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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 91 records · Page 5
All sourcesNASA NTRSDOE OSTI
DOE OSTI2026

Development of SAM Code Capabilities for Safety Analysis of GCR Air-ingress Events

Air-ingress following a depressurized loss-of-forced-cooling (DLOFC) event is a challenging, multiphysics safety scenario for High-Temperature Gas-Cooled Reactors (HTGRs), involving coupled gas composition transport, buoyancy-driven flow redistribution, graphite oxidation, and structural heat-up. Despite its importance — air ingress is a key scenario identified in the PIRT process for the HTGRs — existing system-level safety codes have lacked the integrated capability to simulate the complete event sequence with high confidence. This report documents the development, validation, and demonstration of three new capabilities in the SAM code to address this gap: (1) a multi-component gas mixture flow model with binary diffusion to track the helium-air composition and its effect on system density and flow; (2) a 0-D graphite oxidation model based on the Roes correlation, including oxygen consumption and exothermic heat release; and (3) an isentropic critical flow model for accurate representation of primary system depressurization through a break. These capabilities are validated against two benchmark experiments. The NSTF heavy-gas ingress experiment validates the multi-component flow model: SAM correctly reproduces the rapid buoyancydriven flow stagnation and subsequent natural circulation recovery driven by composition-dependent density changes. The NACOK graphite oxidation experiment validates the oxidation model: SAM predicts a bottom-level graphite weight loss of 25%, in close agreement with the measured 24%, and reproduces the strong axial nonuniformity and block-geometry dependence of oxidation, at a level comparable to the SPECTRA and TINTE codes. The validated capabilities are then exercised together in an integrated, reactor-scale simulation of a DLOFC air-ingress transient in a simplified HTR-PM pebble-bed reactor. In a single calculation spanning approximately 8 days, SAM reproduces the complete accident sequence: rapid depressurization, densityand diffusion-driven air ingress over ˜15 hours, onset of buoyancy-driven natural circulation, exothermic graphite oxidation with a peak fuel temperature at ˜62 hours, and eventual passive cooldown. These results demonstrate that SAM now provides the nuclear community with a preliminarily validated, modern systemlevel tool for HTGR air-ingress safety analysis, filling a recognized capability gap. Future extensions to broaden species tracking, improve oxidation chemistry, and refine the reactor model are discussed.

Yang, Gang↗
DOE OSTI2015

Scalable Preparation of Ternary Hierarchical Silicon Oxide-Nickel-Graphite Composites for Lithium-Ion Batteries

Silicon monoxide is a promising anode candidate because of its high theoretical capacity and good cycle performance. To solve the problems associated with this material, including large volume changes during charge-discharge processes, we report a ternary hierarchical silicon oxide–nickel–graphite composite prepared by a facile two-step ball-milling method. The composite consists of nano-Si dispersed silicon oxides embedded in nano-Ni/graphite matrices (Si@SiOx/Ni/graphite). In the composite, crystalline nano-Si particles are generated by the mechanochemical reduction of SiO by ball milling with Ni. These nano-Si dispersed oxides have abundant electrochemical activity and can provide high Li-ion storage capacity. Furthermore, the milled nano-Ni/graphite matrices stick well to active materials and interconnect to form a crosslinked framework, which functions as an electrical highway and a mechanical backbone so that all silicon oxide particles become electrochemically active. Owing to these advanced structural and electrochemical characteristics, the composite enhances the utilization efficiency of SiO, accommodates its large volume expansion upon cycling, and has good ionic and electronic conductivity. The composite electrodes thus exhibit substantial improvements in electrochemical performance. This ternary hierarchical Si@SiOx/Ni/graphite composite is a promising candidate anode material for high-energy lithium-ion batteries. Additionally, the mechanochemical ball-milling method is low cost and easy to reproduce, indicating potential for the commercial production of the composite materials.

25 ENERGY STORAGE↗
DOE OSTI2018

Preparation of Exfoliated Graphite Modified with Magnesium Ferrite

A magnetic sorbent based on exfoliated graphite modified with magnesium ferrite has been prepared by impregnating oxidized graphite in a mixed solution of FeCl{sub 3} and Mg(NO{sub 3}){sub 2}, followed by heat treatment of the impregnated oxidized graphite in air. X-ray diffraction and Mössbauer spectroscopy results demonstrate that the structure of the magnesium ferrite is an inverse spinel with a degree of inversion of 0.59. The saturation magnetization of the magnesium ferrite-containing exfoliated graphite is 16.1 emu/g, whereas its oil sorption capacity is as high as 54 g/g. Compaction of the exfoliated graphite to a density of 0.03 g/cm{sup 3} reduced its sorption capacity to 26 g/g. Further increasing the density of the material led to a considerable decrease in its sorption capacity.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Fabrication and physicochemical characterization of graphene oxide derived from thermally expanded graphite

Graphene oxide was obtained from expanded graphite according to the modified Hummers method. The reaction time was significantly reduced (from 24 to 8 h) by applying the expanded graphite in the oxidation process. The interlayer distance in obtained samples was equal to 0.70–0.74 nm. Structural features of the material were studied by the powder X-ray diffraction, thermogravimetric analysis, scanning electron microscopy, transmission electron microscopy, XPS spectroscopy, and NMR spectroscopy.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2016

Using CFD tools to model separate effects of HTR air ingress accident phenomena - 18508

The air ingress phenomena under the HTR conditions represent the important area of nuclear safety. Best practice guidelines for the use of CFD in nuclear safety applications are mainly based on water cooled reactors while in HTR the gas is used as a coolant. The ambition of this paper is to define the best recommendations and description of needed settings of CFD models solving the separate effects of air ingress accident phenomena. The JAERI experiments deal with phenomena of air ingress during the early stages of the accident. Experiments investigate the basic features of the flow behavior of the gas mixture and regard the phenomena of the molecular diffusion and the natural convection of the gas mixture with the graphite oxidation reaction. The separate effects simulations of air ingress accident were performed using CFD code ANSYS Fluent. Whole graphite oxidation process including all three main chemical reactions was successfully modeled. The new findings and useful information were gathered to be extrapolated to the integral effects level for the following phase. The role of the computational mesh and all important input parameters were discussed in detail and many in sensitivity studies were performed. (authors)

21 SPECIFIC NUCLEAR REACTORS AND ASSOCIATED PLANTS↗
DOE OSTI2023

Catalyzed oxidation of nuclear graphite by simulated fission products Sr, Eu, and I

The influence of three fission products Sr, Eu, and I on the oxidation of IG-110 nuclear graphite was studied in the temperature range of 400 to 1000 °C. Sr and Eu were introduced as chlorides, and I was introduced as NaI. The temperature dependence of both CO 2 and CO production during the graphite oxidation measured with mass spectroscopy and infrared spectrometry shows that the introduction of these three compounds to graphite significantly decreases the onset temperature for the oxidation of graphite. Among the three compounds, NaI is the most active towards the oxidation reaction, characterized by a significant decrease of the onset temperature from approximately 650 to 400 °C before and after its introduction to graphite. Separate measurements of CO 2 and CO concentration at varying temperatures enable the calculation of the activation energy for the formation of CO 2 and CO. The activation energies for the oxidation of pure and fission product-impregnated graphite samples decrease in the following order: standard IG-110 graphite, EuCl 3 -impregnated IG-110, SrCl 2 -impregnated IG-110, and NaI-impregnated IG-110. This trend indicates that the three compounds catalyze the oxidation of graphite at temperatures relevant to the operation of high-temperature gas-cooled reactors. Furthermore, it is found that the three compounds can also affect the molar ratio of reaction products CO 2 and CO, and the rates of the graphite oxidation. At temperatures higher than about 850 °C, the impregnated samples exhibit lower CO 2 : CO ratios than the pure graphite. Different from EuCl 3 and NaI, the introduction of SrCl 2 decreases the graphite oxidation rates at temperatures higher than about 770 °C. Their catalytic mechanism can be understood based on a redox cycle of the intermediate active species, promoting the dissociation of molecular oxygen and transfer to the carbon.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2023

Nanoscale electrostatic control in ultraclean van der Waals heterostructures by local anodic oxidation of graphite gates

In an all-van der Waals heterostructure, the active layer, gate dielectrics and gate electrodes are assembled from two-dimensional crystals that have a low density of atomic defects. This design allows two-dimensional electron systems with very low disorder to be created, particularly in heterostructures where the active layer also has intrinsically low disorder, such as crystalline graphene layers or metal dichalcogenide heterobilayers. A key missing ingredient has been nanoscale electrostatic control, with existing methods for fabricated local gates typically introducing unwanted contamination. Here we describe a resist-free local anodic oxidation process for patterning sub-100 nm features in graphite gates, and their subsequent integration into an all-van der Waals heterostructure. We define a quantum point contact in the fractional quantum Hall regime as a benchmark device and observe signatures of chiral Luttinger liquid behaviour, indicating an absence of extrinsic scattering centres in the vicinity of the point contact. In the integer quantum Hall regime, we demonstrate in situ control of the edge confinement potential, a key requirement for the precision control of chiral edge states. In conclusion, this technique may enable the fabrication of devices capable of single anyon control and coherent edge-state interferometry in the fractional quantum Hall regime.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Ultracapacitor with a novel doped carbon

Doped activated microwave expanded graphite oxide materials and doped monolayer graphene materials, and methods of making these materials. The materials exhibit increased capacitance relative to undoped activated microwave expanded graphite oxide and monolayer graphene. The materials are suitable for use in, for example, ultracapacitors.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Insights from incorporating reference electrodes in symmetric lithium-ion cells with layered oxide or graphite electrodes

Symmetric cells provide complementary means to probe electrochemical processes in lithium-ion batteries. Here, positive and negative electrodes harvested from conventional oxide/graphite cells are cross-paired, and the assembled reference-electrode-bearing symmetric cells are cycled/aged. For graphite symmetric cells, the electrode potentials and impedances remain nearly constant during calendar aging and the parasitic currents are typically small. However, at higher cell voltages when the “positive” graphite potential exceeds 1.0 V vs. Li/Li + , the capacity loss is higher, indicating that even a mild (but prolonged) overdischarge can damage the SEI. For the layered-oxide symmetric cells there are strong parasitic currents and a persistent slide of the electrode potential over time during calendar aging. Significant cell impedance rise, especially at higher hold voltages, is also observed. Curiously, the impedance rise in the “negative” oxide electrode, which experiences potentials below 4.0 V vs. Li/Li + , is greater than in the “positive” oxide electrode that experiences much higher potentials. We postulate that electrolyte oxidation is responsible for the behavior of these oxide symmetric cells, as it supplies electrons (that bind more Li + into the cathode, causing the potential slide) and protons (that contribute to impedance rise). Furthermore, these insights can guide the development of future lithium-ion cell chemistries.

25 ENERGY STORAGE↗
DOE OSTI2018

Study of YBa{sub 2}Cu{sub 3}O{sub 7−δ} Superconductor/Graphene Oxide Composite

The aim of this research was to fabricate YBa{sub 2}Cu{sub 3}O{sub 7−δ} (YBCO) superconductor composite with graphene oxide nanosheets and to study the effect of the graphene oxide nanosheets on YBCO superconductor properties. For this purpose, the samples of pure superconductor and superconductor composite with 0.001, 0.01, and 0.1 wt.% graphene oxide were synthesized. First, graphite oxide was made by Hummer’s chemical method; after that, graphene oxide nanosheets were produced by bath-keeper ultrasonic. Then, different amounts of graphene oxide were added to the process of superconductor fabrication, which was made by solid-state reaction method. The samples were characterized and studied by Meissner effect test, XRD analysis, FESEM imaging, EDX measurement, and ac magnetic susceptibility. The critical current density (J{sub c}) of samples was measured by four probes method. The results showed that by increasing the weight ratio of graphene oxide, J{sub c} and T{sub c} decrease.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
NASA NTRS1980

Characterization of PMR-15 polyimide composition in thermo-oxidatively exposed graphite fiber composites

The contributions of individual resin components to total resin weight loss in 600 F air aged Celion 6000/PMR-15 polyimide composites were determined from the overall resin weight loss in the composite by chemically separating the PMR-15 matrix resin into its monomeric components. The individual resin components were also analyzed by spectroscopic techniques in order to elucidate curing and degradation mechanisms of the PMR-15 matrix resin. The isothermal weight loss of the individual resin components during prolonged 600 F thermo-oxidative aging of the composite was correlated to the changes observed in the Fourier Transform infrared spectra and Fourier Transform nuclear magnetic resonance spectra of the individual resin components. The correlation was used to identify the molecular site of the thermo-oxidative changes in PMR-15 polyimide matrix resin during 600 F curing the prolonged 600 F thermo-oxidative aging.

Alston, W. B.↗
DOE OSTI2020

Modeling Graphite Behavior (Fracture and Oxidation)

Purpose of this work Oxidation modeling Oxidation of full-scale components Local properties in oxidized components Graphite fracture strength Phase field fracture modeling Microstructurally informed fracture model IG-110 tensile results and comparison to experiment Work in progress and future work

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
NASA NTRS1980

High electrical resistivity carbon/graphite fibers

Carbon/graphite fibers were chemically oxidized in the liquid phase to fibers of graphite oxide. Resistivity increases as high as 10,000 times were obtained, the oxidized fiber decomposed on exposure to atmosphere. A factor of 1,000 remained as a stable increment. The largest change observed was 1,000,000 times. Best results were obtained on the most highly graphitized fibers. Electrochemical oxidation yielded a lower increase--about 10 times, but provided a controllable method of synthesis and insight to the mechanism of reaction. Tensile tests indicated that the strength of the fiber on oxidation was decreased by no more than 25 percent.

Vogel, F. L.↗
DOE OSTI2024

Overview of Graphite Model Development

Overview of graphite model development. Discuss graphite in motel salt, potential degradation mechanisms, stress due to volumetric heating, and the role of different parameters. Also wear modeling, modeling salt infiltration into graphite, oxidation modeling, and the existing graphite models.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗