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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 937 records · Page 52
All sourcesNASA NTRSDOE OSTI
DOE OSTI2019

Neutronic and thermal-hydraulic feasibility studies for High Flux Isotope Reactor conversion to low-enriched uranium silicide dispersion fuel

An iterative design process involving neutronic and thermal-hydraulic modeling and simulation has been employed to assess the feasibility of converting the Oak Ridge National Laboratory (ORNL) High Flux Isotope Reactor (HFIR) from high-enriched uranium (HEU) to low-enriched uranium (LEU) silicide dispersion fuel. ORNL is funded by the National Nuclear Security Administration to evaluate HFIR conversion. Previous HFIR conversion studies focused on U-10Mo monolithic fuel; however, due to potential fabrication issues with the complex HFIR U-10Mo fuel design, ORNL is evaluating U 3 Si 2 -Al dispersion fuel as an alternative LEU fuel system.Fueled by 10.1 kg of HEU and operated at 85 MW, HFIR provides one of the highest steady-state neutron fluxes of any research reactor in the world. Retrofitting a compact, high-power density, HEU-based core with LEU is a challenging problem to solve, especially when considering the conversion requirements. Neutronic and thermal-hydraulic analyses were performed with Shift and HSSHTC, respectively, to predict reactor performance and thermal safety margins. A number of designs were proposed and evaluated using an iterative approach in an effort to show that reactor performance could match that obtained using HEU fuel and that thermal safety margins were adequate. Furthermore this study concludes that conversion of HFIR with U 3 Si 2 -Al LEU fuel is feasible if, among other requirements, the fuel meat region is centered and symmetric about the fuel plate thickness centerline, the active fuel zone length is increased from 50.80 cm to 55.88 cm, the proposed fabrication tolerances can be met, and the fuel can be qualified for HFIR conditions.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2019

Unprecedented peroxidase-mimicking activity of single-atom nanozyme with atomically dispersed Fe–Nx moieties hosted by MOF derived porous carbon

Due to robustness, easy large-scale preparation and low cost, nanomaterials with enzyme-like characteristics (defined as ‘nanozymes’) are attracting increasing interest for various applications. However, most of currently developed nanozymes show much lower activity in comparison with natural enzymes, and the deficiency greatly hinders their use in sensing and biomedicine. Single-atom catalysts (SACs) offer the unique feature of maximum atomic utilization, providing a potential pathway to improve the catalytic activity of nanozymes. Herein, we propose a Fe-N-C single-atom nanozyme (SAN) that exhibits unprecedented peroxidase-mimicking activity. The SAN consists of atomically dispersed Fe-Nx moieties hosted by metal–organic frameworks (MOF) derived porous carbon. Thanks to the 100% single-atom active Fe dispersion and the large surface area of the porous support, the Fe-N-C SAN provided a specific activity of 57.76 U mg-1, which was almost at the same level as natural horseradish peroxidase (HRP). Attractively, the SAN presented much better storage stability and robustness against harsh environments. As a proof-of-concept application, highly sensitive biosensing of butyrylcholinesterase (BChE) activity using the Fe-N-C SAN as a substitute for natural HRP was further verified.

Niu, Xiangheng↗
DOE OSTI2020

Modeling of Hidden Structures Using Sparse Chemical Shift Data from NMR Relaxation Dispersion

NMR relaxation dispersion measurements report on conformational changes occurring on the μs-ms timescale. Chemical shift information derived from relaxation dispersion can be used to generate structural models of weakly populated alternative conformational states. Current methods to obtain such models rely on determining the signs of chemical shift changes between the conformational states, which are difficult to obtain in many situations. Here, we use a “sample and select” method to generate relevant structural models of alternative conformations of the C-terminal-associated region of Escherichia coli dihydrofolate reductase (DHFR), using only unsigned chemical shift changes for backbone amides and carbonyls ( 1 H, 15 N, and 13 C'). We find that CS-Rosetta sampling with unsigned chemical shift changes generates a diversity of structures that are sufficient to characterize a minor conformational state of the C-terminal region of DHFR. The excited state differs from the ground state by a change in secondary structure, consistent with previous predictions from chemical shift hypersurfaces and validated by the x-ray structure of a partially humanized mutant of E. coli DHFR (N23PP/G51PEKN). The results demonstrate that the combination of fragment modeling with sparse chemical shift data can determine the structure of an alternative conformation of DHFR sampled on the μs-ms timescale. Such methods will be useful for characterizing alternative states, which can potentially be used for in silico drug screening, as well as contributing to understanding the role of minor states in biology and molecular evolution.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

Multizonal modeling of SARS-CoV-2 aerosol dispersion in a virtual office building

The dispersion of indoor airborne contaminants across different zones within a mechanically ventilated building is a complex phenomenon driven by multiple factors. In this study, we modeled the indoor dispersion of airborne SARS-CoV-2 aerosols within a US Department of Energy detailed medium office prototype building using CONTAM software. The aim of this study is to improve our understanding about how different parts of a building can experience varying concentrations of the airborne viruses under different circumstances of release and mitigation strategies. Results indicate that unventilated stairwells can have significantly higher concentrations of airborne viruses. The mitigation strategies of morning and evening flushing of conditioned zones were not found to be very effective. Instead, a constant high percentage of outdoor air in the supply mix, and the use of masks, portable HEPA air cleaners, MERV 13 or higher HVAC air filters, and ultraviolet germicidal irradiation disinfection were effective strategies to prevent airborne viral contamination in the majority of the simulated office building.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2025

Activity and selectivity for CO 2 methanation of clusters and nanoplates of ruthenium dispersed on ceria: In-situ studies with XAFS and DRIFTS

The performance of Ru/CeO 2 catalysts under CO 2 hydrogenation conditions was studied using in situ X-ray absorption fine structure (XAFS) and diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) to understand the structural evolution and chemical nature of each component under reaction conditions. The catalysts were prepared using a reverse microemulsion method that maximized the dispersion of RuOx particles on ceria. A RuO x → Ru transformation was observed upon exposure of the RuO x /CeO 2 systems to H 2 at 250 °C. For a sample with 5% molar Ru, two-dimensional clusters (2-4 atoms) of Ru formed on top of the ceria support. An increase in the loading of ruthenium to 20% molar led to the formation of nanoplates of the metal 2-3 atomic layers thick. Both Ru structures were highly dispersed on ceria. They were oxidized after exposure to CO 2 at 250 °C. However, under CO 2 /H 2 mixture, they remained in a metallic state as two-dimensional clusters and nanoplates. In situ DRIFTS studies, the 5% and 20% Ru/CeO 2 catalysts showed distinct reaction intermediates when exposed to CO 2 or CO 2 /H 2 (1/4) reaction mixtures. Normalized to the Ru molar percentage, the 5% Ru/CeO 2 system was the most active catalyst exhibiting a selectivity of ~ 60% CH 4 and 40% CO at 250 °C. On the other hand, under the same reaction conditions, the 20% Ru/CeO 2 system was less active but had a CH 4 selectivity close to 80%. In conclusion, these results highlight the importance of the structure of the metallic Ru particles as a factor that determines the catalytic performance.

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

Acetylene ligands stabilize atomically dispersed supported rhodium complexes under harsh conditions

Facile sintering of atomically dispersed supported noble metal catalysts at catalytically relevant temperatures, particularly under reducing conditions, poses a challenge for their practical applications. Some ligands, such as carbonyls, aid in improving the stability at the expense of severely suppressing the catalytic activity. In this work, we demonstrate that substitution of the carbonyl ligands with reactive acetylene ligands can maintain the atomic dispersion of the supported mononuclear rhodium complex under harsh reducing conditions (>573 K), as confirmed by in-situ X-ray absorption near-edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) spectroscopies. In contrast, the supported rhodium carbonyl complex aggregates into nanoclusters under identical conditions. Furthermore, our results indicate that the acetylene ligands provide this anti-sintering ability while retaining the hydrogenation activity.

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

Influence of MWCNT/surfactant dispersions on the rheology of Portland cement pastes

This work studies the effect of MWCNT/surfactant aqueous dispersions on the rheology of cement paste. Three types of surfactants (sodium dodecyl sulfate, cetylpyridinium chloride and triton TX-100) were used to prepare cement pastes with and without MWCNT. Three rheological parameters were determined for each sample: static yield stress, yield stress, and viscosity. The first was measured directly, while the other two were obtained by fitting a Bingham model to the descending portion of a flow curve. Additionally, X-ray diffraction and isothermal calorimetry were used to follow the hydration reaction of cement during the first hour. It was found that the MWCNT/surfactant dispersions generate an overall shift to higher yield stress values while maintaining viscosity, suggesting a modification of the interparticle attraction. It was concluded that the triple interaction MWCNT-surfactant-cement governs the rheology of cement pastes.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Direct in situ observation of electric field assisted densification of ZnO by energy dispersive X-ray diffraction

Electric field assisted sintering techniques are used to enhance the densification process, reducing sintering time and temperature. Here, we report the in situ characterization of non-isothermal densification behavior of zinc oxide under simultaneous application of thermal and electric field by energy dispersive X-ray diffraction. 99% density was achieved under the electric field of 50 V/mm in the 588–843 °C range in a short time without grain growth. The in-situ energy dispersive X-ray diffraction study revealed the abnormal volumetric unit cell expansion of 0.9% at 843 °C associated with the observed sudden rise of the power absorption by the specimen during densification. Furthermore, the variation in peak broadening as a function of time exhibited singularity in the 588–843 °C range implying the formation and rearrangement of defects correlated with densification during electric field assisted sintering.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Oxide dispersion strengthened 304 L stainless steel produced by ink jetting and laser powder bed fusion

This paper discusses the fundamentals of a novel hybrid method to synthesize oxide dispersion strengthened (ODS) 304 L stainless steel (SS) alloy using a modified laser powder bed fusion (LPBF) machine. Previously, ODS metal matrix composites have been produced by LPBF via ball-milling, which is expensive to scale. Here, we selectively dope yttria nanoparticles into a SS matrix by jetting a precursor chemistry onto the SS substrate prior to laser conversion and consolidation. Here, the new alloy shows good room temperature mechanical properties. Microstructures are studied using electron microscopy, energy dispersive spectroscopy and electron backscatter diffraction.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Modeling oxygen reduction activity loss mechanisms in atomically dispersed Fe–N–C electrocatalysts

Materials degradation is a major factor that limits the wider adoption of renewable and clean energy technologies. This is particularly true for the Pt group metal-free (PGM-free) atomically dispersed metal-nitrogen-carbon (M-N-C) catalysts. Here, while many experimental studies have investigated and reported the phenomenological aspects of M-N-C degradation, only a few modeling studies have considered degradation mechanisms at the atomic level. Understanding the mechanisms responsible for activity loss occurring in atomically dispersed M-N-C’s is crucial towards rationally designing active, durable, and less expensive Earth-abundant catalysts. Towards this end, we have surveyed recent literature concerning the modeling of corrosion mechanisms that impact M-N-C catalysts (Fe–N–C, in particular) and offer our own perspectives on the future direction of this field.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Full-scale composting of sewage sludge and market waste: Stability monitoring and odor dispersion modeling

Highlights: • Composting process of different organic waste was monitored at full-scale. • Relationships among odor emissions and analytical and biological variables were found. • Removal of nitrogen and volatile solids was the main responsible for odor generation. • Biomethanization pretreatment reduced odor impact at the beginning of composting. • The highest odor immission occurred in summer season for a wind speed of 2.6 m/s. The aim of this study was to assess the odor immission derived from full-scale composting of different abundant and highly pollutant organic waste: sewage sludge with bulking agent (SL), sewage sludge pretreated through anaerobic digestion and supplemented with bulking agent (SL-AD), and market waste with olive leaves (MW-OL). The combination of dynamic olfactometry and Gaussian dispersion modeling allowed both the quantification of odor emissions from each waste and the evaluation of their global odorous impact in nearby urban areas. Wind speed, summer and winter seasons, and atmospheric conditions were considered in the dispersion model. The results revealed that high wind speed (2.6 m/s) increases the global odor immission in summer season, independently of atmospheric stability. However, the maximum odor immission concentration recommended for composting process was not exceeded in any case, which depends on each country/region. The experimental results also enable to evaluate the influence of several physico-chemical variables on odor emissions derived from composting. The removal of nitrogen and volatile solids was the main cause for odor generation. Moreover, the microbiological activity of each substrate was monitored throughout the process and different percentages of biodegradability were quantified depending on the type of substrate and pretreatment applied.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2020

Dispersion of cryogenic hydrogen through high-aspect ratio nozzles

Liquid hydrogen is increasingly being used as a delivery and storage medium for stations that provide compressed gaseous hydrogen for fuel cell electric vehicles. In efforts to provide scientific justification for separation distances for liquid hydrogen infrastructure in fire codes, the dispersion characteristics of cryogenic hydrogen jets (50–64 K) from high aspect ratio nozzles have been measured at 3 and 5 bar abs stagnation pressures. These nozzles are more characteristic of unintended leaks, which would be expected to be cracks, rather than conventional round nozzles. Spontaneous Raman scattering was used to measure the concentration and temperature field along the major and minor axes. Within the field of interrogation, the axis-switching phenomena was not observed, but rather a self-similar Gaussian-profile flow regime similar to room temperature or cryogenic hydrogen releases through round nozzles. The concentration decay rate and half-widths for the planar cryogenic jets were found to be nominally equivalent to that of round nozzle cryogenic hydrogen jets indicating a similar flammable envelope. The results from these experiments will be used to validate models for cryogenic hydrogen dispersion that will be used for simulations of alternative scenarios and quantitative risk assessment.

08 HYDROGEN↗
DOE OSTI2021

Amorphous dispersions of flubendazole in hydroxypropyl methylcellulose: Formulation stability assisted by pair distribution function analysis

Here, we use X-ray pair distribution function (PDF) analysis applied to high-energy synchrotron X-ray powder diffraction data to evaluate the amorphous solid dispersions interactions and their aging stability. The obtained systems are based on hydroxypropyl methylcellulose (hypromellose) derivatives and flubendazole (FBZ) drug dispersions prepared using a spray-dryer technique. We carry out stability studies under aging parameters (40 °C/75% relative humidity) to tune the systems’ recrystallization. The results reveal that ion-base interactions between the drug-polymer matrix are responsible for reducing clustering processes yielding slower recrystallization and different ordering in the hypromellose phthalate (HPMCP/FBZ) and hypromellose acetate succinate (HPMC-AS/FBZ) systems and complete drug clustering in hypromellose (HPMC-E3/FBZ). The structural ordering was accessed using differential X-ray PDFs that revealed the region between 3.5 Å and 5.0 Å could be related to FBZ intermolecular interactions and is more ordered for the least stable system (HPMC-E3/FBZ) and less ordered for the most stable system (HPMCP/FBZ). These results show that the ion-base interactions between drug and matrix occur at these intermolecular distances.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2017

Elementary dispersion analysis of some mimetic discretizations on triangular C-grids

Spurious modes supported by triangular C-grids limit their application for modeling large-scale atmospheric and oceanic flows. Their behavior can be modified within a mimetic approach that generalizes the scalar product underlying the triangular C-grid discretization. The mimetic approach provides a discrete continuity equation which operates on an averaged combination of normal edge velocities instead of normal edge velocities proper. An elementary analysis of the wave dispersion of the new discretization for Poincaré, Rossby and Kelvin waves shows that, although spurious Poincaré modes are preserved, their frequency tends to zero in the limit of small wavenumbers, which removes the divergence noise in this limit. However, the frequencies of spurious and physical modes become close on shorter scales indicating that spurious modes can be excited unless high-frequency short-scale motions are effectively filtered in numerical codes. We argue that filtering by viscous dissipation is more efficient in the mimetic approach than in the standard C-grid discretization. Lumping of mass matrices appearing with the velocity time derivative in the mimetic discretization only slightly reduces the accuracy of the wave dispersion and can be used in practice. Thus, the mimetic approach cures some difficulties of the traditional triangular C-grid discretization but may still need appropriately tuned viscosity to filter small scales and high frequencies in solutions of full primitive equations when these are excited by nonlinear dynamics.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2024

Comparison of atmospheric radionuclide dispersion models for a risk-informed consequence-driven advanced reactor licensing framework

Current nuclear facility emergency planning zones (EPZs) are based on outdated distance-based criteria, predating comprehensive dose and risk-informed frameworks. Recent advancements in simulation tools have permitted the development of site-specific, dose, and risk-based consequence-driven assessment frameworks. This study investigated the computation of advanced reactor (AR) EPZs using two atmospheric dispersion models: a straight-line Gaussian plume model (GPM) and a semi-Lagrangian Particle in Cell (PIC). Two case studies were conducted: (1) benchmarking the NRC SOARCA study for the Peach Bottom Nuclear Generating Station and (2) analyzing an advanced INL Heat Pipe Design A microreactor's end-of-cycle inventory. The dose criteria for both cases were 10 mSv at mean weather conditions and 50 mSv at 95th percentile weather conditions at 96 h post-release. Results demonstrated that GPM and PIC estimated similar mean peak dose levels for large boiling water reactors in the farfield case, placing EPZ limits beyond current regulations. For ARs with source terms remaining in the nearfield, PIC modeling without specific nearfield considerations could result in excessively high doses and inaccurate EPZ designations. PIC dispersion demonstrated an order of magnitude higher estimate of nearfield inhalation dose contribution when compared to GPM results. Furthermore, both models significantly reduced EPZ sizing within the nearfield. Thus, reductions in the AR source term may eliminate the need for a separate EPZ.

63 RADIATION, THERMAL, AND OTHER ENVIRON. POLLUTAN↗
DOE OSTI2026

The effect of varying powder feedstock chemistry and printing atmosphere on the microstructure of additively manufactured nickel-based ODS alloys: Role on stabilization of cellular structures vs. oxide dispersion formation

Nickel-based alloys have a wide variety of structural applications due to their high corrosion resistance and mechanical strength which depend on solid solution strengthening, or the formation of oxides and/or intermetallic precipitation for their properties. In this study, the microstructure of six Ni–Cr–Y–Ti–Al powder batches designed for the production of oxide dispersion strengthened nickel were compared. These batches varied in chemistry and atomization technique used which included Gas Atomization Reactive Synthesis (GARS). The batches of powder were then consolidated via Additive Manufacturing (AM) Powder Bed Fusion using Laser Beam (PBF-LB) and characterized via transmission electron microscopy to elucidate the influence of powder feedstock (i.e. synthesis methodology and chemistry) on the PBF-LB microstructure. The study investigates (i) how the amount of yttrium and titanium additions in the powder feedstock and the addition of oxygen during the processing (through GARS) affect the microstructure of the powder itself and the AM printed microstructure, and (ii) how the control of oxygen addition in the printing atmosphere during the PBF-LB printing process itself is another important parameter for achieving the formation of the wanted oxide dispersion versus the stabilization of the cellular structure (often observed in AM processed alloys). Microstructural characterization of both powder particles and additively manufactured nickel alloys in this study provide important insights into the movement of yttrium within the material upon solidification, particularly along cell boundaries, and how yttrium behaves depending on alloy chemistry. When a threshold of yttrium content is reached within the system, yttrium consistently reacts to form an intermetallic along cell boundaries instead of forming oxide nanoparticles.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Selective laser sintering of MA956 oxide dispersion strengthened steel

Oxide Dispersion Strengthened (ODS) steels’ qualities of radiation damage resistance and high strength at high temperature make them promising nuclear structural materials. However, the dispersed yttria that gives ODS steel its beneficial qualities are generally compromised during joining processes, making fabrication difficult and expensive. The selective laser sintering process offers a potential path through this barrier by which net-shape parts can feasibly be built via additive manufacturing without fully melting the structure. By rastering a 400 W laser over a MA956 ODS steel powder bed, here we additively built parts with varying build conditions. Although density was achieved to within 97% of the wrought MA956, ultimate tensile strengths achieved only 65% of the wrought strength. Spectroscopy analysis points to the agglomeration of the yttria nano-particles as a possible explanation for the loss in strength. Further study might benefit from exploration of other parameters such as thinner powder build layers which would require less energy input to achieve sintering while minimizing time above the melting temperature.

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

First-principles study of thermophysical properties of interaction layer products in U-Mo/Al dispersion fuel

Thermophysical properties of interaction layer (IL) formed in U-Mo/Al dispersion fuel are important for the evaluation of its impact on the fuel performance. Binary and ternary phases observed in the IL, however, are not well studied yet. Recently we predicted the thermophysical properties of the binary U-Al compounds in U-Al system using density functional theory (DFT) calculations. In this paper, we investigated the structural, elastic, electronic, vibrational and thermodynamic properties of the ternary U-Mo-Al compounds formed in IL, including (U 0.75 ,Mo 0.25 )Al 3 , U 6 Mo 4 Al 43 and UMo 2 Al 20 , using DFT calculations. The polycrystalline aggregate properties of these compounds were obtained from the predicted single crystal elastic constants. The calculated electronic density of states confirm that all of the compounds exhibit typical metallic behavior with the majority states at the Fermi level dominated by U 5 f electrons. Using quasi-harmonic approximation, we predicted the thermodynamic properties of these compounds by including both electronic and lattice contributions. We also investigated the effect of density on the thermodynamic properties of (U 0.75 ,Mo 0.25 )Al 3 phase. Here, the current results are expected to be helpful to the modeling of the fuel performance of U-Mo/Al dispersion fuel and the thermodynamic modeling of the ternary U-Mo-Al system.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗