Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “uranium”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 1,009 records · Page 56
All sourcesNASA NTRSDOE OSTI
DOE OSTI2018

Carbonate Facilitated Mobilization of Uranium from Lacustrine Sediments under Anoxic Conditions

Sorbed U(IV) species can be major products of U(VI) reduction in natural reducing environments as sediments and waterlogged soils. These species are considered more labile than crystalline U(IV) minerals, which could potentially influence uranium migration in natural systems subjected to redox oscillations. In this work, we examined the role of oxygen and carbonate on the remobilization of uranium from lake sediments, in which ~70% of the 150–300 ppm U is under the form of mononuclear U(IV) sorbed species. Our results show that both drying and oxic incubation only slightly increase the amount of remobilized U after 8 days, compared to anoxic drying and anoxic incubation. In contrast, the amount of remobilized U increases with the quantity of added bicarbonate even under anoxic conditions. Moreover, U L III -edge XANES data show that a significant amount of the solid U(IV) is mobilized in such conditions. Thermodynamic speciation calculations based on the supernatant composition indicates the predominance of aqueous UO 2 (CO 3 ) 3 4– and, to a lesser extent, CaUO 2 (CO 3 ) 3 2– complexes. These results suggest that monomeric U(IV) species could be oxidized into aqueous U(VI) carbonate complexes even under anoxic conditions via carbonate promoted oxidative dissolution, which emphasizes the need for considering such a process when modeling U dynamics in reducing environments.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2018

Stability, Composition, and Core-Shell Particle Structure of Uranium(IV)-Silicate Colloids

Uranium is typically the most abundant radionuclide by mass in radioactive wastes and is a significant component of effluent streams at nuclear facilities. Actinide(IV) (An(IV)) colloids formed via various pathways, including corrosion of spent nuclear fuel, have the potential to greatly enhance the mobility of poorly soluble An(IV) forms, including uranium. This is particularly important in conditions relevant to decommissioning of nuclear facilities and the geological disposal of radioactive waste. Previous studies have suggested that silicate could stabilize U(IV) colloids. Here the formation, composition, and structure of U(IV)-silicate colloids under the alkaline conditions relevant to spent nuclear fuel storage and disposal were investigated using a range of state of the art techniques. The colloids are formed across a range of pH conditions (9-10.5) and silicate concentrations (2-4 mM) and have a primary particle size 1-10 nm, also forming suspended aggregates <220 nm. X-ray absorption spectroscopy, ultrafiltration, and scanning transmission electron microscopy confirm the particles are U(IV)-silicates. Additional evidence from X-ray diffraction and pair distribution function data suggests the primary particles are composed of a UO2-rich core and a U-silicate shell. U(IV)-silicate colloids formation correlates with the formation of U(OH)3(H3SiO4)3 2- complexes in solution indicating they are likely particle precursors. Finally, these colloids form under a range of conditions relevant to nuclear fuel storage and geological disposal of radioactive waste and represent a potential pathway for U mobility in these systems.

Neill, Thomas↗
DOE OSTI2016

Comparison of Analytical Methods for the Determination of Uranium in Seawater Using Inductively Coupled Plasma Mass Spectrometry

Trace element determinations in seawater by inductively coupled plasma mass spectrometry are analytically challenging due to the typically very low concentrations of the trace elements and the potential interference of the salt matrix. In this study, we did a comparison for uranium analysis using inductively coupled plasma mass spectrometry (ICP-MS) of Sequim Bay seawater samples and three seawater certified reference materials (SLEW-3, CASS-5 and NASS-6) using seven different analytical approaches. The methods evaluated include: direct analysis, Fe/Pd reductive precipitation, standard addition calibration, online automated dilution using an external calibration with and without matrix matching, and online automated pre-concentration. The method which produced the most accurate results was the method of standard addition calibration, recovering uranium from a Sequim Bay seawater sample at 101 ± 1.2%. The on-line preconcentration method and the automated dilution with matrix-matched calibration method also performed well. The two least effective methods were the direct analysis and the Fe/Pd reductive precipitation using sodium borohydride

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

Controlling the Reduction of Chelated Uranyl to Stable Tetravalent Uranium Coordination Complexes in Aqueous Solution

The solution-state interactions between octadentate hydroxypyridinone (HOPO) and catecholamide (CAM) chelating ligands and uranium were investigated and characterized by UV-visible spectrophotometry and X-ray absorption spectroscopy (XAS), as well as electrochemically via spectroelectrochemistry (SEC) and cyclic voltammetry (CV) measurements. Depending on the selected chelator, we demonstrate the controlled ability to bind and stabilize U IV , generating with 3,4,3-LI(1,2-HOPO), a tetravalent uranium complex that is practically inert toward oxidation or hydrolysis in acidic, aqueous solution. At physiological pH values, we are also able to bind and stabilize U IV to a lesser extent, as evidenced by the mix of U IV and U VI complexes observed via XAS. Finally, CV and SEC measurements confirmed that the U IV complex formed with 3,4,3-LI(1,2-HOPO) is redox inert in acidic media, and U VI ions can be reduced, likely proceeding via a two-electron reduction process.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

Hyperstoichiometric Uranium Dioxides: Rapid Synthesis and Irradiation-Induced Structural Changes

Uranium dioxide (UO 2 ), the primary fuel for commercial nuclear reactors, incorporates excess oxygen forming a series of hyperstoichiometric oxides. Thin layers of these oxides, such as UO 2.12 , form readily on the fuel surface and influence its properties, performance, and potentially geologic disposal. This work reports a rapid and straightforward combustion process in uranyl nitrate–glycine–water solutions to prepare UO 2.12 nanomaterials and thin films. We also report on the investigation of the structural changes induced in the material by irradiation. Despite the simple processing aspects, the combustion synthesis of UO 2.12 has a sophisticated chemical mechanism involving several exothermic steps. Raman spectroscopy and single-crystal X-ray diffraction (XRD) measurements reveal the formation of a complex compound containing the uranyl moiety, glycine, H 2 O, and NO 3 – groups in reactive solutions and dried combustion precursors. Combustion diagnostic methods, gas-phase mass spectroscopy, differential scanning calorimetry (DSC), and extracted activation energies from DSC measurements show that the rate-limiting step of the process is the reaction of ammonia with nitrogen oxides formed from the decomposition of glycine and uranyl nitrate, respectively. However, the exothermic decomposition of the complex compound determines the maximum temperature of the process. In situ transmission electron microscopy (TEM) imaging and electron diffraction measurements show that the decomposition of the complex compound directly produces UO 2 . The incorporation of oxygen at the cooling stage of the combustion process is responsible for the formation of UO 2.12 . Spin coating of the solutions and brief annealing at 670 K allow the deposition of uniform films of UO 2.12 with thicknesses up to 300 nm on an aluminum substrate. Irradiation of films with Ar 2+ ions (1.7 MeV energy, a fluence of up to 1 × 10 17 ions/cm 2 ) shows unusual defect-simulated grain growth and enhanced chemical mixing of UO 2.12 with the substrate due to the high uranium ion diffusion in films. As a result, the method described in this work allows the preparation of actinide oxide targets for fundamental nuclear science research and studies associated with stockpile stewardship.

38 RADIATION CHEMISTRY, RADIOCHEMISTRY, AND NUCLEA↗
DOE OSTI2023

Extraction of Nitric Acid and Uranium with DEHiBA under High Loading Conditions

We report the mechanism by which high concentrations (1.5 M in n-dodecane) of N,N-di-2-ethylhexylisobutyramide (DEHiBA) extracts HNO 3 and UO 2 (NO 3 ) 2 is under examination. Most prior studies have examined the extractant and the mechanism at a concentration of 1.0 M in n-dodecane, however under the higher loading conditions that can be achieved by a higher concentration of extractant this mechanism could change. Increased extraction of both nitric acid and uranium is observed with an increased concentration of DEHiBA. The mechanisms are examined by thermodynamic modeling of distribution ratios, 15 N NMR, and FTIR spectroscopy coupled with Principal Component Analysis (PCA). Speciation diagrams produced through thermodynamic modeling have been qualitatively reproduced through PCA of the FTIR spectra. The predominant extracted species of HNO 3 (DEHiBA), HNO 3 (DEHiBA) 2 , and UO 2 (NO 3 ) 2 (DEHiBA) 2 are in good agreement with prior literature reports for 1.0 M DEHiBA systems. Evidence for an additional species of either UO 2 (NO 3 ) 2 (DEHiBA) or UO 2 (NO 3 ) 2 (DEHiBA) 2 (HNO 3 ) also contributing to the extraction of uranium species is given.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2025

Alkali Counterion-Dependent Crystallization of Uranium(IV)–Chloro Structural Units

The synthesis, structural characterization, and spectroscopic properties of five tetravalent uranium (U) phases including Li 6 [U 4 (μ 3 -O) 2 Cl 18 (H 2 O) 2 ]·10H 2 O (1), [U(H 2 O) 4 Cl 4 ] (2), [U(H 2 O) 4 Cl 4 ]·KCl (3), Rb 2 UCl 6 (4), and Cs 2 UCl 6 (5) are reported. Notably, a change in the U 4+ solid-state structural unit was observed based on the identity of the alkali counterion used in the synthesis. Li 1+ yielded a tetranuclear oxo-bridged cluster, [U 4 (μ 3 -O) 2 Cl 18 (H 2 O) 2 ] 6– , Na 1+ and K 1+ yielded two structurally distinct [U(H 2 O) 4 Cl 4 ] complexes, and Rb 1+ and Cs 1+ resulted in [UCl 6 ] 2– as the dominant phases. The spectroscopic properties of the compounds were analyzed using Raman and UV–vis–NIR absorption spectroscopy. The UV–vis–NIR spectra of compounds 1–5 exhibited transitions consistent with uranium in the +4 oxidation state. Clear differences in the absorption band splitting were observed and are likely attributed to differences in metal ion coordination, crystal field effects, and outer sphere interactions Overall, this work demonstrates the utility of noncovalent interactions in tuning the crystallization of various metal complexes from otherwise identical reaction solutions and provides further evidence that counterions impact the composition and structure of actinide complexes isolated in the solid state. In this way, this work affords important insight into directing and controlling the structure of actinide complexes and clusters.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2016

Determination of krypton diffusion coefficients in uranium dioxide using atomic scale calculations

We present a study of the diffusion of krypton in UO 2 using atomic scale calculations combined with diffusion models adapted to the system studied. The migration barriers of the elementary mechanisms for interstitial or vacancy assisted migration are calculated in the DFT + U framework using the nudged elastic band method. The attempt frequencies are obtained from the phonon modes of the defect at the initial and saddle points using empirical potential methods. The diffusion coefficients of Kr in UO 2 are then calculated by combining this data with diffusion models accounting for the concentration of vacancies and the interaction of vacancies with Kr atoms. We determined the preferred mechanism for Kr migration and the corresponding diffusion coefficient as a function of the oxygen chemical potential μ O or nonstoichiometry. For very hypostoichiometric (or U-rich) conditions, the most favorable mechanism is interstitial migration. For hypostoichiometric UO 2 , migration is assisted by the bound Schottky defect and the charged uranium vacancy, V U 4– . Around stoichiometry, migration assisted by the charged uranium–oxygen divacancy (V UO 2– ) and V U 4– is the favored mechanism. Finally, for hyperstoichiometric or O-rich conditions, the migration assisted by two V U 4– dominates. Kr migration is enhanced at higher μ O , and in this regime, the activation energy will be between 4.09 and 0.73 eV depending on nonstoichiometry. The experimental values available are in the latter interval. Since it is very probable that these values were obtained for at least slightly hyperstoichiometric samples, our activation energies are consistent with the experimental data, even if further experiments with precisely controlled stoichiometry are needed to confirm these results. Finally, the mechanisms and trends with nonstoichiometry established for Kr are similar to those found in previous studies of Xe.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2018

A Pseudotetrahedral Uranium(V) Complex

A series of uranium amides were synthesized from N,N,N-cyclohexyl(trimethylsilyl)lithium amide [Li][N(TMS)Cy] and uranium tetrachloride to give U(NCySiMe 3 ) x (Cl) 4–x , where x = 2, 3, or 4. The diamide was then isolated as a bimetallic, bridging lithium chloride adduct ((UCl 2 (NCyTMS) 2 ) 2 -LiCl(THF) 2 ), and the tris(amide) was isolated as the lithium chloride adduct of the monometallic species (UCl(NCyTMS) 3 -LiCl(THF) 2 ). The tetraamide complex was isolated as the four-coordinate pseudotetrahedron. Cyclic voltammetry revealed an easily accessible reversible oxidation wave, and upon chemical oxidation, the U V amido cation was isolated in near-quantitative yields. The synthesis of this family of compounds allows a direct comparison of the electronic structure and properties of isostructural U IV and U V tetraamide complexes. Spectroscopic investigations consisting of UV–vis, NIR, MCD, EPR, and U L 3 -edge XANES, along with density functional and wave function calculations, of the four-coordinate U IV and U V complexes have been used to understand the electronic structure of these pseudotetrahedral complexes.

38 RADIATION CHEMISTRY, RADIOCHEMISTRY, AND NUCLEA↗
DOE OSTI2021

Inelastic Neutron Spectra of Uranium Tetrafluoride Hydrate, UF 4 (H 2 O) 2.5

Uranium tetrafluoride hydrate (UFH) is formed by immersing anhydrous UF4 under water for 12 h. UFH is therefore clearly a chemical species of environmental concern, as anhydrous UF4 is an intermediate uranium form in the nuclear fuel cycle. We use inelastic neutron scattering (INS) to probe the full vibrational spectra of UFH and its deuterated analogue in an effort to improve the fundamental understanding of its vibrational spectra. Coupled with density functional theory (DFT) calculations, the first for this compound, and full spectral modeling, we generate the complete vibrational spectra of UFH and compare them to prior optical spectroscopic results. In particular, the combination of DFT with INS allows us to identify multiple distinct chemical environments in the water bending and OH stretching regions. Whereas the water molecules directly bound to the U atoms execute OH stretching around 3600 cm –1 , a second class of H-bonded waters vibrate below 3000 cm –1 , an indicator of strong H bonding. In addition, a class of librational water modes are observed between 400 and 900 cm–1, which themselves can be separated in energy according to their chemical environments. Furthermore, measurements presented herein directly assist in the assignment of certain spectral features in the infrared spectrum and will inform future investigations of UFH for environmental or forensics purposes.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2018

Effects of Fulvic Acid on Uranium(VI) Sorption Kinetics

Many studies by Dr. James A. Davis and others have demonstrated the influence of natural organic matter (NOM) on metal sorption and transport behavior in subsurface environments. Overall, NOM effects on metal sorption have been ascribed to: (1) different sorption affinities of metal-ligand solution complexes compared to ‘free’ metals in solution, and (2) NOM sorption onto minerals leading to competitive sorption behavior and/or changes in mineral surface characteristics. All of these processes have the potential to decrease metal sorption onto mineral surfaces, and alter the pH-dependence of metal sorption characteristics. Maybe even more importantly, a change in metal sorption mechanisms in the presence of NOM may lead to differences in metal surface speciation and affect the potential for later metal desorption and remobilization. Furthermore, it is well-known that overall reaction rates change if the series of elemental reactions comprising a reaction pathway has been altered. In the presence of NOM, metal-ligand dissociation reactions occurring prior to the sorption of ‘free’ metal ions may slow down overall metal sorption kinetics. In addition, a competition between metals and organic ligands binding to the same reactive surface sites may potentially decrease metal sorption rates based on mass action principles. Last, the sorption kinetics of metal-ligand solution complexes may be controlled by the rates of NOM surface reactions, which could be either faster or slower than ‘free’ metal sorption depending on ligand sorption mechanisms. In this presentation, we will use a uranium(VI)-fulvic acid-silica sand system to demonstrate how kinetic sorption experiments – combined with modeling strategies – can provide a powerful tool to study changes in metal sorption mechanisms as a function of organic ligand concentrations. Based on our kinetic sorption data and modeling-based data interpretation, U(VI) sorption onto silica sand can be either faster or slower in the presence of fulvic acid compared to a ligand-free system, depending on the relative concentrations of metals, organic ligands and mineral surface sites. Supporting simulations of U(VI) solution speciation and mineral surface characterization data further allowed us to conclude that a shift occurred from competitive sorption behavior to strong influences of uranium(VI)-fulvic acid complexes with increasing ligand concentrations in this system.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2015

A Novel Method for Molybdenum-99/Technetium-99m Recovery via Anodic Carbonate Dissolution of Irradiated Low-Enriched Uranium Metal Foil

A new method is presented here for digesting irradiated low-enriched uranium foil targets in alkaline carbonate media to recover 99Mo. This method consists of the electrolytic dissolution of uranium foil in a sodium bicarbonate solution, followed by the precipitation of carbonate, base-insoluble fission products, activation products, and actinides with calcium oxide; most of the molybdenum, technetium, and iodine remain in solution. An electrochemical dissolver and mixing vessel were designed, fabricated, and tested for the processing of a full-sized irradiated foil under ambient pressure and elevated temperature. Over 92% of the fission-induced Mo-99 was recovered in a product solution that was compatible with an anion-exchange column for retaining molybdenum and iodine.

Brown, Michael A.↗
DOE OSTI2020

Matrix-Assisted Ionization of Molecular Uranium Species

Matrix-assisted ionization (MAI) demonstrates high sensitivity for a variety of organic compounds; however, few studies have reported the application of MAI for the detection and characterization of inorganic analytes. Trace-level uranium analysis is important in the realms of nuclear forensics, nuclear safeguards, and environmental monitoring. Traditional mass spectrometry methods employed in these fields require combinations of extensive laboratory chemistry sample preparation and destructive ionization methods. There has been recent interest in exploring ambient mass spectrometry methods that enable timely sample analysis and higher sensitivity than what is attainable by field-portable radiation detectors. Rapid characterization of uranium at nanogram levels is demonstrated in this study using MAI techniques. Mass spectra were collected on an atmospheric pressure mass spectrometer for solutions of uranyl nitrate, uranyl chloride, uranyl acetate, and uranyl oxalate utilizing 3-nibrobenzonitrile as the ionization matrix. The uranyl complexes investigated were detectable, and the chemical speciation was preserved. Sample analysis was accomplished in a matter of seconds, and limits of detection of 5 ng of uranyl nitrate, 10 ng of uranyl oxalate, 100 ng of uranyl chloride, and 200 ng of uranyl acetate were achieved. The observed gas-phase speciation was similar to negative-ion electrospray ionization of uranyl compounds with notable differences. Six matrix-derived ions were detected in all negative-ion mass spectra, and some of these ions formed adducts with the uranyl analyte. Subsequent analysis of the matrix suggests that these molecules are not matrix contaminants and are instead created during the ionization process.

38 RADIATION CHEMISTRY, RADIOCHEMISTRY, AND NUCLEA↗
DOE OSTI2022

Abundances of Uranium and Thorium Elements in Earth Estimated by Geoneutrino Spectroscopy

Abstract The decay of the primordial isotopes 238 U, 235 U, 232 Th, and 40 K has contributed to the terrestrial heat budget throughout the Earth's history. Hence, the individual abundance of those isotopes are key parameters in reconstructing contemporary Earth models. The geoneutrinos produced by the radioactive decays of uranium and thorium have been observed with the Kamioka Liquid‐Scintillator Antineutrino Detector (KamLAND). Those measurements have been improved with more than 18‐year observation time, and improvement in detector background levels mainly with an 8‐year nearly reactor‐free period, which now permit spectroscopy with geoneutrinos. Our results yield the first constraint on both uranium and thorium heat contributions. The KamLAND result is consistent with geochemical estimations based on elemental abundances of chondritic meteorites and mantle peridotites. The High‐Q model is disfavored at 99.76% C.L. and a fully radiogenic model is excluded at 5.2 σ assuming a homogeneous heat producing element distribution in the mantle.

58 GEOSCIENCES↗
DOE OSTI2018

Bio-inspired nano-traps for uranium extraction from seawater and recovery from nuclear waste

Nature can efficiently recognize specific ions by exerting second-sphere interactions onto well-folded protein scaffolds. However, a considerable challenge remains to artificially manipulate such affinity, while being cost-effective in managing immense amounts of water samples. Here, we propose an effective approach to regulate uranyl capture performance by creating bio-inspired nano-traps, illustrated by constructing chelating moieties into porous frameworks, where the binding motif’s coordinative interaction towards uranyl is enhanced by introducing an assistant group, reminiscent of biological systems. Representatively, the porous framework bearing 2-aminobenzamidoxime is exceptional in sequestering high uranium concentrations with sufficient capacities (530 mg g –1 ) and trace quantities, including uranium in real seawater (4.36 mg g –1 , triple the benchmark). Using a combination of spectroscopic, crystallographic, and theory calculation studies, it is revealed that the amino substituent assists in lowering the charge on uranyl in the complex and serves as a hydrogen bond acceptor, boosting the overall uranyl affinity of amidoxime.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

Recovery of high specific activity molybdenum-99 from accelerator-induced fission on low-enriched uranium for technetium-99m generators

Abstract A new process was developed to recover high specific activity (no carrier added) 99 Mo from electron-accelerator irradiated U 3 O 8 or uranyl sulfate targets. The process leverages a novel solvent extraction scheme to recover Mo using di(2-ethylhexyl) phosphoric acid following uranium and transuranics removal with tri- n -butyl phosphate. An anion-exchange concentration column step provides a final purification, generating pure 99 Mo intended for making 99 Mo/ 99m Tc generators. The process was demonstrated with irradiated uranium targets resulting in more than 95% 99 Mo recovery and without presence of fission products or actinides in the product.

38 RADIATION CHEMISTRY, RADIOCHEMISTRY, AND NUCLEA↗
DOE OSTI2021

Piezomagnetic switching and complex phase equilibria in uranium dioxide

Abstract Actinide materials exhibit strong spin–lattice coupling and electronic correlations, and are predicted to host new emerging ground states. One example is piezomagnetism and magneto-elastic memory effect in the antiferromagnetic Mott-Hubbard insulator uranium dioxide, though its microscopic nature is under debate. Here, we report X-ray diffraction studies of oriented uranium dioxide crystals under strong pulsed magnetic fields. In the antiferromagnetic state a [888] Bragg diffraction peak follows the bulk magnetostriction that expands under magnetic fields. Upon reversal of the field the expansion turns to contraction, before the [888] peak follows the switching effect and piezomagnetic ‘butterfly’ behaviour, characteristic of two structures connected by time reversal symmetry. An unexpected splitting of the [888] peak is observed, indicating the simultaneous presence of time-reversed domains of the 3-k structure and a complex magnetic-field-induced evolution of the microstructure. These findings open the door for a microscopic understanding of the piezomagnetism and magnetic coupling across strong magneto-elastic interactions.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Harvesting uranium from nuclear waste streams

Nuclear-fuel-cycle wastewater contains a considerable amount of uranium that must be removed. Here, a new electron-buffering adsorbent provides an economically efficient means of recycling uranium to address remediation and fuel resource needs.

Wiechert, Alexander I. [Oak Ridge National Laborat↗