Engineering Commons^™

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 …

Production Of Protactinium-229 Via Deuteron Irradiation Of Thorium-232, Naser Burahmah

Doctoral Dissertations

²²⁵Ac [Actinium-225] is a promising radionuclide for targeted alpha therapy of cancer. ²²⁹Pa can lead to the production of ²²⁹Th [Thorium-229] and ²²⁵Ac [Actinium-225]. Deuteron bombardment on natural thorium targets has been investigated to measure cross sections of protactinium isotopes. In this work, ²²⁹Pa [Protactinium-229] excitation function was measured via deuteron energies up to 50 MeV [Mega electron volt] of thin thorium foils. The irradiation took place at Lawrence Berkeley National Laboratory’s (LBNL) 88-Inch Cyclotron. The target processing and analysis were performed at Oak Ridge National Laboratory (ORNL). The target consisted of 4 thin foils …

Analyses For The Production And Dosimetry Of Adding Uranium-232 As A Tracer To The Uranium Fuel Cycle, Joshua H. Rhodes

Doctoral Dissertations

This dissertation is an examination of the use of uranium-232 as a tracer in nuclear fuel. Decay daughters from ²³²U, particularly thallium-208, produce high energy gamma rays that, when added to uranium, may increase detectability in case of theft or diversion, but are also hazardous in high quantities. Previous studies of the ²³²U decay chain are examined. This work will go in to a dosimetry study to determine how hazardous varying levels of ²³²U are, and how to efficiently produce ²³²U in sufficient quantities.

A dosimetry study was performed to determine the dose hazards due to …

Fundamentals Of Cavity Formation In Α-Fe And Fe-Cr Alloys, Yan-Ru Lin

Doctoral Dissertations

Ferritic-martensitic steels are attractive candidate materials for fusion and advanced fission reactors primarily due to their low swelling characteristic, attractive thermo-mechanical properties, and the potential for development of nanostructured ferritic alloys. However, significant discrepancies exist regarding the effect of solutes and irradiation temperature on cavity swelling under ion versus neutron irradiation conditions. Several mechanisms have been proposed that may affect cavity swelling, but no general theory or model has received complete acceptance to explain these phenomena.

To better understand the formation of cavities in ferritic steels, we have performed multi-temperature (400-550°C) single-beam and simultaneous dual-beam irradiations (ex-situ and in-situ) on …

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 …

Fabrication Of Specialized Scintillators For Nuclear Security Applications, Cordell James Delzer

Doctoral Dissertations

Radiation detectors are important for a variety of fields including medical imaging, oil drilling, and nuclear security. Within nuclear security, they can serve a multitude of purposes whether that be imaging, localization, isotopic identification, or even just activity measurement. Even without directly seeing a nuclear material it is often able to notice their existence without a detector. Scintillators make up an important part of these detectors due to their large intrinsic efficiency, low cost, large volume, and relatively low upkeep. Due to the importance of the large number of purposes these scintillators may be used for, it can often be …

Thermochemical And Continuum Modeling To Understand The Chemical Composition Of Pwr Fuel Crud, Jason T. Rizk

Doctoral Dissertations

Computational modeling of Chalk River Undesirable Deposits (CRUD) allows for the prediction of associated phenomena that impact nuclear power plant performance, reliability, and safety. It also provides insight into the physical mechanisms by which CRUD forms and affects plant performance. A major concern in pressurized water reactors (PWRs) is Axial Offset Anomaly (AOA) which is caused by CRUD’s proficiency at trapping boron within the reactor core. The ability to predict AOA and other phenomena requires a detailed explanation of the chemical composition of CRUD. By pairing computational models that can simulate the structure and species trapping with detailed thermochemical models, …

Collector Probe Measurements Of Sol Impurity Accumulation And The Implications Of Sol Flows On The Accumulation Amount, Shawn Zamperini

Doctoral Dissertations

A collector probe in its simplest form is a rod inserted into a plasma so that impurities are deposited onto it. These probes are then removed and analyzed to determine the deposition profile both along the length of probe and across the width of it. This dissertation covers a series of collector probes experiments and accompanying interpretive modelling all with the main goal of providing evidence for long-hypothesized near scrape-off layer (SOL) accumulation of impurities that can lead to efficient core contamination. The structure of this dissertation is as follows. A brief outline of fusion energy and why we need …

Synthesis And Characterization Of Novel Li-Containing Garnet Ceramic Scintillators For Nuclear Security Applications, Joshua Paul Smith

Doctoral Dissertations

In the field of nuclear security, the ability to detect neutrons is a critical part of the prevention of the smuggling of illicit nuclear materials. The use of dual-mode detector would drastically reduce the number of passive detector systems necessary to meet the detection needs of the nuclear security industry. Li-containing scintillators have been researched for over 70 years; however, relatively few efficient dual-mode detector materials have been discovered. The currently available Li-containing scintillators are relatively low density, very difficult to grow, and highly hygroscopic. These limitations make the wide-spread use of Li-containing scintillators as dual-mode detectors inefficient and expensive. …

Neural-Net-Based Imager Offset Estimation In Fieldable Associated Particle Imaging, Justin R. Powers-Luhn

Doctoral Dissertations

Associated particle imaging with deuterium-tritium generators has been demonstrated to be extremely useful in laboratory settings. The Oak Ridge National Laboratory Nuclear Materials Identification System is once such system. A portable imaging system with similar capabilities could be of value to non-destructive analysis of potentially hazardous items. A neural network modeled after the ResNet architecture was trained to predict the position of the detector array. The network was trained using an MCNP simulation of the NMIS system with the neutron array offset in two position and one rotation dimension. The final network was accurate to within 0.49cm, 0.66cm, and 0.66◦ …

Libowski: A Numerical Framework For Solving Depletion And Mass Transport In Molten Salt Reactors, Robert Z. Taylor

Doctoral Dissertations

Molten salt reactors (MSRs) are a class of next-generation liquid fueled nuclear reactor which show great promise and industrial interest. With this type of reactor comes great difficulty in many modeling and simulation aspects which are required for design, operational efficiency and regulatory licensing. Solving the set of coupled depletion and mass transport equations required for modeling and simulations of these reactors is of great interest. This manuscript discusses the formulation of a numerical framework for solving the complex set of depletion and mass transport problems in MSRs. This is accomplished by first defining the set of equations that must …

Microstructural Investigation Of Hydride Reorientation In Zirconium Based Spent Nuclear Fuel Cladding, Tyler S. Smith

Doctoral Dissertations

Hydride embrittlement and the impact of hydride reorientation are failure phenomena of particular interest during the transportation process of spent nuclear fuel from wet storage to dry storage. This process exposes the cladding to elevated temperatures and high pressure-induced hoop stresses that can release the hydride platelets back into solution and cause them to radially precipitate upon cooling. Though the impact of high temperature and high-pressure conditions on hydride reorientation have been investigated for many nonirradiated specimens, a data gap remains for the coupling effects of irradiation at these conditions in high burnup spent nuclear fuel rods. To simulate this …

Neutron And Photon Imaging Capabilities Of Bismuth-Loaded Plastic, Andrew W. Decker

Doctoral Dissertations

Plastic scintillators utilizing iridium complex fluorophores offer substantial improvements in light yield, and their light yield is not significantly quenched in compositions with bismuth metalorganic loading at 21% weight. These advances may resolve significant capability gaps for low-cost, portable, and durable dual-particle imaging (DPI) systems for nuclear safety, security, and safeguard purposes. However, all candidate materials should first undergo investigation utilizing industry standards to quantify and evaluate their capabilities. As such, a 21% bismuth-loaded polyvinyl toluene (BiPVT) scintillator fabricated by Lawrence Livermore National Laboratory (LLNL) is computationally and experimentally evaluated as a small, pixelated radiographic array, with individual pixel dimensions …

Multiphysics Design And Sensitivity Analysis Of Nuclear Heated Critical Heat Flux Pool Boiling Test Devices In Treat., Richard Hernandez

Doctoral Dissertations

Following the events of the 2011 Fukushima Daiichi accident, there has been a drive to develop accident tolerant fuels (ATF) capable of enhancing safety margins provided by conventional light water reactor (LWR) materials, with a focus on the critical heat flux (CHF) behavior under fast transient heating irradiation conditions. Presented in this dissertation, is the modeling scope of a current effort aimed at elucidating the mechanisms of CHF under in-pile fast transient irradiation conditions using the Transient Reactor Test (TREAT) facility. A heater rodlet made from stainless steel type-304 with tailored natural boron content was held within experimental pool boiling …

Capabilities Of A Closely-Packed, Wearable Radiation Detector Array: Source Localization, Directionality, And Multi-Modal Data Fusion, Carl Glenn Britt

Doctoral Dissertations

The capability of assigning source carrier probabilities by fusing both video and radiation data is demonstrated. Potential targets are automatically detected and tracked with computer vision techniques. Meanwhile, a newly developed method for exploiting the angular response of closely-packed radiation detector arrays points towards a radiation source using short, periodic measurements on the order of 1 s. Source carrier probabilities are then assigned after the object's movement measured from the video data stream is correlated with the radiation directionality estimates over a set period of time. In demonstrating source carrier probability assigned to moving sources, three main contributions were made. …

Development Of A Particle Filter-Based Prognostic Model To Predict Maintenance Dependent Processes, Hang Xiao

Doctoral Dissertations

Components and systems in industrial processes undergo wear and degradation until they are either replaced or repaired. Maintenance actions, mostly imperfect repairs, may not entirely reduce the degradation and may expedite future degradation rates. Those repair and maintenance actions should be considered in prognostics models to accurately predict the components’ health conditions.

Different mechanical components have different fault modes in complex engineering systems, such as Nuclear Power Plants (NPPs). The change of a process variable may be caused by the degradation of a few different components. Effective ways to decouple the fault modes are required to predict each component's Remaining …

An Investigation Of Plastic Scintillators For Radiation Sensing And Mechanical Applications, Caleb J. Redding

Doctoral Dissertations

Plastic scintillators have uses in many fields including defense, high energy physics, health physics, and space applications. In recent years, work has been done to enhance a variety of plastic scintillator properties. These enhancements have largely targeted an increase of the intrinsic gamma efficiency, photopeak efficiency, mechanical robustness, the neutron pulse shape discrimination (PSD) figure of merit, and/or the timing resolution. This body of work seeks to examine these solutions both in a general radiation detection context and in the context of using the plastic scintillator as a frame component of a given detector system; in this work a hypothetical …

Controls And Concepts Of Operation For Load Balancing With Ipwrs In A High Renewables Penetration Grid, Richard J. Bisson

Doctoral Dissertations

The future of commercial nuclear power in the United States is uncertain in the wake of construction delays and several plant closings, especially in deregulated wholesale electricity markets with cheap natural gas and increasing wind and solar penetration. As a firm low carbon resource, nuclear power plants can serve a key role in climate mitigation strategies by displacing the natural gas generators that provide dispatchable peaking capacity in systems with large and increasing variable renewable energy (VRE) shares. Small modular reactors, or SMRs, are among a suite of new reactor technologies that might alleviate the time and cost overruns facing …