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At least 163 records · Page 9
All sourcesNASA NTRSDOE OSTI
DOE OSTI2022

Oxidation kinetics of SPS-densified U 3 Si 2 fuels—Microstructure impact

Here, U 3 Si 2 is a potential candidate for accident tolerant fuels because of its high uranium density and excellent thermal conductivity in comparison to UO 2 . However, U 3 Si 2 suffers from oxidation, steam corrosion, and subsequent disintegration/pulverization. The detailed investigation of kinetics that incorporates fundamental treatment of oxidation of U 3 Si 2 is scarcely reported, and the oxidation mechanisms have not been fully elucidated. In this paper, the oxidation behavior of microcrystalline (mc - ) and nanocrystalline (nc - ) U 3 Si 2 have been systematically investigated using a thermogravimetric analysis (TGA) apparatus through a series of isothermal and non-isothermal kinetic studies. The isothermal kinetic study with a model-fitting approach indicates oxidation activation energy of 85 kJ/mol for dense mc - U 3 Si 2 and 96.4 kJ/mol for nc - U 3 Si 2 pellets, while the isoconversional approach leads to an activation energy in the range of 70–85 kJ/mol for mc - U 3 Si 2 and 75–86 kJ/mol for nc - U 3 Si 2 with three most common model-free methods, including Kissinger–Akahira–Sunose, Flynn–Wall–Ozawa, and Friedman methods. The derivation of oxidation activation energies using both isothermal and isoconversional methods highlights the approach to evaluate the oxidation resistance of nuclear materials using TGA quantitatively and makes it possible to compare among various nuclear fuels.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2023

A guided ion beam investigation of UO 2 + thermodynamics and f orbital participation: Reactions of U + + CO 2 , UO + + O 2 , and UO + + CO

A guided ion beam tandem mass spectrometer was employed to study the reactions of U + + CO 2 , UO + + O 2 , and the reverse of the former, UO + + CO. Reaction cross sections as a function of kinetic energy over about a three order of magnitude range were studied for all systems. The reaction of U + + CO 2 proceeds to form UO + + CO with an efficiency of 118% ± 24% as well as generating UO 2 + + C and UCO + + O. The reaction of UO + + O 2 forms UO 2 + in an exothermic, barrierless process and also results in the collision-induced dissociation of UO + to yield U + . In the UO + + CO reaction, the formation of UO 2 + in an endothermic process is the dominant reaction, but minor products of UCO + + O and U + + (O + CO) are also observed. Analysis of the kinetic energy dependences observed provides the bond energies, D 0 (U + –O) = 7.98 ± 0.22 and 8.05 ± 0.14 eV, D 0 (U + –CO) = 0.73 ± 0.13 eV, and D 0 (OU + –O) = 7.56 ± 0.12 eV. The values obtained for D 0 (U + –O) and D 0 (OU + –O) agree well with the previously reported literature values. To our knowledge, this is the first experimental measurement of D 0 (U + –CO). Furthermore, an analysis of the oxide bond energies shows that participation of 5f orbitals leads to a substantial increase in the thermodynamic stability of UO 2 + relative to ThO 2 + and especially transition metal dioxide cations.

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

From antiferromagnetic and hidden order to Pauli paramagnetism in U M 2 Si 2 compounds with 5 f electron duality

Using inelastic X-ray scattering beyond the dipole limit and hard X-ray photoelectron spectroscopy we establish the dual nature of the U 5 f electrons in U M 2 Si 2 ( M = Pd, Ni, Ru, Fe), regardless of their degree of delocalization. We have observed that the compounds have in common a local atomic-like state that is well described by the U 5 f 2 configuration with the $Γ^{(1)}_1$ and $Γ_2$ quasi-doublet symmetry. The amount of the U 5 f 3 configuration, however, varies considerably across the U M 2 Si 2 series, indicating an increase of U 5 f itineracy in going from M = Pd to Ni to Ru and to the Fe compound. The identified electronic states explain the formation of the very large ordered magnetic moments in UPd 2 Si 2 and UNi 2 Si 2 , the availability of orbital degrees of freedom needed for the hidden order in URu 2 Si 2 to occur, as well as the appearance of Pauli paramagnetism in UFe 2 Si 2 . A unified and systematic picture of the U M 2 Si 2 compounds may now be drawn, thereby providing suggestions for additional experiments to induce hidden order and/or superconductivity in U compounds with the tetragonal body-centered ThCr 2 Si 2 structure.

36 MATERIALS SCIENCE↗
DOE OSTI2024

High-throughput determination of Hubbard $U$ and Hund $J$ values for transition metal oxides via the linear response formalism

DFT+U provides a convenient, cost-effective correction for the self-interaction error (SIE) that arises when describing correlated electronic states using conventional approximate density functional theory (DFT). The success of a DFT+U(+J) calculation hinges on the accurate determination of its Hubbard U and Hund J parameters, and the linear response (LR) methodology has proven to be computationally effective and accurate for calculating these parameters. This study provides a high-throughput computational analysis of the U and J values for transition metal d-electron states in a representative set of over 1000 magnetic transition metal oxides (TMOs), providing a frame of reference for researchers who use DFT+U to study transition metal oxides. In order to perform this high-throughput study, an ATOMATE workflow is developed for calculating U and J values automatically on massively parallel supercomputing architectures. Here, to demonstrate an application of this workflow, the spin-canting magnetic structure and unit cell parameters of the multiferroic olivine LiNiPO4 are calculated using the computed Hubbard U and Hund J values for Ni-d and O-p states, and are compared with experiment. Both the Ni-d U and J corrections have a strong effect on the Ni-moment canting angle. Additionally, including a O-pU value results in a significantly improved agreement between the computed lattice parameters and experiment

36 MATERIALS SCIENCE↗
DOE OSTI2021

Combined Technologies for In Situ Remediation of Tc-99 and U in Subsurface Sediments

In this study, combinations of chemical remedies were tested in bench-scale batch experiments to evaluate a two-step reduction-sequestration approach to effectively stabilize high concentrations of inorganic contaminant mixtures. Bench tests simulated contaminant and geochemical conditions of a perched aquifer located within the Central Plateau at the Hanford Site, located in southeastern Washington State (USA). Pairwise combinations of a reductant [e.g., zero valent iron, sulfur modified iron (SMI), or calcium polysulfide] and a sequestering agent [e.g., calcite, apatite, or dilute alkaline solution (e.g., NaOH)] were evaluated for immobilization and stabilization of technetium (Tc) (50,000 pCi/L), uranium (U) (150 mg/L), and nitrate (NO 3 ) (200 mg/L) in high ionic strength groundwater. The results of these batch studies demonstrated that reduction by SMI and sequestration in apatite or calcite are the most effective combination for these contaminant mixtures and conditions. Aqueous concentrations of Tc and U decreased by 95.6% ± 2.5% and 101.1% ± 5.2%, respectively, with SMI-apatite and 98.3% ± 0.0% and 101.2% ± 5.2%, respectively, with SMI-calcite. Sequential extractions showed that sequestered contaminants had limited capacity for re-oxidation; in fact, less than 10% of immobilized Tc and U was recovered by selective extraction of mineral phases most susceptible to oxidation. In addition, X-ray absorption near edge structure analysis of the sediment samples treated with SMI-calcite showed the presence of only U(IV), while both U(IV) and U(VI) were present in the SMI apatite combination [ratio of 0.43 U(IV):0.59 U(VI)].This study describes preliminary results that a two-step approach for stabilizing contaminant mixtures of long-lived radionuclides can be effective at reducing contaminant fluxes to groundwater from vadose and perched water zones.

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2020

Materials Data on U(SiIr)2 by Materials Project

UIr2Si2 crystallizes in the tetragonal P4/nmm space group. The structure is three-dimensional. U is bonded in a 8-coordinate geometry to eight Ir and eight Si atoms. There are four shorter (3.11 Å) and four longer (3.25 Å) U–Ir bond lengths. There are four shorter (3.14 Å) and four longer (3.17 Å) U–Si bond lengths. There are two inequivalent Ir sites. In the first Ir site, Ir is bonded in a 9-coordinate geometry to four equivalent U and five Si atoms. There are one shorter (2.35 Å) and four longer (2.41 Å) Ir–Si bond lengths. In the second Ir site, Ir is bonded to four equivalent U and four equivalent Si atoms to form distorted IrU4Si4 tetrahedra that share corners with twelve equivalent SiU4Ir4 tetrahedra, edges with two equivalent SiU4Ir4 tetrahedra, edges with four equivalent IrU4Si4 tetrahedra, and faces with four equivalent IrU4Si4 tetrahedra. All Ir–Si bond lengths are 2.44 Å. There are two inequivalent Si sites. In the first Si site, Si is bonded in a 9-coordinate geometry to four equivalent U and five Ir atoms. In the second Si site, Si is bonded to four equivalent U and four equivalent Ir atoms to form distorted SiU4Ir4 tetrahedra that share corners with twelve equivalent IrU4Si4 tetrahedra, edges with two equivalent IrU4Si4 tetrahedra, edges with four equivalent SiU4Ir4 tetrahedra, and faces with four equivalent SiU4Ir4 tetrahedra.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on U(AlAu)2 by Materials Project

UAu2Al2 crystallizes in the tetragonal P4/nmm space group. The structure is three-dimensional. U is bonded in a 12-coordinate geometry to eight Au and eight Al atoms. There are four shorter (3.31 Å) and four longer (3.38 Å) U–Au bond lengths. There are four shorter (3.29 Å) and four longer (3.41 Å) U–Al bond lengths. There are two inequivalent Au sites. In the first Au site, Au is bonded to four equivalent U and four equivalent Al atoms to form distorted AuU4Al4 tetrahedra that share corners with twelve equivalent AlU4Au4 tetrahedra, edges with two equivalent AlU4Au4 tetrahedra, edges with four equivalent AuU4Al4 tetrahedra, and faces with four equivalent AuU4Al4 tetrahedra. All Au–Al bond lengths are 2.58 Å. In the second Au site, Au is bonded in a 5-coordinate geometry to four equivalent U and five Al atoms. There are one shorter (2.44 Å) and four longer (2.57 Å) Au–Al bond lengths. There are two inequivalent Al sites. In the first Al site, Al is bonded to four equivalent U and four equivalent Au atoms to form AlU4Au4 tetrahedra that share corners with twelve equivalent AuU4Al4 tetrahedra, edges with two equivalent AuU4Al4 tetrahedra, edges with four equivalent AlU4Au4 tetrahedra, and faces with four equivalent AlU4Au4 tetrahedra. In the second Al site, Al is bonded in a 5-coordinate geometry to four equivalent U and five Au atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on U(MoO5)12 by Materials Project

U(MoO4)12(O2)6 crystallizes in the trigonal R-3 space group. The structure is zero-dimensional and consists of three hexaoxane molecules, six trioxirane molecules, and three U(MoO4)12 clusters. In each U(MoO4)12 cluster, U is bonded in a cuboctahedral geometry to twelve O atoms. There are six shorter (2.40 Å) and six longer (2.51 Å) U–O bond lengths. There are two inequivalent Mo sites. In the first Mo site, Mo is bonded in a 6-coordinate geometry to six O atoms. There are a spread of Mo–O bond distances ranging from 1.72–2.32 Å. In the second Mo site, Mo is bonded in a 6-coordinate geometry to six O atoms. There are a spread of Mo–O bond distances ranging from 1.73–2.35 Å. There are eight inequivalent O sites. In the first O site, O is bonded in a single-bond geometry to one Mo atom. In the second O site, O is bonded in a single-bond geometry to one Mo atom. In the third O site, O is bonded in a single-bond geometry to one Mo atom. In the fourth O site, O is bonded in a single-bond geometry to one Mo atom. In the fifth O site, O is bonded in a single-bond geometry to one O atom. The O–O bond length is 2.04 Å. In the sixth O site, O is bonded in a distorted rectangular see-saw-like geometry to one U and three Mo atoms. In the seventh O site, O is bonded in a water-like geometry to two Mo and one O atom. In the eighth O site, O is bonded in a distorted rectangular see-saw-like geometry to one U and three Mo atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on U(Fe5Si)2 by Materials Project

UFe10Si2 crystallizes in the orthorhombic Fmmm 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 2.92–3.14 Å. All U–Si bond lengths are 3.14 Å. There are three inequivalent Fe sites. In the first 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 2.37–2.93 Å. Both Fe–Si bond lengths are 2.51 Å. In the second Fe site, Fe is bonded to two equivalent U and ten Fe atoms to form FeU2Fe10 cuboctahedra that share corners with four equivalent SiU2Fe8Si2 cuboctahedra, corners with six equivalent FeU2Fe10 cuboctahedra, edges with four equivalent SiU2Fe8Si2 cuboctahedra, faces with two equivalent FeU2Fe10 cuboctahedra, and faces with four equivalent SiU2Fe8Si2 cuboctahedra. There are two shorter (2.38 Å) and four longer (2.41 Å) Fe–Fe bond lengths. In the third Fe site, Fe is bonded in a 12-coordinate geometry to two equivalent U, eight Fe, and two equivalent Si atoms. There are one shorter (2.52 Å) and one longer (2.58 Å) Fe–Fe bond lengths. Both Fe–Si bond lengths are 2.37 Å. Si is bonded to two equivalent U, eight Fe, and two equivalent Si atoms to form distorted SiU2Fe8Si2 cuboctahedra that share corners with four equivalent FeU2Fe10 cuboctahedra, corners with six equivalent SiU2Fe8Si2 cuboctahedra, edges with four equivalent FeU2Fe10 cuboctahedra, faces with two equivalent SiU2Fe8Si2 cuboctahedra, and faces with four equivalent FeU2Fe10 cuboctahedra. Both Si–Si bond lengths are 2.38 Å.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on U(GeRh)2 by Materials Project

URh2Ge2 crystallizes in the tetragonal P4/nmm space group. The structure is three-dimensional. U is bonded in a 8-coordinate geometry to eight Rh and eight Ge atoms. There are four shorter (3.19 Å) and four longer (3.35 Å) U–Rh bond lengths. There are four shorter (3.23 Å) and four longer (3.25 Å) U–Ge bond lengths. There are two inequivalent Rh sites. In the first Rh site, Rh is bonded to four equivalent U and four equivalent Ge atoms to form distorted RhU4Ge4 tetrahedra that share corners with twelve equivalent GeU4Rh4 tetrahedra, edges with two equivalent GeU4Rh4 tetrahedra, edges with four equivalent RhU4Ge4 tetrahedra, and faces with four equivalent RhU4Ge4 tetrahedra. All Rh–Ge bond lengths are 2.49 Å. In the second Rh site, Rh is bonded in a 9-coordinate geometry to four equivalent U and five Ge atoms. There are one shorter (2.42 Å) and four longer (2.49 Å) Rh–Ge bond lengths. There are two inequivalent Ge sites. In the first Ge site, Ge is bonded to four equivalent U and four equivalent Rh atoms to form distorted GeU4Rh4 tetrahedra that share corners with twelve equivalent RhU4Ge4 tetrahedra, edges with two equivalent RhU4Ge4 tetrahedra, edges with four equivalent GeU4Rh4 tetrahedra, and faces with four equivalent GeU4Rh4 tetrahedra. In the second Ge site, Ge is bonded in a 9-coordinate geometry to four equivalent U and five Rh atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on U(CuSn)2 by Materials Project

UCu2Sn2 crystallizes in the tetragonal P4/nmm space group. The structure is three-dimensional. U is bonded in a 12-coordinate geometry to eight Cu and eight Sn atoms. There are four shorter (3.35 Å) and four longer (3.38 Å) U–Cu bond lengths. There are four shorter (3.32 Å) and four longer (3.50 Å) U–Sn bond lengths. There are two inequivalent Cu sites. In the first Cu site, Cu is bonded in a 12-coordinate geometry to four equivalent U and four equivalent Sn atoms. All Cu–Sn bond lengths are 2.59 Å. In the second Cu site, Cu is bonded in a 9-coordinate geometry to four equivalent U and five Sn atoms. There are one shorter (2.47 Å) and four longer (2.61 Å) Cu–Sn bond lengths. There are two inequivalent Sn sites. In the first Sn site, Sn is bonded in a 4-coordinate geometry to four equivalent U and four equivalent Cu atoms. In the second Sn site, Sn is bonded in a 9-coordinate geometry to four equivalent U and five Cu atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on U(GeIr)2 by Materials Project

UIr2Ge2 crystallizes in the tetragonal P4/nmm space group. The structure is three-dimensional. U is bonded in a 12-coordinate geometry to eight Ir and eight Ge atoms. There are four shorter (3.18 Å) and four longer (3.36 Å) U–Ir bond lengths. There are four shorter (3.23 Å) and four longer (3.24 Å) U–Ge bond lengths. There are two inequivalent Ir sites. In the first Ir site, Ir is bonded to four equivalent U and four equivalent Ge atoms to form distorted IrU4Ge4 tetrahedra that share corners with twelve equivalent GeU4Ir4 tetrahedra, edges with two equivalent GeU4Ir4 tetrahedra, edges with four equivalent IrU4Ge4 tetrahedra, and faces with four equivalent IrU4Ge4 tetrahedra. All Ir–Ge bond lengths are 2.50 Å. In the second Ir site, Ir is bonded in a 9-coordinate geometry to four equivalent U and five Ge atoms. There are one shorter (2.40 Å) and four longer (2.49 Å) Ir–Ge bond lengths. There are two inequivalent Ge sites. In the first Ge site, Ge is bonded to four equivalent U and four equivalent Ir atoms to form distorted GeU4Ir4 tetrahedra that share corners with twelve equivalent IrU4Ge4 tetrahedra, edges with two equivalent IrU4Ge4 tetrahedra, edges with four equivalent GeU4Ir4 tetrahedra, and faces with four equivalent GeU4Ir4 tetrahedra. In the second Ge site, Ge is bonded in a 9-coordinate geometry to four equivalent U and five Ir atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on U(AlCu)6 by Materials Project

UCu6Al6 crystallizes in the orthorhombic Fmmm space group. The structure is three-dimensional. U is bonded in a 4-coordinate geometry to eight Cu and twelve Al atoms. There are four shorter (3.04 Å) and four longer (3.31 Å) U–Cu bond lengths. There are eight shorter (3.23 Å) and four longer (3.36 Å) U–Al bond lengths. There are two inequivalent Cu sites. In the first Cu site, Cu is bonded in a 12-coordinate geometry to two equivalent U, four equivalent Cu, and four equivalent Al atoms. All Cu–Cu bond lengths are 2.70 Å. All Cu–Al bond lengths are 2.43 Å. In the second Cu site, Cu is bonded in a 10-coordinate geometry to one U, three Cu, and six Al atoms. The Cu–Cu bond length is 2.64 Å. There are a spread of Cu–Al bond distances ranging from 2.62–2.73 Å. There are two inequivalent Al sites. In the first Al site, Al is bonded in a 12-coordinate geometry to two equivalent U, four equivalent Cu, and six Al atoms. There are two shorter (2.51 Å) and four longer (2.61 Å) Al–Al bond lengths. In the second Al site, Al is bonded in a 12-coordinate geometry to two equivalent U, six Cu, and four Al atoms. There are one shorter (2.76 Å) and one longer (3.00 Å) Al–Al bond lengths.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on U(NO5)2 by Materials Project

UNO8NO2 crystallizes in the monoclinic Cm space group. The structure is zero-dimensional and consists of two nitrous acid molecules and two UNO8 clusters. In each UNO8 cluster, U is bonded in a distorted linear geometry to eight O atoms. There are a spread of U–O bond distances ranging from 1.80–2.56 Å. N is bonded in a bent 120 degrees geometry to two equivalent O atoms. Both N–O bond lengths are 1.26 Å. There are five inequivalent O sites. In the first O site, O is bonded in a single-bond geometry to one U atom. In the second O site, O is bonded in a single-bond geometry to one U atom. In the third O site, O is bonded in a 2-coordinate geometry to one U and one O atom. The O–O bond length is 1.31 Å. In the fourth O site, O is bonded in a distorted L-shaped geometry to one U and one N atom. In the fifth O site, O is bonded in a distorted L-shaped geometry to one U and one O atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on U(Co5Si)2 by Materials Project

UCo10Si2 crystallizes in the orthorhombic Fmmm space group. The structure is three-dimensional. U is bonded in a 4-coordinate geometry to sixteen Co and four equivalent Si atoms. There are a spread of U–Co bond distances ranging from 2.82–3.08 Å. All U–Si bond lengths are 3.15 Å. There are three inequivalent Co sites. In the first Co site, Co is bonded in a 10-coordinate geometry to one U, seven Co, and two equivalent Si atoms. There are a spread of Co–Co bond distances ranging from 2.48–2.61 Å. Both Co–Si bond lengths are 2.46 Å. In the second Co site, Co is bonded in a 12-coordinate geometry to two equivalent U, eight Co, and two equivalent Si atoms. There are a spread of Co–Co bond distances ranging from 2.38–2.66 Å. Both Co–Si bond lengths are 2.36 Å. In the third Co site, Co is bonded to two equivalent U and ten Co atoms to form CoU2Co10 cuboctahedra that share corners with four equivalent SiU2Co8Si2 cuboctahedra, corners with six equivalent CoU2Co10 cuboctahedra, edges with four equivalent SiU2Co8Si2 cuboctahedra, faces with two equivalent CoU2Co10 cuboctahedra, and faces with four equivalent SiU2Co8Si2 cuboctahedra. Both Co–Co bond lengths are 2.42 Å. Si is bonded to two equivalent U, eight Co, and two equivalent Si atoms to form distorted SiU2Co8Si2 cuboctahedra that share corners with four equivalent CoU2Co10 cuboctahedra, corners with six equivalent SiU2Co8Si2 cuboctahedra, edges with four equivalent CoU2Co10 cuboctahedra, faces with two equivalent SiU2Co8Si2 cuboctahedra, and faces with four equivalent CoU2Co10 cuboctahedra. Both Si–Si bond lengths are 2.42 Å.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Comparative Assessment of U-Net-Based Deep Learning Models for Segmenting Microfractures and Pore Spaces in Digital Rocks

Segmentation of high-resolution X-ray microcomputed tomography (µCT) images is crucial in digital rock physics (DRP), affecting the characterization and analysis of microscale phenomena in the porous media. The complexity of geological structures and nonideal scanning conditions pose significant challenges to conventional image segmentation approaches. Motivated by the recent increasing popularity of deep learning (DL) techniques in image processing, this work undertakes a comparative study of DL models, specifically U-Net and its variants, for segmenting multiple targets with distinguished features in digital rocks, including discrete fracture networks (DFNs), pore spaces, and solid rock. Particularly, DFNs have a smaller volumetric fraction over others, bringing in a substantial challenge of imbalanced segmentation. The primary focus is to evaluate the architecture and feature enhancement strategies of various DL models, including U-Net, attention U-Net, residual U-Net, U-Net++, and residual U-Net++. The models were designed as 2.5D, utilizing a central 2D image and its two adjacent upper and lower 2D images as input to provide a pseudo-3D context. In addition, because the ground truth of segmentation was unknown for real-world digital rocks, we created a benchmark data set following the inverse operations of segmentation. The data synthesis started from the label images (i.e., solid rock, pore spaces, and DFNs), followed by simulating partial volume blurring, adding random background noise, and introducing ring artifacts to mimic real raw X-ray µCT images. The data set, which included various rock types (i.e., sandstone and artificial data), scanning resolution, and magnitudes of noise and artifacts, was divided into training and testing data sets with a 90% and 10% ratio, respectively. Moreover, in addition to the conventional pixel-wise evaluation metrics, the physics-based metric of the lattice-Boltzmann method (LBM) simulated permeability provided more comprehensive assessments. The results demonstrated that the residual connections, nested architectures, and redesigned skip connections contribute to the model performance and give the residual U-Net++ the highest accuracy. The improvements were mainly on the boundaries and small targets, especially the DFNs, which dominate the interconnectivity and therefore affect the permeability greatly. This study also rigorously evaluated the efficiency and generalization of each model, demonstrating that the sophisticated architectures achieved excellent practicability and maintained robust performance on completely unseen data, ensuring their suitability for diverse and challenging DRP applications.

58 GEOSCIENCES↗
DOE OSTI2020

Report to NCSP on 2008 DANCE measurements of 233 U($\eta$,$\gamma$)

Uranium-233 plays an important role in the Th-U fuel cycle, with substantial production in the cycle. This cycle has been proposed as an alternative to the U-Pu fuel cycle due to its reduced production of transuranic elements. An accurate measurement of the 233 U($\eta$,$\gamma$) cross section is required by the National Criticality Safety Program (NCSP) to complete the neutron-induced cross section data, where experimental capture cross section data are scarce and were measured decades ago. The most recent capture cross section data available in the literature were measured in 2007 at the n_TOF facility (CERN); in the 60s measurements were performed at Rensselaer Polytechnic Institute (RPI) and at LANL. Finally, as reported by ORNL, a new evaluation with a revised (renormalized) fission cross section is needed on 233 U. The challenge for this measurement lies in the difficulty of measuring the capture cross section data in the competing fission background, as the fission cross section is around one order of magnitude larger than the capture cross section for 233 U. The accuracy of a capture cross section measurement depends on discrimination between $\gamma$’s produced in capture and fission reactions, for which an experimental setup combining capture and fission detectors is needed. For the ($\eta$,$\gamma$) cross section measurement at LANSCE, this discrimination is achieved by combining the Detector for Advanced Neutron Capture Experiments (DANCE), to measure $\gamma$’s from capture reactions, with a Parallel Plate Avalanche Counter (PPAC) to tag the $\gamma$’s produced by fission. This method was successfully used to measure 235 U and 239 Pu capture cross sections. In these measurements, the neutron capture cross section was determined in a large fission background well above 100 keV. As part of the NCSP nuclear data effort, we have looked at past DANCE measurements on 233 U($\eta$,$\gamma$) and evaluated whether existing data is adequate to apply this technique.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2021

Thermal properties of U-Mo alloys irradiated under high fission power density

A variety of physical and thermal property measurements made on irradiated U-Mo alloy monolithic fuel samples with a Zr diffusion barrier and clad in Al alloy 6061 are reported. These properties form the basis for additional investigations in thermal behavior of U-Mo fuel under high performance research reactor irradiation conditions. Measurements were performed on samples harvested from fuel plates irradiated under high fission power density and surface heat flux and complement previous measurements on samples subjected to moderate fission power density and surface heat flux. Specific heat capacity of irradiated monolithic U-Mo increases with increasing temperature and fission density, but carries large uncertainties associated with thickness measurements used to determine the mass fraction of the layer constituents for extraction of the U-Mo specific heat capacity, specifically the very thin and nonuniform Zr diffusion barrier. Density of irradiated monolithic U-Mo decreases with increasing fission density resulting from fission gas swelling and porosity formation. Thermal diffusivity of irradiated monolithic U-Mo increased with increasing temperature and decreased with increasing fission density. Thermal conductivity of irradiated monolithic U-Mo increased with increasing temperature, and in general, appeared to decrease and become less sensitive to temperature with increasing fission density. Thermal conductivity measurements compared to a semi-empirical model agreed within ±30%. It is suspected that the main driver in deviation between model calculations and measurements is the fission gas swelling determination, which does not account for fission power density or irradiation temperature.

uranium (U), molybdenum, nuclear fuel, thermal con↗