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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 235 records · Page 13
All sourcesNASA NTRSDOE OSTI
DOE OSTI2018

Trace element migration during UF4 bomb reduction: Implications to metal fuel production, worker health and safety, and nuclear forensics

Understanding the migration of trace contaminants during the production of U metal is vital for fabricating advanced nuclear fuels, for managing worker health and safety at foundry and processing facilities, and for advancing nuclear forensic science. A common method used to produce actinide metals is the bomb reduction of suitable U precursors. Here, we report the results of a series of experiments designed to quantitatively track the trace contaminants Th, Ca, and, Mg through a bomb reduction of UF4 using a vacuum induction furnace. In this series, UF4 charges were doped with increasing levels of elemental Th from 0-1000 ppm Th/U. Following reduction, the metal ingot products and the associated slag and crucibles were individually digested and analyzed using inductively coupled plasma-mass spectrometry. The results show that Th fractionation occurred at all concentrations but was most significant, and near quantitative, in samples starting with Th concentrations below 100 ppm. Thorium was found to incorporate into the slag and crucible in roughly equal proportions. A significant amount of U and Ca migrated into the crucible walls, each correlated with Mg migration from the MgO crucible to the U metal product.

Reilly, Dallas D.↗
DOE OSTI2021

Mechanistic insights into selective oxidation and corrosion of multi-principal element alloys from high resolution and in situ microscopy

Multiple principal elements alloys (MPEAs) have drawn significant recent interest from the metallurgical research community. These novel alloys have the potential to replace traditional alloys with a range of tailored mechanical properties, corrosion resistance, and radiation tolerance enabled by complex compositions. The broad alloy design space of MPEAs presents a great opportunity to discover new forms of oxidation and corrosion resistance in extreme environments that break away from conventional corrosion resistant alloy design criteria. However, understanding the oxidation and corrosion response of MPEAs can be a challenging task due the complex composition, structural, and chemical state changes occurring in the corrosion product and at its interface with the base alloy. This perspective discusses the utility of high resolution and in situ microscopy techniques for revealing unique aspects of MPEA oxidation behavior at the near-atomic level. Challenges of studying these alloys and several open questions are presented.

Kautz, Elizabeth J.↗
DOE OSTI2018

Discrete element modeling of grain crushing and implications on reservoir compaction

Depletion-induced formation compaction is a concern for production in hydrocarbon reservoirs. In this study, numerical mechanical tests and digital samples are proposed as an alternative to uniaxial strain experiments for investigating the effects of compaction. We propose a grain crushing model with two-sized subgrains based on the discrete element method and bonded-particle model (DEM-BPM) and perform numerical single grain crushing tests to calibrate the model parameters against the experimental sand grain characteristic strength. Numerical uniaxial strain tests are used to predict porosity and permeability reduction caused by reservoir compaction. Grain crushing incurs a significant reduction of porosity under the uniaxial strain stress path, which becomes more evident for digital samples consisting of larger grains. The stress-dependent changes in porosity and permeability obtained from the DEM simulations can be used as inputs for a reservoir-scale correlation to predict the productivity loss due to reservoir compaction.

nuclear (including radiation effects), carbon sequ↗
DOE OSTI2017

Measurement of key resonance states for the P 30 ( p , γ ) S 31 reaction rate, and the production of intermediate-mass elements in nova explosions

We report the first experimental constraints on spectroscopic factors and strengths of key resonances in the P-30(p, gamma)S-31 reaction critical for determining the production of intermediate-mass elements up to Ca in nova ejecta. The P-30(d,n)S-31 reaction was studied in inverse kinematics using the GRETINA gamma-ray array to measure the angle-integrated cross-sections of states above the proton threshold. In general, negative parity states are found to be most strongly produced but the absolute values of spectroscopic factors are typically an order of magnitude lower than predicted by the shell-model calculations employing WBP Hamiltonian for the negative-parity states. The results clearly indicate the dominance of a single 3/2(-) resonance state at 196 keV in the region of nova burning T approximate to 0.10-0.17 GM, well within the region of interest for nova nucleosynthesis. Hydrodynamic simulations of nova explosions have been performed to demonstrate the effect on the composition of nova ejecta.

Kankainen, A. (ORCID:0000000310827602)↗
DOE OSTI2020

Examination of Molten Salt Reactor Relevant Elements Using Hydrothermal Synthesis

The structural chemistry of elements relevant to the FLiBe molten salt reactor, Th, U, Np, and Zr, including Ce andNd (as analogues for Pu and Am, respectively), have been examined using hydrothermal synthesis at 200 °C. These reactions serve to model the reaction of molten salts under hydrolysis conditions. The results show that U and Np formed LiAnF 5 , while Ce formed Li 4 CeF 8 . The source of U also controlled the crystal quality, where UO 2 gave small crystals, while UO 3 ·2H 2 O gave very large crystals. It is likely that Be incorporation was not observed because of the high solubility of [BeF 4 ] 2– in water. Zr formed a third product, Li 6 BeF 4 ZrF 8 , which features isolated [BeF 4 ] 2– and [ZrF 8 ] 4– units bridged by Li + . Additionally, Li 2 BeF 4 was regularly isolated. As a result, when little to no alkali metal was included in the reaction, M 3 F 12 (H 2 O) was isolated for Np, U, and Ce.

Anions↗
DOE OSTI2022

237 Np Mössbauer Isomer Shifts: A Lesson About the Balance of Static and Dynamic Electron Correlation in Heavy Element Complexes

A large set of neptunium compounds with different oxidation states (III to VII) was assembled to study the Mössbauer isomer shift by wave function calculations and better understand covalency in f-elements complexes. The contact density approach was used to calculate the isomer shift using complete active space self-consistent field (CASSCF) multiconfiguration wave functions, as well as matrix product states [from Density Matrix Renormalization Group (DMRG) algorithms] for large active spaces. Dynamic correlation effects for the isomer shifts were treated via CASPT2 energy derivatives with respect to the nuclear radius. The CASSCF calculations appear to produce different orbital overlocalization errors for low and high Np oxidation states. For compounds with low Np oxidation numbers, the errors can be attributed to the overlocalization of the 5f orbitals. For the compounds with high Np oxidation numbers, the main errors arise from an overlocalization of ligand orbitals and concomitant to weak donation bonding. Attempts to mitigate the overlocalization errors with large active spaces using DMRG were only partially successful, showing that explicit treatment of dynamic correlation is necessary for accurate predictions of Mössbauer isomer shifts. The CASPT2 calculations perform very satisfactorily. For a subset of Np compounds, both static and dynamic correlation effects were substantial. Furthermore, a rational active space selection based on orbital entanglement diagrams proved beneficial for determining the optimal reference wave function.

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

Three-Dimensional Evaluation of Sand Particle Fracture Using Discrete-Element Method and Synchrotron Microcomputed Tomography Images

Recent research showed that fracture of sand particles plays a significant role in determining the plastic bulk volumetric changes of granular materials under different loading conditions. One of the major tools used to better understand the influence of particle fracture on the behavior of granular materials is discrete-element modeling (DEM). This paper employed the bonded block model (BBM) to simulate the fracture behavior of sand. Each sand particle is modeled as an agglomerate of rigid blocks bonded at their contacts using the linear-parallel contact model, which can transmit both moment and force. DEM simulated particles closely matched the actual three-dimensional (3D) shape of sand particles acquired using high-resolution 3D synchrotron microcomputed tomography (SMT). Results from unconfined one-dimensional (1D) compression of a single synthetic silica cube were used to calibrate the model parameters. Particle fracture was investigated for specimens composed of three sand particles that were loaded under confined 1D compression. Breakage energy measured from DEM models matched well with that measured experimentally. The paper studied the effects of contact loading condition and particle interaction on the fracture mode of particles using BBM that can closely capture the 3D shape of real sand particles.

58 GEOSCIENCES↗
DOE OSTI2014

Core-to-valence spectroscopic detection of the CH{sub 2}Br radical and element-specific femtosecond photodissociation dynamics of CH{sub 2}IBr

Element-specific single photon photodissociation dynamics of CH{sub 2}IBr and core-to-valence absorption spectroscopy of CH{sub 2}Br radicals are investigated using femtosecond high-harmonic extreme ultraviolet (XUV) transient absorption spectroscopy. Photodissociation of CH{sub 2}IBr along both the C–I or C–Br reaction coordinates is observed in real-time following excitation at 266 nm. At this wavelength, C–I dissociation is the dominant reaction channel and C–Br dissociation is observed as a minor pathway. Both photodissociation pathways are probed simultaneously through individual 4d(I) N{sub 4/5} and 3d(Br) M{sub 4/5} core-to-valence transitions. The 3d(Br) M{sub 4/5} pre-edge absorption spectrum of the CH{sub 2}Br radical photoproduct corresponding to the C–I dissociation channel is characterized for the first time. Although the radical's singly occupied molecular orbital (SOMO) is mostly localized on the central carbon atom, the 3d(Br) → π{sup *}(SOMO) resonances at 68.5 eV and 69.5 eV are detected 2 eV below the parent molecule 3d(Br) → σ{sup *}(LUMO) transitions. Core-to-valence XUV absorption spectroscopy provides a unique probe of the local electronic structure of the radical species in reference to the Br reporter atom. The measured times for C–I dissociation leading to I and I{sup *} atomic products are 48 ± 12 fs and 44 ± 4 fs, respectively, while the measured C–Br dissociation time leading to atomic Br is 114 ± 17 fs. The investigation performed here demonstrates the capability of femtosecond time-resolved core-level spectroscopy utilizing multiple reporter atoms simultaneously.

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

A fully coupled thermal–microstructural–mechanical finite element process model for directed energy deposition additive manufacturing of Ti–6Al–4V

A fully coupled thermal–microstructural–mechanical finite element modelling framework is developed to investigate the distortion and residual stresses during directed energy deposition (DED) of multi-phase Ti–6Al–4V alloy. The Johnson–Cook constitutive model is used to predict the yield strength of each phase as a function of strain, strain rate and temperature where the flow stress is calculated by a linear mixing rule based on the volumetric phase fractions. A thin-walled rectangular sample is chosen as the reference geometry and the results are compared with experimentally measured in situ thermal history and distortion data, where a reasonable agreement is achieved. The proposed modelling framework with physics-based material constitutive model provides useful information for a better understanding of process–microstructure–property relations in additive manufacturing by DED.

Tunay, Merve↗
DOE OSTI2016

Elemental and lattice-parameter mapping of binary oxide superlattices of (LaNiO 3 ) 4 /(LaMnO 3 ) 2 at atomic resolution

We construct the elemental distribution and lattice strain maps from the measured atomic column positions in a (LaNiO3)(4)/(LaMnO3)(2) superlattice over a large field of view. The correlation between the distribution of B-cations and the lattice parameter in the form of Vegard's law is validated using atomic resolution energy dispersive x-ray spectroscopy (EDS). The maps show negligible Mn intermixing in the LaNiO3 layer, while Ni intermixing in the LaMnO3 layer improves away from the substrate interface to 9.5 atomic% from the 8th period onwards, indicating that the superlattice interfacial sharpness is established as the distance from the substrate increases. The maps allow an observation of the compositional defects of the B-sites, which is not possible by Z-contrast alone. Thus, this study demonstrates a promising approach for atomic scale correlative study of lattice strain and composition, and a method for the calibration of atomic resolution EDS maps.

composition↗
DOE OSTI2020

Nop9 recognizes structured and single-stranded RNA elements of preribosomal RNA

Nop9 is an essential factor in the processing of preribosomal RNA. Its absence in yeast is lethal, and defects in the human ortholog are associated with breast cancer, autoimmunity, and learning/language impairment. PUF family RNA-binding proteins are best known for sequence-specific RNA recognition, and most contain eight α-helical repeats that bind to the RNA bases of single-stranded RNA. Nop9 is an unusual member of this family in that it contains eleven repeats and recognizes both RNA structure and sequence. Here we report a crystal structure of Saccharomyces cerevisiae Nop9 in complex with its target RNA within the 20S preribosomal RNA. This structure reveals that Nop9 brings together a carboxy-terminal module recognizing the 5' single-stranded region of the RNA and a bifunctional amino-terminal module recognizing the central double-stranded stem region. We further show that the 3' single-stranded region of the 20S target RNA adds sequence-independent binding energy to the RNA–Nop9 interaction. Both the amino- and carboxy-terminal modules retain the characteristic sequence-specific recognition of PUF proteins, but the amino-terminal module has also evolved a distinct interface, which allows Nop9 to recognize either single-stranded RNA sequences or RNAs with a combination of single-stranded and structured elements.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2016

Simulating Fragmentation and Fluid-Induced Fracture in Disordered Media Using Random Finite-Element Meshes

Fracture and fragmentation are extremely nonlinear multiscale processes in which microscale damage mechanisms emerge at the macroscale as new fracture surfaces. Numerous numerical methods have been developed for simulating fracture initiation, propagation, and coalescence. In this paper, we present a computational approach for modeling pervasive fracture in quasi-brittle materials based on random close-packed Voronoi tessellations. Each Voronoi cell is formulated as a polyhedral finite element containing an arbitrary number of vertices and faces. Fracture surfaces are allowed to nucleate only at the intercell faces. Cohesive softening tractions are applied to new fracture surfaces in order to model the energy dissipated during fracture growth. The randomly seeded Voronoi cells provide a regularized discrete random network for representing fracture surfaces. The potential crack paths within the random network are viewed as instances of realizable crack paths within the continuum material. Mesh convergence of fracture simulations is viewed in a weak, or distributional, sense. The explicit facet representation of fractures within this approach is advantageous for modeling contact on new fracture surfaces and fluid flow within the evolving fracture network. Finally, applications of interest include fracture and fragmentation in quasi-brittle materials and geomechanical applications such as hydraulic fracturing, engineered geothermal systems, compressed-air energy storage, and carbon sequestration.

97 MATHEMATICS AND COMPUTING↗