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The retention of actinides in different oxidation states (An(X), X = III, IV, VI) by a calcium-silicate-hydrate (C-S-H) phase with a Ca/Si (C/S) ratio of 0.8 was investigated in the presence of gluconate (GLU). The actinides considered were Am(III), Th(IV), Pu(IV), and U(VI). Eu(III) was investigated as chemical analogue for Am(III) and Cm(III). In addition to the ternary systems An(X)/GLU/C-S-H, also binary systems An(X)/C-S-H, GLU/C-S-H, and An(X)/GLU were studied. Complementary analytical techniques were applied to address the different specific aspects of the binary and ternary systems. Time-resolved laser-induced luminescence spectroscopy (TRLFS) was applied in combination with parallel factor analysis (PARAFAC) to identify retained species and to monitor species-selective sorption kinetics. ¹³C and ²⁹Si magic-angle-spinning (MAS) nuclear magnetic resonance (NMR) spectroscopy and X-ray photoelectron spectroscopy (XPS) were applied to determine the bulk structure and the composition of the C-S-H surface, respectively, in the absence and presence of GLU. The interaction of Th(IV) with GLU in different electrolytes was studied by capillary electrophoresis-inductively coupled plasma mass spectrometry (CE-ICP-MS). The influence of GLU on An(X) retention was investigated for a large concentration range up to 10⁻² M. The results showed that GLU had little to no effect on the overall An(X) retention by C-S-H with C/S of 0.8, regardless of the oxidation state of the actinides. For Eu(III), the TRLFS investigations additionally implied the formation of a Eu(III)-bearing precipitate with dissolved constituents of the C-S-H phase, which becomes structurally altered by the presence of GLU. For U(VI) sorption on the C-S-H phase, only a small influence of GLU could be established in the luminescence spectroscopic investigations, and no precipitation of U(VI)-containing secondary phases could be identified., Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe; 1318

The multiple probable oxidation states of actinide elements can lead to their molecular anions to result in complicated yield patterns from a Cs+ sputter ion source. For actinides AMS, two methods can be practiced in order to concentrate the yields into just one or two anion species. The present common practice has been to avoid excessive oxygen reactions in the sputter targets, so that the mono-oxide anions can be produced with good or applicable ionization efficiencies. However, this method requires the typical 860-type Cs+ sputter ion sources to be operated with relatively high Cs+ fluxes, a condition that not all such sources in use can be operated with lasting stability. On the contrary, with low Cs+ fluxes, good or applicable ionization efficiencies can also be achieved for producing element-specific polyatomic oxide, oxyfluoride, or fluoride anions of actinides, if the sputter targets are aided with dominantly oxidizing or fluorinating matrices. This paper describes a systematic study of such phenomena using ZnO and FeF3 to form the respective oxidizing and fluorinating matrices. It was found that using the chosen set of polyatomic fluoride anions and the FeOxHy + FeF3 sputter targets, not only all rare actinides could be measured with low backgrounds matching those using mono-oxides, but also with the available ionization efficiencies fully utilized within a shorter time. A few additional merits are also noted.

A spectroelectrochemical setup has been developed to investigate radioactive elements in small (0.7 to 2 ml) volumes 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., 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 NpO2 2+/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 NpO2 2+/NpO2 + standard potential, determined using Nernst methods, is consistent with measurements based on other techniques. Subsequently, the NpO2 +, NpO2 2+ 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 NpO2 2+/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.

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.

Two plutonium oxides were prepared as unique reference materials for measurement of actinide elements present as trace constituents. Each reference material unit is approximately 200 mg of PuO2 powder in a quartz glass bottle. Characterized attributes of the oxides included mass fractions of plutonium, americium, neptunium, and uranium. Isotope-amount ratios were also determined for plutonium and uranium, but neptunium and americium were observed to be monoisotopic 237Np and 241Am. Measurements for characterization and verification of the attributes show that plutonium and trace actinides are homogeneous with the exception of limited heterogeneity for uranium, primarily observed for the 238U isotope. Model purification ages calculated from measured americium and uranium attribute values are consistent with material histories and indicate that these impurities are predominantly due to the decay of plutonium isotopes.

A comprehensive ab initio study of periodic actinide-ligand bonding trends for trivalent actinides is performed. Relativistic density functional theory (DFT) and complete active-space (CAS) self-consistent field wavefunction calculations are used to dissect the chemical bonding in the [AnCl6]3-, [An(CN)6]3-, [An(NCS)6]3-, [An(S2PMe2)3], [An(DPA)3]3-, and [An(HOPO)]- series of actinide (An = U-Es) complexes. Except for some differences for the early actinide complexes with DPA, bond orders and excess 5f-shell populations from donation bonding show qualitatively similar trends in 5f n active-space CAS vs DFT calculations. The influence of spin-orbit coupling on donation bonding is small for the tested systems. Along the actinide series, chemically soft vs chemically harder ligands exhibit clear differences in bonding trends. There are pronounced changes in the 5f populations when moving from Pu to Am or Cm, which correlate with previously noted "breaks" in chemical trends. Bonding involving 5f becomes very weak beyond Cm/Bk. We propose that Cm(III) is a borderline case among the trivalent actinides that can be meaningfully considered to be involved in ground-state 5f covalent bonding.

The “many ensembles” method was proposed to investigate the influence of nuclear particles’ post-scission emission on mass and charge distributions of fission products. The post-scission approximation was used: each of these ensembles consists of the fission fragments after emission of chains of different lengths, both the beta (β±) particles and neutrons. The theory allows one to find the most probable two-fragment clusters of fission products and study their evolution after the post-scission emission of nuclear particles. The isotope 232Th was chosen as an example, the fission fragments of which have been intensively studied experimentally. It is shown that the post-scission emission of nuclear particles eventually leads to the convergence of the asymmetric peaks, which looks like enhanced symmetric fission mode over the asymmetric mode for fission product yields. A comparison of the theoretical results and experimental data for the 232Th fission fragments indicates their satisfactory matching.

The precise analysis of sub-gram quantities of actinide materials for regulatory and specification requirements currently relies on destructive, wet chemistry methodologies. We report a high-resolution gamma spectrometry approach. Actinide samples were consistently produced in containment to a precise geometry. This allows analysis on actinide materials outside of gloveboxes, which has considerable advantages. The main challenge of the analysis is the precise assay of 240Pu to which we demonstrate approaches. The results show that despite not meeting the precision of other benchmark techniques, the approach is promising as a parallel, rapid, low cost methodology for sample analysis.

Recent interest in compact nuclear reactors for applications in space or in remote locations drives innovation in nuclear fuel design, especially non-oxide ceramic nuclear fuels. This work details neutronic modeling designed to support the development of a new nuclear fuel concept based on a mixture of thorium and uranium nitride. A Monte Carlo N-Particle Version 6.2 (MCNP-6) model of a compact 10 MWe reactor design which incorporates (ThxU1−x)N fuel is presented. In this context, a “compact” reactor is a completely assembled reactor which may be emptied of coolant and transported by specialized commercial vehicle, deployed by a C130J aircraft, or launched into space. Core geometry, reflector barrels, and the heat exchange zones are designed to support reduction of overall reactor volume of core components while maintaining criticality with a fixed total fuel mass of 4500 kg. Dense mixed nitrides of thorium nitride (ThN) additions in uranium nitride (UN) in 5 wt.% increments between $$0.05 \le x \le 0.5$$ 0.05 ≤ x ≤ 0.5 have been considered for calculation of $$k_{\infty }$$ k ∞ and $$k_{{{\text{effective}}}}$$ k effective . ThN additions in UN results in a slight increase in the magnitude of the temperature coefficient of reactivity, which is negative by design. The isotopic distribution of the principal actinide inventory as a function of burnup, time, and initial fuel composition is presented and discussed within the context of the proliferation risk of this core design.

International audience; The sintering of uranium oxide powders prepared by hydrothermal conversion of oxalates was studied. A dilatometric study first showed that among the synthesis conditions, only the pH largely impacted the densification, notably through the powders morphology. Three samples (single crystals-pH = 1, microspheres-pH = 2 and nano-powders-pH = 8) were further selected to study their sintering behaviour. Densitometric and granulometric data then allowed establishing sintering maps. For single crystals and microspheres, densities above 96%TD were obtained at 1700°C. In contrast, only 2 to 8 hours at 1500°C were needed to yield comparable results for nano-powders. These observations confirm that the hydrothermal conversion of oxalates can be considered as a promising route for the synthesis of actinide oxides, which can subsequently be sintered directly.

The design phase and safety assessment of Generation IV liquid metal-cooled fast reactors calls for the improvement of fuel pin performance codes, in particular the enhancement of their predictive capabilities towards uranium-plutonium mixed oxide fuels and stainless-steel cladding under irradiation in fast reactor environments. To this end, the current capabilities of fuel performance codes must be critically assessed against experimental data from available irradiation experiments. This work is devoted to the assessment of three European fuel performance codes, namely GERMINAL, MACROS and TRANSURANUS, against the irradiation of two fuel pins selected from the SUPERFACT-1 experimental campaign. The pins are characterized by a low enrichment (~ 2 wt.%) of minor actinides (neptunium and americium) in the fuel, and by plutonium content and cladding material in line with design choices envisaged for liquid metal-cooled Generation IV reactor fuels. The predictions of the codes are compared to several experimental measurements, allowing the identification of the current code capabilities in predicting fuel restructuring, cladding deformation, redistribution of actinides and volatile fission products. The integral assessment against experimental data is complemented by a code-to-code benchmark focused on the evolution of quantities of engineering interest over time. The benchmark analysis points out the differences in the code predictions of fuel central temperature, fuel-cladding gap width, cladding outer radius, pin internal pressure and fission gas release and suggests potential modelling development paths towards an improved description of the fuel pin behaviour in fast reactor irradiation conditions.

Uranium trichloride (UCl3) is actively researched to develop and improve applications ranging from molten salt reactors to actinide processing, including spent fuel reprocessing. Here, we report for the first time the crystal structure evolution between room temperature and melting point from in situ high-temperature neutron diffraction to quantify, for example, the thermal expansion of the hexagonal a and c lattice parameters. The results are compared with density functional theory calculations. The melting point of UCl3 is determined by differential scanning calorimetry to be 1108.2 ± 0.2 K.

Understanding the chemical behavior of actinide elements is essential for the effective management and use of actinide materials. In this study, we report an unprecedented η2 (side-on) coordination of U by a cyanide in a UCN cluster, which was stabilized inside a C82 fullerene cage. UCN@Cs(6)-C82 was successfully synthesized and fully characterized by mass spectrometry, single crystal X-ray crystallography, cyclic voltammetry, spectroscopy, and theoretical calculations. The bonding analysis demonstrates significant donation bonding between CN- and uranium, and covalent interactions between uranium and the carbon cage. These effects correlate with an observed elongated cyanide C-N bond, resulting in a rare case where the oxidation state of uranium shows ambiguity between U(III) and U(I). The discovery of this unprecedented triangular configuration of the uranium cyanide cluster provides a new insight in coordination chemistry and highlights the large variety of bonding situations that uranium can have.

Anthropogenic radionuclides, including long-lived heavy actinides such as americium and curium, represent the primary long-term challenge for management of nuclear waste. The potential release of these wastes into the environment necessitates understanding their interactions with biogeochemical compounds present in nature. Here, we characterize the interactions between the heavy actinides, Am3+ and Cm3+, and the natural lanthanide-binding protein, lanmodulin (LanM). LanM is produced abundantly by methylotrophic bacteria, including Methylorubrum extorquens, that are widespread in the environment. We determine the first stability constant for an Am3+-protein complex (Am3LanM) and confirm the results with Cm3LanM, indicating a ∼5-fold higher affinity than that for lanthanides with most similar ionic radius, Nd3+ and Sm3+, and making LanM the strongest known heavy actinide-binding protein. The protein's high selectivity over 243Am's daughter nuclide 239Np enables lab-scale actinide-actinide separations as well as provides insight into potential protein-driven mobilization for these actinides in the environment. The luminescence properties of the Cm3+-LanM complex, and NMR studies of Gd3+-LanM, reveal that lanmodulin-bound f-elements possess two coordinated solvent molecules across a range of metal ionic radii. Finally, we show under a wide range of environmentally relevant conditions that lanmodulin effectively outcompetes desferrioxamine B, a hydroxamate siderophore previously proposed to be important in trivalent actinide mobility. These results suggest that natural lanthanide-binding proteins such as lanmodulin may play important roles in speciation and mobility of actinides in the environment; it also suggests that protein-based biotechnologies may provide a new frontier in actinide remediation, detection, and separations.

A rapid analytical method for sequential separation and determination of the most significant α- and β-emitting radionuclidic impurities in 99Tc radiopharmaceutical raw material is presented. Successive HTiO co-precipitation steps were first conducted for effective removal of 99Tc to avoid its spectral interference on the determination of β-emitting nuclides by liquid scintillation counting. A sequential chromatographic method was applied for simultaneous separation and purification of actinide and lanthanide isotopes. A series of K99TcO4 solution spiked with known quantities of 238Pu, 239Pu, 241Pu, 237Np, 241Am, 244Cm and 147Pm were analyzed for method evaluation, demonstrating that the method would meet the analytical requirements for radionuclidic impurity evaluation of K99TcO4 raw material.

The separation of zirconium and hafnium isotopes from the early actinides and rare earth elements (REE) with Eichrom’s Pb resin has been studied. Batch studies were performed to characterize the behavior of actinium, thorium, zirconium, hafnium, lutetium, and yttrium on Pb resin from HCl solutions (0.001 M to 11 M). The early actinides and REE had no affinity for the resin at any concentration of HCl, but zirconium and hafnium showed a moderate uptake at high concentrations of HCl with a maximum extraction at 11 M HCl. Several column separations were tested, including with only tracer isotopes and with mass. Rapid, simple separations of zirconium from actinium, thorium, protactinium, and the REE with high yields and low elution volumes are presented with applications for tracer isotope production and fission product separations. The resin is less suitable for hafnium separations as hafnium tends to bleed off the resin even at high concentrations of HCl.

The coordination of tBuNC and CO with the diarsenido complexes (C5 Me5 )2 An(η2 -As2 Mes2 ), An=Th, U, has been investigated. For the first time, a comparison between isostructural complexes of ThIV and UIV has been possible with CO; density functional calculations indicated an appreciable amount of π backbonding that originates from charge transfer from an actinide-arsenic sigma bond. The calculated CO stretching frequencies in the ThIV and UIV diarsenido complexes are consistent with the experimental measurements, both show large shifts to lower frequency. We demonstrate that the π backbonding is crucial to explaining the red shifts of CO frequency upon AnIV complex formation. Interestingly, this interaction essentially correlates to the parallel orientation of π*(C-O) orbitals relative to the An-As bond.

Actinide molten salts represent a class of important materials in nuclear energy. Understanding them at a molecular level is critical for the proper and optimal design of relevant technological applications. Yet, owing to the complexity of electronic structure due to the 5f orbitals, computational studies of heavy elements in condensed phases using ab initio potentials to study the structure and dynamics of these elements embedded in molten salts are difficult. This lack of efficient computational protocols makes it difficult to obtain information on properties that require extensive statistical sampling like transport properties. To tackle this problem, we adopted a machine-learning approach to study ThCl4-NaCl and UCl3-NaCl binary systems. The machine-learning potential with the density functional theory accuracy allows us to obtain long molecular dynamics trajectories (ns) for large systems (103 atoms) at a considerably low computing cost, thereby efficiently gaining information about their bonding structures, thermodynamics, and dynamics at a range of temperatures. We observed a considerable change in the coordination environments of actinide elements and their characteristic coordination sphere lifetime. Our study also suggests that actinides in molten salts may not follow well-known entropy-scaling laws.

Measurements of highly radioactive actinides such as Np, Pu, Am, or Cm in as-fabricated or irradiated nuclear fuels are crucial to improve the safety and performance of the nuclear fuel cycle, but also necessary to find solutions to the environmental impact of long-lived actinides in nuclear waste. Currently, the most common technique of measuring the quantity and distribution of actinides in nuclear fuel is electron probe microanalysis (EPMA). However, the accurate analysis of actinides by EPMA is accompanied by numerous obstacles such as interferences in the M-line X-ray region, absorption edges, and the lack of reference materials. Therefore, the measurement protocol of radioactive and irradiated samples requires further investigation and most importantly facilitation. Here, we establish a guideline for precise quantification of actinide elements (Th, U, Np, Pu, Am, and Cm) in fabricated or spent nuclear fuels. For this purpose, we have characterized actinide-bearing reference samples to visualize spectral interferences, list peak, and background positions and employ the standardless calibration curve method for the measurements of Am and Cm. This newly derived analytical protocol was successfully tested on an irradiated fuel sample and can be now implemented as an improved guideline for the quantification of actinides.

Nuclear power plants use energy-dense fuel and provide dependable baseload energy without generating greenhouse gas emissions. Despite these advantages, the long-term management of used nuclear fuel (UNF) remains a key challenge due to its lifetime (hundreds of thousands of years) and radiotoxicity. The components of UNF that contribute the most to this challenge are the actinide elements. A potential solution to this issue is to separate these radioisotopes from the bulk of the UNF and recycle them as fuel in advanced nuclear reactors. These separations can be achieved using electrochemical reprocessing, which employs electrochemical conversion and electrodeposition in a high-temperature molten salt electrolyte medium to separate the actinides from UNF. In this short perspective, we review the current status, fundamental challenges, and future prospects of electrochemical reprocessing as they relate to UNF recycling.

Matrices with simulators of actinides (Sm, Nd) and technetium (Re) are produced by self-propagating high-temperature synthesis (SHS). The samples are composed of rare-earth aluminate with a garnet structure, glass, and alloys based on Fe, Re, Ni, and Cr. SEM/EDS analysis in combination with electron backscatter diffraction (EBSD) is used for their characterization. Alloy segregations have a complex structure, which is revealed during their element mapping. According to EBSD data, they are composed of phases of the following structural types: σ, e, bcc (main) and fcc, A13, and P-phase (minor). The reasons for their formation are the heterogeneity of the sample and its local enrichment in different elements, as well as the fast occurrence and nonequilibrium of the SHS process.

We have studied the synthesis of Uranium through all possible fusion reaction reactions. Suitable projectile/target combinations for the synthesis of Uranium is selected by studying the fusion cross section, compound nucleus probability $$P_{CN}$$ , survival probability $$P_{sur}$$ , and evaporation residue cross section. The present work is validated by comparisons with the experiments. The role of entrance channels parameters such as Coulomb interaction parameter (z), mean fissility ( $$\chi _{m}$$ ), charge asymmetry ( $$\alpha _{z}$$ ), and mass asymmetry ( $$\eta _A$$ ) in the synthesis of Uranium is discussed. We have constructed empirical formulae for evaporation residue cross sections in terms of entrance channel parameters. After detailed investigation, it was found that $$^{4}He+^{234}Th$$ is the suitable projectile-target combination which yields the largest production cross section. Furthermore, the possible projectile/target combinations to synthetize the different isotopes of Uranium are presented.

The probable decay modes of actinide nuclei are $$\alpha$$ , $$\beta ^{+}$$ , $$\beta ^{-}$$ , proton decay and spontaneous fission. Dominant decay mode is identified by studying the competition between different decay modes. Half-lives of $$\alpha$$ , $$\beta ^{+}$$ , $$\beta ^{-}$$ , proton decay and spontaneous fission are studied using Coulomb and proximity potential model, modified generalized liquid drop model, effective liquid drop model and many semi-empirical relations. Half-lives produced by the present work are compared with that of experiments. By studying the different decay modes in the actinide region, we have identified two proton emitters, 92 new $$\beta ^{-}$$ emitters, 74 new $$\alpha$$ -emitters and 115 new spontaneous fissionable isotopes. These newly identified isotopes with different half-lives and decay energies find an important application in the field of medicine and industry

An1.33T4Al8Si2 (An = Ce, Th, U, Np; T = Ni, Co) were synthesized in metal flux reactions carried out in aluminum/gallium melts. In previous work, U1.33T4Al8Si2 (T = Co, Ni) analogues were formed by arc-melting U:T:Si and reacting this mixture in Al/Ga flux. However, in the current work, all compounds were synthesized by using AnO2 reactants, taking advantage of the ability of the aluminum in the flux to act as both solvent and reducing agent. While reactions with T = Co yielded hexagonal Gd1.33Fe4Si10-type quaternary phases for all An, reactions with T = Ni produced these compounds only with An = U and Np. For reactions with An = Ce and Th, the reactions led instead to the formation of AnNi3-xSixAl4-yGay phases, with the tetragonal KCu3S4 structure type. Attempts to synthesize plutonium analogues Pu1.33T4Al8Si2 were also unsuccessful, producing the previously reported PuCoGa5 and Pu2Ni5Si6 instead. Magnetic data collected on the neptunium analogues Np1.33T4Al8Si2 (T = Ni, Co) show antiferromagnetic coupling at low temperatures and indicate a tetravalent state for the Np ions.

The importance of spin-orbit effects on the predictions of energetic properties of actinide compounds has been considered for 18 different density functionals, comparing the spin-orbit and non-spin-orbit ("standard") forms of density functional theory (DFT). A set of enthalpies of formation for 66 small actinide (Th-Am) compounds-the An66 set, for which experimental data are available-have been investigated. The set includes actinide halides, oxides, and oxohalides in the general form AnOmXn, where n = 0-6, m = 0-3, and X = F, Cl, Br, or I. The impact of basis set choice was investigated, and to help account for the impact of relativity, the Stuttgart general and segmented contracted atomic natural orbital (ANO) basis sets paired with small core relativistic effective core potentials (RECP) as well as all-electron calculations utilizing the third-order Douglas-Kroll-Hess were considered.

The structure of a new type of polyoxo cluster complex that contains thirteen uranium atoms, {U13}, is reported. The complex crystallized from methanol containing tetravalent uranium (UIV) with a basic organic ligand, and was characterized as dichloridooctacosa-μ2-methanolato-octakis(methanolato)octa-μ4-oxido-tridecauranium, [U13(CH3O)35.7Cl2.3O8] or [U13(μ4-Ooxo)8Cl x (MeO)38–x ] (x = 2.3, MeO = methoxide) (I), by single-crystal X-ray diffraction. The characterized {U13} polyoxo cluster complex (I) possesses a single cubic uranium polyhedron at the centre of the cluster core. To the best of our knowledge, this is the very first example of a polyoxo actinide complex that bears a single cubic polyhedron in its structure. The cubic polyhedron in I is well comparable in shape with those in bulk UO2. The U—O bonds in the cubic polyhedron of I are, however, significantly shorter than those not only in bulk UO2 but also in another analogue in the {U38} cluster. This shortening of U—O bonds, together with BVS calculations and the overall negative charge (2−) of I, suggests that the central uranium atom in I, which forms the single cubic coordination polyhedron, is presumably oxidized to the pentavalent state (UV) from the original tetravalent state (UIV). Complex I is, hence, the first example of a polyoxo cluster possessing a single cubic coordination polyhedron of UV.

In this work, the resin capacity factors of Ac, Am and Th on the DGA extraction chromatographic resin have been investigated between 0.5 and 2.0 M nitric acid without and with addition of elevated concentrations of the selective tetravalent complexant, 343HOPO. The resin capacity factors decreased with increasing 343HOPO concentration but remained high enough to support a selective removal of a tetravalent element. The Ac and Am capacity factors were also investigated under Th loading which yields generally reduced uptake on the resin. It was shown that loading effects could be fully scavenged by the addition of 343HOPO complexant. These results indicate that separation steps for Ac involving significant amounts of Th can be handled by selective tetravalent complexation with the DGA system.

We have studied the alpha decay properties of actinides using seven different proximity potentials MP 77, MP 81, Bass 77, Prox 13, Ng80, DP00 and Prox 00. The values produced by the present work are compared with experiments. Decay chains of actinides are presented. The present work is useful in the study of decay modes of actinides.

Radiation stability is one of the key properties to enable the efficient use of extractants in spent nuclear fuel with high radioactivity. The last several decades have witnessed a rapid progress in the radiation chemistry of extractants. A variety of studies and reviews pertinent to the radiation stability of extractants have been published. However, a thorough summary for the alpha radiolysis results of extractants is not available. In this review, we survey the development of alpha radiolysis of extractants for actinide lanthanide separation and compare their radiolysis behaviors induced by alpha particles and gamma rays. The discussion of alpha radiolysis of extractants is divided into three parts according to the functional groups of extractants (i.e., phosphine oxide, amide and bis-triazinyl bipyridines). Given the importance of radiation source to carry out alpha irradiation experiment, we first give a brief introduction to three practicable alpha radiation sources including alpha emitting isotopes, helium ion beam and reactor. We hope this review will provide useful information and unleash a broad palette of opportunities for researchers interested in radiation chemistry.

Solutions of two nitrilotriacetamide (NTA) ligands, viz., N,N,N’,N’,N”,N”-hexa-n-butylnitrilotriacetamide (HBNTA) and N,N,N’,N’,N”,N”-hexa-n-hexylnitrilotriacetamide (HHNTA) in 20% isodecanol–80% n-dodecane were employed for the extraction of U(VI), Np(IV), Pu(IV), and Am(III) from nitric acid feed solutions. Limitations of ligand solubility and third-phase formation when contacted with nitric acid solutions led to the choice of the diluent composition of 20% isodecanol and 80% n-dodecane. The results of the solvent extraction studies indicated poor extraction of the metal ions with HBNTA as compared to that with HHNTA as the extractant and hence, major part of this work involved HHNTA. Slope analysis suggested extraction of 1:1 (ML) species with Np(IV) and Pu(IV) at 3 M HNO3 and mixed 1:2 (ML2) and 1:3 (ML3) species with U(VI) at pH 2. At 0.5 M HNO3, the observed trend for extraction was Pu(IV) > Np(IV) >> Am(III) > U(VI).

N,N′-dioctyl-N,N′-di-dodecyl-3-oxapentane-1,5-diamide ((DdO)2DGA) is a novel unsymmetrical diglycolamide. Herein, we analyzed the third phase formation and extraction behavior of trivalent actinides and lanthanides with (DdO)2DGA in kerosene. Moreover, FT-IR and UV/Vis spectra of the extracted phase of Nd(III) with (DdO)2DGA were analyzed. The third phase is not formed by the extraction of Nd(III) with 0.10 mol/L (DdO)2DGA at 298 K. The metal ion distribution ratios increase with increased acidity and extractant concentration. Moreover, thermodynamic analysis demonstrates that the extraction is an exothermic reaction with ΔH = − 64.94 kJ/mol and ΔS = − 144.42 J/(mol·K). Both slope and spectroscopic analysis suggest that the extracted species is Nd(NO3)3·3(DdO)2DGA and the change in the acidity or extractant concentration will not change the extracted species.

Due to its associated low CO2 emissions, nuclear energy production is rapidly growing. In this context, the treatment of high-level liquid waste (HLLW) of nuclear plants is of high concern to both scientific and industrial communities. Specifically, the separation of An(III) and Ln(III) cations when processing nuclear fuel is a vitally important, yet challenging, step within HLLW because An(III) and Ln(III) have similar chemical properties in solution. To guide the choice of relevant ligands, anions, and solvents for this separation step, in this work, we calculate and compare the free energy of formation of different Am(III) and Eu(III) complexes (which are typical and important An(III) and Ln(III) cation examples), involving two different ligands and three different counter ions in four different solvents. Based on our calculations, we predict that the chosen solvent is a key factor in the extraction of Am(III) and Eu(III) in treatment of HLLW. This study supports a systematic, computation-assisted screening of solvents and extractive ligands with counter anions as a proficient method to optimize the separation of Ln(III) and An(III).

The properties and stability of ozone in aqueous solutions of various compositions in the рН range of 0–14 were considered. The effect of anions and cations, which are involved in the redox reactions of actinides, on the stability of ozone and its reactivity has been studied. The reactions of О3 with ions of d- and f-elements were analyzed. Depending on the solution composition and рН value, the reaction can occur directly with the O3 molecule (direct mechanism) and/or with short-lived ion-radical products (•OH, HO 2 • / O 2 − • ${\text{HO}}_{2}^{{\bullet}}/{\text{O}}_{2}^{-{\bullet}}$ , H2O2/ HO 2 − ${\text{HO}}_{2}^{-}$ , O 3 − • ${\text{O}}_{3}^{-{\bullet}}$ ) formed upon ozone decomposition in water (indirect mechanism). Ions with inert coordination sphere react with О3 in the outer-sphere fashion with electron transfer. Polyvalent ions with labile coordination spheres are oxidized in acidic medium via О atom transfer, possibly, with intermediate peroxy addition (H2O2, HNO4, H2SO5, etc.). In alkaline medium, О3 is converted to the O 3 − • ${\text{O}}_{3}^{-{\bullet}}$ radical ion, which is the key oxidant for actinides. The results of studies and the mechanisms of reactions of ozone and its intermediates decomposition products with U, Np, Pu, and Am in various oxidation states and with some transition metals (Fe, Mn, Ag, Co, etc.) in aqueous solutions are presented and discussed.

Monitoring and quantification of the photoresponsive behavior of metal-organic frameworks that respond to a light stimulus are crucial to establish a clear structure-activity relationship related to light regulation. Herein, we report the first azobenzene-modified photoresponsive thorium-organic framework (Th-Azo-MOF) with the formula [Th6O4(OH)4(H2O)6L6] (H2L = (E)-2'-p-tolyldiazenyl-1,1':4',4'-terphenyl-4,4″-dicarboxylic acid), in which the utilization of a thorium cluster as a metal node leads to one of the largest pore sizes among all the azobenzene-containing metal-organic frameworks (MOFs). The phototriggered transformation of the trans isomer to the cis isomer is monitored and characterized quantitatively by comprehensive analyses of NMR and UV spectroscopy, which reveals that the maximum isomerization ratio of cisTh-Azo-MOF in the solid state is 19.7% after irradiation for 120 min, and this isomerization is reversible and can be repeated several times without apparent performance changes. Moreover, the isomerization-related difference in the adsorption of the Rhodamine B guest is also illustrated and a possible photoregulated mechanism is proposed. This work will shed light on new explorations for constructing functionalized actinide porous materials by the elegant combination of actinide nodes with tailored organic ligands and furthermore will provide a comprehensive understanding of photoisomerization processes in MOF solids and insight into the mechanism on photoregulated cargo adsorption and release by photoactive MOFs.

Quaternary ammonium salt functionalized silica gel (QA/SiO2) was synthesized and used to remove uranium from the alkaline solution. Batch experiments showed that the saturated adsorption capacity of QA/SiO2 to uranium was 370 mg/g at pH > 8.0. The isothermal adsorption confirms to the Langmuir model. Different co-existing anions have been studied, QA/SiO2 showed a high affinity for uranium. The interaction mechanism is anion exchange. Because of its low cost, operable large particle size and high adsorption capacity, it has a prospect of large-scale industrial application.

The mobility of heavy metal contaminants and radionuclides in the environment is directly controlled by their interactions with charged mineral surfaces, hence an assessment of their potential toxicity, e.g. in the context of nuclear waste disposal sites, requires understanding of sorption processes on the molecular level. Here, we investigate the sorption of a variety of rare earth elements (REE) and trivalent actinides (Am, Cm) on K-feldspar using batch sorption and column transport experiments, time-resolved laser-induced fluorescence spectroscopy (TRLFS), and a surface complexation model. Initially, a reliable pKa for K-feldspar’s surface deprotonation reaction was determined as 2.5 ± 0.02, in excellent agreement with a measured pHIEP of 2.8. Batch sorption experiments over a broad range of experimental conditions in terms of mineral grain size, pH, [M3+], ionic radius, solid/liquid ratio, ionic strength, and equilibration procedures were carried out to quantify macroscopic immobilization. Similar pH-dependent uptake behavior was found for all investigated trivalent REE and actinides. In parallel, spectroscopic investigations provided insight into surface speciation. Cm TRLFS spectra indicate the formation of three inner-sphere sorption complexes with increasing hydrolysis. Additionally, a ternary K-feldspar/Cm/silicate complex was found for pH > 10, and batch and spectroscopic data at low pH (< 4) point to small amounts of outer sphere sorption complexes. Based on TRLFS data, batch sorption, and titration data, a generic geochemical sorption model was developed, that describes sorption edges for all investigated M3+/K-feldspar systems satisfactorily. The derived stability constants for the binary sorption complexes (logK1-4 = −3.6, −7.7, −11.5, and −17.4, respectively) are in good agreement with previous studies on similar systems, and could successfully be used to reproduce literature data. The stability constants obtained for the surface complexes were included into the database for the Smart Kd-concept, which will further improve the safety assessment of potential repositories for radioactive waste.

U(VI) was found to form intrinsic colloids in the natural groundwater. Fluorescence spectra, TEM, SEM techniques and thermodynamic calculation were used to identify the species of U(VI) and characterize the intrinsic uranium colloidal particles in the groundwater. The effect of pH on the formation of U(VI) colloidal particles was studied. It was found that under near-neutral and strong alkaline conditions, several elements, mainly Ca, Na and Si were responsible for the formation of intrinsic U(VI) colloid, and under weak alkaline conditions, U(VI) colloidal particles were not formed due to the formation of calcium uranyl carbonate complex.

A new class of actinide complexes [(L)An(N{SiMe3}2)3] (An = Th or U) (Th1–Th3 and U1–U3) supported by highly nucleophilic seven-membered N-heterocyclic iminato ligands were synthesized and fully characterized by single-crystal X-ray diffraction. These complexes were successfully exploited as powerful catalysts for the addition of alcohols to carbodiimides to yield the corresponding desirable isourea products at room temperature with short reaction times and excellent yields. Thorough stoichiometric, thermodynamic, and kinetic studies were carried out, allowing us to propose a plausible mechanism for the catalytic reaction.

Two phosphoramide extractants, namely, hexapropyl phosphoramide (HPPA) and hexabutyl phosphoramide (HBPA), were developed in our laboratory for their application toward actinide separations. Prelim...

Encapsulating a certain guest molecule in an assigned molecular compartment and then endowing the corresponding potential remains a huge challenge for metal-organic frameworks. To this end, we demonstrate a good example, for the first time, based on an actinide-based MOF. The used MOF (namely, ECUT-300) shows a unique uranyl-TPE anionic skeleton with three distinct cages, viz., mesopore A (2.8 nm), mesopore B (2.0 nm), and micropore C (0.9 nm). Through solid-liquid reaction, a RhB+ molecule can be encapsulated into ECUT-300 with the exact location in mesopore B, whereas the encapsulation of a metal-organic cation of [Fe(tpy)2]3+ was observed with the location in micropore C, suggesting unprecedented classified encapsulation. Impressively, the potential of the resulting guest@MOF composites is also highly dependent on the type of encapsulated guest molecules, for example, white-light emission for RhB+ and selective adsorption of C2H2 over CO2 for [Fe(tpy)2]3+.