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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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All sourcesNASA NTRSDOE OSTI
DOE OSTI2023

Release of a High Temperature Engineering Test Reactor (HTTR) Steady State Multiphysics Model to the Virtual Test Bed

In response to climate change, global governments and private industry have established a common goal of achieving net-zero emissions by 2050 \cite{osti_1865910}. This goal requires a reassessment of current energy demands and production methods. Reducing emissions at an affordable cost while maintaining grid reliability requires a nationwide collaborative effort among government and industry in the United States. Nuclear power is the leading low-carbon electricity generation method. In the past 50 years, the use of nuclear power has reduced carbon dioxide emissions by over 60 gigatons and has played a crucial role in the security of energy supply~\cite{IEA}. In the U.S., nuclear power accounts for 20\% of the electrical supply and provides energy reliably. Advanced reactors will operate at higher temperatures, operate more efficiently, utilize more energy stored within fuel, and reduce the amount of waste produced \cite{osti_1616270}. To face these challenges and goals, the U.S. Department of Energy has created an initiative to focus on the modeling and simulation tools to support future nuclear power plant design, licensing, and operations. The Virtual Test Bed (VTB)~\cite{vtb2023} was launched by the National Reactor Innovation Center (NRIC) in collaboration with the Nuclear Energy Advanced Modeling and Simulation (NEAMS) program to support the advanced nuclear reactor community. The VTB involves teams from both Idaho National Laboratory and Argonne National Laboratory and aims to provide example models for a broad range of both current and future advanced reactor designs. A feature of the VTB is the automatic testing of these models to ensure continued functionality as simulation tools are further developed. The VTB and the advanced reactor models documented there are important resources for this initiative. This work describes the inclusion of a new model on the VTB---a High Temperature Engineering Test Reactor (HTTR) steady-state model \cite{LABOURE2023109838}.

22 GENERAL STUDIES OF NUCLEAR REACTORS↗
DOE OSTI2023

Release of a High Temperature Engineering Test Reactor (HTTR) Steady-State Multiphysics Model to the Virtual Test Bed

The National Reactor Innovation Center (NRIC) accelerates the demonstration and deployment of advanced nuclear energy through inspiring stakeholders and the public, empowering innovators, and delivering successful outcomes. The Virtual Test Bed (VTB) supports this mission by providing an open-source repository of advanced test reactor models for industry, academia, and the public to utilize. During my time at Idaho National Laboratory (INL), I: • Verified the input files of the High Temperature Engineering Test Reactor • Generated computational results • Created user documentation for the HTTR • Uploaded a steady-state HTTR model to the Virtual Test Bed • Authored a conference publication on the model

22 GENERAL STUDIES OF NUCLEAR REACTORS↗
DOE OSTI2016

The many phases of CaC{sub 2}

Polymorphic CaC{sub 2} was prepared by reacting mixtures of CaH{sub 2} and graphite with molar ratios between 1:1.8 and 1:2.2 at temperatures between 700 and 1400 °C under dynamic vacuum. These conditions provided a well controlled, homogeneous, chemical environment and afforded products with high purity. The products, which were characterized by powder X-ray diffraction, solid state NMR and Raman spectroscopy, represented mixtures of the three known polymorphs, tetragonal CaC{sub 2}-I and monoclinic CaC{sub 2}-II and -III. Their proportion is dependent on the nominal C/CaH{sub 2} ratio of the reaction mixture and temperature. Reactions with excess carbon produced a mixture virtually free from CaC{sub 2}-I, whereas high temperatures (above 1100 °C) and C-deficiency favored the formation of CaC{sub 2}-I. From first principles calculations it is shown that CaC{sub 2}-I is dynamically unstable within the harmonic approximation. This indicates that existing CaC{sub 2}-I is structurally/dynamically disordered and may possibly even occur as slightly carbon-deficient phase CaC{sub 2-δ}. It is proposed that monoclinic II is the ground state of CaC{sub 2} and polymorph III is stable at temperatures above 200 °C. Tetragonal I represents a metastable, heterogeneous, phase of CaC{sub 2}. It is argued that a complete understanding of the occurrence of three room temperature modifications of CaC{sub 2} will require a detailed characterization of compositional and structural heterogeneities within the high temperature form CaC{sub 2}-IV, which is stable above 450 °C. The effect of high pressure on the stability of the monoclinic forms of CaC{sub 2} was studied in a diamond anvil cell using Raman spectroscopy. CaC{sub 2}-II and -III transform into tetragonal CaC{sub 2}-I at about 4 and 1GPa, respectively. - Graphical abstract: The famous tetragonal form of CaC{sub 2}, CaC{sub 2}-I, is dynamically unstable. Why does it exist? Display Omitted - Highlights: • Critical review of complex polymorphism of the commodity chemical CaC{sub 2}. • Tetragonal CaC{sub 2}-I is identified as dynamical instable and its existence attributed to disorder. • With pressure monoclinic CaC{sub 2}-II and –III transform into tetragonal CaC{sub 2}-I. • The high temperature form CaC{sub 2}-IV is assigned a key role for understanding the polymorphism of CaC{sub 2}.

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

Transient Spectroscopy of Glass-Embedded Perovskite Quantum Dots: Novel Structures in an Old Wrapping

Semiconductor doped glasses had been used by the research and engineering communities as color filters or saturable absorbers well before it was realized that their optical properties were defined by tiny specs of semiconductor matter known presently as quantum dots (QDs). Nowadays, the preferred type of QD samples are colloidal particles typically fabricated via organometallic chemical routines that allow for exquisite control of QD morphology, composition and surface properties. However, there is still a number of applications that would benefit from the availability of high-quality glass-based QD samples. These prospective applications include fiber optics, optically pumped lasers and amplifiers and luminescent solar concentrators (LSCs). In addition to being perfect optical materials, glass matrices could help enhance stability of QDs by isolating them from the environment and improving heat exchange with the outside medium. We conduct optical studies of a new type of all-inorganic CsPbBr 3 perovskite QDs fabricated directly in glasses by high-temperature precipitation. These samples are virtually scattering free and exhibit excellent waveguiding properties which makes them well suited for applications in, for example, fiber optics and LSCs. However, the presently existing problem is their fairly low room-temperature emission quantum yields of only ca. 1%–2%. Here we investigate the reasons underlying the limited emissivity of these samples by conducting transient photoluminescence (PL) and absorption measurements across a range of temperatures from 20 to 300K. We observe that the low-temperature PL quantum yield of these samples can be as high as ~25%. However, it quickly drops (in a nearly linear fashion) with increasing temperature. Interestingly, contrary to traditional thermal quenching models, experimental observations cannot be explained in terms of a thermally activated nonradiative rate but rather suggest the existence of two distinct QD sub-ensembles of “emissive” and completely “nonemissive” particles. The temperature-induced variation in the PL efficiency is likely due to a structural transformation of the QD surfaces or interior leading to formation of extremely fast trapping sites or nonemissive phases resulting in conversion of emissive QDs into nonemissive. Thus, future efforts on improving emissivity of glass-based perovskite QD samples might focus on approaches for extending the range of stability of the low-temperature highly emissive structure/phase of the QDs up to room temperature.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
NASA NTRS1990

High-temperature thermal storage systems for advanced solar receivers materials selections

Advanced space power systems that use solar energy and Brayton or Stirling heat engines require thermal energy storage (TES) systems to operate continuously through periods of shade. The receiver storage units, key elements in both Brayton and Stirling systems, are designed to use the latent heat of fusion of phase-change materials (PCMs). The power systems under current consideration for near-future National Aeronautics and Space Administration space missions require working fluid temperatures in the 1100 to 1400 K range. The PCMs under current investigation that gave liquid temperatures within this range are the fluoride family of salts. However, these salts have low thermal conductivity, which causes large temperature gradients in the storage systems. Improvements can be obtained, however, with the use of thermal conductivity enhancements or metallic PCMs. In fact, if suitable containment materials can be found, the use of metallic PCMs would virtually eliminate the orbit associated temperature variations in TES systems. The high thermal conductivity and generally low volume change on melting of germanium and alloys based on silicon make them attractive for storage of thermal energy in space power systems. An approach to solving the containment problem, involving both chemical and physical compatibility, preparation of NiSi/NiSi2, and initial results for containment of germanium and NiSi/NiSi2, are presented.

Wilson, D. F.↗
NASA NTRS1976

Preliminary results from screening tests of commercial catalysts with potential use in gas turbine combustors. Part 2: Combustion test rig evaluation

Several commercial monolithic catalysts were tested in a combustion test rig to determine their suitability for use in a gas turbine combuster primary zone. The catalyst test bed consisted of two to four elements of 12-centimeter diameter by 2.5-centimeter long monolith. Results are presented of the measured combustion efficiency and catalyst bed temperature history for an inlet propane-air mixture temperature of 800 K, a pressure of 300,000 newtons per square meter, inlet velocities of 10 to 25 meters per second and equivalence ratios of 0.1 to 0.3. The best catalysts tested gave combustion efficiencies of virtually 100 percent for reaction temperatures ranging from 1,325 K at 10 meters per second to 1,400 K at 25 meters per second. This performance was only possible with fresh catalysts. The catalysts tested were not specifically developed for use at these conditions and showed some loss in activity after about 3 hours' testing.

Anderson, D. N.↗
DOE OSTI2024

Spin Polarons and Ferromagnetism in Doped Dilute Moiré-Mott Insulators

Moiré heterostructures of transition metal dichalcogenides (TMDs) exhibit Mott-insulating behavior both at half filling as well as at fractional fillings, where electronic degrees of freedom form self-organized Wigner crystal states. An open question concerns magnetic states obtained by lifting the pseudospin-1/2 degeneracy of these states at lowest temperatures. While at half filling virtual hopping is expected to induce (weak) antiferromagnetic exchange interactions, these are strongly suppressed when considering dilute filling fractions. We argue that, instead, a small concentration of doped electrons leads to the formation of spin polarons, inducing ferromagnetic order at experimentally relevant temperatures, consistent with recently observed ferromagnetic states in moiré TMD systems. Here, we predict explicit signatures of polaron formation in the magnetization profile.

Kondo lattice model↗
DOE OSTI2017

Enhanced electrical penetration components meet the high safety standards required for China's HTR-PM Shidaowan and generation mPower small modular reactors - 300

Enhanced glass-to-metal feedthroughs will be used to carry key instrumentation and control (I and C) signals in China's high-temperature, gas-cooled pebble-bed modular reactor (HTR-PM) at Shidaowan, and in Small Modular Reactor (SMR) prototyping. Chinergy Co., Ltd and Jiamusi Electric Machine Co., Ltd will use the feedthroughs, also called electrical penetration assemblies (EPAs), at the Shidaowan twin-reactor high temperature reactor (HTR). These feedthroughs are manufactured using specialized processes that make them far more robust than counterparts made with organic or ceramic materials. Improved EPAs manufactured by SCHOTT are the only feedthrough solution that can be used in the primary loop of an HTR because organic seals cannot withstand the high temperatures and pressures of this environment. Glass-to-metal seals (GTMS) are made using inorganic, non-aging materials which enable a virtually unlimited lifespan in high-temperature, high-radiation and high-pressure applications. This I and C technology package is being enhanced by the development and testing of new mineral-insulated (MI) cable connectors and EPAs made of crystallized glass-ceramic combined with superalloys. The EPAs have a maintenance-free lifespan of over 60 years, preventing any outage time related to these components and subsequently reducing costs associated with shutdowns. They are far more robust than organic seals and provide increased safety at a lower lifetime cost. Resistance against high pressure and high temperature are especially ideal qualities that make EPAs a valuable choice for environments with high standards for fire protection, such as nuclear plants, subsea oil drilling, or any other underwater application. Due to their significant offering of safety-relevant qualities, the EPAs have also been chosen by BWXT for implementation in its mPower SMR. Small modular reactor requirements are complex and very challenging but are met by the new EPA components, which will help form a strong I and C safety chain. Unlike ordinary compression glass-to-metal seals, GTMS with crystallized glass-ceramic have the ability to withstand temperatures of over 350 deg. C / 662 deg. F and operating pressures of 3500 bar. Furthermore, their lifetime is qualified for up to 60 years, including pressure and radiation requirements in accordance with the latest IEC/IEEE standards. Higher-specification EPAs and MI cable connectors have been designed into severe accident I and C instruments, including advanced hydrogen and oxygen sensors that exceed the challenging requirements of both HTR and SMR applications. (authors)

21 SPECIFIC NUCLEAR REACTORS AND ASSOCIATED PLANTS↗
NASA NTRS1982

Development of a static feed water electrolysis system

A one person level oxygen generation subsystem was developed and production of the one person oxygen metabolic requirements, 0.82 kg, per day was demonstrated without the need for condenser/separators or electrolyte pumps. During 650 hours of shakedown, design verification, and endurance testing, cell voltages averaged 1.62 V at 206 mA/sq cm and at average operating temperature as low as 326 K, virtually corresponding to the state of the art performance previously established for single cells. This high efficiency and low waste heat generation prevented maintenance of the 339 K design temperature without supplemental heating. Improved water electrolysis cell frames were designed, new injection molds were fabricated, and a series of frames was molded. A modified three fluid pressure controller was developed and a static feed water electrolysis that requires no electrolyte in the static feed compartment was developed and successfully evaluated.

Schubert, F. H.↗
DOE OSTI2018

Predicted Chance That Global Warming Will Temporarily Exceed 1.5 °C

Abstract The Paris Agreement calls for efforts to limit anthropogenic global warming to less than 1.5 °C above preindustrial levels. However, natural internal variability may exacerbate anthropogenic warming to produce temporary excursions above 1.5 °C. Such excursions would not necessarily exceed the Paris Agreement, but would provide a warning that the threshold is being approached. Here we develop a new capability to predict the probability that global temperature will exceed 1.5 °C above preindustrial levels in the coming 5 years. For the period 2017 to 2021 we predict a 38% and 10% chance, respectively, of monthly or yearly temperatures exceeding 1.5 °C, with virtually no chance of the 5‐year mean being above the threshold. Our forecasts will be updated annually to provide policy makers with advanced warning of the evolving probability and duration of future warming events.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2015

Imaging atomic-scale effects of high-energy ion irradiation on superconductivity and vortex pinning in Fe(Se,Te)

Maximizing the sustainable supercurrent density, J C , is crucial to high-current applications of superconductivity, and to achieve this, preventing dissipative motion of quantized vortices is key. Irradiation of superconductors with highenergy heavy ions can be used to create nanoscale defects that act as deep pinning potentials for vortices. This approach holds unique promise for high-current applications of iron-based superconductors because JC amplification persists to much higher radiation doses than in cuprate superconductors without significantly altering the superconducting critical temperature. However, for these compounds, virtually nothing is known about the atomic-scale interplay of the crystal damage from the high-energy ions, the superconducting order parameter, and the vortex pinning processes. We visualize the atomic-scale effects of irradiating FeSe x Te 1$-$x with 249-MeV Au ions and find two distinct effects: compact nanometer-sized regions of crystal disruption or “columnar defects,” plus a higher density of single atomic site “point” defects probably from secondary scattering. We directly show that the superconducting order is virtually annihilated within the former but suppressed by the latter. Simultaneous atomically resolved images of the columnar crystal defects, the superconductivity, and the vortex configurations then reveal how amixed pinning landscape is created, with the strongest pinning occurring at metallic core columnar defects and secondary pinning at clusters of point-like defects, followed by collective pinning at higher fields.

Critical Current by Design↗
NASA NTRS1979

Experimental clean combustor program: Diesel no. 2 fuel addendum, phase 3

A CF6-50 engine equipped with an advanced, low emission, double annular combustor was operated 4.8 hours with No. 2 diesel fuel. Fourteen steady-state operating conditions ranging from idle to full power were investigated. Engine/combustor performance and exhaust emissions were obtained and compared to JF-5 fueled test results. With one exception, fuel effects were very small and in agreement with previously obtained combustor test rig results. At high power operating condition, the two fuels produced virtually the same peak metal temperatures and exhaust emission levels. At low power operating conditions, where only the pilot stage was fueled, smoke levels tended to be significantly higher with No. 2 diesel fuel. Additional development of this combustor concept is needed in the areas of exit temperature distribution, engine fuel control, and exhaust emission levels before it can be considered for production engine use.

Gleason, C. C.↗
NASA NTRS1959

Trajectory Control for Vehicles Entering the Earth's Atmosphere at Small Flight Path Angles

Methods of controlling the trajectories of high-drag-low-lift vehicles entering the earth's atmosphere at angles of attack near 90 deg and at initial entry angles up to 3 deg are studied. The trajectories are calculated for vehicles whose angle of attack can be held constant at some specified value or can be perfectly controlled as a function of some measured quantity along the trajectory. The results might be applied in the design of automatic control systems or in the design of instruments which will give the human pilot sufficient information to control his trajectory properly during an atmospheric entry. Trajectory data are compared on the basis of the deceleration, range, angle of attack, and, in some cases, the rate of descent. The aerodynamic heat-transfer rate and skin temperature of a vehicle with a simple heat-sink type of structure are calculated for trajectories made with several types of control functions. For the range of entry angles considered, it is found that the angle of attack can be controlled to restrict the deceleration down to an arbitrarily chosen level of 3g. All the control functions tried are successful in reducing the maximum deceleration to the desired level. However, in order to avoid a tendency for the deceleration to reach an initial peak decrease, and then reach a second peak, some anticipation is required in the control function so that the change in angle of attack will lead the change in deceleration. When the angle of attack is controlled in the aforementioned manner, the maximum rate of aerodynamic heat transfer to the skin is reduced, the maximum skin temperature of the vehicle is virtually unaffected, and the total heat absorbed is slightly increased. The increase in total heat can be minimized, however, by maintaining the maximum desired deceleration for as much of the trajectory as possible. From an initial angle of attack of 90 deg, the angle-of-attack requirements necessary to maintain constant values of deceleration (1g to 4g) and constant values of rate of descent (450 to 1,130 ft/sec) as long as it is aerodynamically practical are calculated and are found to be moderate in both magnitude and rate. Entry trajectories made with these types of control are presented and discussed.

Eggleston, John M.↗
DOE OSTI2018

Low-Temperature Short-Time SPS Processes to Produce Fine-Grained High-Coercivity Barium Hexaferrite Ceramics from Polyol Nanoparticles

Barium hexaferrite (BaFe{sub 12}O{sub 19}) ceramics were obtained by combination of polyol-synthesized precursors subsequently consolidated by spark plasma sintering (SPS) at a low temperature (800 {sup ∘}C). X-ray powder diffraction studies showed the influence of the experimental parameters to produce a virtually single- or multiphase material. The room temperature magnetic properties exhibited interesting variety of properties, including exchange coupling (spring magnet) between hexaferrite and other magnetic phases. The saturation magnetization and coercive field, at room temperature, are in the 34–70 emu/g and 4.1–5.0 kOe ranges, respectively. The combination of strong coercive field and magnetization resulted in a maximum energy product [(BH)max] = 10.9 kJ/m{sup 3} for the sample with the highest BaFe{sub 12}O{sub 19} content.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗