Nuclear Engineering Commons^™

Design And Feasibility Study Of An Air-Cooled Reactor Cavity Cooling System For Fluoride-Salt-Cooled High-Temperature Reactors, Alexandra D. Martinez

Nuclear Engineering ETDs

Licensing efforts for Fluoride-Salt-Cooled High-Temperature Reactors (FHRs) are dependent on passive safety systems designed for decay heat removal, yet no prior study has evaluated an air-based Reactor Cavity Cooling System (RCCS) for this role. This thesis addresses that gap by determining whether an air-cooled RCCS can be designed to passively remove post-shutdown decay heat from the Mk 1 FHR. An RCCS configuration was developed and sized using a one-dimensional lumped-parameter design methodology, then evaluated through system-level thermal-hydraulic modeling in RELAP5-3D under a conservative, lower-bound post-shutdown transient. The analysis characterizes the radial heat-transfer pathways from the FHR core to the RCCS …

Investigating The Corrosion Behavior Of Stainless Steel 316 In Static Lead Lithium Eutectic Under Applied Stressed Conditions, Daniel E. Levario

Nuclear Engineering ETDs

As fusion power moves closer to feasibility, identifying structural materials compatible with breeding blanket environments remains a critical challenge. Lead-lithium eutectic (LLE) is a leading candidate breeder and coolant material due to its low melting point and combined tritium breeding and neutron multiplication capability. However, the corrosive nature of LLE toward structural steels at elevated temperatures must be characterized before these systems can be reliably deployed. This study investigates the corrosion behavior of Type 316 stainless steel in static LLE under applied stress conditions at 550°C using C-ring stress corrosion specimens. Post exposure analysis via optical microscopy, SEM, EDS, and …

Validation Of Electromagnetic Shower Development In A Reduced Alice Focal-E Detector Model Using Geant4, Isaac Lara Romo

Physics

This project focuses on the preliminary simulation of a reduced FoCal-E detector model for the ALICE experiment at CERN. Beamline tests were simulated using an electron gun at various incident energies, and the results were compared with those of the FoCal group. The longitudinal charge deposition per sensor layer was compared between the two setups to verify that the reduced model exhibited expected calorimeter behavior. Additionally, the transverse signal across the high-granularity sensor layers was examined to determine whether the reduced model reproduced the expected lateral development of electromagnetic showers. The results obtained from these measurements show that the reduced …

Helium Effects In High Entropy Alloys For Fusion Reactor Plasma Facing Components, Shane Evans

Nuclear Engineering ETDs

The plasma facing materials (PFMs) within fusion reactors, such as the divertor, must be able to withstand high temperature (>1000 K) for extended durations of time, in addition to extreme flux from neutrons, helium (He) ash, and neutral species such as deuterium and tritium. These materials must withstand these conditions while maintaining their selected mechanical properties, minimal sputter yield, and low fuel retention. In recent years refractory high entropy alloys (RHEAs) have been investigated due to their improved mechanical and irradiation-resistant properties when compared to pure W, the current material for PFMs. In this work RHEAs have undergone fusion …

Cfd Simulation Analyses Of The Blowdown Phase Of A Depressurized Loss Of Forced Cooling Accident In A Htgr, Keenan Kresl-Hotz

Nuclear Engineering ETDs

This research numerically investigates the helium-air mixing in HTGR containment cavities during the blowdown phase of a simulated DLOFC accident. The results of the performed CFD simulation analyses, using the commercial code STAR-CCM+, are compared with reported measurements from an experiment conducted at CCNY. The analyses investigate the effects of the RANS and LES turbulence models, numerical mesh refinement, time-step size, and flow rate and temperature of the injected hot helium into the scaled reactor cavity. Calculated parameters analyzed include the pressure and spatial distributions of temperature and oxygen concentration in the simulated reactor and steam generator cavities. CFD oxygen …

In-Situ Measurement Of Dynamic Deuterium Retention In Tungsten-Based Alloys Under Plasma Exposure, Ethan Gabriel Rashap

Nuclear Engineering ETDs

Nuclear fusion is a promising pathway for sustainable energy production, but the performance of plasma-facing materials remains a key challenge for reactor operation. In particular, hydrogen isotope retention in tungsten—the leading candidate material for divertor components—affects tritium inventory, fuel recycling, and overall material lifetime. In this work, the temperature-dependent deuterium retention behavior of W–Ti and W–TiTa alloys was experimentally investigated under fusion-relevant ion irradiation conditions between 400 and 700 K. In-situ nuclear reaction analysis (NRA) was used to track retention during plasma exposure and subsequent cooldown, providing depth-resolved insight into deuterium accumulation and release. The results show that deuterium retention …

Development Of A Lead-Lithium Eutectic Magnetohydrodynamic Loop For Corrosion Studies, Xavier S. Angus

Nuclear Engineering ETDs

Lead–lithium eutectic (LLE) is a leading candidate coolant and tritium breeder for fusion reactor blankets due to its favorable heat transfer properties and high tritium breeding ratio. However, LLE is highly corrosive and, in the strong magnetic fields present in fusion reactors, experiences magnetohydrodynamic (MHD) effects that can produce significant pressure drops and flow instabilities. Understanding corrosion behavior in these extreme environments is essential for assessing the viability of LLE blanket systems. This work presents the design and construction of a forced-convection LLE corrosion loop to study corrosion behavior at temperatures up to 425 °C and flow velocities up to …

Design And Analysis Of An Intermediate Heat Exchanger And Passive Decay Heat Removal System For A Generic Fluoride Salt-Cooled High-Temperature Reactor Application, Bao Hoang Nguyen

Nuclear Engineering ETDs

Generation IV reactors, such as the Fluoride salt-cooled High-temperature Reactor (FHR), feature efficient heat transfer and passive heat removal systems. However, accurately predicting thermal behavior under steady-state and transient conditions remains challenging. This work designs and evaluates a twisted tube heat exchanger (TTHX) serving as an intermediate heat exchanger (IHX) and a reactor cavity cooling system (RCCS) serving as a passive decay heat removal system for a generic FHR (gFHR), integrating both systems into a system-level MELCOR model. The TTHX was first designed and assessed using a MATLAB-based framework, followed by detailed MELCOR simulations. The results demonstrate effective heat transfer …

Sensitivity-Informed Resonance Parameter Cross Section Adjustments, Matthew Juan Lazaric

Nuclear Engineering ETDs

This work details the process of developing several new features into the MCNP6.3 Monte Carlo code for use in uncertainty quantification and reduction. These new capabilities, which include the CLUTCH method of calculating k-eigenvalue cross section sensitivities and the Windowed Multipole method of calculating cross sections, are implemented and verified against previous implementations and existing cross section data, respectively. These capabilities are then combined to produce sensitivities of k-eigenvalue to resonance parameters, which are verified against direct perturbation sensitivity estimates. The resonance parameters are calibrated using linear Bayesian methods and the accuracy of the resulting cross section is evaluated via …

Representativeness And Sensitivity Analysis Of Accident Tolerant Fuel Cladding Behavior In Reactivity-Initiated Accidents, Melissa Andrea Moreno

Nuclear Engineering ETDs

Accident Tolerant Fuels (ATFs) such as FeCrAl are being developed to enhance safety margins in light water reactors during transients like Reactivity Initiated Accidents (RIAs). This dissertation evaluates the accuracy and representativeness of TRACE thermal hydraulic models for predicting FeCrAl C36M cladding behavior under steady state and transient flow boiling conditions. Benchmarking against University of New Mexico separate effects experiments shows that TRACE reproduces key thermal trends but underpredicts cladding temperatures near CHF by approximately 25 to 30%. A calibrated uncertainty and global sensitivity analysis, using Sobol indices, demonstrates that CHF and cladding temperature variability are dominated by mass flux, …

Criticality Safety Evaluation To Address Potential Over Conservative Restrictions In 49 Cfr Fissile Materials – Exceptions, Avian Blumhorst

UNLV Theses, Dissertations, Professional Papers, and Capstones

The U. S. Department of Transportation’s (DOT) 49 CFR 173.453 Fissile Exceptions provide a regulatory classification that helps eliminate burdensome regulatory requirements. The current fissile exceptions are based on past technical basis reviews. These reviews may be overly conservative, and the final ruling potentially applied significant administrative over-conservatism. This thesis reviewed and presents several recommendations to the fissile exception criteria, as well as 49 CFR 173.453 section’s additions.

Using Monte Carlo N-Particle (MCNP) code version 6.3.0, several infinite sea mixtures and array systems were modeled for fissile isotopes 233U and 235U. The research demonstrated that for fissile exception (a) there …

Modeling Of Laser-Produced Plasma Plumes: Expansion, Chemistry, And Thin-Film Deposition, Edmund Tsiri Semaha, Edmund Tsiri Semaha

Theses and Dissertations

Abstract

Laser-assisted material processing involves coupled plasma expansion, chemical reactions, and particle transport that govern the quality of thin-film deposition. This dissertation presents a comprehensive computational investigation of these processes using the OpenFOAM framework. First, the performance of the twoPhaseEulerFoam (tPEF), rhoCentralFoam (rCF), and sonicFoam (sF) solvers is evaluated for modeling laser-produced plasma plume expansion under atmospheric conditions, demonstrating that tPEF accurately captures shock-wave propagation, hydrodynamic behavior, and multispecies interactions. Building on this validation, the reactingFoam (rF) solver is employed to investigate the chemistry of aluminum plasma expanding into an air environment (Al–N₂–O₂). The model incorporates appropriate thermodynamic, transport, and …

Improving Modeling Of Corrosion Products In The Primary Circuit Of Light Water Reactors Through The Experimental Determination Of Crud Characteristics, Sri Saravana Konganapuram Narasimma Bharathi

Electronic Theses & Dissertations (2024 - present)

High-temperature water flowing through the coolant circuits in pressurized water reactors (PWRs) creates a harsh environment, deteriorating these materials. This corrosion results in the formation of oxide layer(s) primarily composed of nickel ferrites, iron oxides, nickel oxides, and other nickel-iron-chrome spinel oxides. Being exposed to fluid with high flow rates and pressure, these oxide layers can be eroded, resulting in particulate fouling due to the release of corrosion products (Chalk River Unidentified Deposits, CRUD) into the coolant circuit. When CRUD subsequently deposits on fuel surfaces, it negatively affects the fuel performance (heat transfer and fuel failure); in addition, the particles …

Automated Spectrum Analysis And Radionuclide Identification For Robot-Based Gamma Probes, Kennedy Ochieng Mengoh Alila

UNLV Theses, Dissertations, Professional Papers, and Capstones

Gamma spectroscopy is a technique used for the detection and identification of nuclear materials. Gamma-ray emission by radio nuclides is detected using scintillation detectors or semiconductor detectors such as NaI and CZT. Robot-based gamma probes enable radiation measurements in large areas and hard-to-reach cluttered hazardous environments, which significantly reduces radiation risks to personnel. The robotic probes require automated on-board gamma spectrum analysis and capabilities with platforms (unmanned aerial vehicles and unmanned ground vehicle systems) which use Robot Operating System (ROS). The aim of this thesis was to develop a method of an automated spectral analysis and isotope identification for robot-based …

Non-Destructive Characterization Of Ion Irradiated Yttrium Hydride For Microreactor Applications, Ryan E. Pena

Nuclear Engineering ETDs

As energy demands increase, nuclear reactors, especially microreactors, become a promising energy source. These reactors run at high temperatures (>280°C), requiring moderators that can endure these environments. Yttrium hydride is a possible moderator, but little is known about the material’s phase stability and hydrogen retention under irradiation. Through the use of a gold ion beam, samples with stoichiometries ranging from 1.6 to 2.0 were irradiated and tested. Through Vickers hardness testing, a model was created showing a correlation between hydrogen content and hardness. Raman spectroscopy showed high temperature and irradiated samples have significant hydrogen loss. XRD quantified this hydrogen …

Sequential Low Dose Proton Irradiation And Nanomechanical Testing To Understand Mechanical And Microstructural Property Changes In Alloy 709, Abhishek Kc

Nuclear Engineering ETDs

Alloy 709, a 20Cr25Ni alloy, is an advanced austenitic steel designed for next generation sodium fast reactors. Preliminary studies have shown the potential of Alloy 709 in sodium fast reactors. In this study, Precipitate Treated Alloy 709 specimens are irradiated with 2 MeV H⁺ at 500 °C from 0.0057 dpa to 1.7 dpa. Electron microscopy characterization techniques are used to understand the effects of radiation on mechanical properties as well as microstructure of Alloy 709. The microstructure did not show formation of voids, amorphization of precipitates, or increase in grain size up to 1.7 dpa. Correspondingly nano-indentation and micro-pillar …

Coupled Adjoint-Based Perturbation Theory For Dynamics And Heat Transfer Multiphysics For Nuclear Transients, Alexis Maldonado

Nuclear Engineering ETDs

Nuclear reactor multiphysics modeling and simulation (M&S) enable advanced reactor design by analyzing how systems will react over time to various configurations, scenarios, and perturbations. However, high-fidelity coupled transient M&S for reactor cores are computationally expensive, making robust analyses challenging. This work develops a Coupled Adjoint-based Perturbation Theory for dynAmIcs and heat traNsfer (CAPTAIN) framework to rapidly quantify the impact of uncertainty to overall transient responses by generating sensitivity coefficients for temperature, power, and delayed neutron precursor concentrations using forward and adjoint solutions. This work presents an initial proof of principle, verified with direct perturbations to several inputs. Furthermore, this …

A Risk-Informed Approach To Performing The Pre-Closure Safety Analysis For The Deep Borehole Disposal Of Radioactive Waste, Jennifer Elizabeth Leute

Nuclear Engineering ETDs

Deep borehole disposal is an emerging concept which involves disposing of radioactive

waste in boreholes several kilometers deep then backfilling to minimize radionuclide

transport and distribute weight. Unfortunately, little documentation exists on borehole

safety case development, especially for pre-closure operations. This study aims to close

this gap by proposing a graded approach matrix based on consequence, maturity, and

complexity. Two case studies are used to demonstrate this application: Hanford CsCl

capsules and spent PWR assemblies. Simulations are used to predict potential for dose

exposure, revealing CsCl capsules have a much higher potential for being above the 5

rem public dose …

Analysis Of Heat Transfer And Pressure Drops Associated With Twisted Tube Heat Exchangers, Braden Foderaro

Nuclear Engineering ETDs

Several studies have been done on the effects of twisted tubes in heat exchangers, including the correlations that relate the flow parameters to the heat transfer and pressure drop experienced. These studies are new, with the earliest being performed in 1982. As such, there are many correlations covering only certain flow parameters and geometrical configurations such as the Reynolds number and modified Froude number.

This thesis attempts to cover flow regimes and tube geometries not yet studied and yield correlations. Data are gathered from heat exchangers featuring twisted tubes with water as the working fluid. It is noticed that the …

Pria: Process Risk Identification And Analysis, Raymond Fasano

Nuclear Engineering ETDs

This dissertation proposes and evaluates two approaches, with-in a Process Risk and Analysis (PRIA) framework, that advance data-driven hazard discovery in complex cyber-physical systems. First, a transferability-based clustering method groups subspace-identified segments into operational modes, prioritizing cross-predictive performance over raw feature proximity. Second, a Neural Switching Linear Dynamical System (NeuralSLDS) model anchors learning in identified state-space models with Bayesian residuals, calibrated predictive uncertainty, and context-aware operating mode transitions. Together, these methods generate physics-informed, probabilistic world models that can support model-in-the-loop analysis of hazardous trajectories. The approach is validated on a simulated point-kinetics reactor and a centrifugal chiller dataset, demonstrating coherent …

Thermal Management With Supercritical Carbon Dioxide Under Extreme Applications, Devon Hardy

Doctoral Dissertations and Master's Theses

A unique challenge in thermal system design is minimizing the power required to operate cooling systems while maintaining effective heat removal. Traditional cooling systems utilize single-phase fluids where the heat transfer mechanisms are well understood. To meet a variety of cooling demands, a range of technologies are available, including microchannel forced convection, jet impingement, porous media, nanofluids, pin fin arrays, and film cooling, each offering distinct advantages and limitations. While the performance of single- or two-phase cooling systems are generally predictable, in extreme thermal environments, new cooling solutions are needed to improve overall system efficiency and reliability.

Supercritical fluids, particularly …

Investigating The Impact Of Forest Vegetation On Nuclear Weapon Prompt Radiation Energy Deposition, Paul A. Clement

Theses and Dissertations

This work seeks to answer the unstudied questions “Does a layer of vegetation impact the prompt radiation energy deposition in the soil from an atmospheric nuclear detonation?” and “If yes, by how much?” A new methodology was developed to repeatably automate and streamline a process of generating a three-dimensional geometry for subsequent radiation transport simulations and statistical analysis. The methodology streamlined three diverse applications: a three-dimensional mesh generator, a radiation transport simulation code, and a sensitivity analysis & uncertainty quantification software. The methodology was tested by simulating the quantitative influence that vegetation has on changing the energy deposition into the …

Isotope Production Modeling In Sodium-Cooled Fast Reactors, Aaron W. Burkhardt

Theses and Dissertations

The accurate prediction of isotopic compositions in Sodium-Cooled Fast Reactors (SFRs) is essential for nuclear forensic analyses and international nuclear treaty monitoring, particularly with the increased global deployment of Generation-IV reactors. This research developed and validated a detailed computational model tailored specifically to the Prototype Fast Breeder Reactor (PFBR), employing advanced Monte Carlo neutron transport methods, sophisticated burnup modeling, and variance reduction techniques. Validation against empirical data from the Experimental Breeder Reactor-II confirmed the model’s accuracy, producing a comprehensive database of isotopic compositions across 301 assembly locations and 580 isotopes through the reactor’s initial operation and equilibrium cycle. The model …

Constraining Nuclear Data Uncertainty Requirements For The 19F(A, N)22Na Reaction For Non-Proliferation Applications, Tyler R. M. Smith

Theses and Dissertations

This thesis explores the requirements on nuclear data uncertainties needed for the use of the ¹⁹F(α, n)²²Na reaction for nuclear non-proliferation applications. An overview of how neutrons are produced from alpha decays in a UF₆ medium is discussed. Calculation demonstrate the role nuclear data uncertainties effect the neutron yield and energy spectra as a function of enrichment.

Design And Characterization Of Radiation-Hardened Gaas Hbt-Based Optical Transceivers, Collin Burt

Electrical and Computer Engineering ETDs

Optical transceivers are desirable for their galvanic isolation and natural immunity to electromagnetic interference compared with direct electrical connections. This is true in normal operating environments as well as radiation environments. This work realizes and characterizes GaAs HBT-based optical transceivers across temperature and a range of radiation environments including high dose rate, total ionizing dose, neutron, and heavy ion. The transceiver designs are discussed and specific environmental design considerations are highlighted. Final results for each environment are provided and compared with existing transceivers.

Hybrid Machine Learning And Comparison Error Minimization For Frequency Domain-Based Rapid State Estimation In Structures Subjected To High-Rate Boundary Change, James Scheppegrell

Theses and Dissertations

Dynamic forces and evolving structural boundary conditions pose challenges for various structural systems such as aircraft, orbital infrastructure, and energy harvesting devices. The design, evaluation, and functionality, of such systems can be aided through the collection and analysis of data. However, real-time decision-making for systems experiencing high-rate changes can pose unique challenges, if assessments are to be made accurately and rapidly enough to be relevant. In cases where the systems are well-defined and thoroughly understood, monitoring the frequency response can be instrumental in determining the state of structures subjected to high-rate structural boundary condition changes. This study focuses on investigating …

Assessing The Feasibility Of Transportable Nuclear Reactors: A Radiological Risk Case Study, Robert John Demuth

Theses and Dissertations

The feasibility of a truly transportable nuclear reactor presents significant radiological challenges that must be addressed to ensure compliance with regulatory limits and operational safety. This study evaluates the radiological constraints associated with the transportability of the Transportable Helium-cooled One-megawatt Reactor (THOR), focusing on neutron activation, shielding performance, and external radiation exposure. Using advanced radiation transport and activation modeling within the SCALE framework, a comprehensive analysis was conducted to quantify dose rates during operation, post-shutdown, and transport. A key aspect of this work involved assessing activation products in core materials, auxiliary components, and surrounding environments to determine their contribution to …

Radiation Assessment And Distribution In Changing Atmospheric Structures And Turbulence (Radcast), Steven B. Hernandez

Theses and Dissertations

The accessibility of materials and online information has made radiological dispersal devices (RDDs) a more probable threat than conventional nuclear weapons. This study analyzed five datasets from three test periods, using a correlation analysis between optical turbulence, aerosol concentration, and environmental parameters, and geometric mean diameter (GMD) calculations. The correlation analysis failed to yield meaningful insights, prompted a transition to the GMD analysis, which produced clearer results. Findings show GMD ranged from 38–41 nm, increasing at night and during neutral events as reduced vertical motion and boundary layer contraction correlated with optical turbulence. An alternative GMD dataset, calculated by the …

Measurements Of The Radioisotope Production Cross Section Of 193Ir(N,N')193mIr Between 0.5–9 Mev, Ronnie P. Rera

Theses and Dissertations

This thesis covers a measurements of the radioisotope production cross section of ¹⁹³Ir(n,n′) ^193mIr between 0.5–9 MeV is discussed. The experiment was performed at the University of Notre Dame St.ANA 5U accelerator laboratory. Experimental planning, data collection, analysis, results, and impacts are discussed.

Characterization Of The Neutron Spectrum Produced By A Pulsed Power Generator, Daniel S. Godlasky

Theses and Dissertations

Neutron time-of-flight, activation foils, and spectral unfolding software were used to characterize the energy and fluence of the neutron spectrum created by the Gamble II pulsed power generator. Gamble II is a pulsed power generator that delivers a 1 MV to 2.2 MV and 800 kA electrical pulse peaking at 50 ns. This electrical release creates deuterium ions in the diode that are accelerated to a neutron converter covered with a novel lithium fluoride or deuterated polyethylene to create primarily ⁷Li(d,n) or D(d,n) and ¹²C(d,n) nuclear reactions. In October 2024, two D(d,n) shots occurred, and in November 2024, …