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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 1,369 records · Page 76
All sourcesNASA NTRSDOE OSTI
DOE OSTI2016

Development of a Smart Signal Detection Method for Cyclic Voltammetry via Artificial Neural Intelligence

The electrorefiner (ER) is the heart of pyroprocessing technology which is a high-temperature method for separating uranium from Used Nuclear Fuel (UNF). It is important to improve this technology with respect to nuclear materials detection and accountability. Artificial Neural Intelligence (ANI) is a novel data analysis and simulation method that can be applied to electrochemical data sets. This computational code, which has been performed using the commercial software MATLAB, can be trained to generalize adequate electrical current and potential simulated data sets for the unseen data with a high accuracy of prediction. For this purpose, a massive collection of cyclic voltammetry (CV) data sets by Hoover (2014), for 0.5, 1, 2.5, and 5 wt% of zirconium chloride in LiCl-KCl molten salt with different scan rates at 773 K has been considered. The computer is trained via ANI to predict the unseen data after providing suitable hidden layers and validation numbers. In addition, this work can trace the CV plot for a blind condition by interpolating between two simulated data set. The different hidden layers with various neurons (from 5 to 30) at several validation numbers (from 5 to 30) has been studied and the average percent error between experimental and theoretical data for 0.5 wt% with 200 and 450 mV/s has been calculated. Preliminary results demonstrate that if the number of hidden layers increases from one to three, the average error falls down from 44% to around 8%. The best condition which gives a minimum average percent error has been discovered and the simulated CV graph has been compared with the experimental data. (authors)

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2016

Multi-species Modeling of Molten-Salt Electrochemical Process

Spent nuclear fuel has been produced and stored in over 30 different countries which are operating commercial nuclear power plants. Molten-salt pyroprocessing has been developed for treating both oxide and metal spent nuclear fuels. This process separates long-lived actinide isotopes together as a group from fission products for burning the long-lived isotopes in fast reactors. Main processes of pyroprocessing such as oxide reduction, electrorefining, and electrowinning are based on a concept of electrolytic cell consuming energy to proceed electrochemical reactions. To scale-up the electrochemical processes, the design optimization of the key steps is required to reach high throughput that improves economic competitiveness and reduces an environmental impact. For the optimization, it is significant to compare different unit process designs and find optimum designs and operating conditions. However, this optimization process is very costly if we need to conduct experiments on every case with spent nuclear fuel. Instead, a validated simulation model can help to rapidly calculate and evaluate different case at significantly reduced costs. This paper presents recent development of multi-physics simulation of molten salt electrochemistry for partitioning spent nuclear fuel with limiting factors. (authors)

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2016

Derivation of the Point-Kinetics Parameters for the Coupled Reactors

The design of coupled reactors, which provide two distinct spectral zones (fast and thermal), has recently drawn attention because it can provide configurations that could not be met in current thermal neutron test reactors and thus allows versatile irradiation tasks. A coupled reactor core is characterized by the neutron multiplicity of each zone as well as by the coupling between the two zones. It is desired to evaluate the integral point kinetics parameters that characterize the neutron physics of the coupled system. This summary provides a derivation of the equations for evaluating these point kinetics parameters. Following the strong and the weak form of the multigroup diffusion equation, the weak forms for the partial forward and adjoint solutions, each for a particular active region of the reactor core, are derived. These partial solutions are then used to collapse the weak form into the coupled-reactor point kinetics equations with the approximation of equilibrium. It is noted that these parameters are not meant for transient analysis because of the equilibrium approximation. They are rather used for characterizing the coupled system. The derived reactivity equations are then compared with those in Ref. 1. The equations are implemented in Rattlesnake, the INL MOOSE-based radiation transport application for multi-physics simulations. Numerical results are presented for a simple two-group problem. (authors)

21 SPECIFIC NUCLEAR REACTORS AND ASSOCIATED PLANTS↗
DOE OSTI2016

SAS4A model development for the analysis of postulated severe accidents in metal fuel sodium fast reactors

The SAS4A code has been designed to simulate the events that occur in Sodium Fast Reactor (SFR) during the initiating phase of severe unprotected accidents. The initial SAS4A models were focused on the behavior of oxide fuel cores. An effort to expand the SAS4A models for the analysis of metal fuel cores is currently underway. This paper describes the status of the SAS4A metal fuel model development and presents initial results from the simulation of a postulated fuel assembly blockage accident in the Prototype Gen-IV Sodium Fast Reactor (PGSFR). (authors)

21 SPECIFIC NUCLEAR REACTORS AND ASSOCIATED PLANTS↗
DOE OSTI2017

Analysis of COBRA-TF Critical Heat Flux Models for Triangular Fuel Assembly Pitch

The Coolant Boiling in Rod Arrays-Two Fluid (COBRA-TF) code is a best estimate code which is used to perform thermal-hydraulic analyses of a light water reactor vessel. The COBRA-TF heat transfer package has models calculating the critical heat flux (CHF). In order to verify code's predictive capability for CHF for triangular nuclear fuel assembly pitch, experiment results and system parameters of KS-1 test facility that is single loop model of the VVER primary system located in Kurchatov Institute were simulated using COBRA-TF. In order to calculate CHF for triangular nuclear fuel assembly pitch there is a look-up table generated. In addition, there are some correction factors for critical heat flux values listed the table. In this study, once KS-1 experiment results were simulated using COBRA-TF, correction factors were used to correct CHF results from COBRA-TF calculations.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2018

Application of adaptive multilevel splitting on coupled neutron-photon TRIPOLI-4{sup R} Monte Carlo simulations - 25427

In the context of radiation protection simulations, the Adaptive Multilevel Splitting (AMS) algorithm is a challenging variance reduction (VR) technique that has been recently investigated in the field of particle transport simulation. It has been implemented in the forthcoming version 11 of the Monte Carlo code TRIPOLI-4{sup R} and successfully tested in neutron-only and photon-only configurations. This paper addresses the application of the AMS algorithm to coupled simulations, and particularly to neutron-photon Monte Carlo calculations. The branching process occurring during the Monte Carlo coupled transport is taken into account in the new coupled-AMS algorithm and is explained in this paper. Two different neutron-photon configurations are then investigated, leading to a comparison of the coupled-AMS algorithm with the analog simulation on the one hand, and with the Exponential Transform (ET) on the other hand, which is the standard VR technique of TRIPOLI-4. Gains up to 30 are obtained in terms of Figure of Merit relatively to the analog simulation, which is about 4 to 6 times more efficient than the ET method for these configurations. (authors)

61 RADIATION PROTECTION AND DOSIMETRY↗
DOE OSTI2018

Ab Initio and Monte Carlo Approaches for the Magnetocaloric Effect in BaMnO{sub 3} Oxide Perovskite

The self-consistent ab initio calculations, based on density functional theory approach (DFT) and using full potential linearised augmented plane wave (FLAPW) method, have been used to investigate both electronic and magnetic properties of the BaMnO{sub 3} perovskite. Spin-polarised calculations, including the spin-orbit interaction, are used to determine the energy of the ferromagnetic (FM) and antiferromagnetic (AFM) states of BaMnO{sub 3} perovskite. Obtained data from ab initio calculations are used as input for the Monte Carlo simulations to compute other magnetic parameters. Magnetisation, specific heat and magnetic entropy change have been given using the Monte Carlo simulations. The adiabatic temperature change, transition temperature and relative cooling power have been established.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2017

Modeling and Simulation of the Off-gas in an Electric Arc Furnace

The following paper describes an approach to process modeling and simulation of the gas phase in an electric arc furnace (EAF). The work presented represents the continuation of research by Logar, Dovžan, and Škrjanc on modeling the heat and mass transfer and the thermochemistry in an EAF. Due to the lack of off-gas measurements, Logar et al. modeled a simplified gas phase under consideration of five gas components and simplified chemical reactions. The off-gas is one of the main continuously measurable EAF process values and the off-gas flow represents a heat loss up to 30 pct of the entire EAF energy input. Therefore, gas phase modeling offers further development opportunities for future EAF optimization. This paper presents the enhancement of the previous EAF gas phase modeling by the consideration of additional gas components and a more detailed heat and mass transfer modeling. In order to avoid the increase of simulation time due to more complex modeling, the EAF model has been newly implemented to use an efficient numerical solver for ordinary differential equations. Compared to the original model, the chemical components H{sub 2}, H{sub 2}O, and CH{sub 4} are included in the gas phase and equilibrium reactions are implemented. The results show high levels of similarity between the measured operational data from an industrial scale EAF and the theoretical data from the simulation within a reasonable simulation time. In the future, the dynamic EAF model will be applicable for on- and offline optimizations, e.g., to analyze alternative input materials and mode of operations.

42 ENGINEERING↗
DOE OSTI2018

Motion of Solid Grains During Magnetic Field-Assisted Directional Solidification

In this paper, we report the visible evidence for thermoelectric magnetic forces (TEMFs) during magnetic field-assisted directional solidification, and their potential to control the motion of solid grains(dendrite fragments or equiaxed grains). These motions are observed by means of synchrotron X-ray radiography and compared with analytic calculations for a spherical particle’s motion driven only by TEMFs, which confirms that the observed solid grain motions are the combined result of the TEMFs and gravity. We also carried out corresponding 3D numerical simulations to validate the calculations and further prove our conclusion that TEMF acts on the solid grain and affects its motion trajectory.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Numerical Simulation of Recirculating Flow and Physical Model of Slag–Metal Behavior in an RH Reactor: Application to Desulfurization

Computational fluid dynamics (CFD) techniques and a 1:7.5 physical model of an RH degasser have been used to evaluate the flow of gas and metal inside an RH reactor for vacuum degassing of liquid steel. The effect of gas injection on the gas spatial distribution, steel circulation rate and flow field inside the ladle, snorkels and vacuum chamber have been assessed. N-pentane oil was employed to evaluate the average residence time as well as the slag droplet size distribution. The predicted radial gas distribution and liquid circulation rate have been validated against experimental data from a physical model. The results with incorporation of the virtual mass force coefficient of 0.25 and the turbulence dispersion force showed better predictions of gas distribution in the up-snorkel as well as circulation rate. Full-scale simulations were performed, and the predicted circulation rate was significantly affected by the argon bubble expansion. Data from these simulations were used to analyze the degree of desulfurization performed by the addition of desulfurizing agents inside the vacuum chamber. A model of the kinetics of desulfurization based on the results from the physical model and CFD simulation and on slag dispersion inside liquid steel yields degrees of desulfurization similar to the industrial trials reported in the literature.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Investigation on Cracking Behavior and Development of a Fracture Model of Ti-47Al-2Nb-2Cr Alloy During Hot Deformation

When alloys are strained to a certain limit under the plastic deformation, ductile fracture occurs. Whether the required deformation can be put into effect before fracture appears has become a serious concern. A combination of compression tests, ductile fracture criteria as well as finite element simulation (FEM) were employed in this study to establish the fracture initiation prediction model of Ti-47Al-2Nb-2Cr alloy. To obtain the critical fracture strain, a technique was proposed to calculate the data for deformed cylindrical samples through isothermal compression tests in the temperature range between 1223 and 1423 K with strain rates ranging from 0.001 to 1 s{sup −1}. Five commonly used ductile fracture criteria were compared by FE simulation of compressing tests. It was found that the Brozzo criterion was found to be suitable and accordingly a failure criterion, considering temperature and strain ratio was established. Hot working parameters (critical fracture value and critical strain) in deformation could be obtained through the finite element simulation, revealing that this newly established failure criterion could accurately predict cracking initiation in compressing deformation of Ti-47Al-2Nb-2Cr alloy ingot.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Almost periodic oscillations for delay impulsive stochastic Nicholson’s blowflies timescale model

In this paper, we employ the new concepts of piecewise almost periodic stochastic process on a new periodic time scale and study a type of delay impulsive stochastic Nicholson’s blowflies timescale model under shifts operators. Some sufficient conditions for the existence and exponential stability of piecewise mean-square almost periodic solutions to the model are established. In addition, we provide numerical examples and computer simulations to demonstrate the feasibility of the obtained results. The methods and definitions introduced in the paper can be applied to study other types of stochastic dynamic models involving q-difference models and more.

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2013

Simulation of ion beam transport through the 400 Kv ion implanter at Michigan Ion Beam Laboratory

The Michigan Ion Beam Laboratory houses a 400 kV ion implanter. An application that simulates the ion beam trajectories through the implanter from the ion source to the target was developed using the SIMION Registered-Sign code. The goals were to have a tool to develop an intuitive understanding of abstract physics phenomena and diagnose ion trajectories. Using this application, new implanter users of different fields in science quickly understand how the machine works and quickly learn to operate it. In this article we describe the implanter simulation application and compare the parameters of the implanter components obtained from the simulations with the measured ones. The overall agreement between the simulated and measured values of magnetic fields and electric potentials is {approx}10%.

43 PARTICLE ACCELERATORS↗
DOE OSTI2013

Nonlinear interaction of kinetic Alfven wave and whistler: Turbulent spectra and anisotropic scaling

In this work, we are presenting the excitation of oblique propagating whistler wave as a consequence of nonlinear interaction between whistler wave and kinetic Alfven wave (KAW) in intermediate beta plasmas. Numerical simulation has been done to study the transient evolution of magnetic field structures of KAW when the nonlinearity arises due to ponderomotive effects by taking the adiabatic response of the background density. Weak oblique propagating whistler signals in these nonlinear plasma density filaments (produced by KAW localization) get amplified. The spectral indices of the power spectrum at different times are calculated with given initial conditions of the simulations. Anisotropic scaling laws for KAW and whistlers are presented. The relevance of the present investigation to solar wind turbulence and its acceleration is also pointed out.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2013

2-dimensional ion velocity distributions measured by laser-induced fluorescence above a radio-frequency biased silicon wafer

The dynamics of ions traversing sheaths in low temperature plasmas are important to the formation of the ion energy distribution incident onto surfaces during microelectronics fabrication. Ion dynamics have been measured using laser-induced fluorescence (LIF) in the sheath above a 30 cm diameter, 2.2 MHz-biased silicon wafer in a commercial inductively coupled plasma processing reactor. The velocity distribution of argon ions was measured at thousands of positions above and radially along the surface of the wafer by utilizing a planar laser sheet from a pulsed, tunable dye laser. Velocities were measured both parallel and perpendicular to the wafer over an energy range of 0.4–600 eV. The resulting fluorescence was recorded using a fast CCD camera, which provided resolution of 0.4 mm in space and 30 ns in time. Data were taken at eight different phases during the 2.2 MHz cycle. The ion velocity distributions (IVDs) in the sheath were found to be spatially non-uniform near the edge of the wafer and phase-dependent as a function of height. Several cm above the wafer the IVD is Maxwellian and independent of phase. Experimental results were compared with simulations. The experimental time-averaged ion energy distribution function as a function of height compare favorably with results from the computer model.

36 MATERIALS SCIENCE↗
DOE OSTI2013

GIOVE, a shallow laboratory Ge-spectrometer with 100 μBq/kg sensitivity

A new germanium gamma spectrometer called GIOVE (Germanium spectrometer with Inner and Outer Veto) has been set up at the underground/shallow laboratory (15 m w.e.) of MPI-K. Its double plastic scintillator veto system and neutron moderation interlayer lower the background by more than one order of magnitude compared to the other existing spectrometer at this facility. The integral (40-2700 keV) background rate of about 290 counts (day kg){sup −1} is just a factor 4 to 8 above that of the GeMPI spectrometers operated at LNGS (3800 m w.e.) and thus proves that even under shallow overburden sub mBq/kg sensitivities are achievable. Extended material screening and neutron attenuation studies preceded the final design of the spectrometer. The technical realization of the spectrometer is described in detail with special emphasis on the inner veto system. For its optimisation a simulation model was developed for light collection on small low activity PMT’s under various geometrical conditions. Radon suppression is accomplished by employing a gas tight sample container and a nitrogen flushed glove-box system with an airlock. The active volume of the crystal was modelled by absorption scanning measurements and Monte Carlo simulations. The complete shield is implemented in a Geant4 based simulation framework.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2013

Simulation ensemble for a laser–driven shear experiment

We perform an ensemble of simulations of a laser-driven shear experiment [L. Welser-Sherrill et al., “Two laser-driven mix experiments to study reshock and shear,” High Energy Density Phys. J. 9(3), 496–499 (2013)] in the strong-shock high energy-density regime to better understand material mixing driven by the Kelvin–Helmholtz instability. Each simulation uses a different realization of random initial interface perturbations based on data from targets used in experiments. Validation of the simulations is based on direct comparison of simulation and radiographic data. Simulations are also compared with published direct numerical simulation and the theory of homogeneous isotropic turbulence. Despite the fact that the flow is neither homogeneous, isotropic, nor fully turbulent, there are local regions in which the flow demonstrates characteristics of homogeneous isotropic turbulence. Our analysis shows characteristics consistent with those of incompressible isotropic turbulence. Our results show that turbulent features are present both near the shock front and in a separated region in the wake of the shock. These features develop and decay at different rates. Finally, we use the ensemble of three-dimensional simulations to test the performance of two-dimensional Reynolds-averaged Navier-Stokes simulations. In this context, we also test a presumed probability density function turbulent mixing model extensively used in combustion applications.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2013

Temporal evolution of femtosecond laser induced plasma filament in air and N{sub 2}

We present single shot, high resolution, time-resolved measurements of the relaxation of laser induced plasma filaments in air and in N{sub 2} gas. Based on the measurements of the time dependent electromagnetic signal in a waveguide, an accurate and simple derivation of the electron density in the filament is demonstrated. This experimental method does not require prior knowledge of filament dimensions or control over its exact spatial location. The experimental results are compared to numerical simulations of air plasma chemistry. Results reveal the role of various decay mechanisms including the importance of O{sub 4}{sup +} molecular levels.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗