Nuclear Engineering Commons^™

Characterization Of The Acquisition Parameters Of A Submersible Gamma-Ray Computed Tomography System, Zhongmin Jin

Doctoral Dissertations

"The purpose of this work is to study a component of a submersible gamma-ray computed tomography (CT) system used in the non-destructive testing of irradiated nuclear fuels. The first section of this study proposes two acceleration approaches for rapidly modeling a transmission-type gamma-ray tomography system. The first relies on Monte Carlo simulations with a monodirectionally biased source sampled from a sub-volume of the whole source volume. This method estimates the real count rate using analytical correction factors. The second way of acceleration is based on deterministic calculations that use the Beer-Lambert law and detector response characteristics. It shows that both …

Dynamics Modeling Of Molten Salt Reactors, Visura Umesh Pathirana

Doctoral Dissertations

The abundance of energy is a necessity for the prosperity of humans. The rise in energy demand has created energy shortages and issues related to energy security. Nuclear energy can produce vast amounts of reliable energy without many of the negative externalities associated with other competing energy sources, such as coal and natural gas. As a result, public interest in nuclear power has increased in the past decade. Many new types of nuclear reactor are proposed. These nuclear reactor designs feature many passive technologies that can operate without external influence. Reactors that feature advanced passive safety features are catagorized as …

Development Of A Portable, Tileable, Dual-Particle Radiography System, Christian Xavier Young

Doctoral Dissertations

A scalable, portable, multi-particle neutron radiography device has been developed using commercial-off-the-shelf-parts. The IDEAS ROSSPAD readout module was selected for use in developing the radiography panel due to its single-wire Power-over-Ethernet (PoE) connectivity and its tileable form factor. Each ROSSPAD detector is paired with an 8 by 8 array of 6-mm-pitch Sensl J-Series silicon photomultipliers (SiPMs). With both single and multi-ROSSPAD testing, a detection package consisting of a 3-mm-thick sheet of EJ-200 plastic scintillator and a 3-mm-thick sheet of acrylic light spreader was coupled to the SiPM board face. After both quality assurance of the detector packages and the calibration …

Characterizing The Structure And Radiation Resistance Of Weberite-Type Complex Oxides, Igor M. Gussev

Doctoral Dissertations

Weberite-type A₃BO₇ oxides, where A is a trivalent rare earth and B is a pentavalent element like Ta, have been a focus of research due to the discovery of the weberite-type local atomic arrangement in ceramics with a defect-fluorite structure. Earlier studies primarily examined their long-range structures, leaving gaps in understanding their short-range atomic behavior. This thesis investigates various weberite-type tantalates across all structural scales. There has been debate over the long-range structure of Y₃TaO₇, a medium-sized rare earth tantalate oxide, particularly regarding its spacegroup symmetry. This work identifies Y₃TaO_{7 …}

The Nuclear System-Of-Systems Capabilities Analytic Process, Robert Boone Gilbreath

Doctoral Dissertations

This work includes the first known capabilities-based vulnerability analysis process able to evaluate a system of systems exposed to nuclear weapon environments: the Nuclear System-of-Systems Capabilities Analytic Process (NuSCAPTM). This approach, executed by an automated Python® application, calculates the magnitudes of eight nuclear weapon environment quantities by calling on the US Strategic Command Probability of Damage Calculator (PDCALC) code, the Los Alamos National Laboratory Simple Nuclear Effects Calculator (SNEC) program, and the Monte Carlo N-Particle® (MCNP®) code. Calculated nuclear weapon environment values are compared with user-provided dysfunction thresholds for all components, subsystems, and systems in the model to determine the …

Development Of A Detailed And Reduced-Order Neutronics Models For Fusion Reactor Blanket And Systems Design Optimization, Felipe Santos Novais

Doctoral Dissertations

Fusion neutronics plays a critical role in the design and operation of fusion reactors. However, there are a number of challenges associated with fusion neutronics that must be overcome in order to help achieve practical and sustainable fusion energy. The primary objective of this project is to develop and demonstrate a broad neutronics analysis capability in support of system studies for U.S. concepts such as the Fusion Nuclear Science Facility (FNSF). According to a detailed TBR analysis that included an examination of reaction rates and the impact of facility (FNSf) components on neutron spectra and TBR, Li-6 will generate the …

Nuclear Thermal Rocket Engine Instrumentation Addressing Environmental Limitations On Temperature Measurements, Dan C Floyd

Doctoral Dissertations

The development of nuclear thermal rockets has received renewed interest in recent years due to the benefits that can attained from this method of propulsion. Currently, instrumentation work is focused on the evaluation of current and near-term technology for implementation within a nuclear thermal rocket engine. One aspect of this evaluation is focused on the various instrumentation requirements of the system regarding necessary measurement parameters and environmental conditions for survivability. Historical nuclear rocket programs that have been conducted in the United States provide the basis for this information and indicates a critical need for high temperature measurement technology that can …

Sensitivity Analysis Of Thermophysical Properties Of Molten Salts Using A Molten Salt Demonstration Reactor Model In Transform, Sarah Elizabeth Creasman

Doctoral Dissertations

Molten Salt Reactors (MSRs) are currently of interest due to the push for smaller reactors that are easier to deploy and the need for sustainable energy around the world. Nuclear energy can play an important role in addressing the issue of energy inequality and climate change. One of the main obstacles to deploying MSRs is licensing. An important aspect to understand in terms of licensing is the uncertainty of the thermophysical properties of the molten salt at the beginning of the cycle and during normal operations and transients. MSRs have already been proven as a viable concept; two research reactors—The …

Fabrication, Measurements, And Modeling Of Semiconductor Radiation Detectors For Imaging And Detector Response Functions, Corey David Ahl

Doctoral Dissertations

In the first part of this dissertation, we cover the development of a diamond semiconductor alpha-tagging sensor for associated particle imaging to solve challenges with currently employed scintillators. The alpha-tagging sensor is a double-sided strip detector made from polycrystalline CVD diamond. The performance goals of the alpha-tagging sensor are 700-picosecond timing resolution and 0.5 mm spatial resolution. A literature review summarizes the methodology, goals, and challenges in associated particle imaging. The history and current state of alpha-tagging sensors, followed by the properties of diamond semiconductors are discussed to close the literature review. The materials and methods used to calibrate the …

Improved Spatial Resolution For Double-Sided Strip Detectors Using Lithium Indium Diselenide Semiconductors, Jake Alexander Gallagher

Doctoral Dissertations

This research focuses on the evaluation of lithium indium diselenide (LISe) semiconductors in double-sided strip detector (DSSDs) designs as an example for the potential to achieve unparalleled neutron detection efficiency, spatial resolution, and timing resolution detection. LISe semiconductors offer high neutron detection efficiency due to the ~25% atomic ratio of Lithium-6, maximizing its efficiency of ~75% with 1 mm thickness at 2.8 angstroms. Furthermore, the 4.78 MeV 𝑄-value enables high intrinsic gamma discrimination in a pixelated design (electron range). These characteristics make LISe an alternative option for neutron radiography, energy-resolved imaging, and other neutron interrogation techniques. This dissertation summarizes my …

Development Of A Low-Dose Radiation Therapy Device For Acute Respiratory Distress Syndrome, Thomas Heath Davis

Doctoral Dissertations

This research focuses on developing a low-dose radiotherapy (LD-RT) device for treating acute respiratory distress syndrome (ARDS). This respiratory illness affects millions of people a year. Using orthovoltage (200 – 500 keV) X-ray energy provides many advantages over traditional radiotherapy delivery with linear accelerators, such as low cost and greater accessibility. In addition, X-ray tubes have been shown throughout history to provide good treatment outcomes for pneumonia, and research has shown LD-RT to be just as effective with ARDS. This proposal summarizes my efforts in determining the dosimetric properties of an LD-RT system to deliver treatment quickly and effectively. My …

Total Absorption Spectroscopy Of Mo-106 And Tc-106, Michael Cooper

Doctoral Dissertations

Total absorption spectroscopy is a method of gamma-ray spectroscopy that has gained prominence in the past several decades, as nuclear data revisions are performed on older nuclear data, which is often incomplete. A strong understanding of underlying nuclear data, particularly fission and beta decay data, is essential for nuclear reactors and nuclear fuel decay heat. This PhD work involves the analysis of fission fragments 106Mo [Mo-106] and 106Tc [Tc-106]. These neutron rich isotopes contribute upwards of 6% of the cumulative fission yield of 241Pu [Pu-241] fission, and 4% of 239Pu [Pu-239] fission. Prior data for these two fission fragments only …

Cfd Analysis For Beyond Bubbly Gas-Liquid Two-Phase Flows In A Large Diameter Pipe, Sungje Hong

Doctoral Dissertations

"Due to the complexity of multiphase flow phenomena, numerical analysis for multiphase turbulent flow is not as reliable as single-phase computational fluid dynamics (CFD). A literature review has revealed that the current efforts on multiphase flow simulation have focused on small diameter channels under very restricted flow conditions and have been conducted without identifying some important procedures. To expand CFD applications to a wide range of two-phase flow conditions in large diameter channels, this study aims to validate the current CFD models for vertical concurrent air-water two-phase flow simulations beyond bubbly flows. First, a numerical model developed to describe dynamical …

Determination Of Near-Sol Carbon Impurity Content Due To Divertor Target Leakage Using Carbon-13 Tracers Via Methane Injection On The Diii-D Tokamak, Jonah David Duran

Doctoral Dissertations

Experiments with outer strike point injection of isotopically enriched methane (¹³CD­₄) in DIII-D L-mode discharges have demonstrated the ability to infer near scrape-off-layer (SOL) impurity density profiles based on: far-SOL collector probe (CP) measurements; a stable isotopic mixing model; and SOL impurity transport modelling. This work enables one of the first in-depth investigations on the source and transport of SOL impurities which could hinder performance of future fusion devices. Modelling by DIVIMP and 3DLIM of ¹³C SOL evolution is consistent with diagnostic observations and indicates that the buildup of injected impurities on plasma-facing surfaces must …

First Development And Demonstration Of Fiber Optic Bolometer, Seungsup Lee

Doctoral Dissertations

The fiber optic bolometer (FOB) was demonstrated observing a fusion plasma for the first time, and 2D fiber optic bolometer was developed and demonstrated to have high spatial resolution. The FOB is a novel type of a bolometer that is theoretically immune to EMI. A bolometer that is a sensor that measure the power of the incoming electromagnetic radiation. The most common bolometer used in fusion research is a resistive bolometer that utilize resistors in an electrical circuit. Due to high electromagnetic interferences (EMI) in fusion environment, noise can be a serious problem in determining accurate plasma radiation. The demonstration …

Multiphysics Analyses And Experiments For Safety Of Advanced Light Water Reactor Fuels, Soon K. Lee

Doctoral Dissertations

The Fukushima Daiichi nuclear plant accident in 2011 triggered worldwide research and development initiatives to advance Light Water Reactor (LWR) fuel materials with excellent tolerance to high-temperature oxidation and deformation. Accident Tolerant Fuel (ATF) design concepts are expected to improve safety margin and extend coping time during severe accident progression, owing to their enhanced mechanical strength, oxidation, and degradation resistance. These concepts require a series of assessments to be licensed by the United States (US) Nuclear Regulatory Commission (NRC). In addition to enhanced safety from ATF materials, supported by the NRC, the US nuclear industry is seeking opportunities to increase …

Multi-Objective Optimization Of The Fast Neutron Source By Machine Learning, John L. Pevey

Doctoral Dissertations

The design and optimization of nuclear systems can be a difficult task, often with prohibitively large design spaces, as well as both competing and complex objectives and constraints. When faced with such an optimization, the task of designing an algorithm for this optimization falls to engineers who must apply engineering knowledge and experience to reduce the scope of the optimization to a manageable size. When sufficient computational resources are available, unsupervised optimization can be used.

The optimization of the Fast Neutron Source (FNS) at the University of Tennessee is presented as an example for the methodologies developed in this work. …

Demonstrating The Use Of Multiple Experimental Techniques To Investigate Helium-Hydrogen Synergies In Tungsten, Wendy A. Garcia

Doctoral Dissertations

Polycrystalline W sample discs measuring 6 mm by 0.5 mm have been exposed to a low-energy (70 eV) He plasma using a low flux ( ) [1.3 times 10 to the 17 Helium per meter squared per second] ECR source located at the University of Tennessee in Dr. Donovan's laboratory. The samples were exposed to three different He fluences ( ) [5 times 10 to the 19 Helium per meter squared, 5 times 10 to the 20 Helium per meter squared, 5 times 10 to the 21 Helium per meter squared] at surface temperatures of ~300 K, 600 K and …

Development Of Metal Halide Perovskites For Radiation Detection, Ryan Tan

Doctoral Dissertations

Metal halide perovskite (MHP) semiconductors have attracted significant interest in recent years within photovoltaic and radiation detection communities due to their inexpensive solution growths, high effective atomic number for gamma and X-ray sensing, suitable bandgap, large resistivity, and moderate mobility-lifetime products. The MHP stoichiometry can also be tuned as needed to achieve desired physical and electronic properties. Moreover, the hybrid or organometallic halide perovskite (OMHP) variants contain a large atomic fraction of hydrogen for fast neutron sensing. These qualities make MHPs an attractive low-cost option for meeting detector needs within nuclear security and imaging applications. This work presents the development …

Scale-Bridging Computational Modeling Of Irradiation Effects In Alpha-Zirconium And Its Alloys, Jose Francisco March-Rico

Doctoral Dissertations

One of the issues concerning the long-term lifespan of Zr cladding tubes is an axial expansion and radial contraction that occurs in response to neutron irradiation. This volume-conservative response in the absence of an applied stress has been termed irradiation growth, a consequence of both the inherent anisotropy of alpha-Zr hexagonal close-packed crystal structure, and crystalline texture in tube fabrication. Irradiation growth strains generally saturate at low doses, but suddenly accelerate after an incubation dose. This growth breakaway has been correlated with the nucleation of faulted vacancy loops on basal planes (c-loops); at lower doses, the irradiated Zr microstructure is …

Tokamak 3d Heat Load Investigations Using An Integrated Simulation Framework, Thomas Looby

Doctoral Dissertations

Reactor class nuclear fusion tokamaks will be inherently complex. Thousands of interconnected systems that span orders of magnitude in physical scale must operate cohesively for the machine to function. Because these reactor class tokamaks are all in an early design stage, it is difficult to quantify exactly how each subsystem will act within the context of the greater systems. Therefore, to predict the engineering parameters necessary to design the machine, simulation frameworks that can model individual systems as well as the interfaced systems are necessary. This dissertation outlines a novel framework developed to couple otherwise disparate computational domains together into …

Nuclear Thermal Rocket Engine Control Autonomy Via Embedded Decision, David Sikorski

Doctoral Dissertations

This doctoral dissertation presents an investigation of embedded decision capabilities as a means for developing nuclear reactor autonomous control. Nuclear thermal propulsion (NTP) is identified as a high priority technology for development, and is the focus of this research. First, a background investigation is presented on the state of the art in nuclear thermal rocket (NTR) engine control and modeling practices, resulting in the development of a low order NTR engine dynamic model based on the literature. The engine model was used to perform the following investigation, and is intended to serve as a research platform for the future development …

Effects Of Plastic Deformation From Ultrasonic Additive Manufacturing, Michael Pagan

Doctoral Dissertations

Nuclear energy technology can be exponentially advanced using advanced manufacturing, which can drastically transform how materials, structures, and designs can be built. Ultrasonic Additive Manufacturing (UAM) represents one of the four main additive manufacturing methods, although it is also the newest. As UAM technology and applications develop, a fundamental understanding of the bonding mechanism is crucial to fully realize its potential. Currently UAM bonding is considered to occur through breaking down surface asperities and removing surface oxides. Plastic deformation occurs although its role is currently unclear. This research analyzes material configurations in a variety of geometries, with similar and dissimilar …

Corrosion And Microstructural Characterization Of Molybdenum-Ysz Cermets Following Hydrogen Exposure Up To 2630 K, Taylor G. Duffin

Doctoral Dissertations

Ceramic-metallic (cermet) fuels are a promising fuel type for outer space nuclear thermal propulsion (NTP). A key feasibility issue is the hydrogen chemical compatibility of candidate fuels in the proposed extreme operating temperatures for NTP systems (> 2500 K). In this study, molybdenum matrix cermets containing 40–70 vol% yttria stabilized zirconia (YSZ) particles (as a surrogate for ceramic fuel particles) were produced via spark plasma sintering (SPS) and exposed to flowing hydrogen at high temperature (2000–2630 K). Both steady state and thermally cycled (4 cycles with intermediate cooling to room temperature) conditions were examined for a constant total hot testing …

A High Rate Pixelated Neutron Detector For Neutron Reflectometry At The Spallation Neutron Source, Su-Ann Chong

Doctoral Dissertations

This work presents the development of a high-rate 6Li-based pixelated neutron detector for neutron reflectometry instruments at the Spallation Neutron Source (SNS), Oak Ridge National Laboratory. The current detector technology falls short on the instrument requirements, particularly on the counting rate capability. This detector was designed specifically to overcome the limitation in counting rate by having a fully pixelated design from neutron conversion layer to photodetector and readout system. For the neutron converting layer, a 6Li-based neutron scintillator was used. Each scintillator element was coupled to a photodetector, in this case, a silicon photomultiplier (SiPM). The output of each SiPM …

Effects Of Vacancies And Electron Temperature On The Electron Phonon Coupling In Cubic Silicon Carbide And Their Connection To The Inelastic Thermal Spike, Salah Al-Smairat

Doctoral Dissertations

“The electron-phonon interaction is an important interaction in many solids as it influences transport phenomena and related quantities such as the electrical and thermal conductivities, especially in nuclear and space applications. The importance of the electron-phonon interaction in primary damage production in 3C-SiC is the subject of this research.

The electron-phonon coupling factor was calculated using a hybrid Density Functional Perturbation Theory - Classical Electron Gas model. The coupling factor was calculated as a function of electron temperature in pristine and defective 3C-SiC, and relaxed defective cells. The electron-phonon coupling is found to depend strongly on the electronic temperature and …

Using Computational Methods To Optimize High Heat Flux Component Thermal Performance In Magnetic Confinement Fusion Reactor Research, Monica Gehrig

Doctoral Dissertations

"Heat transfer enhancement by means of internally modified geometries in tubes and channels is an important mechanism to improve the survivability of components in extreme high-heat flux environments. Various features such as ribs and fins are studied using computational fluid dynamics in both uniform and one-sided heating in tubes and rectangular channels respectively to determine the most effective geometries across a variety of different flow and heating conditions. This work examines heat transfer enhancement and rib geometry optimization to support experimental research for nuclear fusion applications. The project begins by designing and analyzing test sections supporting a helium flow loop …

Sensitivity Of The Two-Fluid Model To Constitutive Correlations For Large Diameter Pipes, Alexander Lee Swearingen

Doctoral Dissertations

"Multiphase flows are a significant factor in nuclear reactor operations. In order to understand this behavior in reactor systems, system analysis codes are used to simulate reactor conditions. Due to the nature of the nuclear industry, simulations predicting the void development in the core are required to be highly accurate. This work evaluated the sensitivity of the void fraction and interfacial area concentration predictions to changes in correlations used to calculate three parameters that are used to complete the interfacial drag calculation. The three parameters evaluated were drift-flux, void fraction covariance, and interfacial area concentration. The change in drift-flux correlation …

Impurity Production And Transport In The Prototype Material Plasma Exposure Experiment, Clyde J. Beers

Doctoral Dissertations

The Prototype Material Plasma Exposure eXperiment (Proto-MPEX) is a linear pulse plasma device at Oak Ridge National Laboratory with the purpose of doing the research and development for the heating concepts on the planned full MPEX device. The goal of MPEX is to perform material studies at fusion relevant conditions. To understand the conditions at the material target for performing plasma-material interaction studies the ion temperature and density, the electron temperature and density, and the particle flux and fluence must be known. Impurities within Proto-MPEX can alter the desired conditions at the material target and need to be understood for …

Nuclear Fuel Materials Under Extremes: Redox Behavior And Resulting Defect Structure, William Cureton

Doctoral Dissertations

Oxide nuclear fuel materials and analogues are often subject to complex structural and chemical changes when exposed to extreme environments. For example, oxidation and buildup of fission products cause changes to the local- and long-range structure as well as the chemistry and stoichiometry of UO₂ during operation in light water reactors. Highly ionizing energetic fission fragments have been shown to cause redox effects and associated defect structures in oxide nuclear fuel-type materials. The underlying mechanisms that lead to defect structures produced in a wider range of nuclear fuel material compositions and microstructures is not well understood.

This research project …