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Articles 181 - 210 of 211
Full-Text Articles in Nuclear Engineering
Positive Anisotropic Group Scattering Cross Sections For Radiation Transport, J. Mark Delgrande
Positive Anisotropic Group Scattering Cross Sections For Radiation Transport, J. Mark Delgrande
Theses and Dissertations
In solving the Boltzmann transport equation, most discrete ordinates codes calculate the source term by first approximating the scattering cross section using a Legendre polynomial expansion. Such expansions are insufficient when scattering is anisotropic and the Legendre expansion is truncated prematurely. This can lead to nonphysical negative cross sections, negative source terms and negative angular fluxes. While negative sources are problematic for standard discrete ordinates methods leading to poor convergence or convergence to incorrect results, they are of particular concern to exponential methods, causing such calculations to fail. We've developed and tested a new technique to solve this problem called …
An Investigation Into The Noninvasive Assessment Of Bone Density Using Multiplexed Compton Scattered Tomography, Marc J. Sands
An Investigation Into The Noninvasive Assessment Of Bone Density Using Multiplexed Compton Scattered Tomography, Marc J. Sands
Theses and Dissertations
The purpose of this research is to investigate the application of a Compton scatter imaging technique to measure bone density. A demonstration Multiplexed Compton Scatter Tomograph (MCST) was assembled to demonstrate the feasibility of detecting osteoporosis by modifying a system originally designed to detect hidden corrosion in aluminum aircraft wings. Measurements were performed on an aluminum phantom representing a wrist bone containing varying densities in the center and varying thickness of the cortical shell. The densities in the center are comparable to normal trabecular bone, sixty-percent of normal trabecular bone and a void. The MCST images of the phantom were …
Development Of A Discrete Ordinates Code System For Unstructured Meshes Of Tetrahedral Cells, With Serial And Parallel Implementations, Rodney L. Miller
Development Of A Discrete Ordinates Code System For Unstructured Meshes Of Tetrahedral Cells, With Serial And Parallel Implementations, Rodney L. Miller
Theses and Dissertations
A numerically stable, accurate, and robust form of the exponential characteristic (EC) method, used to solve the time-independent linearized Boltzmann Transport Equation, is derived using direct affine coordinate transformations on unstructured meshes of tetrahedra. This quadrature, as well as the linear characteristic (LC) spatial quadrature, is implemented in our transport code, called TETRAN. This code solves multi-group neutral particle transport problems with anisotropic scattering and was parallelized using High Performance Fortran and angular domain decomposition. A new, parallel algorithm for updating the scattering source is introduced. The EC source and inflow flux coefficients are efficiently evaluated using Broyden's rootsolver, started …
Creating Origen Models, Gregory D. Louden
Creating Origen Models, Gregory D. Louden
Theses and Dissertations
The purpose of this study was to develop a methodology for creating problem dependent cross section libraries for ORIGEN (Oak Ridge Isotope Generation and Depletion Code). The Air Force Technical Applications Center (AFTAC) has a requirement to classify spent nuclear fuel. The ORIGEN codes provide generic models of commercial nuclear reactor designs that are not adequate for the detailed analysis required by AFTAC. After comparing the methods that ORIGEN2 an ORIGEN-S use to develop burnup dependent cross section libraries, the research focused on developing a methodology for creating new ORIGEN-S models. Models of the Ohio State University Research Reactor were …
Total Ionizing Dose Effects In Mosfet Devices At 77 K, Kevin J. Daul
Total Ionizing Dose Effects In Mosfet Devices At 77 K, Kevin J. Daul
Theses and Dissertations
Total ionizing dose effects on thermal oxide and reoxidized nitrided oxide (RNO) MOSFET devices at 77 K were studied. The MOSFETs were immersed in liquid nitrogen and irradiated, using a 60Co source, up to 1 Mrad(Si) at a dose rate of 107 rads(Si)-sec. Drain current-gate voltage characteristics were obtained and used to determine threshold voltage and transconductance. At 77 K the subthreshold slopes indicated no observed buildup of interface states in any of the transistors. Furthermore, all transistors experienced very little change in the transconductance. Typical negative shifts in threshold voltage as dose increased were observed in all of …
Shock Wave Interaction With L-Shaped Structures, Richard C. Miller
Shock Wave Interaction With L-Shaped Structures, Richard C. Miller
Theses and Dissertations
This study investigated the interaction of shock waves with L-shaped structures using the CTH hydrodynamics code developed by Sandia National Laboratories. Computer models of shock waves traveling through air were developed using techniques similar to shock tube experiments. Models of L-shaped buildings were used to determine overpressures achieved by the reflecting shock versus angle of incidence of the shock front. An L-shaped building model rotated 45 degrees to the planar shock front produced the highest reflected overpressure of 9.73 atmospheres in the corner joining the two wings, a value 9.5 times the incident overpressure of 1.02 atmospheres. The same L-shaped …
Excited Atomic Bromine Energy Transfer And Quenching Mechanisms, Ray O. Johnson
Excited Atomic Bromine Energy Transfer And Quenching Mechanisms, Ray O. Johnson
Theses and Dissertations
Pulsed and steady-state photolysis experiments have been conducted to determine the rate coefficients for collisional deactivation of the spin-orbit excited state of atomic bromine, Br(2p1/2). Pulsed lifetime studies for quenching by Br2 and CO2, established absolute rate coefficients at room temperature of kBr2 = 1.2 ± 0.1 x 10-12 and kCO2 = 1.5 ± 0.2 x 10-11 cm3/molecule-s. Steady-state photolysis methods were used to determine the quenching rates for the rare gases, N2, 02, H2, D2, NO, …
Linear Characteristic Spatial Quadrature For Discrete Ordinates Neutral Particle Transport On Arbitrary Triangles, Dennis J. Miller
Linear Characteristic Spatial Quadrature For Discrete Ordinates Neutral Particle Transport On Arbitrary Triangles, Dennis J. Miller
Theses and Dissertations
A new discrete ordinates spatial quadrature for arbitrary triangular cells is derived and compared to its rectangular cell linear characteristic counterpart. The triangular mesh is more flexible, allowing curved surfaces and off-axis angles to be approximated with many fewer spatial cells. The triangle method is consistently more accurate on example problems tested here. Arbitrary orientation and size of the triangles allow non-patterned meshes to be developed which appears to ameliorate numerical diffusion. The triangle linear characteristic quadrature converges at nearly the same rate as rectangular Linear characteristic on Lathrop's problem. Mesh sensitivity measurements show large variations in triangle vertex locations …
Mitigation Of Shock Waves In A Cylindrical Tunnel By Foam, Grant W. Fondaw
Mitigation Of Shock Waves In A Cylindrical Tunnel By Foam, Grant W. Fondaw
Theses and Dissertations
This study investigated the effectiveness of foam linings in mitigating shock waves in tunnels. A polyurethane foam liner of varying density, crush strength and thickness was modeled inside a 1 meter radius tunnel and an explosion of 1.25 kg of plastic explosive was simulated. Using CTH, an Eulerian- Lagrangian hydrodynamics code from Sandia National Laboratories, the overpressures were computed and compared graphically to determine the effect of varying each foam parameter. The walls of the tunnel consisted of a perfectly reflecting boundary, and in some cases, a foam liner. Low density foam provided the most shock attenuation. with a 20 …
Analysis Of Topaz Ii And Space-R Space Nuclear Power Plants Using A Modified Thermionic Model, Otto D. Habedank
Analysis Of Topaz Ii And Space-R Space Nuclear Power Plants Using A Modified Thermionic Model, Otto D. Habedank
Theses and Dissertations
Models based on the TDS thermionic diode model were developed for TOPAZ II and SPACER nuclear power systems. Several parameter studies were conducted with the TOPAZ II model. These determined system performance and efficiency while varying the following: (1) Coolant flow inlet temperatures. (2) Rate of coolant temperature change. (3) Power profile of the core. (4) Cesium reservoir temperature. Analysis of results indicate the model accurately represented the TOPAZ II system, underestimating published data by 10%. Coolant flow studies indicate that raising coolant temperatures up to 100 K higher increases system power by up to 5%. Additional increases in temperature …
Amplification Of Shock Overpressure By Reflection Within Concave Corners, John E. Loftis
Amplification Of Shock Overpressure By Reflection Within Concave Corners, John E. Loftis
Theses and Dissertations
In this study, CTH, a production hydrodynamics code developed and provided by Sandia National Laboratories. modeled the interaction of a shock wave with tall V-shaped buildings with various wall lengths and vertex angles. The purpose of this study was to determine the degree to which the length and vertex angle affect the peak overpressure at the vertex. CTH performed two- dimensional Eulerian-Lagrangian computations to obtain solutions of this problem. The models were cast in two-dimensional rectangular geometry on a horizontal plane because of the computational costs of three-dimensional calculations. This geometry simulates tall buildings exposed to a tall Mach stem …
Afitbunki: A Modified Iterative Code To Unfold Neutron Spectra From Bonner Sphere Detector Data, Sean C. Miller
Afitbunki: A Modified Iterative Code To Unfold Neutron Spectra From Bonner Sphere Detector Data, Sean C. Miller
Theses and Dissertations
The neutron spectrum unfolding code BUNKI, developed at the Naval Research Laboratory in 1983, was modified to incorporate a finer energy group structure, seven initial-guess spectra, and new dose conversion factors. The modified code, AFITBUNKI, unfolds spectra into 54 energy groups between 10-7 and 14.92 MeV. The code calculates fluence, absorbed dose, percent of effective dose equivalent, and percent of ambient dose equivalent as a function of neutron energy. Additionally, AFITBUNKI calculates total energy-integrated fluence (Φ), absorbed dose (D), dose equivalent (H), effective quality factor (Q), ambient dose (D*), both ICRP Publication 26- and ICRP Publication 60-based ambient dose …
Construction And Testing Of A Neutron And Gamma Spectrometry System Using Pulse Shape Discrimination With An Organic Scintillator, Robert S. Pope
Construction And Testing Of A Neutron And Gamma Spectrometry System Using Pulse Shape Discrimination With An Organic Scintillator, Robert S. Pope
Theses and Dissertations
The goal of this thesis was to construct and test a neutron detector to measure the energy spectrum of 1 to 14-MeV neutrons in the presence of gammas. A spectrometer based on the process of pulse shape discrimination (PSD) was constructed, in which the scintillator NE-213 was used. The primary neutron/ gamma sources used were 78-mCi and 4.7-Ci 239PuBe sources, while 4.7-µCi and 97.6-µCi 22Na gamma sources were used for energy calibration and additional testing of the detector. Proton recoil spectra and Compton electron spectra were unfolded with the neutron and gamma unfolding code FORIST to generate the …
Identification Of Significant Outliers In Time Series Data, Keri L. Robinson
Identification Of Significant Outliers In Time Series Data, Keri L. Robinson
Theses and Dissertations
This thesis examines the feasibility of using least median of squares (LMS) procedure applied to a reweighted least squares (RLS) autoregression model to identify significant outliers in time series data. The time series were analyzed for data points that were outliers. In order to perform detailed analysis on an outlier. the analyst must be able to determine that an outlier data point is significantly different from normally distributed data. This thesis examines a new method for identifying these outliers. Data from the field were characterized and fit with time series models using an autoregressive reweighted least squares routine (ARRLS) derived …
Total Hemispherical Emittance Of Niobium-1% Zirconium Fuel Cladding For The Sp-100 Space Reactor, John E. Thomason Iii
Total Hemispherical Emittance Of Niobium-1% Zirconium Fuel Cladding For The Sp-100 Space Reactor, John E. Thomason Iii
Theses and Dissertations
Total hemispherical emittance was measured for the SP-100 reactor fuel cladding alloy (Nb-l% Zr). Based on a standard test method (ASTM C 835-82), experiments were conducted on a reference sample of oxidized stainless steel and then on a sample of actual cladding. The sample is heated in a vacuum by passing DC current through it until reaching equilibrium. Measurements are made of the electrical power dissipated in the sample and of the surface temperature. Using the Stefan-Boltzmann Law and some key assumptions concerning conductive and radiative heat transfer, the measured quantities are used to calculate emittance. Calculated values for unoxidized …
Neutron Fluence And Dose From A Varian Clinic 1800 Accelerator, Richard A. Jackson
Neutron Fluence And Dose From A Varian Clinic 1800 Accelerator, Richard A. Jackson
Theses and Dissertations
The goals of this study were (1) to verify calibration factors determined by previous experiment for relating counts from activated gold foils to neutron fluences, and (2) to use the method to determine neutron fluences under various operating conditions of the Varian Clinac 1800 (18-MeV) electron accelerator at the WPAFB Medical Center. For comparison similar measurements were made of the CGM Saturne 1 at Kettering Memorial Hospital, Dayton, Ohio. Cadmium-difference pairs in a standard graphite pile were employed to verify the counting efficiency of the Geiger-Mueller beta counting system used to count the foil activity. They were also used to …
Design Of A Warm X-Ray Radiation Environment For Nuclear Weapons Effects Testing In The Nova-Upgrade Facility, Jeffrey E. Malapit
Design Of A Warm X-Ray Radiation Environment For Nuclear Weapons Effects Testing In The Nova-Upgrade Facility, Jeffrey E. Malapit
Theses and Dissertations
This engineering design project examined the creation of a radiation environment for warm x-ray effects testing in the Nova Upgrade laser facility. With the use of the MORSE Monte Carlo Code and the DABL69 Broad-group cross section library, the ignition of an inertial confinement fusion pellet using D-T fuel in a test cassette was modeled in the Nova Upgrade's target chamber. Various x-ray scattering materials were used in the test cassette to include enriched lithium hydride, polyethylene, liquid hydrogen, liquid helium, and liquid methane. The lithium hydride produced the best warm x-ray doses and least neutron dose. The predicted x-ray …
Development Of A System For Survey Of Radon Concentration Of The Dayton Area Using A Liquid Scintillation Counter And Analysis Of The Data, Taewon Kim
Theses and Dissertations
A system to do a large scale survey was developed. The data obtained from the survey was analyzed using a database. The database incorporated an equation for converting cpm into radon concentration pCi/ℓ). The equation of conversion, protocol for measuring radon concentration, survey form, and a database program were modified (from previous theses) or developed for this thesis. The elution time constant, adsorption time constant, and calibration factor were calculated for equation of conversion. Two surveys were during the course of the thesis. On the first survey, the arithmetic average radon concentration with standard error of the mean was 2.9 …
Feasibility Of An Antiproton Catalyzed Fission Fragment Rocket, David S. Hidinger
Feasibility Of An Antiproton Catalyzed Fission Fragment Rocket, David S. Hidinger
Theses and Dissertations
The purpose of this project was to investigate the feasibility of an antiproton catalyzed fission fragment rocket (FFR). The FFR is characterized by the extraction of fission fragments from the fuel, and the utilization of their kinetic energy for thrust generation. A significant drawback to previous FFR designs was the required critical nuclear pile as the fission fragment source. The author examined the possibility of replacing the critical pile with a sub- critical pile driven by antiprotons. Recent experiments have revealed that antiprotons stimulate highly energetic fissions in 238U, with a neutron multiplicity of 13.7 neutrons per fissions. This interaction …
Gamma-Ray Effects Testing In Lawrence Livermore National Laboratory's Nova Upgrade Facility, David H. Marchant
Gamma-Ray Effects Testing In Lawrence Livermore National Laboratory's Nova Upgrade Facility, David H. Marchant
Theses and Dissertations
Gamma ray effects testing in Lawrence Livermore National Laboratory's (LLNL) planned Nova Upgrade facility is examined. Emphasis is placed on converting neutron energy from inertial confinement fusion in to gamma rays while shielding the test objects from neutrons and debris. Although predicted gamma doses in the Nova Upgrade facility are an order of magnitude less than those produced in some current facilities, dose uniformity, the ratio of minimum to maximum gamma dose is predicted to be greater than 0.75 across a larger, 13, 000 cm2, test bed. Peak gamma dose rates are predicted to be on the order …
Exponential Characteristic Spatial Quadrature For Discrete Ordinates Neutral Particle Transport In Slab Geometry, Glenn E. Sjoden
Exponential Characteristic Spatial Quadrature For Discrete Ordinates Neutral Particle Transport In Slab Geometry, Glenn E. Sjoden
Theses and Dissertations
A new discrete ordinates spatial quadrature scheme is presented for solving neutral particle transport problems. This new scheme, called the exponential characteristic method, is developed here in slab geometry with isotropic scattering. This method uses a characteristic integration of the Boltzmann transport equation with an exponential function as the assumed from of the source distribution, continuous across each spatial cell. The exponential source function is constructed to globally conserve zeroth and first spatial source moments and is non-negative. Characteristic integration ensures non- negative fluxes and flux moments. Numerical testing indicates that convergence of the exponential characteristic scheme is fourth order …
Model Of A Nuclear Thermal Test Pipe Using Athena, Mark J. Dibben
Model Of A Nuclear Thermal Test Pipe Using Athena, Mark J. Dibben
Theses and Dissertations
Nuclear thermal propulsion offers significant improvements in rocket engine specific impulse over rockets employing chemical propulsion. The computer code ATHENA (Advanced Thermal Hydraulic Energy Network Analyzer) was used in a parametric analysis of fuelpipe. The fuelpipe is an annular particle bed fuel element of the reactor with radially inward flow of hydrogen through it. The outlet temperature of the hydrogen is parametrically related to key effects, including the effect of reactor power at two different pressure drops, the effect of the power coupling factor of the Annular Core Research Reactor, and the effect of hydrogen flow. Results show that the …
An Examination Of The Feasibility Of A Nuclear-Pumped Laser-Driven Inertial Confinement Fusion Reactor With Magnetically Protected Walls, John M. Jacobson
An Examination Of The Feasibility Of A Nuclear-Pumped Laser-Driven Inertial Confinement Fusion Reactor With Magnetically Protected Walls, John M. Jacobson
Theses and Dissertations
A preliminary design study of a nuclear-pumped laser-driven inertial confinement fusion reactor with a magnetically protected first wall using an advanced DT-ignited, DD-fueled pellet demonstrated the feasibility of such a concept. This paper presents a parametric study of the required energy multiplication in the blanket, the pellet injection rate, and the net efficiency of this is conceptual reactor for advanced pellet yields. A model of the reactor energy balance yields a required energy multiplication of 2.4. A cylindrical design for a helium-cooled blanket demonstrates that natural uranium micropellets in a laser pump region provide a multiplication of 2.9 with a …
Design And Construction Of A Channel Electron Multiplier Based Mossbauer Spectroscopy System, Daniel J. Robbins
Design And Construction Of A Channel Electron Multiplier Based Mossbauer Spectroscopy System, Daniel J. Robbins
Theses and Dissertations
A channel electron multiplier (cem) detector system was designed and built to provide a signal to a Mossbauer spectroscopy system in an effort to obtain a better signal-to-noise ratio than achievable with a proportional counter system. Three cems are contained in a vacuum chamber built using standard components. Gamma, rays of 14.4-keV energy from a 57Co source enter from outside the chamber through a window and are absorbed by an 57Fe target near the cems. The target emits internal conversion electrons which are collected by the cems and a Mossbauer spectrometer collects the signal. The system produces a …
Construction, Calibration And Use Of A Neutron Time-Of-Flight Spectrometer, Charles L. Wood
Construction, Calibration And Use Of A Neutron Time-Of-Flight Spectrometer, Charles L. Wood
Theses and Dissertations
The energy spectrum of a 5 curie Pu-Be neutron source is determined by use of a neutron time-of-flight spectrometer. This spectrometer measures the time it takes for a neutron to travel between two plastic scintillator detectors. Using a fixed distance for travel, a time spectrum is generated which is then unfolded into the energy spectrum of the source. The different aspects of equipment selection, connection and calibration of the system are described. With the resolved spectrum the energy resolution of the spectrometer is determined by using a Monte Carlo simulation of the experimental set-up. A dual- parameter experiment is conducted …
An Assessment Of The Accuracy Of Semi-Empirical Quantum Chemistry Calculations Of The Mechanical Properties Of Polymers, James R. Shoemaker
An Assessment Of The Accuracy Of Semi-Empirical Quantum Chemistry Calculations Of The Mechanical Properties Of Polymers, James R. Shoemaker
Theses and Dissertations
The ultimate mechanical properties of polymers, assuming perfect morphology, will be limited by the mechanical properties of a single, ideal polymer chain. Previous calculations of polymer chain moduli using semi- empirical (SE) quantum chemistry methods have resulted in modulus values much higher than experimentally measured. This study investigated the error in the calculated inherent to the method of calculation by comparing SE results for C-C bond potentials in two well characterized polymers, polyethylene and polydiacetylene. It was found that the SE calculation systematically overpredicted bond stiffness in these polymers by approximately 25% to 30%. This is the upper limit on …
An Environmentally Controlled Chamber For The Study Of Radon Detection, William R. Wharton Jr.
An Environmentally Controlled Chamber For The Study Of Radon Detection, William R. Wharton Jr.
Theses and Dissertations
A system was developed to dynamically control and monitor the environment and radon concentration within a glovebox chamber for the study of radon. The system is designed around a personal computer workstation which automates the entire system. The radon concentration is determined by monitoring the count rate from radon and its progeny which are continuously circulated from the radon chamber through a Lucas Cell detection system. This information is then used as a base for controlling a radon injection system. When the concentration within the glovebox drops, the system injects a precisely-measured volume of high activity radon gas into the …
Development Of An Angular Distribution Function For The Study Of Atomic Lattice Structures Used In Atomistic Simulation, David Wesley
Development Of An Angular Distribution Function For The Study Of Atomic Lattice Structures Used In Atomistic Simulation, David Wesley
Theses and Dissertations
An angular distribution function (ADF) was developed as a tool to be used in atom simulation. The ADF lets us easily distinguish between different lattice structures for systems of atoms by looking at the distribution of bond angles. The ADF is also a useful tool for determining the amount of order in a system. First, model structures of simple cubic, FCC, BCC, and diamond were developed. Then, the ADF was used on these model structures so that a set of model graphs of the ADF could be used to compare to real systems. Finally, simulated systems of Ferric Titanate, Nickel …
Hardware Upgrade Of A Segmented Drum Assay System, Claude A. Irvine
Hardware Upgrade Of A Segmented Drum Assay System, Claude A. Irvine
Theses and Dissertations
This paper describes the conversion of a DEC PDP-11/05 computer system, previously used in Canberra's Model 2220B segmented gamma scanner, with an IBM PC. Two tasks necessary for completion of the project involved reestablishing communications with a Canberra Series 35+ multi-channel analyzer and a scan table controller. An additional serial/parallel card was installed in the PC to reinstate comunications with the multi-channel analyzer. For computer control of scan table controller operations a digital input/output card was used along with an external electromechanical relay board; when implemented together this hardware setup replaces functions that were normally processed through a motion control …
Green's Function Approach To The Atmospheric Albedo Neutron Transport Problem, Donald R. Culp Jr.
Green's Function Approach To The Atmospheric Albedo Neutron Transport Problem, Donald R. Culp Jr.
Theses and Dissertations
This study investigated the reflection of neutron radiation off of the earth's upper atmosphere, with the goal of generating a quick-running computer algorithm to estimate the albedo free field flux at any point above the atmosphere. This thesis involved analytic development in the construction of the algorithm and employed Monte Carlo simulation for generating the energy and angle distributions of the reflected radiation. The Green's function approach to modeling the neutron transport process involved approximating each energy bin of the source spectrum as a Dirac pulse in energy and summing the contribution from each source bin. The computer program integrates …