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Thermal properties of thorium nuclear fuels are influenced by the shape and size distribution of thorium oxide particles. The production of thorium oxide is significantly influenced by the size and shape of the thorium oxalate particles which are typically formed during precipitation process. This study investigated the synthesis of these particles in a micro-reactor system. In summary, the findings showed that at high concentrations of oxalic acid, increasing the total flow rate to a certain extent leads to a decrease in the size of the particles. Also, it was found increasing the reaction temperature leads to larger particles. [ABSTRACT FROM AUTHOR]

This investigation reveals the successful incorporation of strontium‐doped thorium oxide (SrThO3) NPs into polyvinyl alcohol (PVA) polymer nanocomposites. The fabrication process of these PVA nanocomposites entails utilizing varying amounts (0.5, 1.0, 2.0, and 4.0 wt%) of SrThO3 nanofillers through a straightforward solution casting technique. The microstructure and overall structure of the resulting polymer nanocomposites were analyzed using powdered x‐ray diffraction for crystalline structure and Fourier transform infrared (FTIR) spectroscopy for molecular composition. The introduced SrThO3 nanofiller demonstrates a strong affinity for the hydroxyl groups present in the PVA polymer, a phenomenon validated through FTIR spectroscopy. In order to comprehend the impact of doping, the surface morphology of the PVA polymer nanocomposites underwent examination via scanning electron microscopy. The absorption and transmission of light were quantitatively assessed using UV–visible spectroscopy. The excitation and emission behaviors of electrons in both the PVA and SrThO3‐doped PVA nanocomposites were scrutinized through photoluminescence spectroscopy. Furthermore, the extent of UV light absorption was investigated by studying the degradation of methylene blue dye, a substance known for its sensitivity to UV light. Results indicate that the intentional incorporation of SrThO3 NPs significantly enhances UV stability. [ABSTRACT FROM AUTHOR]

We report the adiabatic elastic constants of single-crystal thorium dioxide over a temperature range of 77–350 K. Time-domain Brillouin scattering, an all-optical, non-contact picosecond ultrasonic technique, is used to generate and detect coherent acoustic phonons that propagate in the bulk perpendicular to the surface of the crystal. These coherent acoustic lattice vibrations have been monitored in two hydrothermally grown single-crystal thorium dioxide samples along the (100) and (311) crystallographic directions. The three independent elastic constants of the cubic crystal (C11, C12, and C44) are determined from the measured bulk acoustic velocities. The longitudinal wave along the (100) orientation provided a direct measurement of C11. Measurement of C44 and C12 was achieved by enhancing the intensity of quasi-shear mode in a (311) oriented crystal by adjusting the polarization angle relative to the crystal axes. We find the magnitude of softening of the three elastic constants to be ∼2.5% over the measured temperature range. Good agreement is found between the measured elastic constants with previously reported values at room temperature, and between the measured temperature-dependent bulk modulus with calculated values. We find that semi-empirical models capturing lattice anharmonicity adequately reproduce the observed trend. We also determine the acoustic Grüneisen anharmonicity parameter from the experimentally derived temperature-dependent bulk modulus and previously reported temperature-dependent values of volumetric thermal expansion coefficient and heat capacity. This work presents measurements of the temperature-dependent elasticity in single-crystal thorium dioxide at cryogenic temperature and provides a basis for testing ab initio theoretical models and evaluating the impact of anharmonicity on thermophysical properties. [ABSTRACT FROM AUTHOR]

The structure and energetics of charged point defects in thorium dioxide (ThO2) have been investigated using the density functional theory (DFT) and phonon simulations. DFT simulations were performed under both zero-pressure and constant volume conditions. Termed as the free volume change of the point defects, the change in volume of the supercell has been computed in the zero-pressure case. Supercell expansion was observed with the increase of the (nominal) charge state of anion (O) interstitials and cation (Th) vacancies from neutral to its maximum. On the contrary, contraction of the supercell has been observed with anion vacancies and cation interstitials as the defect charge increases. The supercell volume change with respect to the charge state has been correlated with the resulting defect energetics. It has been observed that, as the defect charge increased, the internal energy and entropy of defect formation of the cation vacancies and anion interstitials were found to increase, while that of the cation interstitials and anion vacancies decreased. The temperature dependence of internal energy and entropy has also been examined. It was found that, as the temperature increases, the internal energies of the formation of cation vacancies and anion interstitials decrease, while those of the cation interstitials and anion vacancies increase. An opposite observation is seen for the entropies of formation defects when above room temperatures. [ABSTRACT FROM AUTHOR]

The structure and energetics of charged point defects in thorium dioxide (ThO2) have been investigated using the density functional theory (DFT) and phonon simulations. DFT simulations were performed under both zero-pressure and constant volume conditions. Termed as the free volume change of the point defects, the change in volume of the supercell has been computed in the zero-pressure case. Supercell expansion was observed with the increase of the (nominal) charge state of anion (O) interstitials and cation (Th) vacancies from neutral to its maximum. On the contrary, contraction of the supercell has been observed with anion vacancies and cation interstitials as the defect charge increases. The supercell volume change with respect to the charge state has been correlated with the resulting defect energetics. It has been observed that, as the defect charge increased, the internal energy and entropy of defect formation of the cation vacancies and anion interstitials were found to increase, while that of the cation interstitials and anion vacancies decreased. The temperature dependence of internal energy and entropy has also been examined. It was found that, as the temperature increases, the internal energies of the formation of cation vacancies and anion interstitials decrease, while those of the cation interstitials and anion vacancies increase. An opposite observation is seen for the entropies of formation defects when above room temperatures. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Isotopes is the property of Journal of Isotopes Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The recovery and recycling of metals that generate toxic ions in the environment is of particular importance, especially when these are tungsten and, in particular, thorium. The radioactive element thorium has unexpectedly accessible domestic applications (filaments of light bulbs and electronic tubes, welding electrodes, and working alloys containing aluminum and magnesium), which lead to its appearance in electrical and electronic waste from municipal waste management platforms. The current paper proposes the simultaneous recovery of waste containing tungsten and thorium from welding electrodes. Simultaneous recovery is achieved by applying a hybrid membrane electrolysis technology coupled with nanofiltration. An electrolysis cell with sulphonated polyether–ether–ketone membranes (sPEEK) and a nanofiltration module with chitosan–polypropylene membranes (C–PHF–M) are used to carry out the hybrid process. The analysis of welding electrodes led to a composition of W (tungsten) 89.4%; Th 7.1%; O2 2.5%; and Al 1.1%. Thus, the parameters of the electrolysis process were chosen according to the speciation of the three metals suggested by the superimposed Pourbaix diagrams. At a constant potential of 20.0 V and an electrolysis current of 1.0 A, the pH is varied and the possible composition of the solution in the anodic workspace is analyzed. Favorable conditions for both electrolysis and nanofiltration were obtained at pH from 6 to 9, when the soluble tungstate ion, the aluminum hydroxide, and solid thorium dioxide were formed. Through the first nanofiltration, the tungstate ion is obtained in the permeate, and thorium dioxide and aluminum hydroxide in the concentrate. By adding a pH 13 solution over the two precipitates, the aluminum is solubilized as sodium aluminate, which will be found after the second nanofiltration in the permeate, with the thorium dioxide remaining integrally (within an error of ±0.1 ppm) on the C–PHF–M membrane. [ABSTRACT FROM AUTHOR]

Thermal conductivity (k), as an important thermal property of nuclear fuels, would be deteriorated due to fission products. Therefore, to investigate the effect of fission products on the thermal conductivity of nuclear fuels is essential. Two typical fission products: Xe and Kr with 0–2 % concentration are considered in this work. The lattice constants (L) of ThO2 increase due to fission products at all testing temperatures. The extent of increase in L due to Xe interstitials is the maximum. The fission products significantly reduce the thermal conductivity of ThO2. The extent of reduction in thermal conductivity of ThO2 by the defects follows the trend Xe (interstitials) > Xe (substitutional defects) > Kr (substitutional defects) > Kr (interstitials). Finally, the full-filled Xe/Kr bubble has a nearly identical thermal conductivity as an empty void or half-filled Xe/Kr bubble. The underlying reason may be that the thorium atoms have a lower mobility than uranium atoms. These calculated values can be used to predict the thermal properties of the irradiated ThO2.

Nuclear fuel performance would be deteriorated due to radiation defects. Therefore, investigating the effect of irradiation-induced defects on nuclear fuel properties is essential. Thermal conductivity is an important property of nuclear fuel. In this work, the influence of radiation defects on the thermal conductivity of ThO2 within 600–1500 K has been studied using molecular dynamics (MD) method. Three types of point defects have been investigated in the present work: Frenkel pairs, substitutional Xe and vacancies with concentrations from 0 to 1 %. The results indicate that these irradiation-induced point defects increase the lattice parameter (L) at all studied temperatures. The strength of the dependence of Xe atoms on L is the highest. The analytical models for pure ThO2 and defected ThO2 are developed and there is a good agreement between the MD derived results and the model. The thermal conductivity of ThO2 systems is decreased due to Frenkel pairs, substitutional Xe and vacancies. The thermal resistance to thermal conductivity due to three types of defects are different. The degree of reduction in thermal conductivity by Xe is the largest. The dependence of vacancy cluster size on thermal conductivity is analyzed. For the ThO2 system with 0.5 % porosity, the effect of vacancy cluster size on thermal conductivity is weak. For the ThO2 system with a fixed porosity of 2 %, there exists a critical cluster radius of about 0.6 nm, below which the thermal conductivity increases with the cluster size and above which the thermal conductivity almost remains unchanged. Finally, the thermal conductivity of the amorphous ThO2 is calculated and effects of the amorphous structure and Frenkel pairs on thermal conductivity are compared. The result shows that the thermal conductivity of ThO2 systems can be further degraded by the amorphous structure. All these results indicate irradiation-induced defects could degrade the thermal properties of ThO2 systems and should be considered seriously for estimation of radiation damages in nuclear fuels used in nuclear reactors.

Atomic-scale defects generated in materials under both equilibrium and irradiation conditions can significantly impact their physical and mechanical properties. Unraveling the energetically most favorable ground-state configurations of these defects is an important step towards the fundamental understanding of their influence on the performance of materials ranging from photovoltaics to advanced nuclear fuels. Here, using fluorite-structured thorium dioxide (ThO2) as an exemplar, we demonstrate how density functional theory and machine learning interatomic potential can be synergistically combined into a powerful tool that enables exhaustive exploration of the large configuration spaces of small point defect clusters. Our study leads to several unexpected discoveries, including defect polymorphism and ground-state structures that defy our physical intuitions. Possible physical origins of these unexpected findings are elucidated using a local cluster expansion model developed in this work. [ABSTRACT FROM AUTHOR]

Direct synthesis of Pyridine-2,6-dicarboxylic a-+cid bis-(3-hydroxy phenyl)]amide, (Pydca), chelating ligand was applied for Th(IV) extraction from Abu Rusheid Ore Sample, South Eastern Desert, Egypt, between latitudes 24° 37ʹ 16ʹʹ N and longitudes 34° 46 ʹ 35 ʹʹ E and far from the Red Sea coast by about 42 km west, using poly phosphoric acid catalyst (PPA). The synthesis of new amide via direct condensation of organic acid and aromatic amine was performed in DMF at 100°C. The immediate condensation reaction led to construct the carboxamide derivative in one easy step dismantling the hard activation, halogenation, step resulting in a good yield production. This cross-coupling reaction appears simple, convenient and has a wide scope of activities. This protocol could be extended to industrial large-scale production processes. Experimental measurements have been optimised such as diluent type, pH, contact time, initial Th(IV) concentration, temperature, pydca conc., co-existing ions and stripping agents. It was found that a maximum value of Th(IV) retention (0.86 × 10−3 mol/L) is observed with 0.015 mol/L pydca/CCl4 chelating ligand at room temperature. From kinetic aspects, it was found that Th(IV) extraction follows the pseudo-first order kinetic model. The thermodynamic parameters, ΔS, ΔH and ΔG were also evaluated indicating an endothermic and spontaneous extraction process with increasing the randomness of the extraction system. Th(IV) can be completely back extracted from the loaded pydca chelating ligand using 0.5 M HNO3, 1 M H2SO4 and 1 M HCl. Finally, the optimised factors have been applied for Th(IV) recovery from Abu Rusheid Ore Sample, South Eastern Desert, Egypt, producing a thorium oxide concentrate with Th(IV) content of 81.43% with a purity of 92.67%. [ABSTRACT FROM AUTHOR]

A nuclear fuel-breeding blanket of a hybrid fission-fusion reactor is considered in this work. The blanket design uses the tight layout of cylindrical heat-generating elements. The neutronic analysis of nuclear fuel breeding in a blanket is performed for source materials (metallic uranium and thorium, uranium dioxide, thorium dioxide, uranium nitride, and thorium nitride) in combination with various coolants—lead, sodium–potassium eutectic, carbon dioxide, water, steam–water mixture, and heavy water. The 239Pu breeding rate is about 6 kg/(m2 yr) at the neutron wall load of 0.4 MW/m2 or 15 kg/(MW yr) being normalized to the neutron power on the first wall in front of the fuel part of a blanket (for the most efficient combinations of initial material and coolant). The 233U breeding rate is about 3.5 kg/(m2 yr) at the neutron wall load of 0.4 MW/m2 or 9 kg/(MW yr) being normalized to the neutron power on the first wall in front of the fuel part of a blanket (for the most efficient combinations of initial material and coolant). [ABSTRACT FROM AUTHOR]

Recent investigations analyzed in depth the biochemical and biophysical properties of the endothelial glycocalyx. In comparison, this complex cell-covering structure is largely understudied in alveolar epithelial cells. To better characterize the alveolar glycocalyx ultrastructure, unaffected versus injured human lung tissue explants and mouse lungs were analyzed by transmission electron microscopy. Lung tissue was treated with either heparinase (HEP), known to shed glycocalyx components, or pneumolysin (PLY), the exotoxin of Streptococcus pneumoniae not investigated for structural glycocalyx effects so far. Cationic colloidal thorium dioxide (cThO2) particles were used for glycocalyx glycosaminoglycan visualization. The level of cThO2 particles orthogonal to apical cell membranes (≙ stained glycosaminoglycan height) of alveolar epithelial type I (AEI) and type II (AEII) cells was stereologically measured. In addition, cThO2 particle density was studied by dual-axis electron tomography (≙ stained glycosaminoglycan density in three dimensions). For untreated samples, the average cThO2 particle level was ≈ 18 nm for human AEI, ≈ 17 nm for mouse AEI, ≈ 44 nm for human AEII and ≈ 35 nm for mouse AEII. Both treatments, HEP and PLY, resulted in a significant reduction of cThO2 particle levels on human and mouse AEI and AEII. Moreover, a HEP- and PLY-associated reduction in cThO2 particle density was observed. The present study provides quantitative data on the differential glycocalyx distribution on AEI and AEII based on cThO2 and demonstrates alveolar glycocalyx shedding in response to HEP or PLY resulting in a structural reduction in both glycosaminoglycan height and density. Future studies should elucidate the underlying alveolar epithelial cell type-specific distribution of glycocalyx subcomponents for better functional understanding. [ABSTRACT FROM AUTHOR]

Correction for 'Thorium amidates function as single-source molecular precursors for thorium dioxide' by Mark D. Straub et al., Chem. Commun., 2021, 57, 4954–4957, https://doi.org/10.1039/D1CC00867F. [ABSTRACT FROM AUTHOR]

The infrared-active phonon modes, in single-crystal samples of thorium dioxide (ThO 2) and uranium dioxide (UO 2), were investigated using spectroscopic ellipsometry and compared with density functional theory. Both ThO 2 and UO 2 are found to have one infrared-active phonon mode pair [consisting of one transverse optic (TO) and one associated longitudinal optic (LO) mode], which is responsible for the dominant features in the ellipsometric data. At room temperature, our results for the mode pair's resonant frequencies and broadening parameters are comparable with previous reflectance spectroscopy characterizations and density functional theory predictions. For ThO 2 , our ellipsometry and density function theory results both show that the LO mode broadening parameter is larger than the TO mode broadening. This signifies mode anharmonicity, which can be attributed to the intrinsic phonon–phonon interaction. In addition to the main mode pair, a broad low-amplitude impurity-like vibrational mode pair is detected within the reststrahlen band for both ThO 2 and UO 2. Elevated temperature measurements were performed for ThO 2 in order to study the mechanisms by which the phonon parameters evolve with increased heat. The observed change in the TO resonant frequency is in excellent agreement with previous density functional calculations, which only consider volume expansion of the crystal lattice. This suggests that the temperature-dependent change in the TO frequency is primarily due to volume expansion. The change in the main mode pair's broadening parameters is nearly linear within the temperature range of this study, which indicates the intrinsic anharmonic scattering (via cubic anharmonicities) as the main decay mechanism. [ABSTRACT FROM AUTHOR]

Ultrafast high‐temperature sintering (UHS) and flash sintering are novel methods for rapid sintering of ceramics, often completed in just a few seconds. Here, we show that both also share two additional features: an abrupt rise in electrical conductivity, which is electronic, and electroluminescence. More fundamentally, both are related to phonon physics where MD calculations have shown that proliferation of phonons at the edge of the Brillouin zone can induce Frenkel pairs without the application of electrical fields. Here, we show that, indeed, heating without the application of electric field, can also induce flash: Rapid heating processes of thin films of an oxide‐salt deposited on silk fibers, with a propane torch, are shown to induce electronic conductivity, electroluminescence, and rapid sintering of the oxide. The discussion in this article harkens back to two inventions, more than a century ago, which can now be related to flash and UHS: (i) the Nernst glow lamp circa 1900, made from zirconia, and (ii) the Welsbach mantle, constituted from ceria doped thorium oxide, in the late nineteenth century. Thus, the confluence between high heating rate and electric field induced flash phenomena links the past to the new. The emerging question is how injection of phonons that has been shown to create Frenkels can further induce high electronic conductivity and electroluminescence in oxides. Both electronic conductivity and luminescence are likely related to the generation of electron–hole pairs. [ABSTRACT FROM AUTHOR]

Radioactive materials are widely in industry, nuclear plants and medical treatments. Scientists and workers in these fields are mostly exposed to such materials, and adverse effects on blood and temperature profiles are observed. In this regard, objective of the current study is to model and simulate blood based nanofluid with three very important radioactive materials, named as Uranium dioxide ( UO 2 ), Thorium dioxide ( ThO 2 ) and Radium (Rd). In this modeling blood based nanofluid is considered under the influence of magneto hydrodynamic effect, non-linear mixed convection and thermal radiation, Joule heating, along with velocity and temperature slip. A three-dimensional fluid model is considered in bounded domain to justify flow geometry in arteries. System of partial differential equations are converted to highly nonlinear coupled ordinary differential equations by using suitable transformations. The obtained system is solved numerically using Fehlberg Runge–Kutta algorithm. Validity and convergence of the obtained solutions are confirmed through residual errors, numerical uncertainties and comparison with experimental data. Moreover, effect of pertinent fluid parameters on the velocity (radial, axial, tangential) and temperature profiles of blood flow are analyzed graphically. Furthermore, Skin friction and Nusselt number are also analyzed graphically against volume fraction of involved radioactive materials for the case of UO 2 , ThO 2 and Rd comparatively. Analysis reveals that increase in volume fraction of radioactive elements results in increased blood flow through walls in both radial and tangential directions. In case of slip at fluid solid-interface, the highest skin fraction is observed in case of Radium nanoparticles. [ABSTRACT FROM AUTHOR]

The diffusion phenomenon in the Ti–Ni binary system was investigated at a temperature of 1173 K. Microstructure and texture analysis revealed the formation of three stable intermetallic compounds, namely Ti2Ni, TiNi, and TiNi3, as well as two metastable intermetallic compounds, including Ti3Ni4 and Ti2Ni3, at the interfacial diffusion zone. The nucleation surface energy increase was analytically estimated, and marker experiments were conducted using thoria particles, both of which showed that Ti2Ni was the first compound to form at the Ti–Ni diffusion interface. At a temperature of 1173 K, using the Wagner method, the integrated diffusion coefficients for the Ti2Ni, TiNi, and TiNi3 phases were calculated to be 3.53 × 10−12, 18.1 × 10−15, and 6.2 × 10−15 m2/s, for, respectively. [ABSTRACT FROM AUTHOR]

Copyright of Hydrometallurgy of China is the property of Hydrometallurgy of China Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Graph In this month's editorial, we will highlight two manuscripts describing (1) the use of cationic colloidal thorium dioxide particles as an electron dense marker to investigate the glycocalyx of alveolar type I and type II cells in human and mouse lung in control samples, and following treatment with heparinase and pneumolysin; and (2) a study to examine the potential feasibility and pitfalls of using biopsy samples to analyze by immunohistochemistry mismatch repair proteins in colorectal cancer biopsies and matching surgical samples. The use of electron tomography to obtain data in the I z i dimension yielded improved images displaying very finely detailed cThO SB 2 sb particle labeling of the glycocalyx, revealing hidden details including interconnections between AEII cell microvilli. They imaged both human and mouse cThO SB 2 sb -stained lung samples untreated or treated with either heparinase or the bacterial pore-forming virulence factor pneumolysin (PLY) to disrupt the glycocalyx. [Extracted from the article]

The interband transitions of UO2 are validated independently through cathode luminescence. A picture emerges consistent with density functional theory. While theory is generally consistent with experiment, it is evident from the comparison of UO2 and ThO2 that the choice of functional can significantly alter the bandgap and some details of the band structure, in particular at the conduction band minimum. Strictly ab initio predictions of the optical properties of the actinide compounds, based on density functional theory alone, continue to be somewhat elusive. [ABSTRACT FROM AUTHOR]

A new method is demonstrated for synthesizing thorium dioxide (ThO2) nanoparticles (NPs) by thermal decomposition of an undiscovered thorium‐based metal‐organic framework (MOF). Upon heating at 520 °C, the thorium‐based MOF crystals, designated Th‐MTB, are converted completely to ThO2 NPs with an average size of 150 nm. The MOF‐derived ThO2 NPs are easily sintered to form ThO2 ceramics which have good thermal conductivity. The crystalline grains of ThO2 grow continuously during sintering.The method for the synthesis of ThO2 NPs could have potential applications in the production of nuclear materials. [ABSTRACT FROM AUTHOR]

In this study, a laboratory laser-induced breakdown spectroscopy (LIBS) system was used to measure the gadolinium (Gd) content in thorium (Th) oxide matrix to investigate and assess the ability of the LIBS technique for nuclear material analysis. Five different Gd concentrations were quantitatively spiked into the Th oxide powder and analyzed by the LIBS system. Although a spectrometer with relatively limited resolution was used in the experiment, the characteristic emission lines of Gd were identified and the unresolved Gd II 348 nm-band with no interference with Th lines was selected for Gd quantitative analysis. Results show that the mathematical technique of multi-component Lorentzian Fit can be well utilized to deconvolve the unresolved spectra. Univariate calibration curves for Gd element were constructed using peak area and peak intensity methods. The best calibration curve was obtained using the peak area of the Gd 348.18 nm and yielded the lowest limit of detection (LOD) of 0.60%. The leave-one-out method was employed to further investigate the analytical prediction skills of LIBS for each reference samples. For Gd concentration ≥ 4.33%, using the peak area of 348.18 nm can provide higher accuracy on the predicted concentrations. These results presented here demonstrate that the Gd element can be qualitatively and quantitatively monitored in Th oxide matrix using LIBS with a relatively limited resolution spectrometer. [ABSTRACT FROM AUTHOR]

Leaching of uranium from uranium oxide fuel in contact with water can be a radiation hazard problem in the case of fuel cladding failure, either during nuclear reactor operation or in an interim storage, as well as in a final repository. One way to mitigate this is to reduce the solubility of the fuel matrix by the mixing uranium oxide with a compound which is less soluble but otherwise of similar properties. In this paper, the effect of thorium oxide content on the leaching of the uranium oxide matrix is investigated. The method was to study the leaching of the uranium oxide fuel matrix as a function of a varying content of thorium oxide, using materials manufactured by powder co-milling. It was found that the substitution of more than 25% UO2 with ThO2 reduces the matrix leaching by more than one order of magnitude in most of the different leaching solutions investigated. The substitution of 7% UO2 with ThO2 results in a reduction of matrix leaching by 10–90%, depending on the concentration of borate and dissolved oxygen in the leaching solution. [ABSTRACT FROM AUTHOR]

Predicting materials properties of nuclear fuel compounds is a challenging task in materials science. Their thermodynamical behaviors around and above the operational temperature are essential for the design of nuclear reactors. However, they are not easy to measure, because the target temperature range is too high to perform various standard experiments safely and accurately. Moreover, theoretical methods such as first-principles calculations also suffer from the computational limitations in calculating thermodynamical properties due to their high calculation-costs and complicated electronic structures stemming from f-orbital occupations of valence electrons in actinide elements. Here, we demonstrate, for the first time, machine-learning molecular-dynamics to theoretically explore high-temperature thermodynamical properties of a nuclear fuel material, thorium dioxide. The target compound satisfies first-principles calculation accuracy because f-electron occupation coincidentally diminishes and the scheme meets sampling sufficiency because it works at the computational cost of classical molecular-dynamics levels. We prepare a set of training data using first-principles molecular dynamics with small number of atoms, which cannot directly evaluate thermodynamical properties but captures essential atomistic dynamics at the high temperature range. Then, we construct a machine-learning molecular-dynamics potential and carry out large-scale molecular-dynamics calculations. Consequently, we successfully access two kinds of thermodynamic phase transitions, namely the melting and the anomalous λ transition induced by large diffusions of oxygen atoms. Furthermore, we quantitatively reproduce various experimental data in the best agreement manner by selecting a density functional scheme known as SCAN. Our results suggest that the present scale-up simulation-scheme using machine-learning techniques opens up a new pathway on theoretical studies of not only nuclear fuel compounds, but also a variety of similar materials that contain both heavy and light elements, like thorium dioxide. [ABSTRACT FROM AUTHOR]

Benchmark calculations with a goal to find dispersion-corrected DFT-D3 methods suitable for a reliable estimation of matrix shifts on the vibrational frequency were carried out on the ThO molecule in three rare gas (Rg = Ne, Ar, and Kr) matrices. The matrices were modelled by the explicit approach, in which a single and a double shell of Rg atoms around ThO was considered. The selection of exchange-correlation functionals was based on test calculations on triatomic ThO ... Rg models. The B3LYP, PBE0, CAM-B3LYP, and LC-ωPBE functionals were found to be the best suited for the estimation of matrix shifts. The single shell of Rg's around ThO accounted for a major part of the shifts; the addition of a second Rg shell resulted only in a minor improvement. Continuum solvation models considerably overestimated the effect of Rg matrices both when the whole matrix was treated by the model and when the first shell was treated explicitly and the rest with a continuum solvation model. [ABSTRACT FROM AUTHOR]

A precise theoretical study of the electronic structure of heavy atom diatomic molecules is of key importance to interpret the experiments in the search for violation of time-reversal (T) and spatial-parity (P) symmetries of fundamental interactions in terms of the electron electric dipole moment, eEDM, and dimensionless constant, kT,P, characterizing the strength of the T,P-odd pseudoscalar scalar electron-nucleus neutral current interaction. The ACME collaboration has recently improved limits on these quantities using a beam of ThO molecules in the electronic H³Δ1 state [J. Baron et al., Science 343, 269 (2014)].We apply the combined direct relativistic 4-component and two-step relativistic pseudopotential/restoration approaches to a benchmark calculation of the effective electric field, Eeff, parameter of the T,P-odd pseudoscalar-scalar interaction, WT,P, and hyperfine structure constant in ³Δ1 state of the ThO molecule. The first two parameters are required to interpret the experimental data in terms of the eEDM and kT,P constant. We have investigated the electron correlation for all of the 98 electrons of ThO simultaneously up to the level of the coupled cluster with single, double, and noniterative triple amplitudes, CCSD(T), theory. Contributions from iterative triple and noniterative quadruple cluster amplitudes for the valence electrons have been also treated. The obtained values are Eeff = 79.9 GV/cm, WT,P = 113.1 kHz. The theoretical uncertainty of these values is estimated to be about two times smaller than that of our previous study [L. V. Skripnikov and A. V. Titov, J. Chem. Phys., 142, 024301 (2015)]. It was found that the correlation of the inner- and outer-core electrons contributes 9% to the effective electric field. The values of the molecule frame dipole moment of the ³Δ1 state and the H³Δ1 → X¹∑+ transition energy of ThO calculated within the same methods are in a very good agreement with the experiment. [ABSTRACT FROM AUTHOR]

The surface morphology and chemical states of W-2%ThO2 thermionic cathode during vacuum high-temperature treatment were investigated in this research. The W-2%ThO2 thermionic cathode was prepared by a solid-liquid doping method combined with high-temperature sintering. The morphology and distribution of thorium oxide were observed using a transmission electron microscope and scanning electron microscope. The chemical states of elements at different temperatures were analyzed by X-ray photoelectron spectroscopy. Results indicate that the surface morphology and chemical form of the alloy evolve with the increase of temperature. The matrix had a lamellar structure at low temperatures, and the surface was relatively flat. The samples were heated to 500 °C, 1100 °C, and 1300 °C for 1 h. During the heating process, thorium oxide changed from granular to spherical, and the matrix was recrystallized. As the heating temperature rises, diffusion channels appear inside the cathode. As the temperature increases, the high-priced tungsten gradually decreases, and the zero-valent tungsten content increases. The adsorbed oxygen left the cathode surface, and the lattice oxygen increased. The surface oxygen content decreased, and the thorium and tungsten content increased. [ABSTRACT FROM AUTHOR]

The complex structure of precision X-ray photoelectron spectra (XPS) of valence and core electrons of a ThO2(001) crystal film on Si(100) was obtained and analyzed, and the electronic structure of ThO8, Th13O56, and Th63O216 clusters was calculated. A histogram of the calculated XPS spectrum of electrons of the outer (from 0 to ~15 eV, OVMO) and inner (from ~15 to ~35 eV, IVMO) valence MOs was plotted. The calculated spectrum was in good agreement with the experimental one. Significant overlap of Th 6d atomic orbitals (AO) as well as Th 6p, 5f AO with oxygen orbitals is noted, which brings about the covalent nature of the bond in this dioxide. The contribution of the OVMO and IVMO electrons to the chemical bond was estimated based on the values of the bond populations. It was shown that the IVMO electrons weaken the chemical bond caused by OVMO electrons. It is assumed that the complex structure in the spectra of the Th 5s and Th 5p electrons is largely due to the dynamic effect, which does not allow observing the structure in the spectrum of the Th 5s electrons in ThO2. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

In the present study, 2-(2-Amino-3-((4-bromophenyl) diazenyl)pyrazolo [1,5-a]pyrimidin-7-yl) cyclohexanone (PPC) as an organic ligand was evaluated in the liquid-liquid (water-chloroform) extraction to extract Th (IV) from thorium sulphate solution. The characterisation of the ligand was carried out using elemental analysis, fourier-transform infrared spectroscopy (FTIR), nuclear magnetic resonance spectroscopy (NMR), mass spectrum (MS) and carbon-13 nuclear magnetic resonance (NMR13C). The extraction experiments were carried out to determine the optimum conditions of thorium extraction; these controlling conditions include pH, contact time, organic concentration, initial thorium concentration, and aqueous/organic phase ratio. Thorium stripping from the loaded organic solvent was investigated. The effect of different parameters on the stripping process has been evaluated. The applicability of the prepared (PPC) organic ligand for thorium extraction from a real sample that was obtained from monazite sand was also investigated. Finally, thorium was precipitated using ammonia solution in the form of thorium oxide. [ABSTRACT FROM AUTHOR]

[Display omitted] The local environment of thorium in murataite ceramics (Al,Ca,Ti,Mn,Fe,Zr,Th)O x and ThO 2 (001) crystalline film on Si(100) substrate as a reference was explored by X-ray absorption spectroscopy (XAS) for the first time. It was found that Th4+ is located in the center of a cube formed by 8 oxygen atoms [ r (Th–O) = 2.37 ± 0.03 Å] in murataite ceramics and ThO 2 film. The Th4+ second coordination sphere [ r (Th–M) ≈ 3.5 Å] in murataite is represented by 3 d metals: titanium, iron or manganese [ABSTRACT FROM AUTHOR]

This article investigates the mineralogical characterization of a thorium ore taken from the Choghart iron mine, Yazd, Iran. The mineralogical studies revealed that the main thorium content mineral of the ore was thorite, and it was mainly disseminated as a valuable mineral in different forms in minor quantity along the edge or within the intergranular spaces of gangue silicate minerals and magnetite. The XRF analysis of a radiometric sorting concentrate sample indicated that the sample contained approximately 0.25% thorium oxide, 66.28% silicate compositions, 9.14% iron oxide and significant amounts of rare earth elements. Sink and Float tests of different sizes of the sample using diiodomethane and bromoform resulted in a 2.22% concentrate with 85.7% thorium recovery. Liberation degree studies by SEM-EDX and image processing indicated that a size range of (−125, +75) µm was the optimum liberation size, and it was recommended for further beneficiation tests. [ABSTRACT FROM AUTHOR]

The article discusses the process of plasma chemical synthesis of uranium-thorium oxide powders for a new generation dispersion nuclear fuel. In the course of research, the combustion parameters of the precursors were calculated. Precursors were water-organic nitrate solutions based on uranyl nitrate and thorium nitrate (fissile components), as well as magnesium nitrate (matrix material). The organic component of the solutions was acetone due to the sufficiently high calorific value and good mutual solubility. In the course of thermodynamic calculations, the optimal modes of processing of the water-organic nitrate solutions in low-temperature plasma were determined. These modes ensured the synthesis of oxide powders of the necessary stoichiometry without impurities of unoxidized carbon (soot). Experiments to obtain the samples of powders were carried out with the model solutions in which uranyl and thorium nitrates were replaced by neodymium and cerium ones, which are in the same group of the periodic table. The synthesis was carried out with the use of a plasma chemical unit based on a high frequency torch plasmatron. The synthesized powders were subjected to a number of analyzes including electron microscopy, particle size analysis, X-ray phase analysis and BET analysis. The results showed that the powders can be classified as nanosized. [ABSTRACT FROM AUTHOR]

Monazite ore is mainly composed of rare earth elements (such as Ce, Nd, La, etc.). These rare earth elements are widely used in several high technology and industrial products. Thailand Institute of Nuclear Technology has performed research on the separation and purification of rare earth elements from Thai monazite ore for supporting industrial applications. In this work, the raw material, intermediate and by-product samples obtained from Thai monazite ore processing were characterized by various physicochemical techniques (WDXRF, XRD and SEM-EDS) for understanding their structural and morphological characteristics. The WDXRF analysis showed that the monazite ore sample contained primarily cerium (30.37 wt% of CeO2) which matched well with the XRD result. An increase in CeO2 concentration up to 39.19 wt% and 64.62 wt% in the intermediate mixed rare earth and cerium hydroxide cake samples were observed after alkali digestion and nitric acid leaching of monazite ore, respectively. No rare earth elements could be detected in the tri-sodium phosphate by-product. Thorium oxide at 6.34% in uranium cake sample was observed. A considerable amount of NaOH in thorium cake sample was noticed. [ABSTRACT FROM AUTHOR]

Crystallite orientation identification is invaluable, but is often limited to small area identification or requires a large area sample. Nondestructive optical methods such as polarized Raman spectroscopy, in contrast, can be used to completely map a variety of sample sizes, but their potential is not yet fully realized. Here, we report a systematic study of polarized Raman scattering of high‐quality, hydrothermally grown, single crystals of urania and thoria. The peak intensity variations for as‐grown major crystal planes, post‐growth polished crystal planes, and a post‐growth polished non‐crystallographic plane are directly linked to crystallographic orientation and crystal rotation, and agree with computed models. In particular, the parallel polarized peak intensity results are directly correlated with metal–oxygen–metal chains in the fluorite structure and can be used to determine both orientation and rotational alignment of a given crystal face if sufficiently small rotational steps are applied. These results are structure based, being applicable to the larger fluorite phase space, which is useful for optical, semiconductor, nuclear, and solid oxide fuel cell industries. Further, these results suggest that Raman spectroscopy can identify non‐crystallographic orientations that are not discernable by traditional means. [ABSTRACT FROM AUTHOR]

Kinetic energy dependent reactions of Th+ with O2 and CO are studied using a guided ion beam tandem mass spectrometer. The formation of ThO+ in the reaction of Th+ with O2 is observed to be exothermic and barrierless with a reaction efficiency at low energies of k/kLGS = 1.21 ± 0.24 similar to the efficiency observed in ion cyclotron resonance experiments. Formation of ThO+ and ThC+ in the reaction of Th+ with CO is endothermic in both cases. The kinetic energy dependent cross sections for formation of these product ions were evaluated to determine 0 K bond dissociation energies (BDEs) of D0(Th+-O) = 8.57 ± 0.14 eV and D0(Th+-C) = 4.82 ± 0.29 eV. The present value of D0(Th+-O) is within experimental uncertainty of previously reported experimental values, whereas this is the first report of D0(Th+-C). Both BDEs are observed to be larger than those of their transition metal congeners, TiL+, ZrL+, and HfL+ (L = O and C), believed to be a result of lanthanide contraction. Additionally, the reactions were explored by quantum chemical calculations, including a full Feller-Peterson-Dixon composite approach with correlation contributions up to coupled-cluster singles and doubles with iterative triples and quadruples (CCSDTQ) for ThC, ThC+, ThO, and ThO+, as well as more approximate CCSD with perturbative (triples) [CCSD(T)] calculations where a semi-empirical model was used to estimate spin-orbit energy contributions. Finally, the ThO+ BDE is compared to other actinide (An) oxide cation BDEs and a simple model utilizing An+ promotion energies to the reactive state is used to estimate AnO+ and AnC+ BDEs. For AnO+, this model yields predictions that are typically within experimental uncertainty and performs better than density functional theory calculations presented previously. [ABSTRACT FROM AUTHOR]

Recently, improved limits on the electron electric dipole moment, and dimensionless constant, kT,P, characterizing the strength of the T,P-odd pseudoscalar-scalar electron-nucleus neutral current interaction in the H³Δ1 state of ThO molecule were obtained by the ACME collaboration [J. Baron et al., Science 343, 269 (2014)]. The interpretation of the experiment in terms of these fundamental quantities is based on the results of theoretical study of appropriate ThO characteristics, the effective electric field acting on electron, Eeff, and a parameter of the T,P-odd pseudoscalar-scalar interaction, WT,P, given in Skripnikov et al. [J. Chem. Phys. 139, 221103 (2013)] by St. Petersburg group. To reduce the uncertainties of the given limits, we report improved calculations of the molecular state-specific quantities Eeff, 81.5 GV/cm, and WT,P, 112 kHz, with the uncertainty within 7% of the magnitudes. Thus, the values recommended to use for the upper limits of the quantities are 75.8 GV/cm and 104 kHz, correspondingly. The hyperfine structure constant, molecule-frame dipole moment of the H³Δ1 state, and the H³Δ1 → X¹S+ transition energy which, in general, can serve as a measure of reliability of the obtained Eeff and WT,P values are also calculated. In addition, we report the first calculation of g-factor for the H³Δ1 state of ThO. The results are compared to the earlier experimental and theoretical studies, and a detailed analysis of uncertainties of the calculations is given. [ABSTRACT FROM AUTHOR]

In this study, the lattice dynamics and thermal characteristics of thorium dioxide are calculated using the first-principle calculations based on the density functional theory (DFT). The Gibbs free energy, isothermal bulk moduli, Debye temperature, thermal Grüneisen parameter as well as vibrational contributions of Helmholtz free energy, internal energy and entropy of thorium dioxide are studied for the first time under high temperatures and pressures. Thermal properties are compared using generalized gradient approximation (GGA) and local density approximation (LDA) under a novel model based on the quasi-harmonic Debye–Einstein method. The results of the simulation reveal that the lattice constant calculated by LDA is less than the one calculated by GGA, while the Gibbs free energy, Debye temperature, adiabatic and isothermal bulk modulus obtained from LDA are greater than ones obtained from GGA. The volumetric thermal expansion coefficient and vibrational contribution of entropy obtained from GGA and LDA increase with rise in temperature. [ABSTRACT FROM AUTHOR]

We report the synthesis of four homoleptic thorium(IV) amidate complexes as single-source molecular precursors for thorium dioxide. Each can be sublimed at atmospheric pressure, with the substituents on the amidate ligands significantly impacting their volatility and thermal stability. These complexes decompose via alkene elimination to give ThO2 without need for a secondary oxygen source. ThO2 samples formed from pyrolysis of C-alkyl amidates were found to have higher purity and crystallinity than ThO2 samples formed from C-aryl amidates. [ABSTRACT FROM AUTHOR]

This article reports the first measurements of the yield of the radioisotopes 230,232,233Pa on irradiation of thick ThO2 targets by 1,2H and 3.4He. The experimental yield was compared with the computed yield using constants from the TENDL-2019 library and the SRIM computer code was used to calculate the travel distance. Most experimental values differ from the computed values. It is shown that the highest yield of 230Pa – 3.47 MBq/(μA∙h) – can be obtained by irradiating with a proton beam a thorium dioxide target in the U-150 cyclotron at the NRC Kurchatov Institute. It is concluded that 230U with activity sufficient for clinical use can be produced using the cyclotron. [ABSTRACT FROM AUTHOR]

This paper investigates a method for separation and purification of thorium from leach liquors containing rare-earth elements (REE). Iron, which causes problems in the stage of thorium extracting, was first removed by using Adogen 464 solvent. Thorium was extracted with 30% D2EHPA-in kerosene with 1/3 organic/aqueous ratio and stoichiometry of the thorium-D2EHPA complex was calculated as 1:2.6 from slope analysis. After the extraction, LREE and HREE were scrubbed from the extracted organic with 0.25 M H2SO4 and 6 M HCl, respectively. Thorium oxalate was precipitated by oxalic acid and calcined at 1,050 °C. It was, after calcination, determined that purity of thorium oxide is 99.23%, based on the ICP-OES analysis. [ABSTRACT FROM AUTHOR]