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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 523 records · Page 29
All sourcesNASA NTRSDOE OSTI
DOE OSTI2016

SUPERGRANULATION AS THE LARGEST BUOYANTLY DRIVEN CONVECTIVE SCALE OF THE SUN

The origin of solar supergranulation remains a mystery. Unlike granulation, the size of which is comparable to both the thickness of the radiative boundary layer and local scale-height in the photosphere, supergranulation does not reflect any obvious length scale of the solar convection zone. Moreover, recent observations of flows in the photosphere using Doppler imaging or correlation or feature tracking show a monotonic decrease in horizontal flow power at scales larger than supergranulation. Both local area and global spherical shell simulations of solar convection by contrast show the opposite, an increase in horizontal flow amplitudes to a low wavenumber. We examine these disparities and investigate how the solar supergranulation may arise as a consequence of nonlocal heat transport by cool diving plumes. Using three-dimensional anelastic simulations with surface driving, we show that the kinetic energy of the largest convective scales in the upper layers of a stratified domain reflects the depth of transition from strong buoyant driving to adiabatic stratification below caused by the dilution of the granular downflows. This depth is quite shallow because of the rapid increase of the mean density below the photosphere. We interpret the observed monotonic decrease in solar convective power at scales larger than supergranulation to be a consequence of this rapid transition, with the supergranular scale the largest buoyantly driven mode of convection in the Sun.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2016

NON-LTE INVERSIONS OF THE Mg ii h and k AND UV TRIPLET LINES

The Mg ii h and k lines are powerful diagnostics for studying the solar chromosphere. They have become particularly popular with the launch of the Interface Region Imaging Spectrograph ( IRIS ) satellite, and a number of studies that include these lines have lead to great progress in understanding chromospheric heating, in many cases thanks to the support from 3D MHD simulations. In this study, we utilize another approach to analyze observations: non-LTE inversions of the Mg ii h and k and UV triplet lines including the effects of partial redistribution. Our inversion code attempts to construct a model atmosphere that is compatible with the observed spectra. We have assessed the capabilities and limitations of the inversions using the FALC atmosphere and a snapshot from a 3D radiation-MHD simulation. We find that Mg ii h and k allow reconstructing a model atmosphere from the middle photosphere to the transition region. We have also explored the capabilities of a multi-line/multi-atom setup, including the Mg ii h and k, the Ca ii 854.2 nm, and the Fe i 630.25 lines to recover the full stratification of physical parameters, including the magnetic field vector, from the photosphere to the chromosphere. Finally, we present the first inversions of observed IRIS spectra from quiet-Sun, plage, and sunspot, with very promising results.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2016

Sustainable Remediation of Radionuclides By a Common Sense Approach to Enhanced Attenuation - 16441

Development of in situ and relatively passive remedies for treatment of groundwater contaminated by metals and radionuclides is becoming more important because of the difficulty and cost - both to the environment and financially -- of removing these types of contaminants from the subsurface by pump-and-treat or excavation. In situ technologies rely on reactions that tend to remove contaminants from groundwater by partitioning them to solid phases in the aquifer. Monitored natural attenuation (MNA) relies solely on natural reactions to achieve remedial goals. Enhanced attenuation (EA) uses engineered approaches to supplement remediation when MNA is not sufficient to meet remedial goals. Both approaches leave contaminants in the subsurface and require a high burden of proof that contaminants will not be mobilized and become a risk in the future. Proof of the sustained effectiveness of an EA remedy is made much easier by strategic design. In multi-contaminant plumes, it is important to prioritize contaminants according to the risk they pose, with the recognition that one remedy rarely treats all contaminants. The goal for the engineered portion of the remedy should be maximum risk reduction with minimal engineering. Natural attenuation or negotiated alternate concentration levels will often allow low risk contaminants to go untreated. Whenever possible, the remedy should be consistent with the geochemical evolution of the waste site, insuring that the treated immobilized contaminants are likely to remain relatively immobile for long time frames. Finally, use what nature provides geologically, hydrologically, geochemically, or microbiologically in the remedy design. One of the impediments faced by waste site managers in implementing EA remedies is paralysis by perceived complexity. There are things that must be known to design an effective EA remedy, but there is always the temptation to know everything to eliminate the possibility of failure. Furthermore, there are plenty of people warning of failure if all is not known and they are usually willing to help the design team know all, for a price. Yet, the price of trying to eliminate all risk is never implementing an innovative remedy. All parties involved -- scientists/engineers, waste site managers, regulators and stakeholders must assume some degree of risk to deploy an EA remedy. If all parties are to assume some risk, then trust built through close communication from the start is required. The U.S. Department of Energy Office of Environmental Management has funded an applied field research initiative for several years focused, in part, on developing EA remedies for metals and radionuclides using these guiding principles. This approach to EA remedies grew out of developing and deploying a remediation strategy to replace a pump-and-treat system at the F-Area Seepage Basins on the Savannah River Site. The pump-and-treat system was energy intensive, produced several thousand cubic feet of solid radioactive waste per year, and cost $ 1 million per month to operate. The EA remedy that replaced the pump-and-treat is energy efficient, produces no waste, and costs approximately $1 million per year to maintain. At the F-Area Seepage Basins approximately 7 billion liters of low level radioactive waste solutions were disposed in three unlined basins resulting in contaminated groundwater containing various radionuclides and other contaminants. The primary contaminants of concern are tritium, strontium-90, uranium, and iodine-129. Other key features of the contaminant plume are its acidic nature with pH values as low as 3.2, its vertical stratification in the water table aquifer, and the tendency of the most contaminated portions to follow troughs in the top of the clay separating the upper aquifer zone from the lower aquifer zone. The geology was exploited by installing a funnel-and-gate system into the clay with the barrier portion blocking contaminant flow paths in the troughs in the clay. This forces the most contaminated water to flow through the gates where it encounters an in situ treatment zone created by periodic injections of alkaline solution. The flux of tritium has been reduced significantly by the barrier walls. Strontium-90 and uranium are treated by enhanced sorption in the circum-neutral pH treatment zone, consistent with natural geochemical evolution of the waste site from acidic to more neutral pH. An additional in situ treatment zone was created up-gradient of the one of the gates to treat iodine-129. Sub-micrometer diameter silver chloride particles were injected into the aquifer by direct push methods to create the treatment zone. In the laboratory and in a field pilot test the poorly soluble silver chloride particles reacted with iodide to form much less soluble silver iodide. Evaluation of the effectiveness of the silver chloride is ongoing. (authors)

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2016

Assessment of Core Status of Fukushima Daiichi Nuclear Power Plant

There were some events and phenomena that occurred which have been deemed specific to the Fukushima Daiichi NPP. The primary issues were as follows: - Direct steam leakage from the reactor pressure vessels (RPVs) to the dry-wells through the gaskets of the safety relief valves and/or due to creep damage of the main steam line, and damage of the in-core monitor guide tubes due to buckling. - Direct corium leakage from the RPVs to the pedestal floors through the melt portions of the in-core monitor housings. - Alternative water injection by the fire trucks with large amount of leakages through the branch lines. - Partial load operation of the Reactor Core Isolation Cooling system and the High Pressure Coolant Injection system. - Gas leakage from the primary containment vessels to the reactor buildings due to over pressure than the design maximum value. - Thermal stratification in the suppression pool resulting in incomplete steam condensation in the pool. The accident progressions were analyzed with the newly developed physical models for the above issues. And also considering the qualitatively estimated core status based on the plant parameters measured after the accident, the current core status was assessed.

21 SPECIFIC NUCLEAR REACTORS AND ASSOCIATED PLANTS↗
DOE OSTI2016

Severe Accident Research Directions after Fukushima

The accidents at the Fukushima Daiichi nuclear power station in March of 2011 renewed interest globally in the nature, causes, and health and economic consequences of severe accidents involving core damage and containment impairment. As a result of these accidents, research has been conducted into the modeling and phenomenological understanding of the accidents at Fukushima and the response and effectiveness of mitigating measures such as emergency water injection, primary system depressurization and containment venting actions. An important example of this is the jointly conducted OECD-NEA organized Benchmark of the Fukushima Accidents (BSAF project) where accident reconstruction analyses using computer codes such as MELCOR and MAAP are ongoing. Even prior to the Fukushima accidents, the Sandia/NRC sponsored State of Art Reactor Consequence Analyses (SOARCA) foreshadowed the accidents in Japan where long-term and short-term station blackout accidents in boiling water reactors with Mark-1 containment were analyzed showing striking similarities to the accidents at Fukushima. These analyses also highlighted important differences in our prior understanding, in particular the importance of suppression pool thermal stratification and the extraordinary operation of the Fukushima Unit-2 reactor core isolation cooling (RCIC) system, prompting addition research into both of these areas. Additionally, the focus of the world's major computer codes on modeling the Fukushima accidents in the BSAF effort, led to several 'Crosswalk' comparisons between code predictions, highlighting subtle but important modeling differences between the codes and identifying areas where modeling improvements can be made. Collectively, these research areas are aimed at improving our understanding of severe accident progression and real-world response of safety related systems and components, and should lead to improved accident response and mitigation capabilities in the future. (authors)

22 GENERAL STUDIES OF NUCLEAR REACTORS↗
DOE OSTI2016

High-fidelity simulation-driven model development for coarse-grained computational fluid dynamics

Nuclear reactor safety analysis requires analysis of a broad range of accident scenarios and determining their consequences. For a nuclear power plant behavior, it is impossible to obtain experimental data at sufficiently large scales to support calibration and validation of various system models. In single-phase flow convective problems, high-resolution methods of Computational Fluid Dynamics (CFD) such as Direct Numerical Simulation (DNS) and Large Eddy Simulation (LES) can provide high fidelity results under conditions where physical measurements are unavailable. However, such high-resolution simulations are computationally expensive and not suitable for simulation of long transient scenarios in nuclear reactor accidents. In this work, we investigate the use of a high fidelity simulation-driven approach to model sub-grid scale (SGS) effect in Coarse Grained Computational Fluid Dynamics CG-CFD. Notably, fine-mesh simulations are used to construct physics-informed statistical surrogate of coarse-mesh SGS model. For an initial analysis, we consider a case of turbulent natural convection in a volumetrically heated fluid layer with a thermally insulated lower boundary and isothermal upper boundary. This scenario of unstable stratification is relevant to turbulent natural convection in a severe nuclear reactor accident, as well as in containment mixing and passive cooling. For this type of flow, the SGS effect is modeled by an added turbulent diffusivity in the energy equation. It is shown that a global correction for the energy equation is sufficient to achieve a significant improvement to the CG-CFD prediction of thermal mixing in the fluid layer. (authors)

22 GENERAL STUDIES OF NUCLEAR REACTORS↗
DOE OSTI2016

Density Effects on Lock Exchange Flow During a DCC

The High Temperature Test Facility (HTTF) is a scaled, electric model at Oregon State University (OSU) of the Modular High Temperature Gas Reactor (MHTGR) by General Atomics. There are a few major differences between the design and the OSU facility. In the HTTF the reactor pressure vessel and the reactor cavity are in two separate tanks connected by a crossover duct similar to the crossover duct that would be seen between the reactor core and the steam generator in the MHTGR. This feature allows for the facility to open two main break valves simulating a Double-Ended Guillotine Break (DEGB) of the cross over duct, synonymous to a crossover duct break in the MHTGR. The density gradient driven flow phenomena in the HTTF duct can then be studied further. This break would cause a depressurization of the reactor and a loss of flow. It is called the Depressurized Loss of Forced Convection Accident (D-LOFC), also known as the Depressurized Conduction Cool-Down Event for High Temperature Gas Reactors (HTGRs) because heat removal is by conduction through the core and radiation out of the vessel. The HTTF was built and scaled to maintain the highest accuracy for the DCC. Prototypical temperatures with an inlet temperature of 259 deg. C and an outlet temperature of 687 deg. C are maintained in the HTTF. The temperature profile is also maintained in the smaller volume by using a ceramic core. The HTTF uses graphite heaters because the resistive heat produced does not change significantly with temperature . In order to produce a facility of similar temperatures within the allotted budget, sacrifices had to be made in other areas. The HTTF is scaled one-fourth in diameter, one-fourth in height and one-eighth in pressure of the MHTGR. There are also a few limitations for the HTTF. While in the MHTGR, the cavity is filled with air, the HTTF uses highly pure Nitrogen and does not have the ability to simulate a full depressurization. The DCC event is traditionally comprised of multiple stages: depressurization, molecular diffusion and natural circulation. However, this traditional interpretation ignores lock exchange flow which will occur immediately following depressurization and could have significant consequences in the reactor. It was found that the traditional model underestimates the amount of air ingress by at least 660 times according to Oh and Kim in their theoretical research of air ingress. Molecular diffusion also decreases with stratification. Any model that specifies the gases are stratified has further underestimated the air ingress of the DCC event. In addition, molecular diffusion is a much slower process, allowing the reactor to shut down and cool off considerably from operating temperatures. Thus, understanding lock exchange flow, the air ingress concentrations and the time scale is critical to MHTGR research and licensing. (authors)

21 SPECIFIC NUCLEAR REACTORS AND ASSOCIATED PLANTS↗
DOE OSTI2016

CFD-grade Experiments Addressing Thermal Fatigue in Nuclear Reactor Branch Lines

Thermal fatigue has been identified as one of the main degradation mechanisms contributing to Loss of Coolant Accident frequencies in Light Water Reactors (LWRs). Thermal fatigue in stagnant branch lines departing from hot or cold legs of LWRs has become of high interest to the nuclear industry, as the current management program has had mixed effectiveness in preventing loss of power incidents. In fact, at least 8 such events involving branch lines have been registered at US plants over the past 2 years. Thermal cycling in a branch line occurs at the fluctuating boundary created by the penetration of hot fluid from the main flow into the cold stagnant fluid of the branch line. Penetration occurs as the fast moving flow of the main line crosses the opening of a branch line, causing cavity flow. Turbulent cavity flow dissipates to a disturbed flow further into the branch line and then to a laminar spiral flow. At the extent of the spiral flow, hot and cold fluids stratify to create the fluctuating boundary of interest. Qualitative experimental techniques, such as visualization of tracer particles, have been employed in past research efforts to capture the large scale evolution from cavity flow to the formation of the fluctuating stratified layer. The insight gained has been crucial in understanding the fundamentals of thermal cycling and stratification in branch lines; however, this qualitative information is insufficient for improving the current methods of predicting thermal fatigue in branch lines. High resolution quantitative measurements of the flow, capturing the small scale motions that affect the thermal cycling at the pipe wall, are needed to shed more light on the phenomenon and improve the industry fatigue management program, especially in terms of reliability. In the work presented here, time-resolved particle image velocimetry (PIV) is employed to investigate the flow in a stagnant branch line. Both time-averaged and time-dependent velocity fields of interest were captured, providing the groundwork for the experimental campaign that will be translated into model enhancement. (authors)

21 SPECIFIC NUCLEAR REACTORS AND ASSOCIATED PLANTS↗
DOE OSTI2017

Development of a Small Liquid Sodium Purification Loop

Generation IV nuclear reactors provide management solutions to address spent fuel problems. The most researched Generation IV reactor is the sodium cooled fast reactor (SFR). Improved engineering is has allowed for systematic improvements in both the safety and efficiency of power production. However, before a SFR can be brought back online in the Untied States, constructive research must be pursued on numerous scales to ensure the capabilities of aforementioned reactors. While larger research facilities such as the one at Argonne National Laboratory or the University of Wisconsin - Madison address some of the larger scale studies surrounding the SFR, Fort Lewis College (FLC) is aiming to provide small scale studies on liquid sodium as a thermal hydraulic cooling system. The sodium diagnostic loop at FLC is constructed to conduct research that includes: analyzing pumping characteristics, thermal stratification, freeze plug analysis, and corrosion studies. The FLC loop is attached to an inert glovebox so these experiments can be conducted with an additional layer of safety. The objective of this sodium research apparatus is to combine the best features of each instrument commonly associated with sodium research loops in a cost effective manner while still obtaining high fidelity data. Furthermore, an innovative design of the loop maximizes the volume of available research space inside of the glovebox by mounting the diagnostic loop adjacent to the glovebox.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2016

A periodic freshwater patch detachment process from the Block Island Sound estuarine plume: BIS PERIODIC FRESHWATER PATCH DETACHMENT

Previous observations suggest periodic freshwater patches separating from the Block Island Sound (BIS) estuarine plume. In this study, the dynamics of the separation process is investigated through a series of numerical experiments using the Regional Ocean Modeling System (ROMS). In addition, we explore the seasonal variability of the freshwater patches and their response to river discharge and ambient current. The model results indicate that episodic freshwater patches are triggered by small changes in tidal currents over the spring-neap tidal cycle. The spring-neap variation in tidal currents causes significant, monthly fluctuations in turbulent mixing and vertical stratification in BIS, modulating the freshwater discharge thereby generating episodic freshwater patches that move both downstream along the southern shore of Long Island and toward Rhode Island Sound (RIS). The realistically configured model shows that the freshwater patches experience strong seasonal variability. They are largest in spring when the river discharge peaks, and smallest in summer due to the weak river discharge and a robust upstream ambient current from RIS. According to the analysis of the freshwater transport out of BIS, we conclude that such detachment occurs at tidal mixing fronts.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2016

Prolonged El Niño conditions in 2014-2015 and the rapid intensification of Hurricane Patricia in the eastern Pacific: EL NIÑO AND HURRICANE PATRICIA

Hurricane Patricia was the most intense tropical cyclone on record in the eastern North Pacific or Atlantic, reaching a peak intensity of 95 m s -1 only 30 hours after attaining hurricane status (33 m s -1 ). Here it is shown that exceptionally warm sea surface temperatures (SSTs), a deeper than normal thermocline, and strong near-surface salinity stratification all aided Patricia’s rapid intensifciation, combining to increase its Dynamic Potential Intensity by 10–21 m s -1 . Anomalous surface warming and thermocline deepening along Patricia’s track were driven by prolonged El Niño during 2014–15 and punctuated by the buildup to the extreme El Niño of 2015–16. In the region where Patricia intensified, SST was 1.5°C higher and sea surface height was 10 cm higher compared to conditions during the last extreme El Niño in 1997, emphasizing the extraordinary nature of the 2015 anomalies.

58 GEOSCIENCES↗
DOE OSTI2024

A Pseudo Planar Heterojunction Structure for Eco‐Friendly Printable Organic Solar Cells Achieving 19.05% Efficiency

Abstract Obtaining a well‐accurate vertical distribution active layer morphology through the air‐printing process is an essential task for achieving efficient scalable large‐area organic solar cells (OSCs). In this target, the desired and controllable pseudo planar heterojunction (PPHJ) active layer structure with suitable phase separation is developed by pre‐deposited D18‐Cl layer under the PM6:BTP‐eC9 film via an eco‐friendly manufacturing method. The addition of the D18‐Cl regulates molecular crystallization and leads to an ideal vertical stratification while simultaneously suppressing voltage loss, optimizing energetic disorder, and carrier management. Impressively, the optimal PPHJ devices perform superior power conversion efficiencies (PCEs) of 19.05% (100 nm), 17.33% (300 nm), and 14.14% (4 cm 2 ) compared to the BHJ devices. Importantly, the PPHJ OSCs also exhibit an impressive extrapolated T 80 (the time required to reach 80% of initial PCE) of long‐time storage and operational stability, as well as thermal stability.

Chemistry↗
DOE OSTI2016

Interfacial Characteristics of Efficient Bulk Heterojunction Solar Cells Fabricated on MoOx Anode Interlayers

The role of the interface between an MoOx anode interlayer and a polymer:fullerene bulk heterojunction is investigated. Processing differences in the MoOx induce large variations in the vertical stratification of the bulk heterojunction films. These variations are found to be inconsistent in predicting device performance, with a much better gauge being the quantity of polymer chemisorbed to the anode interlayer.

14 SOLAR ENERGY↗
DOE OSTI2021

Structural Color Production in Melanin-Based Disordered Colloidal Nanoparticle Assemblies in Spherical Confinement

Melanin is a ubiquitous natural pigment that exhibits broadband absorption and high refractive index. Despite its widespread use in structural color production, how the absorbing material, melanin, affects the generated color is unknown. Using a combined molecular dynamics and finite-difference time-domain computational approach, here we investigates structural color generation in one-component melanin nanoparticle-based supraparticles (called supraballs) as well as binary mixtures of melanin and silica (nonabsorbing) nanoparticle-based supraballs. Experimentally produced one-component melanin and one-component silica supraballs, with thoroughly characterized primary particle characteristics using neutron scattering, produce reflectance profiles similar to the computational analogs, confirming that the computational approach correctly simulates both absorption and multiple scattering from the self-assembled nanoparticles. These combined approaches demonstrate that melanin's broadband absorption increases the primary reflectance peak wavelength, increases saturation, and decreases lightness factor. Additionally, the dispersity of nanoparticle size more strongly influences the optical properties of supraballs than packing fraction, as evidenced by the production of a larger range of colors when size dispersity is varied versus packing fraction. For binary melanin and silica supraballs, the chemistry-based stratification allows for more diverse color generation and finer saturation tuning than does the degree of mixing/demixing between the two chemistries.

broadband absorption↗