Nuclear Engineering Commons^™

Modeling Of Dislocation Channel Formation And Evolution In Irradiated Metals, Peter James Doyle

Masters Theses

Defect-free dislocation channel formation has been reported to promote plastic instability during tensile testing via localized plastic flow, leading to a distinct loss of ductility and strain hardening in many low-temperature irradiated materials. In order to study the underlying mechanisms governing dislocation channel width and formation, the channel formation process is modeled via a simple stochastic dislocation-jog process dependent upon grain size, defect cluster density, and defect size. Dislocations traverse a field of defect clusters and jog stochastically upon defect interaction, forming channels of low defect-density. Based upon prior molecular dynamics (MD) simulations and in-situ experimental transmission electron microscopy (TEM) …

Positron Emission Particle Tracking Software Maturation Project, Eric Michael Moore

Masters Theses

Positron Emission Particle Tracking (PEPT) software at the University of Tennessee (MultiPEPT) has demonstrated promising performance in multiple measurement domains. In order to contribute to its further development, a full codebase audit and three focused performance assessments were undertaken. Several improvements were made to the codebase as a result of the audit. The assessments demonstrated a linear axial detector- MultiPEPT response, the effect of mesh size variation, and the effect of temporal overlap variation. A number of best practices are compiled for effective use of MultiPEPT.

Improvements To Nestle: Cross Section Interpolation And N-Group Extension, William Matthews Kirkland

Masters Theses

The NESTLE program is a few-group neutron diffusion reactor core simulator code utilizing the nodal expansion method (NEM). This thesis presents two improvements made to NESTLE regarding cross-section interpolation and multigroup capability.

To quickly and accurately obtain cross sections from lattice physics input data, a new cross section interpolation routine was developed utilizing multidimensional radial basis function interpolation, also known as thin plate spline interpolation. Testing showed that, for existing NESTLE lattice physics input, accuracy was retained but not improved and processing time was longer. However, the new interpolation routine was shown allow much greater exibility in the case matrix …

The Development Of Cesium Calcium Bromo-Iodide Scintillator For X-Ray And Gamma Ray Detection, Matthew Starr Loyd

Masters Theses

CsCaI₃:Eu [cesium calcium iodide doped with europium] is a promising scintillator material that can be grown from the melt, but undergoes a tetragonal to orthorhombic phase transition upon cooling at 255 °C [degrees Celsius], causing twinning and cloudiness. The purpose of this work is to suppress this solid to solid phase transition in the CsCaI₃:Eu scintillator, which has a light yield of ~40000 ph/Mev and energy resolution at 662keV of ~4%, by halide replacement to form the compound CsCaBr_xI_3-x:Eu [cesium calcium bromo-iodide doped with europium]. Crystals 8 cm³ [cubic centimeters] in …

Hot Filament Chemical Vapor Deposition Of Semiconducting Boron Carbide Thin Films, Michael Dylan Richardson

Masters Theses

A highly efficient, low-power, compact thermal neutron detection system with excellent gamma-ray discrimination is desired for a number of applications. ¹⁰B [boron- 10] has a large cross section for thermal values and a Q-value of 2.78 MeV. For this reason, investigations into boron carbide, boron nitride, and boron phosphide semiconductor neutron detectors are underway. Because boron carbide has the highest fraction of boron of the three, it holds the highest potential. With this in mind, a hot filament chemical vapor deposition (HFCVD) system was designed and built in order to grow thin films of boron carbide onto n-type silicon …

Practical Methods For Optimizing Equipment Maintenance Strategies Using An Analytic Hierarchy Process And Prognostic Algorithms, Gregory Michael Bosco

Masters Theses

Many large organizations report limited success using Condition Based Maintenance (CbM). This work explains some of the causes for limited success, and recommends practical methods that enable the benefits of CbM. The backbone of CbM is a Prognostics and Health Management (PHM) system. Use of PHM alone does not ensure success; it needs to be integrated into enterprise level processes and culture, and aligned with customer expectations. To integrate PHM, this work recommends a novel life cycle framework, expanding the concept of maintenance into several levels beginning with an overarching maintenance strategy and subordinate policies, tactics, and PHM analytical methods. …

Development Of Nuclear Underground Engineered Test Surrogates For Technical Nuclear Forensics Exploitation, Robert Boone Gilbreath

Masters Theses

A method for formulation and production of Nuclear UnderGround Engineered Test Surrogates (NUGETS) based on notional improvised nuclear device (IND) detonations in an underground environment analogous to the Nevada National Security Site (NNSS) is presented. Extensive statistical analyses of precursory geochemical and geophysical characteristics are combined with an augmented surrogate debris cooling technique and predictive IND contributions from the ORIGEN Fallout Analysis Tool. Precursory and resultant elemental compositions, cooling curve calculations, and visual comparison of NUGETS to genuine underground debris are reported. Application of NUGETS methodology to future studies in urban, underground post-detonation technical nuclear forensic (TNF) analysis is suggested.

Analysis Of Highly-Enriched Uranium Spectra Obtained With Lanthanum Bromide Scintillation Detection Systems, Danielle Lynn Mcfall

Masters Theses

Cerium-doped lanthanum bromide scintillation detection systems have recently been examined as an alternative to conventional detection systems, namely high-purity germanium, cadmium zinc telluride, and thallium-doped sodium iodide systems for various reasons including portability, sizing, and efficacy. As a non-destructive assay technique, these detectors quantify gamma rays from various samples to measure and identify specific radioisotopes. In nuclear facilities specializing in uranium, these detectors are mainly utilized to detect characteristic low-energy gamma rays of uranium-235, specifically, 143 keV, 163 keV, 186 keV, 202 keV and 205 keV gamma rays. Accurately distinguishing closely-spaced gamma rays in spectral data is a common challenge …

Effects Of Grain Size And Dopants On The Irradiation Response Of Actinide Oxides, Jeffrey Morgan Walters

Masters Theses

High energy irradiation can induce physical and chemical changes in nuclear materials, impacting their properties and performance in reactor systems. Of particular interest is the radiation response of actinide oxides, such as UO₂ [Uranium Dioxide] and ThO₂ [Thorium Dioxide], as well as analogue materials such as CeO₂ [Cerium Dioxide]. During the course of reactor operations, these nuclear materials are exposed to high energy ionizing radiation in the form of nuclear fission fragments. This study simulates the extreme conditions found in a nuclear reactor by utilizing accelerated heavy ions with mass and kinetic energy comparable to fission fragments …

Cfd Validation And Scaling Of Condensation Heat Transfer, Varun Kalra

Masters Theses

"A CFD study was performed using STAR-CCM+ to validate the software for its competence in the prediction and scaling of condensation heat transfer in the presence of air acting as a non-condensable gas. Three vertical concentric tube heat exchanger geometries with different diameters were studied in the CFD analysis. It was seen that the steam bulk temperatures predicted by STAR-CCM+ closely matched the experimental data. However, the temperatures of outer wall of the steel condenser tubes showed a deviation of 2% to 11% from the experimental values. The error in adiabatic water wall temperatures were found to range from 18% …

Analysis And Implementation Of Accident Tolerant Nuclear Fuels, Benjamin Joseph Prewitt

Masters Theses

"To improve the reliability and robustness of LWR, accident tolerant nuclear fuels and cladding materials are being developed to possibly replace the current UO₂/zirconium system. This research highlights UN and U₃Si₂, two of the most favorable accident tolerant fuels being developed. To evaluate the commercial feasiblilty of these fuels, two areas of research were conducted. Chemical fabrication routes for both fuels were investigated in detail, considering UO₂ and UF₆ as potential starting materials. Potential pathways for industrial scale fabrication using these methods were discussed.

Neutronic performance of 70%UN-30%U₃Si₂ composite …

A Study Of The Potential Applications Of Am241, And Determining The Feasibility Of Using Gamma Spectroscopy For Future Physical Validation, Eric A. Feissle

Masters Theses

“Am241 is typically produced via Pu241 decay in a uranium fueled reactor. Presence of Am241 can be used as the age estimation tool for spent fuel, which is a focus of this thesis along with the interest of the measurement and the ratio of production rates of Am241’s activation products; Americium-242 and its first excited state of Americium-242m. MCNP models of the core and BEGe 3825 detector were built. These models were compared with established and physical measurements of gamma/x-ray standards that were available at the reactor. Thermal fluxes at 200 kW for potential foils centered in the source holder …

Comparison Of ²⁵²Cf Time Correlated Induced Fission With Amli Induced Fission On Fresh Mtr Research Reactor Fuel, Jay Prakash Joshi

Masters Theses

"The effective application of international safeguards to research reactors requires verification of spent fuel as well as fresh fuel. To accomplish this goal various nondestructive and destructive assay techniques have been developed in the US and around the world. The Advanced Experimental Fuel Counter (AEFC) is a nondestructive assay (NDA) system developed at Los Alamos National Laboratory (LANL) combining both neutron and gamma measurement capabilities. Since spent fuel assemblies are stored in water, the system was designed to be watertight to facilitate underwater measurements by inspectors. The AEFC is comprised of six ³He detectors as well as a shielded …

The Viability Of Advantg Deterministic Method For Synthetic Radiography Generation, Andrew Albert Bingham

Masters Theses

"Time sensitive and high resolution image simulations are needed for synthetic radiography generation. The standard stochastic approach requires lengthy run times with poor statistics at higher resolutions. The investigation of the viability of a deterministic approach to synthetic radiography image generation was explored. The aim was to analyze a computational time decrease over the stochastic method. ADVANTG was compared to MCNP in multiple scenarios including a Benchtop CT prototype, to simulate high resolution radiography images. By using ADVANTG deterministic code to simulate radiography images the computational time was found to decrease over 10 times compared to the MCNP stochastic approach"--Abstract, …

Design And Analysis Of A Passive Heat Removal System For A Small Modular Reactor Using Star Ccm+, Raymond Michael Fanning

Masters Theses

"Next generation nuclear power plants, specifically small modular reactor designs, are the best alternative to fossil fuels for power generation due to their power density and low carbon emissions and constant awareness of safety concerns. A promising safety feature of new designs is the removal of heat by passive systems in accident scenarios. The passive systems require no moving parts and no intervention by personnel. These systems must be accurately simulated for better understanding of the heat transport phenomena: natural convection cooling. Due to the fact that most work developing these passive heat removal systems are proprietary information, a passive …