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At least 145 records · Page 8
All sourcesNASA NTRSDOE OSTI
DOE OSTI2024

Evaluation of Sb-Nd and Te-Nd phases within the U-Zr fuel matrix and their interactions with HT9 alloy

Antimony (Sb) and tellurium (Te) were investigated as potential additives for U-10Zr (wt.%) metallic fuel to limit the fuel-cladding chemical interaction (FCCI) with HT-9 alloy. Neodymium (Nd) was utilized to simulate the formation of lanthanide-based solid fission products which are known to play a detrimental role in FCCI. Fuel alloys of U-Zr-Sb-Nd and U-Zr-Te-Nd were evaluated in their annealed condition and compared against their as-cast conditions. Isothermal diffusion couple experiments were performed between U-Zr-Nd, U-Zr-Sb-Nd, and U-Zr-Te-Nd against the cladding alloy HT9 to evaluate the effectiveness of the additives to stabilize Nd within the fuel alloys, as well as investigate the interaction regions that form between the different fuel alloys and HT9. Further, SbNd and Sb 3 Nd 4 , and TeNd are found to be the primary neodymium-based phases formed in the U-Zr-Sb-Nd and U-Zr-Te-Nd alloys, respectively. The zirconium-based phase, Zr 2 Sb, is also found to form within the former alloy. All phases were found to remain stable through the diffusion experiments and exhibited no interaction with HT9 constituent elements. Preferential interaction between Nd with additivities Te and Sb compared to constituting elements in HT9 was further verified based on density functional theory (DFT) calculated enthalpy of mixing.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2020

Materials Data on U(Cr3P2)2 by Materials Project

U(Cr3P2)2 crystallizes in the orthorhombic Pmmn space group. The structure is three-dimensional. U is bonded to six Cr and six P atoms to form distorted UCr6P6 cuboctahedra that share corners with four equivalent CrU2P4 tetrahedra, edges with eight CrU2P4 tetrahedra, and faces with two equivalent UCr6P6 cuboctahedra. There are two shorter (2.97 Å) and four longer (3.01 Å) U–Cr bond lengths. There are four shorter (2.84 Å) and two longer (2.87 Å) U–P bond lengths. There are four inequivalent Cr sites. In the first Cr site, Cr is bonded to two equivalent U and four P atoms to form distorted CrU2P4 tetrahedra that share corners with two equivalent UCr6P6 cuboctahedra, corners with ten CrU2P4 tetrahedra, edges with three equivalent UCr6P6 cuboctahedra, edges with five equivalent CrU2P4 tetrahedra, and faces with two CrU2P4 tetrahedra. There are a spread of Cr–P bond distances ranging from 2.33–2.35 Å. In the second Cr site, Cr is bonded in a 5-coordinate geometry to five P atoms. There are a spread of Cr–P bond distances ranging from 2.39–2.41 Å. In the third Cr site, Cr is bonded to two equivalent U and four P atoms to form distorted CrU2P4 tetrahedra that share corners with four equivalent CrU2P4 tetrahedra, edges with two equivalent UCr6P6 cuboctahedra, edges with two equivalent CrU2P4 tetrahedra, and faces with two equivalent CrU2P4 tetrahedra. There are two shorter (2.31 Å) and two longer (2.35 Å) Cr–P bond lengths. In the fourth Cr site, Cr is bonded in a 5-coordinate geometry to five P atoms. There are four shorter (2.39 Å) and one longer (2.48 Å) Cr–P bond lengths. There are three inequivalent P sites. In the first P site, P is bonded in a 8-coordinate geometry to eight Cr atoms. In the second P site, P is bonded in a 8-coordinate geometry to two equivalent U and six Cr atoms. In the third P site, P is bonded in a 9-coordinate geometry to two equivalent U and seven Cr atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on U(GaFe)6 by Materials Project

UFe6Ga6 crystallizes in the orthorhombic Immm space group. The structure is three-dimensional. U is bonded in a 8-coordinate geometry to twelve Fe and eight Ga atoms. There are four shorter (3.19 Å) and eight longer (3.28 Å) U–Fe bond lengths. There are a spread of U–Ga bond distances ranging from 2.90–3.03 Å. There are two inequivalent Fe sites. In the first Fe site, Fe is bonded to two equivalent U, four Fe, and six Ga atoms to form a mixture of distorted corner, edge, and face-sharing FeU2Ga6Fe4 cuboctahedra. There are two shorter (2.51 Å) and two longer (2.52 Å) Fe–Fe bond lengths. There are a spread of Fe–Ga bond distances ranging from 2.50–2.63 Å. In the second Fe site, Fe is bonded to two equivalent U, four equivalent Fe, and six Ga atoms to form a mixture of distorted corner, edge, and face-sharing FeU2Ga6Fe4 cuboctahedra. There are a spread of Fe–Ga bond distances ranging from 2.60–2.67 Å. There are three inequivalent Ga sites. In the first Ga site, Ga is bonded in a 10-coordinate geometry to one U, six Fe, and three Ga atoms. There are one shorter (2.65 Å) and two longer (2.84 Å) Ga–Ga bond lengths. In the second Ga site, Ga is bonded in a 12-coordinate geometry to two equivalent U, six Fe, and four Ga atoms. Both Ga–Ga bond lengths are 2.98 Å. In the third Ga site, Ga is bonded in a 8-coordinate geometry to one U, six Fe, and three Ga atoms. The Ga–Ga bond length is 2.65 Å.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on U(GePt)2 by Materials Project

U(PtGe)2 crystallizes in the tetragonal P4/nmm space group. The structure is three-dimensional. U is bonded in a 12-coordinate geometry to eight Pt and eight Ge atoms. There are four shorter (3.28 Å) and four longer (3.33 Å) U–Pt bond lengths. There are four shorter (3.26 Å) and four longer (3.33 Å) U–Ge bond lengths. There are two inequivalent Pt sites. In the first Pt site, Pt is bonded to four equivalent U and four equivalent Ge atoms to form distorted PtU4Ge4 tetrahedra that share corners with twelve equivalent GeU4Pt4 tetrahedra, edges with two equivalent GeU4Pt4 tetrahedra, edges with four equivalent PtU4Ge4 tetrahedra, and faces with four equivalent PtU4Ge4 tetrahedra. All Pt–Ge bond lengths are 2.55 Å. In the second Pt site, Pt is bonded in a 9-coordinate geometry to four equivalent U and five Ge atoms. There are one shorter (2.41 Å) and four longer (2.51 Å) Pt–Ge bond lengths. There are two inequivalent Ge sites. In the first Ge site, Ge is bonded to four equivalent U and four equivalent Pt atoms to form distorted GeU4Pt4 tetrahedra that share corners with twelve equivalent PtU4Ge4 tetrahedra, edges with two equivalent PtU4Ge4 tetrahedra, edges with four equivalent GeU4Pt4 tetrahedra, and faces with four equivalent GeU4Pt4 tetrahedra. In the second Ge site, Ge is bonded in a 9-coordinate geometry to four equivalent U and five Pt atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on U(SiNi5)2 by Materials Project

UNi10Si2 crystallizes in the orthorhombic Immm space group. The structure is three-dimensional. U is bonded in a 8-coordinate geometry to sixteen Ni and four equivalent Si atoms. There are a spread of U–Ni bond distances ranging from 2.67–3.09 Å. All U–Si bond lengths are 3.16 Å. There are four inequivalent Ni sites. In the first Ni site, Ni is bonded in a 8-coordinate geometry to one U, eleven Ni, and two equivalent Si atoms. There are a spread of Ni–Ni bond distances ranging from 2.42–2.96 Å. Both Ni–Si bond lengths are 2.54 Å. In the second Ni site, Ni is bonded in a 1-coordinate geometry to one U, eleven Ni, and two equivalent Si atoms. There are a spread of Ni–Ni bond distances ranging from 2.48–2.71 Å. Both Ni–Si bond lengths are 2.40 Å. In the third Ni site, Ni is bonded in a 2-coordinate geometry to two equivalent U, nine Ni, and two equivalent Si atoms. There are four shorter (2.44 Å) and one longer (2.83 Å) Ni–Ni bond lengths. Both Ni–Si bond lengths are 2.50 Å. In the fourth Ni site, Ni is bonded to two equivalent U, eight Ni, and two equivalent Si atoms to form distorted NiU2Si2Ni8 cuboctahedra that share corners with four equivalent SiU2Ni10 cuboctahedra, corners with ten equivalent NiU2Si2Ni8 cuboctahedra, edges with two equivalent SiU2Ni10 cuboctahedra, edges with four equivalent NiU2Si2Ni8 cuboctahedra, faces with four equivalent SiU2Ni10 cuboctahedra, and faces with six equivalent NiU2Si2Ni8 cuboctahedra. Both Ni–Ni bond lengths are 2.40 Å. Both Ni–Si bond lengths are 2.30 Å. Si is bonded to two equivalent U and ten Ni atoms to form distorted SiU2Ni10 cuboctahedra that share corners with six equivalent SiU2Ni10 cuboctahedra, corners with eight equivalent NiU2Si2Ni8 cuboctahedra, edges with three equivalent SiU2Ni10 cuboctahedra, edges with four equivalent NiU2Si2Ni8 cuboctahedra, a faceface with one SiU2Ni10 cuboctahedra, and faces with eight equivalent NiU2Si2Ni8 cuboctahedra.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on U(Fe5Si)2 by Materials Project

UFe10Si2 crystallizes in the orthorhombic Immm space group. The structure is three-dimensional. U is bonded in a 12-coordinate geometry to sixteen Fe and four equivalent Si atoms. There are a spread of U–Fe bond distances ranging from 2.85–3.17 Å. All U–Si bond lengths are 3.09 Å. There are four inequivalent Fe sites. In the first Fe site, Fe is bonded in a 8-coordinate geometry to one U, eleven Fe, and two equivalent Si atoms. There are a spread of Fe–Fe bond distances ranging from 2.38–2.91 Å. Both Fe–Si bond lengths are 2.58 Å. In the second Fe site, Fe is bonded in a 10-coordinate geometry to one U, eleven Fe, and two equivalent Si atoms. There are a spread of Fe–Fe bond distances ranging from 2.44–2.68 Å. Both Fe–Si bond lengths are 2.54 Å. In the third Fe site, Fe is bonded in a 12-coordinate geometry to two equivalent U, eight Fe, and two equivalent Si atoms. All Fe–Fe bond lengths are 2.46 Å. Both Fe–Si bond lengths are 2.56 Å. In the fourth Fe site, Fe is bonded to two equivalent U, eight Fe, and two equivalent Si atoms to form a mixture of distorted corner, edge, and face-sharing FeU2Fe8Si2 cuboctahedra. Both Fe–Fe bond lengths are 2.36 Å. Both Fe–Si bond lengths are 2.36 Å. Si is bonded in a 12-coordinate geometry to two equivalent U and ten Fe atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on U(AlFe)6 by Materials Project

UFe6Al6 crystallizes in the orthorhombic Immm space group. The structure is three-dimensional. U is bonded in a 12-coordinate geometry to twelve Fe and eight Al atoms. There are four shorter (3.16 Å) and eight longer (3.28 Å) U–Fe bond lengths. There are a spread of U–Al bond distances ranging from 2.91–3.02 Å. There are two inequivalent Fe sites. In the first Fe site, Fe is bonded in a 12-coordinate geometry to two equivalent U, four Fe, and six Al atoms. There are two shorter (2.47 Å) and two longer (2.50 Å) Fe–Fe bond lengths. There are two shorter (2.50 Å) and four longer (2.61 Å) Fe–Al bond lengths. In the second Fe site, Fe is bonded to two equivalent U, four equivalent Fe, and six Al atoms to form a mixture of distorted corner, edge, and face-sharing FeU2Al6Fe4 cuboctahedra. There are two shorter (2.62 Å) and four longer (2.64 Å) Fe–Al bond lengths. There are three inequivalent Al sites. In the first Al site, Al is bonded in a 10-coordinate geometry to one U, six Fe, and three Al atoms. There are one shorter (2.62 Å) and two longer (2.79 Å) Al–Al bond lengths. In the second Al site, Al is bonded in a 8-coordinate geometry to one U, six Fe, and three Al atoms. There are one shorter (2.69 Å) and two longer (2.93 Å) Al–Al bond lengths. In the third Al site, Al is bonded in a 12-coordinate geometry to two equivalent U, six Fe, and four Al atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on U(Al3Fe)3 by Materials Project

UFe3Al9 crystallizes in the monoclinic C2/m space group. The structure is three-dimensional. U is bonded in a 12-coordinate geometry to six Fe and fourteen Al atoms. There are four shorter (3.36 Å) and two longer (3.37 Å) U–Fe bond lengths. There are a spread of U–Al bond distances ranging from 3.05–3.35 Å. There are two inequivalent Fe sites. In the first Fe site, Fe is bonded in a 10-coordinate geometry to two equivalent U and ten Al atoms. There are a spread of Fe–Al bond distances ranging from 2.53–2.71 Å. In the second Fe site, Fe is bonded in a 12-coordinate geometry to two equivalent U, two equivalent Fe, and eight Al atoms. Both Fe–Fe bond lengths are 2.53 Å. There are a spread of Fe–Al bond distances ranging from 2.50–2.65 Å. There are three inequivalent Al sites. In the first Al site, Al is bonded in a 12-coordinate geometry to two equivalent U, three Fe, and seven Al atoms. There are a spread of Al–Al bond distances ranging from 2.62–2.91 Å. In the second Al site, Al is bonded in a 10-coordinate geometry to one U, three Fe, and six Al atoms. There are one shorter (2.72 Å) and one longer (2.75 Å) Al–Al bond lengths. In the third Al site, Al is bonded in a 2-coordinate geometry to two equivalent U, two equivalent Fe, and eight Al atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Anionic G•U pairs in bacterial ribosomal rRNAs

Wobble GU pairs (or G•U) occur frequently within double-stranded RNA helices interspersed between standard G=C and A-U Watson–Crick pairs. Another type of G•U pair interacting via their Watson–Crick edges has been observed in the A site of ribosome structures between a modified U34 in the tRNA anticodon triplet and G + 3 in the mRNA. In such pairs, the electronic structure of the U is changed with a negative charge on N3(U), resulting in two H-bonds between N1(G)…O4(U) and N2(G)…N3(U). Here, we report that such pairs occur in other highly conserved positions in ribosomal RNAs of bacteria in the absence of U modification. An anionic cis Watson–Crick G•G pair is also observed and well conserved in the small subunit. These pairs are observed in tightly folded regions.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2022

U–Pb Geochronology and Stable Isotope Geochemistry of Terrestrial Carbonates, Lower Cretaceous Cedar Mountain Formation, Utah: Implications for Synchronicity of Terrestrial and Marine Carbon Isotope Excursions

The terrestrial Lower Cretaceous Cedar Mountain Formation, Utah, is a critical archive of paleoclimate, tectonics, and vertebrate ecology and evolution. Early Cretaceous carbon cycle perturbations associated with ocean anoxia have been interpreted from this succession, as expressed in stable carbon isotopes. However, refining the timing of the observed stable isotope excursions remains a key challenge in understanding how marine anoxia affects the Earth system, and is ultimately recorded in the terrestrial realm. The geochronology and geochemistry of a terrestrial carbonate near the base of this succession, which potentially records the Ap7 global carbon isotope excursion, is studied here. Petrographic and geochemical analyses are used to test plausible mechanisms for U incorporation into the calcite lattice in this sample. Using these methods, the hypothesis that the incorporation of U was at or close to the timing of carbonate precipitation is evaluated. U–Pb geochronology of calcite indicates a plausible Early Cretaceous age. However, comparison of the new U–Pb ages of calcite with detrital zircon maximum depositional ages immediately beneath the studied sample indicates a disparity in the apparent sedimentation rates if both types of geochronologic information are interpreted as reflecting the timing of sediment deposition. The totality of data supports an early, and high-temperature, diagenetic timing of U incorporation, with potential for minor leaching of U in subsequent fluid–rock interaction. The most likely mechanism for U transport and immobilization in these samples is hydrothermal fluid–rock interaction. Therefore, the radiometric ages, and corresponding stable isotope composition of U-bearing carbonate domains in this sample, indicate early subsurface fluid–rock interactions and not a record of atmosphere–soil geochemical reactions.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Understanding neutron capture processes in uranium deposits using combined U-Sm-Nd isotopic compositions

Valuable insights into the history and evolution of a geologic deposit can be found by investigating neutron capture reactions. Thermal neutron capture reactions occur within both the samarium (Sm) and the uranium (U) systems, where 149 Sm and 235 U can capture neutrons to become 150 Sm and 236 U, respectively. Although largely unexplored, paired measurements of 150 Sm and 236 U could be important for understanding neutron capture effects within uranium ore bodies, and such measurements are potentially useful in nuclear forensics for assessing a material's provenance or mineral exploration. In this work, we refined measurement procedures of Sm isotope compositions utilizing MC-ICPMS. While geologic reference materials were found to have indistinguishable Sm isotope compositions, we found significant isotope variations consistent with nuclear field shift among synthetic Sm standards. Here, this observation highlights that future high-precision Sm isotope investigations need to carefully evaluate synthetic standard(s) against geologic reference materials until an unfractionated and agreed-upon standard is identified. Here, we applied this method to a set of nine uranium ores from the South Australian Beverley North uranium deposits. Although 236 U excesses had been previously reported for these U ores, we found no measurable isotopic shifts in 149 Sm- 150 Sm at the current level of precision (±5 parts per million). One possible explanation for this disparity in the observed neutron capture signatures between U and Sm is that the source(s) of the U and Sm in these ores may be decoupled. This is consistent with the finding that these ores have variable 143 Nd/ 144 Nd, thus demonstrating that diverse sources were involved in the formation of the Beverley North deposits. Alternatively, this deposit may be too young (<50Ma) to have accumulated measurable neutron capture effects in Sm to be detected with the methods employed here.

Mineral exploration↗
DOE OSTI2023

The large decline in carbonate $\delta^{238}$U from a PETM section at Tingri (South Tibet) was driven by local sea-level changes, not global oceanic anoxia

Uranium isotope compositions (δ 238 ) and Th/U in carbonates are being explored as paleoredox proxies to study global oceanic anoxia. However, the impact of changes to local depositional environments that might cause a decline in δ 238 U and an increase in Th/U has not been thoroughly investigated. Here we report a decline in δ 238 U (from +0.1 to -0.3‰) and an increase in Th/U from shallow-marine carbonates during the Paleocene-Eocene thermal maximum at Tingri (south Tibet). Changes of δ 238 U and Th/U are not fully coupled. The decline in δ 238 U coincided with a local sea-level fall, whereas the increase in Th/U occurred mainly during a sea-level rise. The decline in δ 238 U likely results from changes in redox conditions of pore waters and in primary carbonate mineralogy. The increase in Th/U is ascribed to reduced authigenic U(IV) accumulation. Here our results suggest that changes in local depositional environments can cause behavior of δ 238 U and Th/U resembling that induced by expanded global oceanic anoxia. This finding calls for caution to consider local factors before applying δ 238 U and Th/U as global paleoredox proxies.

58 GEOSCIENCES↗
DOE OSTI2023

The impact of feedstock size and composition on the hydrothermal growth of (U,Th)O 2

Bulk crystal growth of refractory oxides requires unique approaches, and the U x Th 1-x O 2 solid solution is no exception. Hydrothermal transport reactions of U 0.1 Th 0.9 O 2 onto ThO 2 seeds with feedstocks comprised of U 0.1 Th 0.9 O 2 or mixtures of UO 2 and ThO 2 with a nominal composition of U 0.1 Th 0.9 O 2 are investigated with µ-Raman spectroscopy and X-ray fluorescence. In each case, the trends in stoichiometry as a function of distance from the seed are analyzed and the deviations from the nominal stoichiometry discussed. When the feedstock is composed of mixed oxides, the particle surface area’s influence on the feedstock dissolution rate is the dominant factor and can produce U-rich stoichiometries as high as U 0.75 Th 0.25 O 2 . When composed solely of U 0.1 Th 0.9 O 2 , the total growth amount depends on the particle size, but the obtained stoichiometry is the product of differing solubilities. Although the U0.1Th0.9O 2 feedstock produces the most homogeneous growth, the ending growth of the smallest particle UO 2 /ThO 2 mixture yields the stoichiometry closest to U 0.1 Th 0.9 O 2 . How to obtain desired stoichiometries from mixtures by matching the particle size and solubilities is briefly discussed.

36 MATERIALS SCIENCE↗
DOE OSTI2025

High resolution microstructural, chemical studies and localized burnup analysis in an irradiated U–10Zr metallic fuel

This study involves high resolution characterization of a sodium bonded solid uranium (U)-10 wt% zirconium (Zr) metallic fuel irradiated in Fast Flux Test Facility (FFTF). The fuel centerline temperature during irradiation was estimated to be around 675 °C with the peak burnup 13.1 atomic percent. Samples for transmission electron microscopy (TEM) and atom probe tomography (APT) were prepared from different regions/zones in the fuel cross section radially to elucidate the microstructural changes and chemical redistribution of solute elements as well as fission products during irradiation experiment. TEM results indicate the irradiation in fast flux testing leads to the formation of extensive Zr-rich precipitates with varying sizes in the U–Zr fuel matrix. APT analysis performed to investigate redistribution of Zr, U and fission products along the radial direction of fuel pin showed Zr-rich precipitates entrapping the fission products in higher concentration as compared to the α-U phases. Here, the local burnup ( 235 U depletion) is found to be consistent, calculated by quantification of 235 U, 236 U and 238 U isotopes from mass spectrum obtained from APT along the radial direction. Zr-rich precipitation and its implication on fuel constitutional redistribution are discussed based on SEM, TEM and APT results.

APT↗
DOE OSTI2026

Synthesis and Reactivity of Heteroleptic U 4+ Alkyl, Benzyl, and Hydride Imidophosphorane Complexes

A series of heteroleptic U 4+ benzyl, neopentyl, and methyl complexes supported by the imidophosphorane ligand, [N = P(N,N′-ditert-butylethylenediamide)(diethylamide)] 1− (NP*), were synthesized from the monoiodide precursor, [UI(NP*) 3 ]. These heteroleptic complexes were synthesized through the selective formation of [UI(NP*) 3 ] under transmetalation conditions in the reaction between [UI 4 (1,4-dioxane) 2 ] and K[NP*]. Formation of the homoleptic complex [U(NP*) 4 ] was not observed even in the presence of excess K[NP*]. The oxidation and hydrogenolysis reactivity of the neopentyl complex, [U(Npt)- (NP*) 3 ] (Npt = neopentyl) was explored. While cyclic voltammetry indicates a potentially isolable U5+ alkyl cation, chemical oxidation of the neopentyl complex results in the isolation of a cationic U 4+ complex with a bound diethyl ether in the primary coordination sphere, [U4+(NP*)) 3 (Et 2 O)][(BArF 24 )] (BArF 24 = tetrakis(3,5-bis(trifluoromethyl)phenyl)borate). Notably, hydrogenolysis of [U(Npt)(NP*) 3 ] with H2 gas at −20 °C results in the formation of a terminal hydride intermediate confirmed by in situ NMR spectroscopy and deuterium labeling with D 2 . The connectivity and structural parameters of this hydride intermediate, [UH(NP*) 3 ], which rapidly thermally decomposes to the homoleptic complex, [U(NP*) 4 ], can be confirmed by single-crystal X-ray diffraction studies of a crystal grown by chilling the reaction mixture. The identity of [U(NP*) 4 ] was confirmed by its direct, bulk synthesis from [U(Me)(NP*) 3 ] and HNP* in a protonolysis reaction.

Alkyls↗
DOE OSTI2021

Effect of Diel Cycling Temperature, Relative Humidity, and Synthetic Route on the Surface Morphology and Hydrolysis of α -U 3 O 8

The speciation and morphological changes of α-U 3 O 8 following aging under diel cycling temperature and relative humidity (RH) have been examined. This work advances the knowledge of U-oxide hydration as a result of synthetic route and environmental conditions, ultimately giving novel insight into nuclear material provenance. α-U 3 O 8 was synthesized via the washed uranyl peroxide (UO 4 ) and ammonium uranyl carbonate (AUC) synthetic routes to produce unaged starting materials with different morphologies. α-U 3 O 8 from UO 4 is comprised of subrounded particles, while α-U 3 O 8 from AUC contains blocky, porous particles approximately an order of magnitude larger than particles from UO 4 . For aging, a humidity chamber was programmed for continuous daily cycles of 12 “high” hours of 45 °C and 90% RH, and 12 “low” hours of 25 °C and 20% RH. Samples were analyzed at varying intervals of 14, 24, 36, 43, and 54 days. At each aging interval, crystallographic changes were measured via powder X-ray diffraction coupled with whole pattern fitting for quantitative analysis. Morphologic effects were studied via scanning electron microscopy and 12-way classification via machine learning. While all samples were found to have distinguishing morphologic characteristics (93.2% classification accuracy), α-U 3 O 8 from UO 4 had more apparent change with increasing aging time. Nonetheless, α-U 3 O 8 from AUC was found to hydrate more quickly than α-U 3 O 8 from UO 4 , which can likely be attributed to its larger surface area and porous starting material morphology.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2023

USc 2 C 2 and USc 2 NC Clusters with U–C Triple Bond Character Stabilized Inside Fullerene Cages

The chemistry of f-block metal–carbon multiple bonds is underdeveloped compared to well-established carbene complexes of the d-block transition metals. Herein, we report two new actinide-rare earth mixed metal carbides and nitrogen carbide cluster fullerenes, USc 2 C 2 @D 5h (6)-C 80 and USc 2 NC@D 5h (6)-C 80 , which contain U–C bonds with triple bond character and were successfully synthesized and characterized by mass spectrometry, UV–vis–NIR spectroscopy, Fourier transform infrared spectroscopy, single crystal X-ray diffraction, and DFT calculations. Crystallographic studies show that the two previously unreported clusters, USc 2 C 2 and USc 2 NC, are stabilized in the D 5h (6)-C 80 carbon cage and adopt unique trifoliate configurations, in which C 2 /NC units are almost vertically inserted into the plane defined by the U and two Sc atoms. Combined experimental and theoretical studies further reveal the bonding structure of USc 2 C 2 and USc 2 NC, which contain C=U(VI)=C and C=U(V)=N bonding motifs. The electronic structures of the two compounds are determined as U 6+ (Sc 2 ) 6+ (C 4– ) 2 @D 5h (6)-C 80 4– and U 5+ (Sc 2 ) 6+ (N) 3– (C) 4– @D 5h (6)-C 80 4– , respectively. Quantum-chemical studies confirm that the U–C bonds in both molecules show unprecedented multicenter triple-bond character. Furthermore, the discovery of this unique U–C multiple bond offers a deeper understanding of the fundamentals of uranium chemistry.

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

Accelerating phase field simulations through a hybrid adaptive Fourier neural operator with U-net backbone

Prolonged contact between a corrosive liquid and metal alloys can cause progressive dealloying. For one such process as liquid-metal dealloying (LMD), phase field models have been developed to understand the mechanisms leading to complex morphologies. However, the LMD governing equations in these models often involve coupled non-linear partial differential equations (PDE), which are challenging to solve numerically. In particular, numerical stiffness in the PDEs requires an extremely refined time step size (on the order of 10 -12 s or smaller). This computational bottleneck is especially problematic when running LMD simulation until a late time horizon is required. This motivates the development of surrogate models capable of leaping forward in time, by skipping several consecutive time steps at-once. In this paper, we propose a U-shaped adaptive Fourier neural operator (U-AFNO), a machine learning (ML) based model inspired by recent advances in neural operator learning. U-AFNO employs U-Nets for extracting and reconstructing local features within the physical fields, and passes the latent space through a vision transformer (ViT) implemented in the Fourier space (AFNO). We use U-AFNOs to learn the dynamics of mapping the field at a current time step into a later time step. We also identify global quantities of interest (QoI) describing the corrosion process (e.g., the deformation of the liquid-metal interface, lost metal, etc.) and show that our proposed U-AFNO model is able to accurately predict the field dynamics, in spite of the chaotic nature of LMD. Most notably, our model reproduces the key microstructure statistics and QoIs with a level of accuracy on par with the high-fidelity numerical solver, while achieving a significant 11, 200 × speed-up on a high-resolution grid when comparing the computational expense per time step. Finally, we also investigate the opportunity of using hybrid simulations, in which we alternate forward leaps in time using the U-AFNO with high-fidelity time stepping. We demonstrate that while advantageous for some surrogate model design choices, our proposed U-AFNO model in fully auto-regressive settings consistently outperforms hybrid schemes.

36 MATERIALS SCIENCE↗