Engineering Commons^™

Methodology For Generating Simplified Cross Section Data Sets For Neutron Transport Calculations, Thomas Jay Harrison

Doctoral Dissertations

Neutron shielding problems involve radiation transport calculations over a wide range of energies. Fission neutrons have initial energy on the order of MeV, fusion neutrons have initial energy on the order of 10s of MeV, and space-origin neutrons have initial energy on the order of 100s of MeV or higher. Shielding calculations must track the neutrons from their initial energies until they are no longer of interest; for deep-penetration neutrons, this final energy can be on the order of eV before the neutron is no longer tracked. Thus, for deep-penetration space radiation shielding problems, the calculation may require tracking the …

Quantification Of Fast-Neutron Sources With Coded Aperture Imaging, Timothy Donald Jackson

Doctoral Dissertations

Quantification of the mass of plutonium in facilities that process plutonium is important for both nuclear safeguards concerns and safety concerns, and multiple methods to nondestructively quantify plutonium sample characteristics have been proposed, particularly when the sample is located directly adjacent to or within the measurement device. In prior work, coded-aperture fast neutron imaging has been developed to demonstrate the imaging of neutron emitting radiation sources in a qualitative fashion, where the sources may be located meters to tens of meters away. Building upon prior work, this work develops the use of a Maximum Likelihood Expectation Maximization (MLEM) reconstruction technique …

Study Of Secondary Particles Produced From Heavy-Ion Interactions, Pi-En Tsai

Doctoral Dissertations

The study of secondary particles produced from heavy-ion interactions is important in heavy ion radiotherapy, space radiation protection, and shielding at accelerator facilities. This dissertation focuses on the study of secondary neutron production as they are of special concern among all secondary particles.

The first part of this dissertation is the measurement of secondary neutrons created from ⁴He [helium] stopped in various target materials together with the model calculations accomplished by PHITS, FLUKA, and MCNP transport codes. The comparison results show that the physics models need improvements particularly in the predictions of 1) neutrons created from the ⁴He …

Development And Characterization Of A Directional Radiation Detection System Using A Fuzzy Logic Algorithm, Michael Joseph Willis

Doctoral Dissertations

Traditional radiation detection equipment consists of various types of devices that are capable of determining the presence of radioactive sources in the vicinity of the detection unit. Use of these systems typically consists of survey and search methods that employ broad area sweeps to narrow down the location of a radioactive source. Although these methods are effective, they are typically inefficient and lack the ability to produce a directional bearing of the source relative to the measurement location. More efficient methods that provide relative direction information for detected sources would facilitate a more timely response to a potential radiological threat. …

Ion Irradiation-Induced Microstructural Change In Sic, Chien-Hung Chen

Doctoral Dissertations

The high temperature radiation resistance of nuclear materials has become a key issue in developing future nuclear reactors. Because of its mechanical stability under high-energy neutron irradiation and high temperature, silicon carbide (SiC) has great potential as a structural material in advanced nuclear energy systems.

A newly developed nano-engineered (NE) 3C SiC with a nano-layered stacking fault (SFs) structure has been recently considered as a prospective choice due to enhanced point defect annihilation between layer-type structures, leading to outstanding radiation durability.

The objective of this project was to advance the understanding of gas bubble formation mechanisms under irradiation conditions in …

Template-Based Imaging Analysis Of Arbitrary Nuclear Material Configurations Using Time And Directionally-Tagged Fast Neutrons, Kirsten Elise Pena

Doctoral Dissertations

Reduction of nuclear material worldwide requires that robust methods for template measurement systems be developed. For nuclear material in metal form, two scenarios where it is necessary to verify and account for the material include storage and treaty verification. In both of these scenarios, the nuclear material’s high density, as well as possible heavy shielding or high radiation background, are obstacles to verifying the materials and configuration of an object with a high degree of confidence in a timely manner.

Addressing the need for confident verification, the template analysis method investigated in this work— the Kolmogorov-Smirnov (K-S) goodness-of-fit test—uses tagged …

Ion Irradiation Induced Damage And Dynamic Recovery In Single Crystal Silicon Carbide And Strontium Titanate, Haizhou Xue

Doctoral Dissertations

The objective of this thesis work is to gain better understanding of ion-solid interaction in the energy regime where electronic and nuclear energy loss are comparable. Such responses of materials to ion irradiations are of fundamental importance for micro-electronics and nuclear applications. The ion irradiation induced modification for the crystal structure, the physical and chemical properties etc. may strongly affect the performance of functional materials that needs to be better understood.

Experimentally, ion irradiation induced damage accumulation and dynamic recovery in SiC [silicon carbide] and SrTiO₃ [strontium titanate] were studied in this dissertation project. Five chapters are presented: Firstly, …

Characterization Of Mechanically Cooled High Purity Germanium (Hpge) Detectors At Elevated Temperatures, Joseph Benjamin Mccabe

Doctoral Dissertations

High resolution gamma spectroscopy is a tool used in nuclear security applications due to its achievable energy resolution and associated ability to identify special nuclear material. This identification ability is achieved by identifying the characteristic gamma-rays of a material. The challenges that have confronted industry concerning the use of hand-held high purity germanium (HPGe) in homeland security applications have centered on weight, geometry, and cool-down time. Typical liquid nitrogen cooled detectors ranging in size from 10% to 150% detectors will cool down sufficiently within 2-6 hours of filling. The cool-down time achieved in this research ranges from 45 min on …

Electronic Energy Loss Of Heavy Ions And Its Effects In Ceramics, Ke Jin

Doctoral Dissertations

Energy loss of medium energy heavy ions (i.e. Cl, Br, I, and Au) in thin compound foils containing light elements (i.e. silicon carbide and silicon dioxide) is directly measured using a time-of-flight elastic recoil detection analysis (ToF-ERDA) technique. An improved data analysis procedure is proposed to provide the experimentally determined electronic stopping powers. This analysis procedure requires reliable predictions of nuclear stopping. Thus, the nuclear stopping predicted by the Stopping and Range of Ions in Matter (SRIM) code is validated by measuring the angular distribution of 1 MeV Au ions after penetrating a thin silicon nitride foil, using a secondary …

Hybrid K-Edge Densitometry As A Method For Materials Accountancy Measurements In Pyrochemical Reprocessing, Matthew Tyler Cook

Doctoral Dissertations

Pyrochemical reprocessing is a proven method to recover useful fissile material from spent nuclear fuel. The process requires high temperatures and an inert atmosphere thus complicating the prospect of making materials accountancy measurements. Development of a measurement method for materials accountancy measurements has become necessary since pyroprocessing is receiving more attention as a possible compliment to aqueous reprocessing methods. If pyroprocessing is to be adapted from the engineering scale to a commercially viable reprocessing method a comprehensive safeguards measurement method and strategy must be developed.

Hybrid k-edge densitometry (HKED) has been applied to aqueous reprocessing measurements in commercial facilities. This …

Evaluation, Construction, And Verification Of A Subchannel Steady State Heat Transfer Code For Plate-Fueled Reactors, Cory Landon Griffard

Doctoral Dissertations

Several high performance research reactors use plate fuel that is clad with aluminum and cooled with forced convection of subcooled water. High resolution multiphysics simulation tools have been developed to allow the performance of the core in these reactors to be assessed in more detail. The high resolution multiphysics (HRMP) simulation tools must go through verification and validation (V&V) to ensure the additional detail of the outcomes is accompanied with quantifiable uncertainties and confidence intervals. As an example of V&V, a one-dimensional subchannel code with conventional engineering flow and heat transfer models may be used to check the performance of …

Molecular Dynamics Simulation Of Irradiation Damage In Multicomponent Alloys, Wei Guo

Doctoral Dissertations

The development of the generation IV reactors calls for radiation resistant materials. This thesis proposes that the newly developed single phase solid solution of high-entropy alloys (HEAs) can be such candidates. HEAs can undergo the crystalline to amorphous to crystalline (C-A-C) transitions under radiation. The radiation induced amorphous structure is a highly radiation resistant medium as shown by previous studies, and it further transforms to crystalline phases without much structural defects. In this thesis, by reviewing the formation rules of solid solutions and amorphous metallic glasses, it is suggested that the atomic size plays a key role affecting the C-A-C …

Assessment Of Reactivity Equivalence For Enhanced Accident Tolerant Fuels In Light Water Reactors, Nathan Michael George

Doctoral Dissertations

The neutronic behavior of accident tolerant fuel (ATF) concepts was simulated in light water reactors (LWRs) to establish design parameters to match reactivity lifetime requirements of standard UO₂ [uranium dioxide]/Zircaloy fuel. The two concepts discussed in this dissertation are fully ceramic micro-encapsulated (FCM) fuel and alternate cladding concepts. To compare the required fuel alterations against standard UO₂/Zircaloy fuel, a 2D lattice-physics based reactivity equivalence method was established to estimate excess reactivity at the completion of each weighted batch cycle.

In the case of FCM fuel, the uranium-based tristructural isotropic (TRISO) kernel and the surrounding particle layers/matrix material …

Iterative Ct Reconstruction From Few Projections For The Nondestructive Post Irradiation Examination Of Nuclear Fuel Assemblies, Muhammad Imran Khan Abir

Doctoral Dissertations

The core components (e.g. fuel assemblies, spacer grids, control rods) of the nuclear reactors encounter harsh environment due to high temperature, physical stress, and a tremendous level of radiation. The integrity of these elements is crucial for safe operation of the nuclear power plants. The Post Irradiation Examination (PIE) can reveal information about the integrity of the elements during normal operations and off‐normal events. Computed tomography (CT) is a tool for evaluating the structural integrity of elements non-destructively. CT requires many projections to be acquired from different view angles after which a mathematical algorithm is adopted for reconstruction. Obtaining many …

Characterization Of Bending Fatigue Mini-Specimens For Nuclear Materials, Ahmed Suliman R. Haidyrah

Doctoral Dissertations

"New materials with superior radiation and corrosion resistance are needed to improve the economy and performance of current nuclear reactors as well as future nuclear reactors. Measurement of mechanical properties of the material of equipment is required to estimate its safe operating life. Studying fatigue of irradiated specimens is challenging due to space limitation in research reactors (e.g. ATR). The mini-specimen bending fatigue (Krouse-type) of nuclear materials was used to study fatigue properties and compare the obtained results with that of reference data of full size specimen. These Krouse-type were made of austenitic SS304, SS316, HT9 ferritic martensitic steel, and …

Impact Of Thorium Based Molten Salt Reactor On The Closure Of The Nuclear Fuel Cycle, Safwan Qasim Mohammad Jaradat

Doctoral Dissertations

"Molten salt reactor (MSR) is one of six reactors selected by the Generation IV International Forum (GIF). The liquid fluoride thorium reactor (LFTR) is a MSR concept based on thorium fuel cycle. LFTR uses liquid fluoride salts as a nuclear fuel. It uses ²³²Th and ²³³U as the fertile and fissile materials, respectively. Fluoride salt of these nuclides is dissolved in a mixed carrier salt of lithium and beryllium (FLiBe). The objective of this research was to complete feasibility studies of a small commercial thermal LFTR. The focus was on neutronic calculations in order to prescribe core design …

Active - Passive Spent Fuel Interrogation Using Neutrons And Photons, Tayfun Akyurek

Doctoral Dissertations

“This dissertation consists of three main parts. The first part is devoted to the comprehensive dead-time calculations with different detectors and conditions using different dead-time models as well as computer simulations. The minimum time that must separate two detectable events is called the counting system’s dead-time. If events take place during the system’s dead-time, they will not be recorded and will be lost. Such lost information is very important in many applications including high-intensity spectroscopy and nuclear spent fuel interrogations. The second part, a multitude of fission products identified as candidates have been scrutinized for their suitability of burnup analysis …