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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.

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At least 847 records · Page 47
All sourcesNASA NTRSDOE OSTI
DOE OSTI2026

Physicochemical evolution of uranium nitride kernel microstructure with varying carbon distribution for advanced TRISO fuel forms

Uranium nitride (UN) has emerged as a fuel candidate for advanced nuclear reactor concepts due to its superior uranium density, thermal conductivity, and high melting temperature. However, the fabrication route for converting UO 2 to UN is complex and difficult to standardize. Although the chemistry of this conversion process is well-studied, more insight into the physicochemical dynamics of this conversion using advanced characterization techniques can help further our understanding of this material system. This work leveraged thermogravimetric analysis (TGA), X-ray diffraction (XRD), and nondestructive 3D X-ray computed tomography (XCT) to characterize dynamic microstructural changes in the UO 2 → UCO → UN fabrication pathway for two kernels with a varying carbon distribution in the starting composition. TGA and XRD were used to quantify changes in the mass, density, and chemical composition of the two kernels, while three-dimensional image processing and segmentation of XCT data were used to quantify the volume, surface area, and spatial distribution of features within each kernel for multiple steps along the fabrication pathway. The analysis indicates distinct differences between the two kernels that are correlated to downstream conversion efficiency. In conclusion, this work is among the first to perform 3D quantification of physicochemical evolution during UN conversion, providing quantitative correlation between processing, properties, and expected fuel performance.

Nuclear fuel↗
DOE OSTI2016

Synthesis and characterization of a new and electronically unusual uranium metallacyclocumulene, (C 5 Me 5 ) 2 U(η 4 -1,2,3,4-PhC 4 Ph)

A new uranium metallacyclocumulene, (C 5 Me 5 ) 2 U(η 4 -1,2,3,4-PhC 4 Ph), was synthesized by both reaction of (C 5 Me 5 ) 2 UCl 2 with 1,4-diphenylbutadiyne in the presence of KC 8 and by ligand exchange between (C 5 Me 5 ) 2 U(η 2 -Me 3 SiC 2 SiMe 3 ) and 1,4-diphenylbutadiyne. Lastly, full characterization of (C 5 Me 5 ) 2 U(η 4 -1,2,3,4-PhC 4 Ph) is reported, including the solid-state structure. (C 5 Me 5 ) 2 U(η 4 -1,2,3,4-PhC 4 Ph) displays an unusually detailed UV–visible spectrum, which is rare for uranium(IV) metallocene complexes.

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

In situ X-ray characterization of uranium dioxide during flash sintering

The in situ response of stoichiometric and non-stoichiometric uranium dioxide during flash sintering is examined using high energy X-ray diffraction. Our results show that the onset of flash is driven by an increase in temperature and controlled by the applied field with no evidence of an accumulation of defects. The incubation time, that is the time after the application of the field before the flash occurs, is found to be material specific with hyper-stoichiometric samples requiring lower fields to flash. For low current/voltage fields we quantify very little change in the atomic and microstructure of the different uranium dioxide samples post-flash. Microstructural changes are identified for high fields and currents, where joule heating and sample temperatures are high, resulting in the complete transformation of the U 4 O 9 phase. Our results highlight the usefulness of high energy X-ray characterization in understanding the subtle structural changes that occur during the flash sintering process.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Uranium measurements in the field using high-resolution cadmium zinc telluride detectors

A new generation of cadmium zinc telluride (CZT) detectors has become available and is being evaluated by the International Atomic Energy Agency (IAEA) for safeguards verifications in the field. The new CZT detector, model M400, is a room temperature spectrometer manufactured by H3D, Inc. The M400 demonstrates superior energy resolution, effective isotope identification capabilities, and convenient usability features when tested in a controlled laboratory environment. These characteristics define the M400 as a potential platform for IAEA field detection applications, which could become suitable for nuclear material characterization (e.g., enrichment verification) and nuclear safeguards missions. The capabilities of gamma spectrometry codes including Fixed energy, Response function Analysis with Multiple efficiencies (FRAM) from Los Alamos National Laboratory, CZT for Uranium (CZTU) from Lawrence Livermore National Laboratory, and Gamma Detector Response and Analysis Software (GADRAS) from Sandia National Laboratories were adapted for M400 spectra, and the performance of the codes has been validated. This was reported in a prior work. To further validate the performance of the high-energy resolution CZT detector and the isotopic analysis codes, a field measurement campaign consisting of uranium hexafluoride (UF 6 ) cylinder measurements was conducted at a fuel fabrication facility. A total of 34 Type 30B cylinders containing UF6 were measured using three different M400 CZT detectors. Each detector was outfitted with a custom rectangular collimator and shield made out T-Flex®, a tungsten-impregnated polymer. Measurements were performed at three different locations of the cylinder, ensuring that the measurement geometry satisfied the infinite thickness criterion. The spectra from the M400 CZT were analyzed using the code General Enrichment Meter (GEM). For analyzing the gamma-ray spectra from UF 6 cylinder, the GEM code is the appropriate tool since it relies only on the gamma-ray emissions from 235 U and not from other isotopes. Results from the spectral analysis were compared with the known abundance of 235 U in the cylinders, as well as with the International Target Values 2020 (ITV2020). The suitability of the different underlying techniques used by the various codes for UF 6 analysis is discussed. The challenges of measuring UF 6 contained in cylinders and mitigation strategies are highlighted.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2025

Spectral emission characteristics near 646 nm and plasma properties of laser-induced plasma of gaseous uranium hexafluoride

We present a detailed investigation of the temporal evolution of line and continuum emissions in laser-induced breakdown spectroscopy (LIBS) of gaseous uranium hexafluoride (UF 6 ), focusing on the spectral region near 646 nm. Spectral emission features, signal-to-background ratios (SBRs) of selected uranium lines, and spectral linewidths were examined under varying UF 6 pressures (15–60 Torr) and laser pulse energies (10–60 mJ). Higher pressures and pulse energies enhanced continuum emission and reduced SBRs but did not cause significant spectral congestion. Additional studies with the use of different laser systems, including nanosecond-pulsed Nd:YAG lasers (at fundamental and various harmonics) and a femtosecond-pulsed Ti:sapphire laser, revealed long-lived plasma continua in all cases. This persistent continuum is attributed to a pseudo-continuum from overlapping molecular emissions, as its intensity scales linearly with electron number density, deviating from the expected quadratic dependence of classical ion–electron interactions for free-free and free-bound continuum emission. Based on plasma persistence time, SBR, U II/U I intensity ratios, and electronic excitation temperature, no fundamental advantage was found for femtosecond-pulsed lasers over conventional nanosecond-pulsed ones for UF 6 enrichment assay with direct LIBS measurement.

Laser-induced breakdown spectroscopy↗
DOE OSTI2021

Growth and characterization of uranium oxide thin films deposited by polymer assisted deposition

A thin film of uranium oxide was deposited by polymer assisted deposition on a single crystal lanthanum aluminate - strontium aluminum tantalate substrate. The deposition resulted in formation of epitaxial thin film of uranium oxide, which could be attributed to α-U 3 O 8 or α-UO 3 . X-ray diffraction revealed preferential orientation along (100) in case of α-U 3 O 8 or (001) for α-UO 3 for the thin film. A combination of x-ray and neutron reflectometry proved the sample to be α-U 3 O 8 . Furthermore, the film was of 17 nm thickness covered by a capping layer. The less dense capping layer could be a manifestation of surface water adsorbed on the sample.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Rapid Determination of Uranium Isotopic Abundance from Cotton Swipes: Direct Extraction via a Planar Surface Reader and Coupling to a Microplasma Ionization Source

The collection of solid particulates and liquids from surfaces by the use of cloth swipes is fairly ubiquitous. In such methods, there is a continuous concern regarding the ability to locate and quantitatively sample the analyte species from the material. In this effort, we demonstrate the initial coupling of an Advion Plate Express plate reader to a liquid sampling–atmospheric pressure glow discharge (LS-APGD) microplasma ionization source with an Orbitrap mass spectrometer to perform uranium isotopic analyses of solution residues on cotton swipes. The Plate Express employs a sampling probe head to engage and seal against the swipe surface. Subsequentially, the analyte residues are desorbed and transported within a 2% HNO 3 electrolyte flow to the ionization source. Quantitative recoveries were observed following a single 30 s extraction step, with the absolute mass sampled per extraction being ~100 ng. While the intrasample variability in the analytical responses for triplicate sampling of the same swipe yield ~30% RSD, this lack of precision is offset by the ability to determine isotope ratios for enriched uranium specimens with a precision of better than 10% RSD. Pooled, intersample precision ( n = 9) was found to be <5%RSD across the various sample compositions. Finally, 235 U/ 238 U determinations (ranging from 0.053 to 1.806) were accurate with errors of <10%, absolute. The 234 U- and 236 U-inclusive ratios were determined with similar accuracy in enriched samples. While the driving force for the effort is in the realm of nuclear nonproliferation efforts, the ubiquitous use of cloth swipes across many application areas could benefit from this convenient approach, including the use of versatile, reduced-format mass spectrometer systems.

38 RADIATION CHEMISTRY, RADIOCHEMISTRY, AND NUCLEA↗
DOE OSTI2018

Automated Separation of Uranium and Plutonium from Environmental Swipe Samples for Multiple Collector Inductively Coupled Plasma Mass Spectrometry

A fully automated method for the separation of low-concentration uranium from plutonium in environmental swipe samples has been developed. The offline chromatography system features renewable 1 mL Eichrom TEVA and UTEVA column generation from bulk resin slurry. Discrete fractions of the separated actinides are delivered into user defined vials for future analysis. Clean room background levels were achieved outside of a cleanroom environment with this method. Purification of uranium and plutonium from various sample matrixes and at various concentrations was successful. Major and minor isotope ratios for both elements were measured via multiple collector inductively coupled plasma mass spectrometry and were in good agreement with certified reference values. Lastly, validation of the separation method was conducted on archived environmental samples and agreed with values previously reported using standard column chemistry.

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

Complexity of Uranyl Peroxide Cluster Speciation from Alkali-Directed Oxidative Dissolution of Uranium Dioxide

Solid UO 2 dissolution and uranium speciation in aqueous solutions that promote formation of uranyl peroxide macroanions was examined, focusing on the role of alkali metals. UO 2 powders were dissolved in solutions containing XOH (X = Li, Na, or K) and 30% H 2 O2. Inductively coupled plasma optical emission spectroscopy (ICP-OES) measurements of solutions revealed linear trends of uranium versus alkali concentration in solutions resulting from oxidative dissolution of UO 2 , with X:U molar ratios of 1.0, showing that alkali availability determines the U concentrations in solution. The maximum U concentration in solution was 4.36 x 10 5 parts per million (ppm), which is comparable to concentrations attained by dissolving UO 2 in boiling nitric acid, and was achieved by lithium hydroxide-promoted dissolution. Lastly, Raman spectroscopy and electrospray ionization mass spectrometry (ESI-MS) of solutions indicate that dissolution is accompanied by formation of various uranyl peroxide cluster species, the identity of which is alkali concentration-dependent, revealing remarkably complex speciation at high concentrations of base.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Complex Topologies from Simple Building Blocks: Uranium(IV) Thiophosphates

Six new uranium thiophosphates Cs 5 Na 6 [U(PS 4 ) 4 ](PS 4 ) (1), Rb 5 Na 3 [U(PS 4 ) 4 ] (2), CsNa[U(PS 4 ) 2 ] (3), Cs 1.67 Na 0.52 I 0.19 [U(PS 4 ) 2 ] (4), Cs 1.033 Na 1.343 I 0.376 [U(PS 4 ) 2 ] (5), and Rb 1.35 Na 0.93 I 0.28 [U(PS 4 ) 2 ] (6) were obtained from halide flux reactions and characterized using single crystal X-ray diffraction. The structures of these compounds consist of a pseudo-tetrahedral uranium unit that in combination with a set of PS 4 group coordination modes can result in an isolated [U(PS 4 ) 4 ] 8– unit, a [U(PS 4 ) 2 ] 2– chain, or a [U(PS 4 ) 2 ] 2– slab. Optical and magnetic properties of 3 and 4 were collected. Both compounds exhibit paramagnetic behavior, and CsNa[U(PS 4 ) 2 ] (3) exhibits a magnetic transition at 200–225 K between two paramagnetic states that both have similar effective magnetic moments of 4.13 and 4.19 µ B /F.U., and strong antiferromagnetic interactions with θ = -183 and -172 K, for the high- and low-temperature states, respectively.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2019

Targeted Synthesis of Uranium(IV) Thiosilicates

Two new uranium(IV) thiosilicates, Cs 2 Na 4 [U 2 (SiS 4 ) 2 (Si 2 S 8 )] and Cs 2.12 Na 3.88 [U 2 (SiS 4 ) 2 (Si 2 S 7 )], were obtained by flux crystal growth using SiS 2 as a silicon source. The former compound contains a novel Si 2 S 8 6– unit that features a terminal persulfide group. The magnetic susceptibility measurements performed on this compound revealed paramagnetic behavior with a moment of 3.49 μ B per uranium atom as obtained from a Curie–Weiss law fit and showed no magnetic transition down to 2 K. Finally, the structures are based on closely related isomeric planar and 3D topologies that can be transformed into one another by a rotation of the structural units.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2026

Uranium Hexafluoride Hydrolysis Reaction Dynamics from Cryogenic Layering, FTIR Spectroscopy, and Isotopic Substitution

The first direct evidence that the hydrolysis reaction of uranium hexafluoride (UF 6 ) follows multiple competing pathways which are driven by the ratio of water to UF 6 , temperature, and isotopic composition is presented. Using temperature dependent infrared spectroscopy, it is shown the hydrolysis can be prevented at temperatures below 150 K, and that water-rich environments promote the formation of uranium oxyfluoride intermediates. Spectral shifts reveal isomeric transitions and the growth of polymeric species, with reaction reversibility observed at high water concentrations. Additionally, controlled heating rates affect the emergence of intermediates. The final particulate product consistently forms as uranyl fluoride hydrate, though its morphology and spectral signature vary with reaction conditions and annealing. These findings help clarify long-standing uncertainties surrounding UF 6 hydrolysis.

Chemical reactions↗
DOE OSTI2014

Photochemical route to actinide-transition metal bonds: synthesis, characterization and reactivity of a series of thorium and uranium heterobimetallic complexes

A series of actinide-transition metal heterobimetallics has been prepared, featuring thorium, uranium and cobalt. Complexes incorporating the binucleating ligand N[-(NHCH2PiPr2)C6H4]3 and Th(IV) (4) or U(IV) (5) with a carbonyl bridged [Co(CO)4]- unit were synthesized from the corresponding actinide chlorides (Th: 2; U: 3) and Na[Co(CO)4]. Irradiation of the isocarbonyls with ultraviolet light resulted in the formation of new species containing actinide-metal bonds in good yields (Th: 6; U: 7); this photolysis method provides a new approach to a relatively rare class of complexes. Characterization by single-crystal X-ray diffraction revealed that elimination of the bridging carbonyl is accompanied by coordination of a phosphine arm from the N4P3 ligand to the cobalt center. Additionally, actinide-cobalt bonds of 3.0771(5) and 3.0319(7) for the thorium and uranium complexes, respectively, were observed. The solution state behavior of the thorium complexes was evaluated using 1H, 1H-1H COSY, 31P and variable-temperature NMR spectroscopy. IR, UV-Vis/NIR, and variable-temperature magnetic susceptibility measurements are also reported.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2017

Uranium extraction: Fuel from seawater

Over four billion tonnes of uranium are currently in the oceans that could be harvested for nuclear fuel, but current capture methods have limited performance and reusability. Now, an electrochemical method using modified carbon electrodes is shown to be promising for the extraction of uranium from seawater.

38 RADIATION CHEMISTRY, RADIOCHEMISTRY, AND NUCLEA↗
DOE OSTI2014

Carbonate-H2O2 Leaching for Sequestering Uranium from Seawater

Uranium adsorbed on amidoxime-based polyethylene fiber in simulated seawater can be quantitatively eluted at room temperature using 1M Na2CO3 containing 0.1 M H2O2. This efficient elution process is probably due to formation of an extremely stable uranyl-peroxo-carbonato complex in the carbonate solution. After washing with water, the sorbent can be reused with little loss of uranium loading capacity. Possible existence of this stable uranyl species in ocean water is also discussed.

carbonate-peroxide leaching sequestering uranium s↗
DOE OSTI2016

Critical Need for Plutonium and Uranium Isotopic Standards with Lower Uncertainties

Certified reference materials (CRMs) traceable to national and international safeguards database are a critical prerequisite for ensuring that nuclear measurement systems are free of systematic biases. CRMs are used to validate measurement processes associated with nuclear analytical laboratories. Diverse areas related to nuclear safeguards are impacted by the quality of the CRM standards available to analytical laboratories. These include: nuclear forensics, radio-chronometry, national and international safeguards, stockpile stewardship, nuclear weapons infrastructure and nonproliferation, fuel fabrication, waste processing, radiation protection, and environmental monitoring. For the past three decades the nuclear community is confronted with the strange situation that improvements in measurement data quality resulting from the improved accuracy and precision achievable with modern multi-collector mass spectrometers could not be fully exploited due to large uncertainties associated with CRMs available from New Brunswick Laboratory (NBL) that are used for instrument calibration and measurement control. Similar conditions prevail for both plutonium and uranium isotopic standards and for impurity element standards in uranium matrices. Herein, the current status of U and Pu isotopic standards available from NBL is reviewed. Critical areas requiring improvement in the quality of the nuclear standards to enable the U. S. and international safeguards community to utilize the full potential of modern multi-collector mass spectrometer instruments are highlighted.

98 NUCLEAR DISARMAMENT, SAFEGUARDS, AND PHYSICAL P↗
DOE OSTI2016

Isotope ratio characteristics and sensitivity for uranium determinations using a liquid sampling-atmospheric pressure glow discharge ion source coupled to an Orbitrap mass analyzer

Abstract The continued development of the liquid sampling-atmospheric pressure glow discharge (LS-APGD) microplasma as an ion source for diverse, elemental/isotopic analysis applications continues. To this end, characterization of the capabilities in performing precise and accurate isotope ratio (IR) determinations is essential. Based on past experience with the Thermo Exactive Orbitrap mass analyzer, the LS-APGD was interfaced with this instrument for these tests. While the Orbitrap platform has demonstrated excellent mass resolution and accuracy in “organic” mass spectrometry (MS) applications, work using an Orbitrap for IR analysis is very sparse. These efforts build off previous work in this coupling, where the importance of a few of the LS-APGD discharge parameters and Orbitrap data acquisition methods on IR precision and accuracy were probed. Presented here are the results of a study that evaluated the analytical precision for natural uranium sample (assumed 235U/238U = 0.0072) determinations. The instrumental parameters evaluated include the number of microscans and scans making up a data acquisition set, uranium concentration/signal level, sample make-up, and Fourier transform digitization window. Ultimately, a precision of 0.41% relative standard deviation (RSD) can be achieved for a single determination, with a reproducibility of 1.63 %RSD over 10 separate analytical measurements. A preliminary study of matrix effects on IR measurements of U is presented, highlighting the importance of pre-mass selection before injection into the Orbitrap. The analytical system sensitivity is suggested with the ability to produce a calibration function having an R2 value of >0.99 over a range of 4 orders of magnitude of concentration (~1 – 1000 ng mL-1). These efforts demonstrate the very promising pairing of the LS-APGD ionization source and the Orbitrap, pointing as well to definitive paths forward to better utilize both components in high quality isotope ratio mass spectrometry (IRMS).

Environmental Molecular Sciences Laboratory↗
DOE OSTI2015

A two-dimensional, finite-difference model of the oxidation of a uranium carbide fuel pellet

The oxidation of spent uranium carbide fuel, a candidate fuel for Generation IV nuclear reactors, is an important process in its potential reprocessing cycle. However, the oxidation of uranium carbide in air is highly exothermic. A model has therefore been developed to predict the temperature rise, as well as other useful information such as reaction completion times, under different reaction conditions in order to help in deriving safe oxidation conditions. Finite difference-methods are used to model the heat and mass transfer processes occurring during the reaction in two dimensions and are coupled to kinetics found in the literature.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗