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A nuclear reactor is disclosed including a reactor core and a reflector assembly surrounding the reactor core. The reflector assembly includes a stationary reflector component including a graphite support structure comprising a plurality of channels defined therein and a plurality of beryllium-oxide pins positioned in the channels.
Carbon fiber preforms are printed in a Quasi-Isotropic layup, where the fibers are aligned to the X and Y axes, and ±45° in plane. Thermal and electrical conductivity values along the fiber axes are comparable to graphite but are extremely low through the Z axis. Low conductivity (high resistivity) in the axis of current flow enables more efficient Joule heating.
Presentation for 2024 U.S. Department of Energy National Energy Technology Laboratory Resource Sustainability Project Review Meeting, Pittsburgh, Pennsylvania.
Abstract Developing functionally complex carbon materials from small aromatic molecules requires an understanding of how the chemistry and structure of its constituent molecules evolve and crosslink, to achieve a tailorable set of functional properties. Here, molecular dynamics (MD) simulations are used to isolate the effect of methyl groups on condensation reactions during the oxidative process and evaluate the impact on elastic modulus by considering three monodisperse pyrene‐based systems with increasing methyl group fraction. A parameter to quantify the reaction progression is designed by computing the number of new covalent bonds formed. Utilizing the previously developed MD framework, it is found that increasing methylation leads to an almost doubling of bond formation, a larger fraction of the new bonds oriented in the direction of tensile stress, and a higher basal plane alignment of the precursor molecules along the direction of tensile stress, resulting in enhanced tensile modulus. Additionally, via experiments, it is demonstrated that precursors with a higher fraction of methyl groups result in a higher alignment of molecules. Moreover, increased methylation results in the lower spread of single molecule alignment which may lead to smaller variations in tensile modulus and more consistent properties in carbon materials derived from methyl‐rich precursors.
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Application of advanced anode and cathode materials in commercial lithium-ion batteries is attracting attention due to their high capacity. Silicon (Si)/graphite anodes and nickel (Ni)-rich lithium nickel manganese cobalt oxide with layered structures have been paired in commercial 18650 high energy density cells (~270 Wh/kg). It is crucial to investigate the cell performance and the aging behavior of this commercial cell. In this study, we present commercial cell degradation mechanisms by comparing fresh and aged electrodes, including changes of crystal structure, morphology, elemental composition, and electrochemical properties. The quantitative analysis was done based on dV/dQ incremental capacity analysis of 18650 cells. To determine the amount of cyclable lithium ions (Li + ) and active material loss, the lithiation and delithiation capacity were compared for fresh and aged electrodes in half coin cells. Results showed that even with 5% (by mass) of Si added in the anode, cracks occurred across the anode leading to contact loss and thickening of the solid electrolyte interphase (SEI) layer. Additionally, the average fluorine (F) ratio of the aged anodes was higher compared to that of the fresh anodes. More severely, the F content on the Si aggregations on aged anodes increased to as high as 5 times that of the fresh anode, indicating SEI growth, especially on Si particles. Solid 7 Li nuclear magnetic resonance results showed no detectable Li metal deposition on the aged anode. On the cathode side, cracks on the primary particle interfaces contributed to cathode material loss, contact loss, and impedance rise. Furthermore, Li + loss into the thickened SEI layer, particle cracking, and impedance rise are the main reasons behind cell degradation.
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Highlights: • Bulk g-C{sub 3}N{sub 4} and its exfoliated form have been synthesized at different temperatures and characterized in detail. • Exfoliation proces increased oxidizing power of holes and enabled direct phenol degradation. • High-power visible LEDs improved significantly photocatalytic production of H{sub 2}O{sub 2} over exfoliated g-C{sub 3}N{sub 4}. • Synergistic effect between LEDs and exfoliated g-C{sub 3}N{sub 4} materials was observed. - Abstract: Exfoliated g-C{sub 3}N{sub 4} materials were prepared by thermal treatment of bulk materials synthesized from melamine at 4 different temperatures in range from 500 to 600 °C. The exfoliated g-C{sub 3}N{sub 4} synergically increased the photocatalytic degradation of phenol as effects like the fast production of H{sub 2}O{sub 2}, the presence of more active holes for direct phenol degradation and the use of high-power visible (416 nm) LEDs as irradiation source. The amount of phenol initially present was 99% converted in 15 min. All materials were also tested for comparison only in UVA region by using high-power UV (370 nm) LEDs. All prepared materials were thoroughly characterized by several analytical methods. In this work, the combination of g-C{sub 3}N{sub 4} after thermal treatment and high-power visible LEDs reduced the time needed for complete phenol degradation from several hours to just a few minutes. The mechanism of phenol degradation was also studied by introducing different active species scavengers into the reaction medium.
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