

Controlled-potential in situ thin-layer spectropotentiometry was leveraged to generate visible/near-infrared (VIS/NIR) absorption spectral data sets for the development of chemometric models to quantify Np(III/IV/V/VI) oxidation states in HNO3. This technology would be valuable in laboratory studies and when monitoring process solutions to guide feed adjustments for radiochemical separations—the performance of which depends on oxidation state. This approach successfully isolated and stabilized Np species in pure (∼99%) oxidation states without compromising solution optical properties. Multivariate curve resolution–alternating least squares models were evaluated to resolve spectral and component concentrations from a scan that sequentially produced Np(VI), Np(V), Np(IV), and Np(III) spectra with mixtures of two valences at a time. Although it provided a useful approximation, the method was not able to quantitively resolve each component likely because of rotational ambiguity. Additionally, partial least squares regression models were built from artificial and electrochemically generated VIS/NIR spectral training sets to study the effect of interionic interactions on spectral characteristics. Models built with true Bi-chemical mixtures of coexisting Np oxidation states and spectra generated from additive combinations of pure end points had similar prediction performance. This methodology can be used to directly quantify Np concentration and the ratio of Np oxidation states and other actinides in remote settings such as hot cells.

In this work, EIS was applied to characterize the temporal recovery of uranium from UCl4 onto a tungsten electrode in molten LiCl-KCl salt between sets of pulse reverse-pulse (PRP) deposition steps. Impedance measurements were fitted to an equivalent circuit (EC) model of the electrode interface using Simplex optimization to calculate the double layer capacitance, charge transfer resistance, Warburg impedance, and CPE-restricted diffusion. Diffusion of uranium towards the electrode surface dominated the surface interactions for the first 80 cycles, followed by a transition to kinetic control for the remaining 520 cycles. A decrease in the Warburg impedance showed depletion of uranium from the bulk melt, which was confirmed to be a 52.5% reduction through ICP-OES. Reduction in the phasance from CPE-restricted diffusion suggested the formation of pores in the uranium deposits, which was confirmed through SEM characterization.

The purpose of this research was to determine the isotope concentration of the actinide radioelements 238U, 232Th series, and 239Pu in biological samples (urine) using the alpha spectroscopy system. The samples were selected from the residence of high natural background radiation (HNBR) area and analyzed using chemical procedure. The separated sample was placed on a membrane filter by the sedimentation method, and it was prepared for counting with the alpha spectrometry system. The average radioactive concentrations found in these samples were as follows: 234U > 226Ra > 230Th > 228Ra > 228Th > 224Ra > 232Th > 239Pu. The average concentrations of 234U and 226Ra were much greater than the other radionuclides. [ABSTRACT FROM AUTHOR]

Separations relevant to trivalent actinides and lanthanides have been a focus of the f-element community in the past few decades. A central focus of this effort has been optimizing ligands for separations. From a fundamental perspective, one must investigate the metal–ligand interactions for optimal ligand design. A well-explored class of ligands, phenanthroline diamides, is reviewed to further elucidate the actinide or lanthanide–ligand interactions of primarily Am3+, Cm3+, and Eu3+. Mixed nitrogen and oxygen donors of this nature are of interest to explore due to their increased selectivity for the trivalent actinides over the trivalent lanthanides. Phenanthroline diamide ligands have shown to have promise in industrial-scale separations compared to bipyridine and pyridine diamide ligands with larger selectivity for the trivalent actinides. These interactions are studied through solvent extraction, spectroscopic, and thermodynamic techniques. Further analysis provided in this review includes an overview of the computational results provided and relevant comparisons to experimental data. The computational parameters considered are the calculated bond lengths, thermodynamic parameters, and values that provide insight to a discussion of covalent interactions between metal and ligand. The information provided is important to benchmark the state-of-the-art basic, applied, and computational chemistry of the phenanthroline diamide class of ligands. [ABSTRACT FROM AUTHOR]

A reaction of acyl chlorides derived from 1,10-phenanthroline-2,9-dicarboxylic acids with piperazine allows the preparation of the corresponding 24-membered macrocycles in good yield. The structural and spectral properties of these new macrocyclic ligands were thoroughly investigated, revealing promising coordination properties towards f-elements (Am, Eu). It was shown that the prepared ligands can be used for selective extraction of Am(III) from alkaline–carbonate media in presence of Eu(III) with an SFAm/Eu up to 40. Their extraction efficiency is higher than calixarene-type extraction of the Am(III) and Eu(III) pair. Composition of macrocycle–metal complex with Eu(III) was investigated by luminescence and UV-vis spectroscopy. The possibility of such ligands to form complexes of L:Eu = 1:2 stoichiometry is revealed. [ABSTRACT FROM AUTHOR]

The most stable Cm3+ sorption species at the water-gibbsite interface are predicted to be a tridentate surface complex, [t 7 -S(OH) 3 –Cm(H 2 O) 5 ]3+, in weakly acidic/neutral solution condition and a bidentate one, [b 6 -S(OH) 2 –Cm(OH)(H 2 O) 4 ]2+, in the alkaline solution condition by combining the AIMD simulations and static DFT geometry optimization calculations. Based on the high-accuracy SO-CAS(7e,7o)SCF/NEVPT2 calculations, the simulated emission spectra of the Cm3+ aquo ion and the two surface complexes show a gradual decrease trend in the emission energy in good agreement with TRLFS experimental observation of a red shift of peak maximum with pH increasing from 5 to 11. [Display omitted] The information of structure and stability of actinide species is key to understand the sorption mechanism of actinides at mineral–water interface. Such information is approximately derived from experimental spectroscopic measurements and needs to be accurately obtained by a direct atomic-scale modelling. Herein, systematic first-principles calculations and ab initio molecular dynamics (AIMD) simulations are carried out to study the coordination structures and absorption energies of Cm(III) surface complexes at gibbsite-water interface. Eleven representative complexing sites are investigated. The most stable Cm3+ sorption species are predicted to be a tridentate surface complex in weakly acidic/neutral solution condition and a bidentate one in the alkaline solution condition. Moreover, luminescence spectra of the Cm3+ aqua ion and the two surface complexes are predicted based on the high-accuracy ab initio wave function theory (WFT). The results give a gradually decreasing emission energy in good agreement with experimental observation of a red shift of peak maximum with pH increasing from 5 to 11. This work is a comprehensive computational study involving AIMD and ab initio WFT methods to gain the coordination structures, stabilities, and electronic spectra of actinide sorption species at the mineral–water interface, thus providing important theoretical support for geological disposal of actinide waste. [ABSTRACT FROM AUTHOR]

Despite the potential application of uranyl‐organic coordination polymers (UOCPs) in detecting metal cations and radiation rays, their luminescence properties have not been sufficiently studied at the molecular level. Herein, we synthesized a series of UOCPs (UOCP1–9) with new construction based on bipyridinium salts and diverse auxiliary ligands. The physicochemical properties of the complexes with high purity were systematically characterized, especially the luminescence spectra. A deep theoretical investigation was conducted to illustrate the relation between uranyl coordination and the luminescence spectral property. The results show that the influence of ligand type on the uranyl luminescent spectral properties increases in the order of hydroxide>oxalate>aromatic carboxylate, which can be attributed to the magnitude of orbital interaction between uranyl and ligand. This work helps to profoundly understand uranyl optical properties and electronic structure at the molecular level, providing important hints for recognizing the nature of luminescent spectral features of uranyl‐containing materials, as well as the fundamental chemistry of actinide elements. [ABSTRACT FROM AUTHOR]

This article describes several extraction chromatographic materials aiming to offer improved potential for isolating trace elements with high charge/ionic radius ratio from accompanying matrix elements in natural samples. Starting with commercially available, field-proven, TRU- and RE-Spec materials (Eichrom Technologies), three resins containing less TBP in the CMPO-TBP mixtures, or even neat CMPO only, have been prepared and characterized through measurement of the distribution ratios of some fifty elements in HNO3 and HCl media of variable strength. These resins were further evaluated for analytical applications on geochemical samples. The results highlight a strong enhancement of weight distribution ratios of many elements of interest in geochemistry, cosmochemistry, and environmental sciences (Lanthanides, naturally occurring Actinides, High Field Strength Elements). Combined with good chromatographic characteristics, these high Dw's make it possible to achieve excellent group separations by using very small columns operated at relatively high, gravity-driven flow rate. Moreover, in an attempt to further improve the selectivity against Fe(III) and Ti(IV), preliminary investigations were made on an additional pair of resin prototypes impregnated with a CMPO-substituted calixarene. Although promising distribution ratio data were obtained, these prototypes did not permit to prepare columns with satisfactory chromatographic characteristics, and this approach still waits for a better impregnation methodof the porous inert support. [ABSTRACT FROM AUTHOR]

A new uranyl containing metal-organic framework, RPL-1: [(UO2)2(C28H18O8)] . H2O (RPL for Radiochemical Processing Laboratory), was prepared, structurally characterized, and the solid-state photoluminescence properties explored. Single crystal X-ray diffraction data reveals the structure of RPL-1 consists of two crystallographically unique three dimensional, interpenetrating nets with a 4,3-connected tbo topology. Each net contains large pores with an average width of 22.8 Å and is formed from monomeric, hexagonal bipyramidal uranyl nodes that are linked via 1,2,4,5-tetrakis(4-carboxyphenyl)benzene (TCPB) ligands. The thermal and photophysical properties of RPL-1 were investigated using thermogravimetric analysis and absorbance, fluorescence, and lifetime spectroscopies. The material displays excellent thermal stability and temperature dependent uranyl and TCPB luminescence. The framework is stable in aqueous media and due to the large void space (constituting 76 % of the unit cell by volume) can sequester organic dyes, the uptake of which induces a visible change to the color of the material.

The recently discovered all-boron fullerene(D2d B-/040) opened a new chapter in borospherene chemistry. Similar to fullerenes, metal doping is also an important way for modification and functionalization of borospherenes. This work predicts a series of stable actinide metal-doped borospherenes ［An@B39］n+ (An=U, n=3; An=Cm, n=2) by using density functional theory. Theoretical calculations show that these borospherenes are all endohedral borospherenes, among which the lowest energy structures of ［U@B39］3+ has C3 symmetry, while ［Cm@B39］2+ is a C1 structure. Bonding nature analysis shows that delocalized σ and π bonds exist in ［U@B39］3+ and ［Cm@B39］2+. In addition, the covalent interaction of the U-B bond in ［An@B39］n+ is stronger than that of the Cm-B bond. Therefore, the covalency in the An-B bonds may be essential for the formation of these metal-doped borospherenes. This work expands the borospherenes system and provides theoretical clues for the design of novel stable metal endohedral borospherenes.

Pertraction of Np(IV) across a PTFE membrane containing two different aza-crown ether-based multiple diglycolamide (DGA) ligands termed as LI (3 DGA arms) or LII (4 DGA arms) was investigated using nitric acid as feed solution. A few of the studies were also carried out with Pu(IV) for comparison purposes. The kinetics of the extraction of Np(IV) and Pu(IV) was fast at 3 M HNO3 and within 10 min reaches the equilibrium distribution (D) ratio with both ligands. However, the stripping kinetics was slower especially with ligand LII. The extraction and transport studies were carried out using 1.0 × 10−3 M ligand solution in 95% n-dodecane + 5% isodecanol. The transport rates were slower with ligand LII than with LI at higher nitric acid concentrations (>1 M HNO3) and the transport rates decreased with nitric acid concentration with both ligands. The effective diffusion coefficients (Deff) of Np(IV) were estimated using the lag-time method as 6.2 × 10−8 cm2 s−1 (LI) and 4.6 × 10−8 cm2 s−1 (LII). The stability data suggest that the LI containing supported liquid membrane (SLM) is comparatively more stable than that of LII and the transport flux remains the same up to nine days of operation in case of ligand LI. [ABSTRACT FROM AUTHOR]

Chemistry of f-element gains importance in several fields due to the extensive scope of their applications. The aim of this study is to understand the subtle differences in bonding in the structurally similar actinides (An) and their homologous (isovalent) lanthanides (Ln) with several donors, which may lead to their covalency mediated separation. Several experimental and theoretical studies have been reported to address this aspect. However, to the best of our knowledge, a systematic study on the variation in the bonding patterns of the isovalent 'Ln' and 'An' pairs encompassing the effect of valence f-orbital participation was not attempted. In this study, the minute differences in covalent interactions of these An/Ln pairs having same number of f-electrons with chalcogenide ions of varying softness was probed using relativistic density functional theory (DFT). The f-electronic configurations of the metal ions were observed to play an important role in the f-orbital participation. [AnX]+/[LnX]+ pairs with f0, f7 (half-filled) configurations show resistance to f-orbital directed bonding, unlike the systems having f5, f6 electronic configurations where the f-orbital directed covalency is more pronounced in the [AnX]+ systems. The nature of covalency was identified to be near degeneracy-driven. This enhanced covalency was found to increase with the subsequent increase in the softness of the donor centres. [ABSTRACT FROM AUTHOR]

Actinide concentration and activity analysis of the nuclides resulted from the burnup (depletion) process during nuclear reactor operation lifetime is an essential problem in reactor design. Inventory and the corresponding activities of the Tehran Research Reactor (TRR) are evaluated using different methods and compared with each other. WIMS-CITATION, ORIGEN, and MCNP codes are used for plate type inventory calculations. The important actinides, fission products, and fissile inventory ratio of TRR have been calculated at different burnup steps. It is worth noting to mention that knowing the value of inventory helps us for safe handling of the spent fuels and to have a perfect design for transport cask of spent fuels. In this work, the fuel isotope inventories were calculated for the first and 83rd core configuration of the Tehran Research Reactor, which is named "Core01" and "Core83" respectively. The calculations were first performed using WIMS-D5 and CITATION neutronic codes and then the results are compared with that of ORIGEN and MCNPX code. The total radioactivity of the TRR core at the end of the reactor core life (Core83) is estimated to be 6.47×105 Ci. [ABSTRACT FROM AUTHOR]

Generalised gradient approximation and hybrid density functional theory is used to study the geometries, electronic structures and spin state energetics of a series of high symmetry multi‐layer "Matryoshka" actinyl peroxide manganese nanoclusters "E@Mn12@An20n+" (An=U, Np, Pu; E=S, Se, Te, n=2; E=Br, n=3; E=Xe, n=4). These systems are all highly open shell, with up to 100 unpaired electrons in the case of the highest spin state plutonyl complexes. Very strong linear correlations are found in all cases between the number of unpaired electrons and the energies of the complexes, with the highest spin states being much the most stable. We confirm a key conclusion from our previous work in this area (Chemistry, A European Journal24 (2018) 347) i. e. that the highest spin states of the chalcogen‐centred systems are the ground states only when the chalcogen is present; removal of the central group 16 element causes lower spin states to become the most stable. The compositions of the molecular orbitals associated with the changing spin states are studied in detail, and the relative energies of the highest and next highest spin states of the E‐free uranyl and plutonyl clusters rationalized on the basis of the characters of the orbitals whose occupation changes between the different spin states. [ABSTRACT FROM AUTHOR]

The self-assembly of actinides represents a cutting-edge research topic in the field of chemical materials, among which the actinide metal organic frameworks(An-MOF) emerge as the most shining star due to their tailorable structure, abundant coordination modes and versatile functionality, and have gained significant progress in recent years. In this review, the domestic and foreign advances of the synthesis and property investigation of An-MOF are first summary. Then a systematic introduction of uranium- and thorium- MOFs developed in our group is presented. Finally, the future direction of actinide self-assembly chemistry is briefly prospected.

Extended X-ray absorption fine structure (EXAFS) is a comprehensive and usable method for characterizing the structures of various materials, including radioactive and nuclear materials. Unceasing discussions about the interpretation of EXAFS results for actinide nanoparticles (NPs) or colloids were still present during the last decade. In this study, new experimental data for PuO2 and CeO2 NPs with different average sizes were compared with published data on AnO2 NPs that highlight the best fit and interpretation of the structural data. In terms of the structure, PuO2, CeO2, ThO2, and UO2 NPs exhibit similar behaviors. Only ThO2 NPs have a more disordered and even partly amorphous structure, which results in EXAFS characteristics. The proposed new core-shell model for NPs with calculated effective coordination number perfectly fits the results of the variations in a metal–metal shell with a decrease in NP size.

Stable actinide colloids and nanoparticles are of interest because of their potential to affect the transportation of radionuclides in the near-field of a nuclear waste repository. At high concentrations, thorium(IV) can precipitate to form intrinsic colloids. In the present study, polynuclear thorium colloids and thorium dioxide crystallites, formed by the condensation of hydrolyzed Th4+ solutions (3 mM; initial pH 5.5) aged for up to 18 months, were studied using small-angle X-ray scattering. Scattering profiles were fitted using a unified Guinier/power-law model (Beaucage model) to extract the radii of gyration and Porod exponents. Analysis of the scattering profiles from a dispersion aged for 5 months indicated that both polymer coils and more compacted structures (radius of gyration Rg ≃ 10 nm) were present, which translated in the Kratky plots as a plateau and a peak maximum, respectively. After 18 months, the SAXS data were consistent with the presence of agglomerates of ThO2 particles suspended in aqueous solution (pH 3.2; [Th] = 1.45 mM). The measured radius of gyration (Rg) of the agglomerates was 5.8 nm, whereas the radius of the ThO2 particles was 2.5 nm.

A detailed spectroscopic simulation of the original Pu N 4,5 and O 4,5 X-Ray Absorption Spectroscopy (XAS) has been performed. Additionally, a fundamental flaw in the Electron Energy Loss Spectroscopy (EELS) measurement has been corrected. Thus, the determination of the 5f occupation (n) in elemental Pu has been re-evaluated with the result that n = 5.0 ± 0.1 for αPu and n = 4.9 ± 0.2 for δPu. These values are significantly lower than the value of ∼5½ that was propagated earlier. • The 5f population in αPu is 5.0 ± 0.1. • The 5f population in δPu is 4.9 ± 0.2. • The 2nd Derivative Mode in EELS should not be used in quantitative BR analyses. [ABSTRACT FROM AUTHOR]

A spectroelectrochemical setup has been developed to investigate radioactive elements in small volumes (0.7 to 2 ml) under oxidation–reduction (redox) controlled conditions by X-ray absorption spectroscopy (XAS). The cell design is presented together with in situ XAS measurements performed during neptunium redox reactions. Cycling experiments on the NpO22+/NpO2+ redox couple were applied to qualify the cell electrodynamics using XANES measurements and its ability to probe modifications in the neptunyl hydration shell in a 1 mol l−1 HNO3 solution. The XAS results are in agreement with previous structural studies and the NpO22+/NpO2+ standard potential, determined using Nernst methods, is consistent with measurements based on other techniques. Subsequently, the NpO2+, NpO22+ and Np4+ ion structures in solution were stabilized and measured using EXAFS. The resulting fit parameters are again compared with other results from the literature and with theoretical models in order to evaluate how this spectroelectrochemistry experiment succeeds or fails to stabilize the oxidation states of actinides. The experiment succeeded in: (i) implementing a robust and safe XAS device to investigate unstable radioactive species, (ii) evaluate in a reproducible manner the NpO22+/NpO2+ standard potential under dilute conditions and (iii) clarify mechanistic aspects of the actinyl hydration sphere in solution. In contrast, a detailed comparison of EXAFS fit parameters shows that this method is less appropriate than the majority of the previously reported chemical methods for the stabilization of the Np4+ ion.

The first structural examples of complexes with uranium–germanium bonds are presented, namely, bis[3,5-bis(trifluoromethyl)phenyl-2κC1](hydrido-2κH)(iodido-1κI)bis[1,1(η5)-pentamethylcyclopentadienyl]germaniumuranium(Ge—U), [GeU(C10H15)2(C8H3F6)2HI], and bis[3,5-bis(trifluoromethyl)phenyl-2κC1](fluorido-1κI)(hydrido-2κH)bis[1,1(η5)-pentamethylcyclopentadienyl]germaniumuranium(Ge—U), [GeU(C10H15)2(C8H3F6)2FH]. The two complexes both have a long U—Ge bond [distances of 3.0428 (7) and 3.0524 (7) Å].

Qualitative differences in the reactivity of trivalent lanthanide and actinide complexes have long been attributed to differences in covalent metal‐ligand bonding, but there are few examples where thermodynamic aspects of this relationship have been quantified, especially with U3+ and in the absence of competing variables. Here we report a series of dimeric phosphinodiboranate complexes with trivalent f‐metals that show how shorter‐than‐expected U−B distances indicative of increased covalency give rise to measurable differences in solution deoligomerization reactivity when compared to isostructural complexes with similarly sized lanthanides. These results, which are in excellent agreement with supporting DFT and QTAIM calculations, afford rare experimental evidence concerning the measured effect of variations in metal‐ligand covalency on the reactivity of trivalent uranium and lanthanide complexes. [ABSTRACT FROM AUTHOR]

Despite the fact that in the mass consciousness nuclear power is associated with increased environmental risks, this type of energy today remains one of the cleanest, most efficient and carbon neutral. Further development of nuclear energy is hampered by the problem of appropriate handling of spent nuclear fuel (SNF). A very attractive concept of the closed nuclear cycle has been developed to solve it. A real-life implementation of this concept requires the development of technological processes for the efficient separation of minor actinides from the rest of the SNF components. Recent progress in this area has been closely associated with N,O-hybrid donor ligands for liquid–liquid extraction. This work systematically reviews the available literature on the topic and provides detailed explanations on the behavior of the most perspective ligands. Notably, another important aspect of the application of N,O-hybrid donor ligands in nuclear cycle analytics through their incorporation in chemical sensors is also discussed. [ABSTRACT FROM AUTHOR]

A reaction of acyl chlorides derived from 1,10-phenanthroline-2,9-dicarboxylic acids with piperazine allows the preparation of the corresponding 24-membered macrocycles in good yield. The structural and spectral properties of these new macrocyclic ligands were thoroughly investigated, revealing promising coordination properties towards f-elements (Am, Eu). It was shown that the prepared ligands can be used for selective extraction of Am(III) from alkaline–carbonate media in presence of Eu(III) with an SFAm/Eu up to 40. Their extraction efficiency is higher than calixarene-type extraction of the Am(III) and Eu(III) pair. Composition of macrocycle–metal complex with Eu(III) was investigated by luminescence and UV-vis spectroscopy. The possibility of such ligands to form complexes of L:Eu = 1:2 stoichiometry is revealed.

This study explores the potential benefit to flowsheets for recovering actinides from used nuclear fuel of a process simplification in the head-end portion. The process simplification replaces acid dissolution of used nuclear fuel with dissolution in the tri-butyl phosphate solvent used in the industrially mature Plutonium Uranium Reduction Extraction flowsheet. Though characterized by considerable uncertainty, simplified flowsheets appear feasible and potentially offer significant reductions in process complexity, nitrate inventory, secondary liquid effluent generation, and plant footprint. [ABSTRACT FROM AUTHOR]

Separation properties of asymmetric N -donor ligands with Am(III)/Eu(III) complexes have been investigated by DFT methods. [Display omitted] • Chosen the theoretical method of PBE0/6-311 g*&RECP to Carry out full-text calculation. • Using Visual Molecular Dynamics software package to visualise the interaction between complexes, especially the natural bond orbital. • Comparing the thermodynamic properties of different reactions, the choice of solvent is crucial. • The f orbital occupies the major contribution in metal–ligand bonds. • Ligands with o-phenanthroline backbone have excellent extraction properties, and ligands with asymmetric side chains have good separation effects. In the reprocessing of spent nuclear fuel, nitrogen-donor extractants are more effective in separating actinides and lanthanides. In this article, a series of heterocyclic N -donor ligands with different backbones and different side chain substituents are systematically investigated to analyze their extraction selectivity and complexation abilities for Am(Ⅲ) and Eu(Ⅲ) by using scalar relativistic density functional theory (DFT). Through the analysis of geometric structures and bond properties of the complexes by means of the NBO and QTAIM methods, it was observed that the coordination ability of the N -donor ligand with Am(Ⅲ) was stronger than with Eu(Ⅲ). Thermodynamic analysis showed that these ligands have good extraction ability and separation performance for Am(III) and Eu(III), the backbone and side chain substituents of the ligands and also the organic solvents have significant influences on the extraction selectivity of the ligands for Am(III) and Eu(III) ions. This work provides some theoretical insights for the design of N -donor extractants with good separation performance for lanthanides and actinides. [ABSTRACT FROM AUTHOR]