Search

Actinides are inherently radioactive; thus, ionizing radiation is emitted by these elements can have profound effects on its surrounding chemical environment through the formation of free radical species. While previous work has noted that the presence of free radicals in the system impacts the redox state of the actinides, there is little atomistic understanding of how these metal cations interact with free radicals. Herein, we explore the effects of radiation (UV and γ) on three U(VI) trinitrate complexes, M[UO2(NO3)3] (where M=K+, Rb+, Cs+), and their respective nitrate salts in the solid state via electron paramagnetic resonance (EPR) and Raman spectroscopy paired with Density Functional Theory (DFT) methods. We find that the alkali salts form nitrate radicals under UV and γ irradiation, but also note the presence of additional degradation products. M[UO2(NO3)3] solids also form nitrate radicals and additional DFT calculations indicate the species corresponds to a change from the bidentate bound nitrate anion into a monodentate NO3• radical. Computational studies also highlight the need to include the second sphere coordination environment around the [UO2(NO3)3]0,1 species to gain agreement between the experimental and predicted EPR signatures. [ABSTRACT FROM AUTHOR]

Absorbed dose rate in air for the Tehri Garhwal region of Uttarakhand state, India was measured using a vehicle-mounted NaI(Tl) scintillation spectrometer. The average values of absorbed dose rate in air for Jakhana and New Tehri areas in this region were 150 nGy h−1 and 88 nGy h−1, respectively, and the respective estimated average external effective doses for the areas were 1.06 mSv y−1 and 0.62 mSv y−1. Higher dose rates observed in the Jakhana area were possibly related to uraninite and sericite which were formed as a result of hydrothermal alteration and found in the area. [ABSTRACT FROM AUTHOR]

Uranium dioxide (UO2) is a widely studied material due to its use as fuel in pressurised water reactors (PWR), and Raman spectroscopy is a technique of choice to characterise the evolution of its microstructure. UO2 crystallises in a fluorite CaF2 (space group Fm‐3m) structure that gives rise to a unique Raman signature, the T2g band. However, several other bands are often detected whose attribution remains unclear. The present study gives new insights on the Raman spectrum of UO2 thanks to the combination of isotopic labelling with 18O and Raman imaging. In addition to the expected T2g, U2 (LO), 2LO and U3 bands, we have detected a doublet at 885 and 925 cm−1, a U* band at 555 cm−1 in some specific areas and two bands located at 367 and 1196 cm−1. All Raman bands shift under the effect of the replacement of 16O by 18O, excepting for the U* band that could not be detected anymore. The isotopic shift ratio could be determined for 20% and 30% 18O labelling. No discrepancy in band position is observed between grains and grain boundaries, except for the U2(LO) band. We also evidence a difference between the U defect bands and the 885 and 925 cm−1 doublet bands evolution under labelling, although the latter also seems to be connected to the presence of defects in the material. [ABSTRACT FROM AUTHOR]

UCl4, UBr4, UBr5, or UO2Cl2 reacted with excess liquid ammonia – in adventitious presence of moisture and/or air – and formed some peculiar uranium compounds of which we present the crystal structures. [(NH3)7(N3)U(μ‐O)U(NH3)8]Cl5 ⋅ 7NH3 contains a dinuclear μ‐O‐bridged uranium(IV) cation, [{(NH3)4UO2}2(μ‐O)]Cl2 ⋅ 4NH3 features a dinuclear μ‐O‐bridged uranyl(VI) cation, while the compounds [(U(VI)O2)2(U(V)O2)2(μ3‐O)2(NH3)12]Br2 ⋅ 6NH3 and [(U(VI)O2)4(U(V)O2)4(μ3‐O)4(NH3)22]Br4 ⋅ 16NH3 are mixed‐valent containing uranyl(V)‐uranyl(VI) units. For these tetra‐ and octanuclear complex cations we observed that the O atoms of the uranyl(V) units can be μ2‐ and even μ3‐bridging to uranyl(VI) units, while the O atoms of the latter are acting as terminal ligands only. [(NH3)8U(μ‐N)U(NH3)5(μ‐N)UO2(NH3)4]Br6 ⋅ 18NH3 presents the first example of a compound where the isoelectronic species UO22+ and UN2 formed a complex with the NUN unit bridging to the U atom of the uranyl(VI) cation. As it is can be difficult to distinguish between N and O atoms with X‐ray diffraction, quantum‐chemical calculations at the DFT‐PBE0/TZVP level of theory were carried out which unequivocally confirmed the atom assignments in the crystal structures. The chemical bonding in the complex cations was studied using intrinsic bonding orbitals and allowed for an additional discrimination of the U(V) and U(VI) atoms in the mixed‐valent compounds. [ABSTRACT FROM AUTHOR]

The distribution of neodymium dopant (as surrogate for americium) within the porous network of sintered (U,Nd)O 2 microspheres prepared via a sol-gel infiltration technique was comprehensively assessed. Powder X-ray diffraction (XRD) results indicated the formation of a neodymium oxyapatite secondary phase with Nd 4.69 (SiO 4) 3 O composition, alongside the principal U 1-y Nd y O 2 face-centered cubic phase for y = 20 and 30 mol%. The hexagonal oxyapatite phase was likely formed during sintering under reducing conditions, when volatile SiO from an external contamination reacted with the Nd3+ in the microspheres. Transmission electron microscopy (TEM) analyses on lamellae prepared via focused ion beam (FIB) further confirmed a distinct phase separation between the main (fluorite U 1-y Nd y O 2) phase and the oxyapatite phase, without mutual solubility of Si and U. To gain a deeper insight into the microstructure, energy dispersive X-ray spectroscopy (EDS) and electron probe microanalysis (EPMA) were performed at different locations in cross-sectioned U 1-y Nd y O 2 microspheres. The elemental mappings showed a higher intensity of combined Nd and Si content in the periphery region, where a higher filling of the porosity network is to be expected. XRD lattice parameter analysis was found to be the most reliable method to elucidate the Nd metal fraction y in U 1-y Nd y O 2 , as compared to local quantification methods using electron beam induced X-ray fluorescence. The sintered microspheres with a targeted 20 and 30 mol% Nd dopant concentration contain around 3 ± 2 wt% and 5 ± 2 wt% Nd-oxyapatite phase. The formation mechanism of the oxyapatite phase appears to involve capillary infiltration in the liquid state, during high temperature sintering, and it may be of interest for other applications. Despite the phase heterogeneity, the method was successful in infiltrating Nd throughout the porous microspheres at high loading levels, as intended for the fabrication of transmutation targets. The distribution of the Nd-dopant throughout the microsphere was achieved as desired, and this study presents a successful fabrication and detailed characterization of porous uranium oxide microspheres doped with Nd3+, contributing to the development of transmutation target research. [Display omitted] [ABSTRACT FROM AUTHOR]

The direct C−H to C−N bond conversion at room temperature using heterogeneous visible‐light catalysts is both interesting and challenging. Herein, we disclosed visible‐light‐promoted hydroacylation of azodicarboxylates using uranyl‐organic framework [UO2(OH)(cpt)]n (Ucpt, Hcpt=4‐(4′‐carboxyphenyl)‐1,2,4‐triazole) as an efficient heterogeneous hydrogen atom transfer photocatalyst. In this procedure, diverse benzaldehydes are compatible using dimethyl carbonate (DMC) as a green solvent at room temperature, achieving direct conversion of C−H to C−N bond with excellent yields (up to 99%). The key to excellent catalytic activity lies in the fact that the coordination of the conjugated ligand changes the HOMO energy level of Ucpt, resulting in more active sites and longer‐lived photo excitons. Simultaneously, this heterogeneous photocatalyst can be easily separated and reused for seven successive cycles and maintain high catalytic activity, showing outstanding sustainability and recyclability. [ABSTRACT FROM AUTHOR]

Large-grain UO 2 has attracted much attention due to its advantage of suppressing fission gas release by reducing the specific surface area of grain boundaries. In this study, a single grain growth additive MnO is selected to modify UO 2 by conventional pressureless sintering method. The effect of MnO modification on UO 2 densification and grain growth at temperatures between 1200 and 1700 °C was investigated in detail. 0.5 wt%MnO-UO 2 pellets can reach nearly 95% T.D. when sintered at 1200 °C for 24 h. An average grain size greater than 300 µm can be obtained at 1700 °C for 24 h. A series of sintering experiments were designed and conducted to verify the specific mechanism of MnO on the grain growth of UO 2. The classical grain growth kinetics indicates that the grain growth exponent of MnO modified UO 2 in the early stage is 3, which corresponds to the lattice diffusion under pore control, while that of UO 2 is 2 and conforms to the grain boundary migration control. The SEM results show that there is solute segregation of MnO at the grain boundaries, followed by nucleation of lamellar structure in the form of piles and plates on the boundaries after high temperature treatment and traces of liquid phase in some region. Diffusion sintering experiments show that the mechanism of MnO-promoted UO 2 grain boundary migration is based on solid phase diffusion. The XRD results of UO 2 modified with different amounts of MnO demonstrate that the growth degree of UO 2 grains can be related to the variation of lattice parameters resulted from the MnO modification. This is due to the enhanced mobility of UO 2 grain boundaries because of the large distortion of surrounding lattice caused by Mn modification. These results can provide new ideas for the manufacture of UO 2 ceramic fuels. [ABSTRACT FROM AUTHOR]

Frustrated antiferromagnets offer a captivating platform to study the intricate relationship of magnetic interactions, geometric constraints, and emergent phenomena. By controlling spin orientations, these materials can be tailored for applications in spintronics and quantum information processing. The research focuses on the interplay of magnetic and exchange anisotropy effects in artificial heterostructures based on a canonical frustrated antiferromagnet, UO2. The potential to manipulate the spin directions in this material and switch between distinct antiferromagnetic (AFM) states is investigated using substrate‐induced strain. The phenomenon is probed using exchange bias effects in stoichiometric UO2/Fe3O4 bilayers. By employing many‐body first‐principles calculations magnetic configurations in the UO2 layers are identified. Even a minor tetragonal distortion triggers a transition between AFM states of different symmetries, driven by a robust alteration of single‐ion anisotropy due to the distortion. Consequently, this change influences the arrangement of magnetic moments at the UO2/Fe3O4 interface, affecting the magnitude of exchange bias. The findings showcase how epitaxial strain can effectively manipulate the AFM states in frustrated antiferromagnets by controlling single‐site anisotropy. [ABSTRACT FROM AUTHOR]

The Singhbhum Shear Zone, eastern India is known for its large uranium and copper resources. Uraninite, the most abundant U-ore mineral, occurs as inclusions in magnetite, ilmenite, apatite, tourmaline, biotite, chlorite and allanite. Shared grain boundaries of uraninite with magnetite and ilmenite are common. Uraninite also shows complex symplectic intergrowth with ilmenite. In some places, the symplectite shares a straight grain boundary with ilmenite and magnetite and is surrounded and enveloped by magnetite. The symplectite could be formed by the reaction of separate U-bearing and Fe–Ti-bearing minerals or by the breakdown of a single U–Ti–Fe-bearing mineral under changed physicochemical conditions. Using the textural settings, geochemistry, and known occurrence of brannerite (UTi2O6) in the shear zone, we propose that the uraninite–ilmenite symplectite is most likely formed by the breakdown of brannerite by interaction with a Fe-bearing hydrothermal fluid. Based on in-situ EPMA chemical dating of uraninite in the symplectite and the known ages of uraninite formation/recrystallization in the shear zone, we further suggest that the symplectite formed during 950±50 Ma, an age which represents a pervasive tectonothermal event in the shear zone. [ABSTRACT FROM AUTHOR]

The DL deposit is a typical tabular-shaped U deposit hosted in sandstones of the Upper Cretaceous Yaojia Formation in the southwestern Songliao Basin, northeast China. Owing to its recent discovery, the origin of the deposit remains unclear. In this study, mineralogical and geochemical data were used to constrain the genesis of the DL deposit. Two sources of U were recognized: (1) pre-ore U enrichment in the Yaojia Formation during diagenesis; and (2) the provenance of the Yaojia Formation, which comprises late Permian–Early Cretaceous granitic rocks from the southern Great Xing'an Range and northern margin of the North China Craton, rather than the oils and diabase dikes in the study area. Mineralogical and geochemical characteristics indicate that organic matter (OM) in the Yaojia Formation was derived mainly from plant debris and hydrocarbons. In situ S isotope data for pyrite from the ore-bearing sandstones show that most of the pyrite has similar δ34S values (−43.8‰ to −20.6‰) to those of pyrite associated with bacterial sulfate reduction (BSR). The pyrite is often typically replaced and/or overgrown by pitchblende, which has a high P2O5 content (0.07–1.64 wt.%), indicative of a genetic relationship between BSR and U mineralization. The geological, mineralogical, and geochemical features suggest that the U mineralization in the DL deposit was mainly associated with BSR. [ABSTRACT FROM AUTHOR]

N,N′‐bis(2,4‐dihydroxy benzaldehyde‐1,2‐diaminobenzene) (H4L) formed from the reaction of 2,4‐dihydroxybenzaldehyde and 1,2‐diaminobenzene was complexed with Cu (II), Co (II), Ni (II), Mn (II), and UO2(II) ions. The formed complexes have been characterized by their physical data, spectral studies such as FT‐IR, Uv–Vis., 1H & 13C NMR, Mass, elemental microanalysis (C.H.N.), thermal analysis, X‐ray diffraction, and magnetic susceptibility measurements. The molecular docking between the protein receptors of the H4L ligand and its complexes was studied as theoretical method. The ligand and its metal complexes (1–5) were tested for their ability to inhibit the growth of various pathogenic microbial strains. The biological significance of the Schiff base compound and complexes as antifungal, antibacterial, and anticandidal agents as well as cytotoxicity was studied. The tested microorganisms respond better to the metal complexes than the Schiff base ligand. In comparison to the ligand, complexes, and penicillin, the UO2(II) complex (5) demonstrated the strongest antibacterial activity. In comparison to ligand, complexes, and miconazole, the UO2(II) complex (5) has antifungal activity against Aspergillus niger and Candida albicans. Complexes (1) and (5) have higher activity of antibacterial than other complexes against Pseudomonas sp. and the highest antifungal and anticandidal activity in comparison with miconazole. The ligand and its complexes showed a dose‐dependent antibacterial action according to the minimum inhibition concentration test. Using Tafel polarization and electrochemical impedance spectroscopy experiments, the protective impact of the bis‐Schiff base ligand (H4L) ligand versus Q235 Steel and its adsorption performance were investigated. The interaction between H4L Schiff base and complexes (1)–(5) and calf thymus DNA shows hypochromism effect coupled with obvious bathochromic shift. [ABSTRACT FROM AUTHOR]

This work is an investigation of the assemblages of supergene minerals occurring in hydrothermal REE–U–Au quartz-vein mineralisation at the Prakovce-Zimná Voda site, Slovakia. Heterogeneous uranyl arsenates and minor phosphates of the autunite group (nováčekite, kahlerite, threadgoldite, autunite, arsenuranospathite and chistyakovaite) together with scorodite and Sb–Bi-rich philipsbornite–segnitite-series minerals formed by oxidising fluids during decomposition and leaching of primary hypogene uraninite, brannerite and base-metal sulfides and sulfosalts. A progressive change of pH from acidic to near-neutral due to the gradual consumption of sulfides resulted in the formation of late phosphuranylite, pharmacosiderite and arseniosiderite. Goethite and other Fe oxides represent the latest hydrous ferric mineral phases and were formed after most of the As was already fixed in Fe arsenates. Antimony and Bi were taken up only into philipsbornite–segnitite and suggest unusual conditions during this process. X-ray absorption spectroscopy indicates that Sb in the philipsbornite–segnitite is fully oxidised (0.1–0.4 apfu Sb5+, octahedral coordination on the G site). Pentavalent Sb together with the presence of ferric oxides and arsenates and uranyl minerals suggest oxidative conditions during weathering. This study also indicates that hydrous ferric arsenates are dominant and stable secondary minerals in a supergene environment in a quartz vein rich in Fe and As accompanied by elevated concentrations of U, Pb, Sb, Bi, S, P, Ca and Ba under oxidising conditions. [ABSTRACT FROM AUTHOR]

Uranium can be found in the Earth's crust in different reservoirs, with igneous rocks being the primary source of this element from which many types of secondary deposits are formed. Fluorspar deposits generally do not contain uranium, but in some cases, fluorite can carry both uranium in solid solutions and inclusions of uranium minerals. We studied the concentration (ICP-MS), composition (electronic microprobe), and spatial distribution (microscopy and auto-radiography) of elemental uranium and uranium minerals at different scales (microscopy and auto-radiography in fluorite from the La Azul fluorspar deposit (Taxco, Mexico) to assess the origin of uranium and its significance in this ore deposit. Auto-radiography images with the CR-39 detector were found to be impressive in their ability to elucidate uranium distribution at the millimeter scale. The limit between the solid solution of elemental uranium in natural fluorite and the appearance of uranium oxides as inclusions appeared to be between 20 μg g−1 and 40 μg g−1 bulk uranium concentration in this fluorspar ore. The maximum concentration of U in fluorite from the La Azul deposit was about 100 μg g−1. Using Raman spectroscopy and microprobe analysis, we identified the micro-inclusions of uranium minerals as uraninite (of the pitchblende variety); its composition suggested a hydrothermal origin for this fluorspar deposit. We also calculated a chemical age that can be compared with the previously published regional geology and isotopic (U-Th-Sm)/He ages in fluorite. Micro-thermometric studies of fluid inclusions were carried out in different samples of uranium-rich fluorite to identify the nature and origin of the mineralizing fluid and the precipitation mechanisms of uranium minerals. We concluded that the uranium-rich fluorite precipitated in the initial phases of mineralization from a reducing fluid, with low salinity (<8% NaCl eq.) and an intermediate temperature (110–230 °C), and that the presence of organic compounds and sulfides (mainly pyrite) favored the simultaneous precipitation of uraninite (pitchblende variety) and fluorite. [ABSTRACT FROM AUTHOR]

To investigate the leaching rules and mechanism of a hard rock uranium ore, this paper conducted conventional leaching experiments based on the chemical composition and mineral occurrence status of the ore. Various factors affecting leaching were explored, and experimental data were fitted using the shrinking-core model. The results showed that uranium in the ore mainly existed in the form of pitchblende and coffinite, and the uranium grade of the sample was 0.15%. Under the leaching conditions of a temperature of 50 °C, a particle size of − 100 mesh, an acid dosage of 32 kg t−1, a pyrolusite dosage of 10 kg t−1, a liquid–solid ratio of 1:1, and an 8 h duration, the leaching rate of the uranium ore reached 99.12%. The leaching process was controlled by solid film diffusion, and the apparent activation energy was 11.6 kJ mol−1. Insoluble substances were present on the surface of the slag, and the solid film product was the main reason hindering leaching. [ABSTRACT FROM AUTHOR]

BACKGROUND: The eastern Liaoning Province represents the eldest hydrothermal uranium ore cluster area in China. Two ore types are classified, including independent uranium mineralization and uranium mineralization associated with Precambrian sedimentary-metamorphic iron deposits. The ore-forming age of the former type has been well constrained at ~1.85Ga, whereas the age of the latter type remains uncertain. Iron deposit-associated uranium mineralization developed in the Wengquangou B-Mg-Fe deposit, the Gaojiagou Fe deposit, and the Gongchangling Fe deposit. Geochronological studies on uraninite of the Wengquangou deposit yielded variable ages ranging from 2.0 to 1.8Ga, with some ages even older than the depositional ages of the hosting Liaohe Group (2.05 to 1.93Ga). This inconsistency suggests that some uraninite grains used for dating are detrital in origin. The lack of reliable age constraints on the iron deposit-associated uranium mineralization has raised questions about its origin. It remains unknown whether the iron deposit-associated uranium mineralization resulted from the same hydrothermal process and formed at the same tectonic setting when compared with the independent uranium mineralization. OBJECTIVES: To determine the metallogenic age and verify the accuracy of the age in uranium. METHODS: The instrument JXA-iHP200F was used for analysis, and the age was calculated according to Ranchin’s empirical formula. The analytical conditions were 20kV acceleration voltage, 50nA beam current, and 5μm beam spot size. A further LA-ICP-MS U-Pb dating method was used to verify the EPMA chemical ages of the uraninite, using a 193nm GeoLasPro and Agilent 7900 ICP-MS with a laser spot size of 16μm. RESULTS: The calculated age of the Wengquangou deposit ranges from 1899 to 1324Ma, but it is mainly concentrated from 1899 to 1741Ma. Two peaks at 1859Ma and 1784Ma are constrained by an age frequency distribution histogram. This result is younger than the deposition age of the Liaohe Group. The age of the Gongchangling deposit ranges from 1858Ma to 1715Ma, with two peaks at 1865Ma and 1743Ma constrained by an age frequency distribution histogram. In the Wengquangou deposit, the position for uraninite LA-ICP-MS U-Pb dating corresponds to EPMA analytical points. The weighted mean ages are grouped into 1840±16Ma (MSWD=2.0) and 1787±8Ma (MSWD=0.95), which are consistent with the results obtained by EPMA. The loss of Pb can result in disruption of U-Th-Pb isotope system and thus affect the calculated ages. The loss of Pb can be probed because it is generally considered to be positively correlated with Si, Ca and Fe contents. The SiO2+CaO+FeO contents of most measuring spots of uraninite of the two deposits is less than 1%, and show no correlation with Pb contents, indicating that the loss of Pb is negligible. CONCLUSIONS: The uranium mineralization associated with iron deposits has been constrained at ~1.85Ga and then experienced hydrothermal superposition at ~1.78Ga. The age results indicate that both the independent and iron ore-associated uranium mineralization in the eastern Liaoning Province was formed at ~1.85Ga, linking to a Proterozoic post-orogenic extensional environment in the eastern North China craton. The ore-forming fluids of different deposits of iron associated uranium deposits are all alkaline and oxidated but vary in fluid composition and temperature. This study highlights combined application of EPMA and LA-ICP-MS dating methods on uraninite, realizing the complementary advantages of spatial resolution and dating precision. [ABSTRACT FROM AUTHOR]

The interaction of alpha radiation from UO2 micro- and nanoparticles (uraninite) with the substance is visualized using alpha-autoradiography data on A-2 thick-layer nuclear photographic emulsions. The spherical area of action of alpha particles around UO2 micrograins, up to 100 μm in size, is a deeply transformed substance with a high density of radiation defects. The translation of these results on a living organism leads to a conclusion about the specific type of impact exerted by micro- and nanoparticles of depleted uranium under which prolonged internal irradiation of the whole organism in small doses is combined with catastrophically high doses of alpha radiation in local zones in the vicinity of UO2 micro- and nanoparticles. [ABSTRACT FROM AUTHOR]

In this work, the sintering kinetics of pure UO2 and 0.5 wt.%MnO‐doped UO2 was studied by a high‐temperature dilatometer heated up to 1500°C. In addition, the sintering behavior of pure UO2 and 0.5 wt.%MnO‐doped UO2 was studied by pressureless sintering technique. The results showed that MnO doping enhanced the grain boundary diffusion of UO2, which can effectively decrease the densification temperature and promote grain growth. The sintering temperature of UO2 was significantly reduced by about 200°C with the addition of 0.5 wt.%MnO. The microscopic morphology studies showed that there were still fine particles agglomerated, forming sintered spheres in the matrix even if no severe agglomeration and bimodal size distribution were observed in raw UO2 powder. The microstructure evolution of the sintered sphere and UO2 matrix during the densification process was studied by isothermal sintering. Finally, the present analyses indicated that the densification of UO2 matrix can be accelerated by adding MnO or increasing the sintering temperature, thus improving the densification inhomogeneity of UO2 matrix. [ABSTRACT FROM AUTHOR]

With the gradual depletion of high-grade uranium resources in southern China, it is necessary to recover uranium from low-grade complex and refractory uranium resources However, the traditional acid mining process has certain drawbacks such as high acid consumption, low uranium recovery, and potential environmental pollution. There is an urgent need to develop new technologies for the extraction of refractory uranium ores. A tonne-scale column bioleaching for low-grade refractory vocanogenic uranium ore containing brannerite and pitchblende was performed. The uranium leaching efficiency reached 85.86% with an acid consumption of only 10.15% after leaching for 130 d. In the bioleaching stage, the Fe3+ concentration had a good correlation with the Eh value; the higher the Fe3+ concentration, the better was the leaching of uranium. The solution pH was kept below 2.5 during the leaching process, which avoided the precipitation of iron and ensured a higher Fe3+ concentration in the solution. Efficient leaching of uranium from UTi2O6 and UO2 was achieved through oxidation of Fe3+ and the action of microorganisms. The results may provide technical support for industrial leaching of low-grade volcanogenic uranium deposits. [ABSTRACT FROM AUTHOR]

The current distribution structure of the thermal conductivity (TC) enhancements in UO 2 matrix can be divided into three categories: dispersed structure, continuous structure and oriented structure. This paper develops a new semi-continuous structure to improve the TC of UO 2. Ti 3 SiC 2 is selected as the enhancement in this paper due to its excellent irradiation resistance and high TC at elevated temperature. The semi-continuous structure of Ti 3 SiC 2 is formed through a simple centrifugal spheroidization of UO 2 and a followed powder mixing process. Both the theoretical prediction and experimental results indicate the semi-continuous structure has a close TC enhancing efficiency to the continuous structure. Meanwhile, the semi-continuous structure has the advantages of simplifying the fabrication process and can be applied to more kinds of enhancements compared to the continuous structure. The TC of Ti 3 SiC 2 /UO 2 is remarkably improved at elevated temperature compared with pure UO 2 , which is beneficial to the fuel safety. [ABSTRACT FROM AUTHOR]

The effects of irradiation‐induced defects on the fluorite‐structured dioxide materials were investigated in the literature and explained with complex physical phenomena. An interpretation that can simply explain their effects on the structure has not been put forward so far. However, in a recent atomistic simulation study, a specific defect was found to be directly responsible for the α‐particle irradiated UO2 lattice dilatation, and there was a linear relationship between them. It was also determined that this linear equation has two different slopes at low and high defect concentrations. In this paper, it was found that these phenomenon were not specific to UO2 and applicable to all fluorite‐structured actinide and lanthanide dioxides studied here (CmO2, AmO2, CeO2, UO2, NpO2, PuO2, ThO2). The findings provide clues to the existence of more general law. The results have the potential to lead to significant improvements, such as why different radiation types (α‐particle, α‐decay, fission) swell the lattice at different saturation levels. [ABSTRACT FROM AUTHOR]

Nano‐reduced iron (NRI) is a promising uranium adsorbent due to its strong reducibility and good selectivity, but it still faces the challenges of slow kinetics, limited and non‐renewable active sites. In this work, we realized high efficiency uranium extraction under ultra‐low cell voltage (−0.1 V) in seawater with 20 ppm UO2(NO3)2 solution by coupling electrochemical mediated FeII/FeIII redox and uranium extraction. The adsorption capacity and extraction efficiency of NRI after electrochemical uranium extraction (EUE) could reach 452 mg/g and 99.1 %, respectively. Combined with quasi‐operando/operando characterization technologies, we clarified the mechanism of EUE and revealed that continuously regenerating FeII active sites by electroreduction could significantly enhance the property of EUE. This work here provides a new electrochemical mediated and low energy consumption uranium extraction strategy which also provides a reference for other metal resource recovery. [ABSTRACT FROM AUTHOR]

Nano‐reduced iron (NRI) is a promising uranium adsorbent due to its strong reducibility and good selectivity, but it still faces the challenges of slow kinetics, limited and non‐renewable active sites. In this work, we realized high efficiency uranium extraction under ultra‐low cell voltage (−0.1 V) in seawater with 20 ppm UO2(NO3)2 solution by coupling electrochemical mediated FeII/FeIII redox and uranium extraction. The adsorption capacity and extraction efficiency of NRI after electrochemical uranium extraction (EUE) could reach 452 mg/g and 99.1 %, respectively. Combined with quasi‐operando/operando characterization technologies, we clarified the mechanism of EUE and revealed that continuously regenerating FeII active sites by electroreduction could significantly enhance the property of EUE. This work here provides a new electrochemical mediated and low energy consumption uranium extraction strategy which also provides a reference for other metal resource recovery. [ABSTRACT FROM AUTHOR]

Submillimetre uraninite fragments are embedded in anthraxolite, oil-derived bitumen found in Permian rocks of the Vrchlabí formation (Czech Republic). The radiogenic system appears unaltered as indicated by the elemental and lead isotopic composition of uraninite. Low compositional variances in uraninite indicate protective properties of the bitumen envelope. The highly radiogenic composition of lead in uraninite allows dating by the SEM/EDX based chemical method, which confirms the Permian age of the mineralization. The studied association is considered to be a prospective natural analogue of long-term geological disposal of actinide-bearing bituminized radioactive waste. [ABSTRACT FROM AUTHOR]

The thermochemical state of UO2‐based nuclear fuel is a key parameter for which experimental data are difficult to obtain. A new experimental procedure using in situ oxido‐reduction indicators was applied to irradiated fuel, and we aim to use it with chromium‐doped unirradiated UO2. Nevertheless, we had first to characterise the chemical state of the chromium precipitates in our sample before. Here, we present the method we used for statistical characterisation of these precipitates using several methods, amongst which Raman spectroscopy plays a major role. Moreover, the Raman spectra of the precipitates were interpreted as evidence of a uranium stabilised Cr3O4 phase. [ABSTRACT FROM AUTHOR]

Hybrid nanofluids are extensively analyzed in recent studies due to their better performance in numerous areas such as heat and mass transfer enhancement, biological fluid movement, medical equipment, heat exchangers, electronic cooling and automotive industry. In current study the nanoparticle concentration utilized is much important in biomedical industry. Major applications include drug delivery, radio-pharmaceuticals, centrifuging blood to obtain red blood cells and plasma, medical implants, onco therapeutics and photo thermal cancer therapy. In this regard, the primary focus of this study is to simulate a blood based unsteady hybrid nanofluid flow between two rotating, stretching disks and convective boundaries. The two nanoparticles in this study are uranium dioxide U O 2 and multi-walled carbon nanotubes MWCNTs. The hybrid nanofluid is under the influence of magnetohydrodynamic effects and chemical reaction with activation energy. The governing partial differential equations (PDEs) are transformed into ordinary differential equations (ODEs) using suitable similarity transform. Homotopy analysis method is used to solve the non-linear system of ODEs and ħ -curves are plotted to find suitable region of ħ i for convergent series solution. Velocity profile is examined for axial, radial and tangential direction against various fluid parameters. Temperature and concentration profiles are analyzed for both convective and non-convective cases. It is observed that convective boundaries result in elevated temperature when compared with non-convective case. Moreover, skin friction, heat and mass transfer rates are also examined with respect to changing volume fraction φ U O 2 .The results revealed that skin friction and rate of heat transfer increases with increase in volume fraction of both nanoparticles U O 2 and MWCNTs while the mass transfer rate depicts contrasting behavior. [ABSTRACT FROM AUTHOR]

Amidoximated absorbents (AO‐PAN) effectively remove U(VI) from aqueous solution, but previous studies reported more variability for complex natural waters that contain additional confounding ions and molecules. Ternary phases containing U(VI), M(III) (M=Fe(III), Al(III), Ga(III)), and organic molecules exist under these conditions and cause heterogeneous U(VI) uptake on AO‐PAN. The goal of the current study is to provide additional insights into the structural features ternary complexes using N‐(2‐hydroxyethyl)‐iminodiacetic acid (HEIDI) as the model organic chelator and explore the relevance of these species on U(VI) capture. Three model compounds ([(UO2)(Fe)2(μ3‐O)(C6NO5H8)2(H2O)4] (UFe2), ([(UO2)(Al)2(μ2‐OH)(C6NO5H8)2(H2O)3] (UAl2) and [(UO2)(Ga)2(μ2‐OH)(C6NO5H8)2(H2O)3] (UGa2)) were characterized by single‐crystal X‐ray diffraction. Raman spectra of the model compounds were compared with solution data and the ternary phases were noted in the case of Al(III) and Ga(III), but not in the Fe(III) system. U(VI) adsorption onto AO‐PAN was not impacted by the presence of HEIDI or the trivalent metal species. [ABSTRACT FROM AUTHOR]

In this study, we investigated uranium dioxide (UO2) dissolution under geological repository conditions by applying a three-dimensional (3D) thermal-chemical reactive transport model. The transport of chemical species and thermal conduction in UO2 fuel pellets and chemical dissolutions of UO2 were considered. The mathematical and numerical formulations of the model are described in the paper. Fluid-UO2 reactions were modeled to demonstrate the validity of modeling reaction processes. UO2 dissolution under low (25°C) and high temperatures (250°C) was simulated, taking into account the changes in aqueous uranium species with temperature. The predicted lifetime of one UO2 pellet is greatly dependent on the temperature. To illustrate the effect of uranium species on reaction rates, numerical studies were conducted at the same temperatures but with different reaction types and chemical species. It was found that reactions that produce UCl40 enhance the dissolution rates of UO2 by consuming the Cl− in solutions. UO2 dissolution with varying pH values was also modeled. When pH increased to 6, the average dissolution rate of a UO2 fuel pellet was eight times slower than it was at pH=2. Dissolution simulations were carried out on the images of fractured UO2 pellets. The impact of microfractures on UO2 dissolution was illustrated. The developed model is able to quantify UO2 dissolution behaviors and identify key parameters controlling the physiochemical processes involved. The model can be used as a predictive tool for applications such as spent UO2 fuel sequestration, contaminant transport, and geothermal resources development. [ABSTRACT FROM AUTHOR]

A new three metal complexes of La(III), Ce(IV) and UO2(II) ions have been synthesized based on a Schiff base derived from the condensation of L-histidine and anisaldehyde. All prepared compounds were characterized by different spectroscopic techniques and Density-functional theory (DFT) calculations. The complexes were proposed to have an octahedral structure based on the investigated results. The optimized shape, numbering system, and dipole moment vector of Ligand and La, Ce, and UO2 (1:1) chelates were investigated. The Schiff base ligand and complexes exhibit moderate action against all of the bacteria tested, with P. aeruginosa, Klebsiella sp., and E. faecalis respectively being the order of inhibition. [ABSTRACT FROM AUTHOR]

A hydrothermal quartz vein with REE-U-Au mineralization in the Zimná Voda (Gemeric Unit, Western Carpathians, Slovakia) is associated with contact metamorphism between Permian granites and host phyllites and metaquartzites. It contains unique REE minerals of the monazite and xenotime groups. Monazite-(Ce), monazite-(Nd), monazite-(Sm), and Gd-dominant monazite ["monazite-(Gd)"], along with xenotime-(Y) to Gd-dominant xenotime ["xenotime-(Gd)"] and Gd-rich hingganite-(Y) show heterogeneous compositions and reflect a strong fractionation trend toward the enrichment of MREE (Sm to Dy), particularly Gd. Here, the gadolinium abundance reported in "monazite-(Gd)" (≤23.4 wt% Gd2O3) and Gd-rich xenotime-(Y) to "xenotime-(Gd)" (≤28.7 wt% Gd2O3) and accompanied by Gd-rich hingganite-(Y) (≤15.8 wt% Gd2O3), is among the highest Gd concentrations ever reported in natural minerals. The Gd-richest compositions show the following formulas: (Gd0.31Sm0.24 Nd0.15Ce0.10La0.05Dy0.03Y0.03...)0.98PO4 ["monazite-(Gd)"], (Gd0.36Y0.32Dy0.13Sm0.08Tb0.05...)0.98 (P0.96As0.04)1.00O4 ["xenotime-(Gd)"] and (Y0.71Gd0.43Dy0.23Sm0.22Tb0.06Er0.04Nd0.06...Ca0.06)1.96 ( ◻ 0.87 Fe 0.13 2 +) 1.00 (B e 1.82 B 0.18 ) 2.00 (S i 1.90 A s 0.10 ) 2.00 O 8 (O H 1.70 O 0.30 ) 2.00 [hingganite-(Y)]. The MREE-rich monazites, xenotimes, and hingganite-(Y) precipitated in response to the alteration of primary uraninite, brannerite, and fluorapatite by low-temperature hydrothermal fluids of heterogeneous compositions on a microscale. These are responsible for the strong enrichment of individual MREE, especially Gd in the secondary minerals. This is accompanied by the advancing development of the W-type tetrad effect on REE through monazite species. The substantial incorporation of Gd into both REE-selective monazite and xenotime structures that are accompanied by LREE vs. HREE segregation indicates the possibility of differently sized REE3+ miscibility in REEPO4 solid solutions, as well as the stabilization of the Gd-rich orthophosphate structure by substitution of the remaining A-site cations with smaller HREE+Y in the xenotime-type, and/or larger LREE in the monazite-type structure. [ABSTRACT FROM AUTHOR]

A convenient and portable smartphone-assisted method for the colorimetric detection of uranyl ions (UO2 2+) in aqueous solutions is proposed using rifampicin and 2-(5-bromo-2-pyridylazo)-5- diethylaminophenol (Br-PADAP) as chromogenic agents. The addition of UO2 2+ would cause reaction with chromogenic agents to form complexes, changing the colour from orange to dark red in the rifampicin system and from yellow to light pink in the Br-PADAP system. To achieve the on-site estimation of the trace UO2 2+ concentration range, digital images of colour changes captured by the smartphone under fixed lighting conditions were imported into the built-in application named "Detect" to obtain HSV (hue, saturation, and value) and HSL (hue, saturation, lightness) information, which could be associated with the concentration of uranyl ions. For more precise laboratory-level detection, ultraviolet-visible (UV-vis) spectroscopy was employed as well. The absorbance of the rifampicin system exhibited strong linearity with the UO2 2+ concentration in the range from 4 to 50 µM at 375 nm with a method detection limit (MDL) of 3.17 µM by the UV-vis-based method, while that of Br-PADAP system had a linear relationship with the concentration from 0.9 to 7 &#181, M at 562 nm with an MDL of 0.89 µM. The two strategies may be combined to detect UO2 2+ across a larger concentration range, and this method has been successfully used to analyze real samples including soil around uranium mines. [ABSTRACT FROM AUTHOR]

EXAFS provides the capability to interrogate nanoparticle (NP) structure in atomistic detail without relying on long‐range crystallinity. There is a limitation in that EXAFS provides averaged structural information, making it difficult to separate a small amount of heterogeneous structure from bulk. In this work, models were developed to extract surface‐specific information from conventional EXAFS measurements collected on UO2 NPs of varying size. Specifically, the surface terminating species of UO2 NPs was determined from comparison of coordination numbers with geometric models while the origin of static disorder was interrogated from user‐defined simulations. Results show that the degree of oxygenation on the NP surface does not significantly deviate from bulk surface and that static disorder is highly enhanced in NP surface layers but cannot be attributed to surface relaxation effects alone. The approach described herein has the potential to be adapted to a range of inorganic NP systems to interrogate surface structure. [ABSTRACT FROM AUTHOR]

The presence of uranium in groundwater is a cause of concern all over the world. In mineralized regions where elevated concentrations of uranium are possible in groundwater, mining activities can further degrade the water quality. Hence, it is essential to document the baseline uranium concentration in groundwater before the commencement of mining. This study was carried out with the objective of assessing the concentration of uranium in groundwater around a proposed uraninite mining site in the Gogi region, Karnataka, India. Gogi is a village in the Yadgir district of Karnataka where groundwater is the main source of water for domestic needs. The uranium mineralized zone in this region occurs along the major E-W trending Gogi-Kurlagere fault at a depth of about 150 m. Groundwater samples were collected every three months from January 2020 to October 2020 from 52 wells located in this area. The concentration of uranium in groundwater ranged from 1.5 ppb to 267 ppb. The USEPA and WHO have recommended a permissible limit of 30 ppb, while the Atomic Energy Regulatory Board of India has a limit of 60 ppb for the purpose of drinking water. Based on these permissible limits for uranium in drinking water, concentrations exceeded the limit in about 25% of wells within 20 km from the mineralized region. Wells present in the granitic and limestone terrain exhibited higher concentrations of uranium in this area. Uranium concentration in groundwater changes depending on the degree of weathering, lithology, and rainfall recharge. This study will serve as a baseline and will help to assess the impact of mining activities in this region in the future. In wells where the uranium concentration exceeds permissible limits, it is suggested not to use groundwater directly for drinking purposes. These sites need to be explored further for the possible presence of uranium-bearing minerals. [ABSTRACT FROM AUTHOR]

We have undertaken a study of the rare ammonium uranyl sulphate mineral, ammoniozippeite, from the Jáchymov ore district, Krušné hory Mountains (Czech Republic). It has been found on a few specimens and forms rich crystalline aggregates in thin cracks of supergene altered rocks with uraninite veinlets in association with gypsum. Its radially arranged aggregates are composed by well-developed flattened acicular crystals up to 1 mm in length. Ammoniozippeite is bright yellow and locally even yellow-orange with pale yellow streak and fluoresces yellow, weak or dull under 254 nm and 366 nm UV-radiation, respectively. Ammoniozippeite crystals are transparent to translucent and have an intensive vitrous luster. It is a very brittle and at least one system of perfect cleavage (along {010}) was observed. The quantitative chemical analyses of ammoniozippeite agree well with the proposed ideal composition and correspond to the following empirical formula [(NH4 )1.96K0.11] Σ2.07[(UO2 )2 (SO4 )1.98O2.06]·H2 O (on the basis of 2 U atoms pfu). Ammoniozippeite is orthorhombic, the space group Ccmb, with the unit-cell parameters refined from X-ray powder diffraction data: a 8.7862(13), b 14.1579(19), c 17.162(2) Å and V 2134.8(4) ų . Vibrational (Raman and infrared) spectroscopy documented the presence molecular water, ammonium, uranyl and suphate units in the crystal structure of ammoniozippeite. [ABSTRACT FROM AUTHOR]

[{Mn(TPA)I}{UO2(Mesaldien)}{Mn(TPA)I}]I formula (here TPA=tris(2‐pyridylmethyl)amine and Mesaldien=N,N'‐(2‐aminomethyl)diethylenebis(salicylidene imine)) reported by Mazzanti and coworkers (Chatelain et al. Angew. Chem. Int. Ed. 2014, 53, 13434) is so far the best Single Molecule Magnet (SMM) in the {3d–5f} class of molecules exhibiting barrier height of magnetization reversal as high as 81.0 K. In this work, we have employed a combination of ab initio CAS and DFT methods to fully characterize this compound and to extract the relevant spin Hamiltonian parameters. We show that the signs of the magnetic coupling and of the g‐factors of the monomers are interconnected. The central magnetic unit [UVO2]+ is described by a Kramers Doublet (KD) with negative g‐factors, due to a large orbital contribution. The magnetic coupling for the {Mn(II)‐U(V)} pair is modeled by an anisotropic exchange Hamiltonian: all components are ferromagnetic in terms of spin moments, the parallel component JZ twice larger as the perpendicular one J⊥. The spin density distribution suggests that spin polarization on the U(V) center favors the ferromagnetic coupling. Further, the JZ/J⊥ ratio, which is related to the barrier height, was found to correlate to the corresponding spin contribution of the g‐factors of the U(V) center. This correlation established for the first time offers a direct way to estimate this important ratio from the corresponding gS‐values, which can be obtained using traditional ab initio packages and hence has a wider application to other {3d–5f} magnets. It is finally shown that the magnetization barrier height is tuned by the splitting of the [UVO2]+ 5 f orbitals. [ABSTRACT FROM AUTHOR]

The intracratonic Paleoproterozoic Nonacho Basin, deposited on the western margin of the Rae craton, contains historic polymetallic (i.e., U, Cu, Fe, Pb, Zn, Ag) occurrences spatially associated with its unconformable contact with underlying crystalline basement rocks and regionally occurring faults. This study presents the paragenesis, mineral chemistry and geochemistry of uranium mineralized rocks and minerals of the MacInnis Lake sub-basin of the Nonacho Basin, to evaluate the style and relative timing of uranium mineralization. Mineralization is restricted to regionally occurring deformation zones, and post-dates widely spread and pervasive albitization and more local Ba-rich K-feldspar alteration of host rocks. Uranium mineralized rocks show elevated concentration of Cu, Ag and Au relative to variably altered host rocks. Microscopic and compositionally heterogeneous altered uraninite occurs (i) as overgrowths on partially dissolved Cu-sulphides with magnetite in chlorite ± quartz, calcite veins, and (ii) with minor uranophane in hematite-sericite-chlorite ± quartz breccia and stockwork. Both uraninite types are Th poor (<0.09 wt.% ThO2) and variably rich in SO4 (up to 2.26 wt.%), suggesting a low-temperature hydrothermal origin in a relatively oxidized environment. Rare-earth element (+Y) concentrations in type-i uraninite are high, up to 9.5 wt.% Σ(REE+Y)2O3 with CeN/YN values > 1, similar to REE compositions of uraninite in metasomatic iron and alkali-calcic systems (MIAC), including low-temperature hematite-type IOCG-deposits (e.g., Olympic Dam, Gawler Craton, Australia) and albitite-hosted uranium deposits (e.g., Southern Breccia, Great Bear Magmatic Zone, Canada, and Gunnar Deposit, Beaverlodge District, Canada). Both uraninite types are variably rich in Ba (up to 3 wt.% BaO), a geochemical marker for MIAC systems, provided by the dissolution of earlier secondary Ba-rich K-feldspar. Chemical U-Th-Pb dating yields resetting ages of <875 ± 35 Ma for type-ii uraninite-uranophane, younger than strike-slip movement along regional structures of the basin that are spatially associated with the uranium occurrences. We suggest that MacInnis Lake uranium occurrences formed from oxidized hydrothermal fluids along previously altered (albitized, potassically altered) regional-scale faults. Uranium minerals precipitated on earlier Fe-rich sulfides (chalcopyrite, bornite), which acted as a redox trap for mineralization, in low-temperature (~310–330 °C, based on Al-in-chlorite thermometry) breccias and stockwork zones, late in a metasomatic iron and alkali-calcic alteration system. [ABSTRACT FROM AUTHOR]

In the framework of the project RemoteALPHA, an optical scanning system for remote sensing of alpha emitters using radioluminescence is being developed. After the feasibility of the technique was proven, current work aims at improving the sensitivity for detection of low surface activities. As calibration standard, pitchblende minerals were prepared. Their surface count rate of 80 Bq cm-2 to 105 Bq cm-2 was measured by alpha-track-detection and alpha-spectroscopy. Subsequently, radioluminescence measurements were performed in a sealed chamber filled with different gas atmospheres. The radioluminescence signal was measured in UVC and UVA spectral ranges for all samples. [ABSTRACT FROM AUTHOR]

Uranium dioxied is used as a nuclear fuel. Depending on the temperature and oxygen partial pressure, it is incredibly versatile and can accept a wide variety of stoichiometry. Many meth- ods are used to estimate the non-stoichiometric O/U ratio such as the coulometric titration, gravimetric and voltammetric methods. These methods have some disadvantages and may be time and cost-consuming. This work develops an approach to determine the stoichiometric ratio by using MCNP-5 code and hyper pure germanium detector to estimate the count rate at 185.7 keV for UO2 pellets. The studied pellets are proposed to have 235U mass content (3 %, 4%, and 5%) and I cm away from the detector. The mass of the oxide within the pellets is 7.8995 grams. The relation between volume and density has been studied during different steps in which temperature increases. Finally, a reliable model is established to describe the process of converting green pellets to sintered pellets. The model is supported by employing artificial intelligence to predict some features and the overall correlation equals 0.99929. [ABSTRACT FROM AUTHOR]

This new comprehensive in situ mineral‐chemical characterisation of the Happy Jack uraninite has discovered additional information regarding matrix effects and trace element homogeneity, relevant to proposals that it could serve as a reference material (RM). On the LA‐ICP‐MS instrumentation used, there was an absence of discernible matrix effects relative to the silicate glass NIST SRM 610. Lanthanides and Y are found to be very homogeneously distributed in Happy Jack uraninite, Zr, Nb and Ti mass fractions reproducible but only within individual fragments, and other elements still generally heterogeneous. This means that the Happy Jack uraninite can serve as a secondary RM for quality control in studies of natural uraninites. In terms of absolute accuracy and intermediate measurement precision, the Happy Jack uraninite can be used for the homogeneous elements. For elements that are homogeneous within individual fragments only, intermediate measurement precision can still be evaluated, while information values will be obtained for the generally heterogeneous elements. Two distinct groups (high vs. low Zr) were distinguished to exist among different Happy Jack fragments in association with minor variation of REE mass fractions, which possibly explains the observed (heavy) REE discrepancy between in situ laser ablation and bulk solution ICP‐MS analyses. [ABSTRACT FROM AUTHOR]

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]

The unconformity-related uranium (URU) deposits in the Proterozoic Athabasca Basin (Canada) represent the richest, and one of the most important, uranium endowments in the world. Most of the URU deposits are associated with pre-existing graphitic basement faults that were reactivated after the formation of the basin. These graphite-rich structures have been widely used as a vector for exploration, but the nature of the association of the URU deposits with graphitic basement faults has been debated for over four decades. Proposed roles of graphite include: (1) as a direct reducing agent to reduce U6+ to U4+ and precipitate uraninite; (2) as a precursor of hydrocarbons (mainly CH4) produced in situ or nearby and then used as a reducing agent for uraninite precipitation; (3) as a precursor of hydrocarbons produced at depth that were remobilized to the site of mineralization and acted as a reducing agent for uraninite precipitation; and (4) as a lubricant facilitating faulting and fluid flow that led to uranium mineralization. This paper uses the Phoenix uranium deposit in the southeastern Athabasca Basin as a case study to address these uncertainties. Petrographic studies indicate that there is no direct contact between graphite and uraninite at microscopic scales, and the content of graphite in the graphitic metapelite along the ore-controlling WS Shear Zone does not show a systematic change with the distance from the unconformity surface. Raman spectroscopic studies of graphite suggest that the degree of structural disorder of graphite, expressed by various parameters related to the D bands and G band ratios, does not change systematically with the distance from the unconformity surface either. The minor irregularities in these parameters near the unconformity are better explained by paleo-weathering related to the unconformity and/or diagenetic processes than by hydrothermal activity related to uranium mineralization. Based on these observations and interpretations, the role of graphite as an in situ reducing agent, either directly or as a provider of hydrocarbons, is discounted. It is proposed that hydrocarbons derived from graphite at depth, tapped by episodic reactivation or seismicity of the basement faults that was facilitated by graphite as a lubricant, were responsible for URU mineralization. [ABSTRACT FROM AUTHOR]

The combination of electronic and nuclear energy deposition can have an effect on the defect production and evolution that is not simply the sum of both independent contributions. In nuclear reactors, the fuel is exposed to the irradiation of several particles such as the fission fragments (FF) whose electronic to nuclear energy loss ratio evolves along their path. To understand the impact of this energy-loss coupling on the fuel microstructure, single and dual-beam ion irradiations of uranium dioxide (UO 2) were carried out. The damage evolution was investigated by Raman spectroscopy analysis correlated with Transmission Electronic Microscopy observations. It was found a significant acceleration effect of the electronic energy dissipation on the formation and evolution of defects induced by the nuclear energy deposition. The magnitude of this acceleration was shown to depend on both the electronic energy loss level and the microstructure at the moment when the coupling occurs. [Display omitted] [ABSTRACT FROM AUTHOR]

Stibioústalečite, Cu12(Sb2Te2)Se13, was approved as a new mineral species from the Ústaleč mine, 15 km west of Horažďovice, SW Bohemia, Czech Republic. It occurs as metallic anhedral grains up to 0.1-0.3 mm in size, dark grey in color, in a calcite gangue. It is directly associated with hakite-(Hg), berzelianite, the not-yet approved phase Cu12(As2Te2)Se13 and uraninite. Stibioústalečite is brittle, with an indistinct cleavage and a conchoidal fracture; the calculated density is 5.676 g/cm3. In reflected light, stibioústalečite is isotropic, and grey in color; internal reflections were not observed. Reflectance data for the four COM wavelengths in air are [λ (nm): R (%)]: 470: 33.3; 546: 33.2; 589: 33.1; 650: 33.0. Electron microprobe analysis for holotype material (grain used for single-crystal X-ray study) gave (in wt. % - average of 7 spot analyses): Cu 34.10, Ag 1.22, Fe 0.04, Zn 0.09, Hg 0.33, Sb 9.39, As 0.70, Te 12.41, S 3.76, Se 37.59, total 99.63. On the basis of (As + Sb + Te) = 4 atoms per formula unit (apfu), the empirical formula of stibioústalečite is M(2)(Cu5.75Ag0.25)Σ6 M(1)(Cu5.93Hg0.04Zn0.03Fe0.02)Σ6.02 X(3)(Te2.12Sb1.68As0.20)Σ4(Se10.36S2.55)Σ12.91. The ideal formula is Cu6Cu6(Sb2Te2)Se13, which requires Cu 33.33, Sb 10.64 Te 11.16 Se 44.87, total 100 wt. %. Stibioústalečite is cubic, I4̄ 3m, with unit-cell parameters a = 10.828(4) Å, V = 1269.6(9) Å3, Z = 2. The crystal structure of stibioústalečite was studied by single--crystal X-ray diffraction data and it is isotypic with other members of the tetrahedrite group. The mineral is named after its type locality Ústaleč and its chemical composition, being the (Sb/Te) end-member in the possible ústalečite series. [ABSTRACT FROM AUTHOR]

We analysed with different methods the densification of UO 2 nanopowders in SPS under constant heating rate (CHR) and isothermal sintering conditions. The apparent activation energy of densification in SPS (75 kJ/mol with CHR method) is significantly smaller than in conventional sintering. It is shown that this is likely not an effect of the applied current. We also observed a threshold stress at 64 MPa for the transition from pressure-insensitive sintering (stress exponent n ≈0) to pressure-assisted sintering, suggesting that the contribution of the capillary stresses in such nanopowders is comparable with the typical stress applied in SPS. [ABSTRACT FROM AUTHOR]

Two heteroleptic uranyl(VI) complexes [UO2(L)(phen)] (1) and [UO2(L)(pypzH)] (2) [where, H2L=N2O2‐benzil bis(isonicotinoyl hydrazone) ligand, phen=1,10‐phenanthroline and pypzH=3‐(2‐pyridylpyrazole)] were synthesized and characterized by elemental analysis, mass spectrometry, UV‐Visible, 1H NMR, FT‐IR and TGA techniques. The time‐dependent density functional theory (TD‐DFT) calculations of both the complexes were carried out to obtain the insights into the structure and spectral properties. According to results obtained, the title complexes have highly distorted structures deviating from the expected hexagonal bipyramidal structures. The computed results show that the LUMO of the complex is mainly stabilized by uranium. Both the complexes exhibit similar UV‐Visible spectra within the region 325–600 nm with their intense bands at ∼450 nm primarily due to the HOMO→LUMO transitions. A weak absorption band which appears at ∼335 nm for each complex has been attributed to n→π* transition. In contrast to complex 2,the complex 1 exhibits maximum deviation from the Oyl‐U‐Oyl linearity. [ABSTRACT FROM AUTHOR]

The paper presents results of modeling the chemical interactions of Quaternary meteoric waters with siltstones of the upper part of the Vendian Padun Formation of the Mezen Syneclise, Arkhangelsk region, Russia. Equilibrium and equilibrium-kinetic approaches were applied. It is shown that under conditions of intensive water exchange and low temperature, due to low rates of interaction of minerals with water, the redox buffer of rock-forming minerals at this stage of the process makes a subordinate contribution to the dissolution of uranium. Therefore, for a sufficiently long time, the main agent of mobilization of uranium in rocks is oxygen dissolved in water. [ABSTRACT FROM AUTHOR]

The Proterozoic Vindhyan Supergroup overlying Bundelkhand Granite Complex (BGC) presents an ideal environment for exploration of uranium mineralisation. Recent exploratory drilling in Kaimur Group of sandstone overlying unconformably the basement Bundelkhand granite at Maha Rampura area has revealed a significant correlatable uranium mineralisation. The mineralisation hosted by subfeldspathic arenite with reddish/ greenish shale intercalations enriched with organic matter is delineated. The subfeldspathic arenite has a definite marker bed with 1–2 m thickness located ∼ 30 m to 40 m above the unconformity. Organic matter (OM) is disseminated in subfeldspathic arenite and occurs within intergranular spaces as rounded globules. Uranium occurs within the subfeldspathic arenite as primary minerals i.e. uraninite and coffinite as well as in adsorbed form on organic matter and clay within the marker horizon. Significant correlatable uranium mineralisation with primary uranium minerals in Maha Rampura area thus opens up a broad exploration target in the entire Vindhyan Basin. [ABSTRACT FROM AUTHOR]

Results of multi-method geochronological study (U-Pb, Pb-Pb and Sm-Nd), on uranium mineralized rocks along the albitite line in the North Delhi Fold Belt (NDFB, Rajasthan, India) are presented. The Pb-Pb ages obtained, on uranium mineralized core samples, from Rohil uranium deposit, Sikar district, Rajasthan (south western part of NDFB), are 836 ± 5 Ma (Pb Sequential Leaching-PbSL, weighted average of 11 isochron ages), 826 ± 9 Ma (Pb-Pb isochron age on uraninite), 842 ± 18 Ma (U-Pb concordia upper intercept age, on uraninite). Similar ages of uraninites were also obtained from areas close to Rohil uranium deposit i.e. Jahaz (823 ± 10 Ma, U-Pb and 826 ± 14 Ma, Pb-Pb) and Ghateshwar areas (834 ± 14 Ma, U-Pb concordia upper intercept age and 826 ± 25 Ma, Pb-Pb isochron age). The ages of uranium mineralisation (PbSL) further in northeastern part of NDFB i.e. in Gorir area, Jhunjhunu district, Rajasthan, are 827 ± 7 Ma, 818 ± 24 Ma (PbSL) and in Dhancholi area, Mahendragarh Dist., Haryana, are 824 ± 12 Ma (U-Pb) and 824 ± 6.5 Ma (Pb-Pb). The above age data in general indicates age of uranium mineralization as 830 Ma in the NDFB. These ages are consistent with age of uranium mineralization in albitites from Brazil. The Sm-Nd isochron age on uraninite (Rohil) is 824 ± 85 Ma with µNdi 830 Ma= −14 that indicates source of uranium from crustal rocks which is around 1400 Ma older than the age of present dated uraninites. Probably metasediments of the Paleoproterozoic Delhi/ Aravalli Supergroup (c. 2200 Ma) or basement granite gneisses are the main source of uranium in the studied samples. [ABSTRACT FROM AUTHOR]

Allanite, being one of the most common REE bearing mineral phases in the multimetallic mineralized domain of Singhbhum Shear Zone, has always attracted attention from researchers. The present paper outlines a detailed petromineralogical study on various textural types of allanites. The allanite is categorized into 6 different types falling under three major categories on the basis of deformation, metamictisation and darkening of pleochroic halos. On the basis of mineral assemblage and probe analysis of allanite it follows that the optical and textural variations are an implication of not only multiple generations of their formation but rather significant variation in nature of hydrothermal fluids as evidenced by the differences in co-crystallized assemblages. They hint at relatively reducing hydrothermal conditions in Singhbhum Shear Zone responsible for REE-U-Th mineralization overprinting earlier event of oxidizing hydrothermal mineralization in which the well-known Th-poor uraninite, crystallized. Majority of the allanite appeared post or at the most syn-tectonic in their formation. The available geochronological data of allanite suggests them to be formed around 1.8 Ga. Considering textural criteria as seen in the present study, it appears that the majority of allanite owing to their undeformed morphology must have formed later to or at the most during waning stages of shearing and hence the minimum age of shearing in SSZ could be considered around 1.8 Ga instead of 1.6 Ga. [ABSTRACT FROM AUTHOR]

High U concentrations (reaching up to 14,850 mg ⋅ kg−1), were determined in soils and sediments of a wetland downstream of a former U mine in France. This study aims to identify the origin of radioactive contaminants in the wetland by employing Pb isotope fingerprinting, (234U/238U) disequilibrium, SEM, and SIMS observations. Additionally, information about U and 226Ra transport processes was studied using U-238 series disequilibrium. The results of Pb fingerprinting highlighted inherited material inputs of different U-mines with mainly two types of U-ores: i) pitchblende (UO 2), and ii) parsonsite (Pb 2 (UO 2)(PO 4) 2). Moreover, significant disequilibrium of (230Th/238U) and (226Ra/230Th) activity ratios highlighted the mobility of 238U and 226Ra in the wetland, primarily driven by the water table fluctuations. Finally, this work uncovered a limitation of Pb isotope fingerprinting in the case of parsonsite materials, as the high natural Pb content of this mineral may hide the uranogenic Pb signature in the samples. [Display omitted] • U-Pb isotopic tracing efficiently identified U-mining input in the environment. • Pitchblende and torbernite exhibit high radiogenic Pb signature. • Parsonsite lacks radiogenic Pb signature due to its high natural Pb content. • SIMS analysis confirm the presence of pitchblende and neoformed U-bearing phases. • U-series disequilibrium highlights U and Ra mobilities in the wetland. [ABSTRACT FROM AUTHOR]

High resolution synchrotron powder X-ray diffraction analysis of Cr-doped UO 2 samples with additions of Cr 2 O 3 as 0, 500, 1000, 1500, 2500 to 3500 ppm prepared under sintering conditions of -420 kJ/mol and 1700 °C is reported. The lattice dependence from Cr doping is established through the Rietveld refinement method where the rate of linear lattice parameter contraction from Cr doping, Δa cr , was found to be considerably smaller and more subtle than previously described. This investigation highlights the need for high resolution and precise specimen preparation when measuring and interpreting subtle changes to nuclear material crystal structures due to trace doping. [ABSTRACT FROM AUTHOR]