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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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All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

NaGaS 2 - an Elusive Layered Compound with Dynamic Water Absorption and Wide-Ranging Ion Exchange Properties

Most ternary sulfides belonging to the MGaS 2 structure-type have been known for many years and are well-characterized. Surprisingly, there have been no reports of the NaGaS 2 composition, which contains Na, a monovalent cation slightly larger in size than Li, found in LiGaS 2 , a compound known for its non-linear optical properties. Herein we demonstrate for the first time that the unique reversible water absorption in NaGaS 2 has resulted in its absence from the literature due to the difficulties that one encounters when characterizing this compound by SC XRD. The layered structure of this compound coupled with uniquely easy migration of water molecules between the layers allows for ion exchange with 3d and 5f metal cations. We established that some cations, e.g. Ni 2+ , facilitate exfoliation of the layers, providing a facile synthetic route to a new class of 2D chalcogenide materials and, in addition, demonstrating that NaGaS 2 can readily uptake uranyl species from aqueous solutions.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

f‐ block MOFs: A Pathway to Heterometallic Transuranics

Abstract A novel series of heterometallic f ‐block‐frameworks including the first examples of transuranic heterometallic 238 U/ 239 Pu‐metal–organic frameworks (MOFs) and a novel monometallic 239 Pu‐analog are reported. In combination with theoretical calculations, we probed the kinetics and thermodynamics of heterometallic actinide(An)‐MOF formation and reported the first value of a U‐to‐Th transmetallation rate. We concluded that formation of uranyl species could be a driving force for solid‐state metathesis. Density of states near the Fermi edge, enthalpy of formation, band gap, proton affinity, and thermal/chemical stability were probed as a function of metal ratios. Furthermore, we achieved 97 % of the theoretical maximum capacity for An‐integration. These studies shed light on fundamental aspects of actinide chemistry and also foreshadow avenues for the development of emerging classes of An‐containing materials, including radioisotope thermoelectric generators or metalloradiopharmaceuticals.

Park, Kyoung Chul↗
DOE OSTI2025

Ligand‐Directed Actinide Oxo‐Bond Manipulation in Actinyl Thiacalix[4]arene Complexes

Understanding the chemistry of the inert actinide oxo bond in actinyl ions AnO2 2+ is important for controlling actinide behavior in the environment, during separations, and in nuclear waste (An=U, Np, Pu). The thioether calixarene TC4A (4-tert-butyltetrathiacalix[4]arene) binds equatorially to the actinyl cation forming a conical pocket that differentiates the two trans-oxo groups. The 'ate' complexes, [A]2[UO2(TC4A)] (A=[Li(DME)2], HNEt3) and [HNEt3]2[AnO2(TC4A)] (An=U, Np, Pu), enable selective oxo chemistry. Silylation of the UVI oxo groups by bis(trimethylsilyl)pyrazine occurs first at only the unencapsulated exo oxo and only one silylation is needed to enable migration of the endo oxo out of the cone, whereupon a second silylation affords the stable UIV cis-bis(siloxide) [A]2[U(OSiMe3)2(TC4A)]. Calculations confirm that only one silylation event is needed to initiate oxo rearrangement, and that the putative cis dioxo isomer of [UO2(TC4A)]2- would be stable if it could be accessed synthetically, at only 23 kcal.mol-1 in energy above the classical trans dioxo. Calculations for the transuranic cis[AnO2(TC4A)]2- (An=Np, Pu) are at higher energies, 30-35 kcal.mol-1, retaining the U complexes as the more obvious target for a cis-dioxo actinyl ion. The aryloxide (OAr) groups of the macrocycle are essential in stabilizing this as-yet unseen uranyl geometry as further bonding in the TC4A U-OAr groups stabilizes the U=O 'yl' bonds, explaining the stability of the putative cis[UO2(TC4A)]2- in this ligand framework.

Pyrch, Mikaela M↗
DOE OSTI2025

A new HALEU isotopic certified reference material

Candidate certified reference material (CRM) U196 was prepared by gravimetrically mixing and dissolving NNSA NRMP CRM 112-A (natural uranium metal) and CRM 116-A (highly enriched 93.2% 235 U metal) to achieve a high-assay low-enriched uranium (HALEU) isotopic abundance reference material. CRM U196 will be certified for the 233 U/ 238 U, 234 U/ 238 U, 235 U/ 238 U, and 236 U/ 238 U ratios. Gravimetrically determined uranium isotope amount ratios and values derived from the isotope data were calculated from the buoyancy corrected mass data and from certified values for the metal CRMs used to create the solution. The 235 U isotope amount fraction (·100) and expanded uncertainty is 19.5846 ± 0.0028. For attribute verification, total evaporation and modified total evaporation isotope ratio measurements were performed. In conclusion, the reference material is to be distributed as a unit containing 5 mg uranium as dry uranyl nitrate.

High-assay low-enriched uranium↗
DOE OSTI2023

On silica's roles in controlling americium migration in contaminated sediments

Two studies in the early 1980s described the leaching behavior of americium (Am) disposed as part of acidic high-salt processing wastes from the Hanford Site’s Plutonium Finishing Plant to nearby ground sediments. Here these batch leach experiments showed that the Am concentrations followed a linear log [Am] versus pH relationship with a slope of –1. Column leach experiments in the second study, however, did not follow this relationship and only ~30% of the americium desorbed even after extensive column leaching. Here, the 1980s research is re-examined along with previously unpublished information and, in light of recent published work, a plausible mechanism is proposed to explain these phenomena. Amorphous silica in the contaminated sediments is postulated to be the substrate responsible for both the exchangeable Am available for leaching and the retained low-leachable Am made evident in the column leach experiments. The exchangeable Am 3+ in the contaminated sediment leach experiments behaves with pH dependence similar to that observed for uptake onto amorphous silica of sodium (Na + ), calcium (Ca 2+ ), barium (Ba 2+ ), cadmium (Cd 2+ ), uranyl (UO 2 2+ ), ferric (Fe 3+ ), chromic (Cr 3+ ), cupric (Cu 2+ ), plumbous (Pb 2+ ), uranium(IV) (U 4+ ), plutonium(IV) (Pu 4+ ), zirconium (Zr 4+ ), analogue lanthanide (gadolinium, Gd 3+ , europium, Eu 3+ , and lutetium, Lu 3+ ) and curium (Cm 3+ ) ions as well as other studies with Am 3+ . Correspondingly, the residual low-leachable Am 3+ revealed in the column leach experiments is attributed to incorporation of Am 3+ within amorphous silica by dynamic Am 3+ sorption and silica precipitation processes.

58 GEOSCIENCES↗
DOE OSTI2022

Irradiation-induced amorphization of UO 2 films prepared by spraying-assisted combustion synthesis

Spraying-assisted combustion synthesis with uranyl nitrate – acetylacetone – 2-methoxyethanol solutions was used to prepare UO 2 films on an aluminum alloy substrate. The tuning of the spraying parameters and annealing temperatures allowed the preparation of UO 2 films with thicknesses varying from 10–300 nm and 5–10 nm UO 2 grain size. High-resolution electron microscopy and X-ray photoelectron spectroscopy showed that increasing the annealing temperature promotes Mg diffusion from the substrate into the films. The incorporation of Mg reduced the overall crystallinity of the films. The irradiation with Ar 2+ ions (1.7 MeV energy and a fluence of 2 × 10 16 ions/cm 2 ) did not degrade the quality of the films. However, the Mg content significantly influenced the irradiation-induced restructuring of the UO 2 films. Irradiated films with low or no Mg content exhibit high crystallinity, and the UO 2 /Al interfacial layer becomes highly porous. Films with higher Mg content are mostly amorphized after irradiation. The origin of irradiation-induced amorphization was related to the formation of Mg y U 1-y O 2±x solid solutions. Chemically complex, pore-free, and amorphous Mg-Al-O film/substrate interfacial layers enable continuous Mg diffusion during irradiation. As a result, the gradual increase in Mg amounts triggers irradiation-induced precipitation of a crystalline MgO-rich phase within the amorphous films.

38 RADIATION CHEMISTRY, RADIOCHEMISTRY, AND NUCLEA↗
DOE OSTI2022

Spectroscopic investigation of historical uranium glasses

Here, we present spectroscopic investigations of uranium in two historical glasses. A 1920's-1930's Art Deco (Bagley Carnival) green soda-lime-silica uranium glass bowl and a 1930's-1940's (Thomas Webb) yellow full lead crystal uranium glass vase were studied using optical absorption spectroscopy, XRF and SEM-EDX, X-band EPR and High- Energy Resolution Fluorescence-Detected (HERFD)-XANES. Uranium speciation may be different in the two glasses. Uranium occurs as uranyl groups (UO 2 2+ ) with minority reduced uranium species, mostly as U(V), more important in the Webb glass than in the Bagley glass. The differences between the two glasses arise from the fining procedure and result from the presence of other multivalent elements and differences in base glass composition. Electron Paramagnetic Resonance (EPR) spectra show the presence of an incipient signal close to g~2, partially annealed by heating to 550 °C, which we assign to a small concentration of radiation-induced defects caused by uranium decay. The presence of multivalent glass components in addition to U (As + Cu + Fe in the Bagley glass and Sb + Fe in the Webb glass) can trap the electron-hole pairs generated by the presence of uranium. This may explain the weakness of this signal in these glasses that anyway received a limited radiation dose since their fabrication. The low activity of these glasses, close to the background radiation, confirms that there is no danger to exhibiting them in museums.

36 MATERIALS SCIENCE↗
DOE OSTI2026

Predicting U 3 O 8 powder processing conditions: An AI/ML approach analyzing deep learning embeddings of SEM micrographs

High-resolution SEM images of uranium-oxide powders encode micro- and nanoscale clues to their synthesis route and calcination temperature. We trained a ResNet-50 model on 11 commercial-scale U₃O₈ classes, ammonium diuranate (ADU) or uranyl peroxide (H₂O₂) precursors calcined at temperatures ranging from 400 to 750 °C and added a 256-D projection head before the classifier to analyze the learned representation. The best of eight seeds reached 92.4 % accuracy on reserved testing data, but our focus is the structure of the embedding space rather than the accuracy and labels. We quantify class relatedness in the original 256-D space using centroid similarity and distributional distances, and we use Uniform Manifold Approximation Projection (UMAP) for visualization. ‘Unknown’ images from different preparation methods, SEM operators, and from the literature localized near the expected classes under a nearest-centroid analysis without retraining, as well as clustered in similar UMAP space. In conclusion, this embedding-centered workflow complements black-box classification by providing quantitative, similarity-based comparisons of U₃O₈ morphologies and reduces storage space by up to 98 % for image data used in millisecond vector search comparisons.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Uranium(VI) attenuation in a carbonate-bearing oxic alluvial aquifer

Uranium minerals are commonly found in soils and sediment across the United States at an average concentration of 2–4 mg/kg. Uranium occurs in the environment primarily in two forms, the oxidized, mostly soluble uranium(VI) form, or the reduced, sparingly soluble reduced uranium(IV) form. Here we describe subsurface geochemical conditions that result in low uranium concentrations in an alluvial aquifer with naturally occurring uranium in soils and sediments in the presence of complexing ligands under oxidizing conditions. Groundwater was saturated with respect to calcite and contained calcium (78–90 mg/L) with elevated levels of carbonate alkalinity (291–416 mg/L as HCO 3 -). X-ray adsorption near edge structure (XANES) spectroscopy identified that sediment-associated uranium was oxidized as a uranium(VI) form (85%). Calcite was the predominant mineral by mass in the ultrafine fraction in uranium-bearing sediments (>16 mg/kg). Furthermore, groundwater geochemical modeling indicated calcite and/or a calcium-uranyl-carbonate mineral such as liebigite in equilibrium with groundwater. The δ 13 C (0.57‰ ± 0.15‰) was indicative of abiotic carbonate deposition. Thus, solid-phase uranium(VI) associated with carbonate is likely maintaining uranium(VI) groundwater levels below the maximum contaminant level (MCL; 30 µg/L), presenting a deposition mechanism for uranium attenuation rather than solely a means of mobilization.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2023

Accumulation mechanisms for contaminants on weak-base hybrid ion exchange resins

Mechanism of hexavalent chromium removal (Cr(VI) as CrO 4 2- ) by the weak-base ion exchange (IX) resin ResinTech® SIR-700-HP (SIR-700) from simulated groundwater is assessed in the presence of radioactive contaminants iodine-129 (as IO 3 - ), uranium (U as uranyl UO 2 2+ ), and technetium-99 (as TcO 4 - ), and common environmental anions sulfate (SO 4 2- ) and chloride (Cl-). Batch tests using the acid sulfate form of SIR-700 demonstrated Cr(VI) and U(VI) removal exceeded 97%, except in the presence of high SO 4 2- concentrations (536 mg/L) where Cr(VI) and U(VI) removal decreased to ≥ 80%. However, Cr(VI) removal notably improved with co-mingled U(VI) that complexes with SO 4 2- at the protonated amine sites. These U–SO 4 2- complexes are integral to U(VI) removal, as confirmed by the decrease in U(VI) removal (<40%) when the acid chloride form of SIR-700 was used instead. Solid phase characterization revealed that CrO 4 2- is removed by IX with SO 4 2- complexes and/or reduced to amorphous Cr(III)(OH) 3 at secondary alcohol sites. Tc(VII)O 4 - and I(V)O 3 - also undergo chemical reduction, following a similar removal mechanism. Oxyanion removal preference is determined by the anion reduction potential (CrO 4 2 - >TcO 4 - >IO 3 - ), geometry, and charge density. For these reasons, 39% and 69% of TcO 4 - and 17% and 39% of IO 3 - are removed in the presence and absence of Cr(VI), respectively.

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

Coupling geophysical, geological, geochemical and mineralogical assessments to examine preferential contaminant transport pathways in interbedded fractured bedrock

This study shows that a multi-faceted approach, combining borehole geophysical logging and surface seismic P-wave first-arrival tomography with confirmatory coring, well installation, and chemical and mineralogical analysis, is effective for identifying difficult-to-locate preferential contaminant transport pathways in deeper fractured bedrock. Seismic tomography detected porous 10–20 m wide elongated fractured conduits that allow acidic groundwater contaminated with uranium (U) and nitrate (NO 3 - ) to migrate within interbedded shale-limestone bedrock over 1000 m from a former disposal facility (S-3 Ponds site) located at the DOE Y-12 National Security Complex in Tennessee (USA). Conventional drilling techniques would easily miss these conduits because they are oriented parallel with fractured bedding planes. Synchrotron analysis of aquifer solids revealed that > 95 % of the U is hexavalent (U VI ). This uranyl (UO 2 2+ ) species is coordinated with carbonate, iron oxide, silicate and phosphate minerals within cemented white to yellow precipitates, which contain U concentrations as high as ∼21.6 % by weight fraction. Identifying the presence of these mineral phases, enables a further understanding of the potential effectiveness of remediation actions. The combination of methodologies presented here can also be applied to other explorations, such as the detection of water supply.

Fate and transport↗
DOE OSTI2024

Optical vibrational spectroscopic signatures related to U 3 O 8 production processes

Uranium ore concentrates are materials found early within the nuclear fuel cycle and contain high concentrations of uranium in an easily transported form, making the concentrates a likely target for illegal diversion. These concentrates are typically converted to U 3 O 8 for further processing and, therefore, may lose specific physicochemical characteristics in determining the materials’ source and processing history. In this work, we explore the Raman spectra of eight oxide samples produced from various uranium ore concentrates and processing pathways to examine the presence of spectroscopic signatures relating to each sample's process history. Samples produced from amine extraction and dialkylphosphoric acid extraction processes show unique characteristics due to high concentrations of α-UO 3 , whereas samples calcinated from metallic diuranates do not form pure α-U 3 O 8 because of metallic ion inclusions. Pure α-U 3 O 8 oxide samples are obtained through calcination of ammonium diuranate, ammonium uranyl carbonate, and metastudtite intermediates. The Raman spectra of these oxide samples show close agreement with pristine α-U 3 O 8 spectra. However, deviations from the pristine spectra are observed in the 300–460 cm -1 spectral range. In conclusion, these deviations are unique identifying signatures that were likely created by lasting effects from the process history. Spectral center of mass calculations indicate grouping of samples based on processing history.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2025

Rehydration of metastudtite in the alteration kinetics of α– and β–U 3 O 8 in dilute aqueous solutions of hydrogen peroxide

The formation of alteration phases on uranium ore concentrates and used nuclear fuels under oxidizing conditions is key to understanding the potential mobility of radionuclides in the environment and designing optimal storage conditions of materials. However, the time-dependent distribution of alteration phases on α– and β–U 3 O 8 under oxidizing conditions has yet to be explored. Here, in this study, crystalline powders of α– and β–U 3 O 8 were submerged in aqueous solutions of hydrogen peroxide (1.6 × 10 −1 to 5.4 × 10 −5 M) with aliquots of solution and solid removed for analysis at 1, 8, 15, 22, 29, 36, 46, 58, 71, and 83 days. Within one day there is significant alteration of U 3 O 8 to the uranyl peroxide metastudtite, [(UO 2 )(O 2 )(H 2 O) 2 ], that is replaced by studtite, [(UO 2 )(O 2 )(H 2 O) 2 ]·2H 2 O, within a week regardless of the polymorph of U 3 O 8 or the initial concentration of H 2 O 2 in solution, as determined by partial least squares regression (PLSR) of Raman spectra collected from the solids. A dissolution/reprecipitation mechanism is proposed for both the alteration of U 3 O 8 to metastudtite and the subsequent alteration of both U 3 O 8 and metastudtite to studtite. The two polymorphs of U 3 O 8 exhibit similar rates and extents of alteration over time. The rehydration of metastudtite to studtite has not been previously reported and highlights the need for future work to determine the mechanism by which metastudtite is converted to studtite and what other conditions facilitate this rehydration.

Alteration of U3O8↗
DOE OSTI2023

Advancing Elemental and Isotopic Analysis of Uranium Mineral Inclusions: Rapid Screening via Laser-Induced Breakdown Spectroscopy and High-Resolution Laser Ablation-ICP-MS Mapping

The work presented herein employs two laser-based analytical techniques (laser-induced breakdown spectroscopy (LIBS) and laser ablation – inductively coupled plasma – mass spectrometry (LA-ICP-MS)) to spatially determine the elemental and isotopic composition of uranium bearing minerals. Uniquely, this work leverages the high-speed applicability of LIBS to “screen” the sample(s) for their elemental constituents. After determining the location of the uranium inclusions (via LIBS), high-resolution LA-ICP-MS was employed to further characterize the inclusions. The high-resolution (sub-µm) capabilities of LA-ICP-MS were able to extract important information from the uranium minerals including discerning its chemical form (e.g., finchite from carnotite, Sr- and K-bearing uranyl vanadates, respectively) as well as their 235 U/ 238 U isotopic composition. This approach, LIBS followed by LA-ICP-MS, significantly reduces the analysis time (~95 %) in comparison to employing a LA-ICP-MS only approach. Furthermore, this work presented a novel approach to analyzing inclusions via a particle/inclusion analysis tool which is commercially available within the iolite 4 software. This tool allowed for a more accurate characterization of the isotopic distribution of the inclusions, as well as allowing for rapid sizing of the inclusions. Finally, this analytical approach could readily be applied to other sample types in which the target species (e.g., µm-sized inclusions) are embedded in complex matrices (e.g., cm-sized samples).

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2024

Absolute Branching Ratios of Prominent $γ$ Rays Following $α$ Decay of 233 U

The absolute $γ$-ray branching ratios (emission probabilities) for 19 prominent peaks in the $α$ decay of 233 U are reported with energies ranging from 97 to 366 keV. The branching ratios were obtained from $α-γ$ coincidence measurements, normalized to the $α$ singles. The high-purity 233 U material (> 99.98%) was separated from its decay products before preparation of a 4.74-mg/cm 2 uranyl nitrate foil with a 6-mm diameter. Furthermore, this is the first report on the absolute normalization of the branching ratios since 1984 and it is the only measure by $α-γ$ coincidences, where the $α-γ/α$ ratio removes several potential systematic biases. Overall, the results are consistent with the adopted literature, and they validate the quantities most relevant to the non-destructive assay of fissile 233 U material, which is relevant to the thorium fuel cycle and associated safeguards.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2020

Effect of Bicarbonate, Calcium, and pH on the Reactivity of As(V) and U(VI) Mixtures

Natural or anthropogenic processes can increase the concentration of uranium (U) and arsenic (As) above the maximum contaminant levels in water sources. Bicarbonate and calcium (Ca) can have major impacts on U speciation and can affect the reactivity between U and As. We therefore investigated the reactivity of aqueous U and As mixtures with bicarbonate and Ca for acidic and neutral pH conditions. In experiments performed with 1 mM U and As mixtures, 10 mM Ca, and without added bicarbonate (pCO 2 = 3.5), aqueous U decreased to <0.25 mM at pH 3 and 7. Aqueous As decreased the most at pH 3 (~0.125 mM). Experiments initiated with 0.005 mM As and U showed similar trends. X-ray spectroscopy (i.e., XAS and EDX) and diffraction indicated that U-As-Ca- and U-Ca-bearing solids resemble uranospinite [Ca(UO 2 ) 2 (AsO 4 ) 2 ·10H 2 O] and becquerelite [Ca(UO 2 ) 6 O 4 (OH) 6 ·8(H 2 O)]. These findings suggest that U-As-Ca-bearing solids formed in mixed solutions are stable at pH 3. However, the dissolution of U-As-Ca and U-Ca-bearing solids at pH 7 was observed in reactors containing 10 mM bicarbonate and Ca, suggesting a kinetic reaction of aqueous uranyl-calcium-carbonate complexation. Our study provides new insights regarding U and As mobilization for risk assessment and remediation strategies.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2020

Computationally Guided Investigation of the Optical Spectra of Pure β-UO 3

Single-phase β-UO 3 is synthesized by flash heating UO 2 (NO 3 )·6H 2 O in air to 450 °C and annealing for 60 h under the same conditions. For the first time, we report the Raman spectra of pure β-UO 3 . To facilitate the assignment of Raman and infrared vibrational modes, we use density functional theory with density functional perturbation theory. By employing a novel analysis scheme that includes the mode frequencies as well as a quantitative analysis of the mode eigenvectors, we assign the observed spectral features to individual chemical modes. In particular, the density functional theory optimized structure, observed Raman spectrum, and eigenvector analysis suggest the presence of four crystallographically distinct uranyl ions, one more than has previously been suggested.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

Periodic Trends within Actinyl(VI) Nitrates and Their Structures, Vibrational Spectra, and Electronic Properties

In this work, a series of actinyl(VI) nitrate salts of the form MAnO 2 (NO 3 ) 3 , where M = NH 4 + K + , Rb + , Cs + , and Me 4 N + and AnO 2 2+ = U, Np, Pu, and AnO 2 (NO 3 ) 2 (H 2 O) 2 ·H 2 O, and the uranyl tetranitrates M 2 UO 2 (NO 3 ) 4 have been synthesized from aqueous solution and their structures determined using single-crystal X-ray diffraction. Together, these complexes represent an isostructural series of actinide complexes among the salts crystallized with the same charge-compensating cation and have been studied using vibrational spectroscopy including Raman and Fourier-transform infrared. Periodic trends in both the structural properties of these complexes and their vibrational spectra are presented and discussed, in particular the invariant nature of the O≡An≡O asymmetric stretching frequencies observed across the actinyl series. Electronic structure calculations were performed at a variety of levels of theory to aid in the interpretation of the vibrational data and to correlate trends in the data with the underlying electronic properties of these molecules.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗