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 …

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, …

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 …

Training Machine Learning Algorithms For The Transient Startup Of A Long-Life Modular Microreactor, Ahmad N. Shaheen

Nuclear Engineering ETDs

There is an increasing interest in developing and deploying small modular nuclear reactors (SMRs) and micro modular reactors (MMRs). They could be operated with minimal on-site personnel or remotely with a high degree of autonomy. This can be enabled through the use and application of Artificial Intelligence (AL) and Machine Learning (ML) algorithms and methods. The objective of the present work is to train machine learning algorithms for remote control mimicking the transient startup of the Very-Small, Long-LIfe, Modular (VSLLIM) microreactor. This walk-away safe microreactor design and a fully integrated transient model have been developed at the University of New …

Deterministic Transport Of Coupled Energetic Light-Ions And Neutrons With Application To Inertial Confinement Fusion, Kyle Beling

Nuclear Engineering ETDs

Numerical simulations of an inertial confinement fusion (ICF) target during the implosion process require high fidelity models of the radiation transport process. This work is interested in the transport of high-energy light-ions and neutrons in a background ICF plasma. As these energetic particles slow down, they experience knock-on (recoil) and thermonuclear (TN) collisions with the light-ions in the background plasma. These recoil and TN collisions excite the background light-ions causing them to transport through the plasma further exciting background light-ions. Mathematically, this cascading effect is described as a system of linear Boltzmann transport equations coupled through recoil and TN collision …

Methods For Efficient Computation Of Neutron Multiplicity Distributions And Snm Sample Characterization, Jawad Ribhi Moussa

Nuclear Engineering ETDs

This dissertation advances neutron multiplicity counting (NMC) by developing a hierarchy of computational methods that combine deterministic and stochastic techniques with modern machine learning for improved special nuclear material (SNM) characterization. A system state-updating Monte Carlo method is introduced in addition to a dynamic point kinetic model based on a backward Master equation (BME) formulation. These models, along with newly developed distribution reconstruction methods, enable more efficient computation of neutron count distributions in a fixed detector time-gate. NMC limitations associated with finite-size and neutron phase effects are also addressed by extending the BME model to account for time-gated neutron count …

Coupled Monte Carlo And Adjoint Depletion Sensitivity Coefficient Methods, Benjamin R. Murphy

Nuclear Engineering ETDs

Recent advances in adjoint-based, continuous-energy Monte Carlo generalized perturbation theory (GPT) sensitivity coefficients are combined with adjoint-based depletion perturbation theory (DPT) sensitivities to obtain fully coupled depletion sensitivity coefficients in OpenMC. These depletion sensitivity coefficients are compared with direct perturbation results and found to have generally good agreement, though discrepancies exist. Some shortfalls of the DPT method include the inefficient initial numeric integration scheme for calculating the DPT sensitivities and the lack of stochastic uncertainty estimates for the DPT sensitivities. However, despite these shortcomings, the methodology provides the means to obtain high fidelity depletion sensitivity coefficients. With refinements to the …

Development And Evaluation Of Muon Scattering Tomography Reconstruction Techniques For Spent Fuel Verification, Jesus J. Valencia

Nuclear Engineering ETDs

The International Atomic Energy Agency has acknowledged the need to “efficiently verify and maintain knowledge of spent fuel in shielding/storage/transport containers at all points in their life cycle”. Cosmic-ray muon scattering tomography has shown potential to create reconstruction images of dry cask contents that would be useful for in-situ verification of spent fuel within dry casks.

In this document, several muon scattering tomography reconstruction techniques are explored using experimental track data through a partially filled dry cask container and steel drum test object. Two three-dimensional reconstruction techniques, a backprojection and newly developed combined depth of field algorithm, are evaluated. The …

Improving Criticality Safety Benchmark Coverage By Developing A Benchmark Evaluation Of The Unm Agn-201m Reactor, Rowdy Davis

Nuclear Engineering ETDs

This research aimed to improve the benchmark coverage of the International Criticality Safety Benchmark Evaluation Project (ICSBEP) handbook and the International Reactor Physics Experiment Evaluation Project (IRPhEP) with respect to High-Assay, Low-Enriched Uranium Fuel (HALEU). This was accomplished by creating a benchmark of the University of New Mexico’s Aerojet General Nucleonics model 201-M reactor and submitting it to the ICSBEP. This research then aimed to quantify to what extent this benchmark improves coverage of the benchmark suites for HALEU and TRISO fuel applications. This investigation utilized WHISPER, TSUNAMI-IP, and TSURFER with 36 application cases developed in SCALE and 2,929 experiments …

Design And Analysis Of Free Piston Stirling Engines For Microreactor Applications, Phat D. Doan

Nuclear Engineering ETDs

Through the development of microreactors, a free piston Stirling engine (FPSE) is an excellent candidate to support the development of the microreactors applications. This study proposes a 20 kWe design of the FPSE for microreactor applications. The model has been developed and analyzed through a MATLAB code that was verified and benchmarked with both RE-1000 engine’s experiment data and Sage software. The MATLAB code has been developed from scratch using the first and second order approximation to simulate the engine’s steady state operation. There are three operating conditions that were applied to the code such as ideal isothermal, ideal adiabatic, …

Physical Properties Of Copper Niobium Nanolamellar Composites Fabricated By Accumulative Roll Bonding, Jared Justice

Nuclear Engineering ETDs

Nanolamellar composites with high interface density have increased strength due to interfaces serving as barriers to dislocation movement and high radiation damage resistance. However, these interfaces also serve as barriers to electron motion, reducing the electrical resistivity and thermal conductivity. This work seeks to understand the inherent tradeoff between strength and physical properties of nanolamellar composites produced by accumulative roll bonding with layer thickness ranging from 25 nm to 193 nm. The electrical resistivity was investigated over temperatures ranging from 2 K to 300 K. The effect of longitudinal rolling and cross rolling was also investigated. Electrical resistivity results were …

Application Of An Empirical Density Law Via Python For Aqueous Plutonium Chloride Systems For Mcnp6, Riley Bulso

Nuclear Engineering ETDs

A predictive density law has been implemented and developed into a Python tool to reduce bias and the high degree of conservatism in criticality safety calculations for aqueous plutonium chloride systems. Based upon available data and parameters, an empirical method was used to create this law. This method was used in the development of a Python tool to predict the density and composition of such a solution, which may then populate material data in an MCNP6 input file.

This tool and the density law equation have been verified against experimental data points for accuracy. Density is predicted with a maximum …

A Comparison Of Fixed Versus Moving Eulerian Meshes For 1-D Radiative Shock Problems, Dylan Weatherred

Nuclear Engineering ETDs

Testing codes used to solve the radiation-hydrodynamics equations requires the use of radiative shock problems. These problems contain stiff shocks and test the coupling of the material motion and the energy exchange between the radiation and material. However, these problems are difficult to solve due to large differences in time scale between radiation and material equations, resolving shocks, and modeling radiation and material interactions. This thesis will look to solve radiative shock problems in 1-D using the Eulerian formulation on fixed and moving meshes. The moving mesh method proposed takes advantage of the more simple Eulerian formulation of the radiation …

Miniature, Submersible Electromagnetic Pumps Of Molten Lead And Sodium For Gen-Iv Nuclear Reactors Development, Ragai M. Altamimi

Nuclear Engineering ETDs

Heavy metals and alkali Liquid Metals are suitable coolants for Generation IV terrestrial nuclear reactors for operating at elevated temperatures for achieving plant thermal efficiency more than 40% and the thermochemical generation of hydrogen fuel. In addition, the low vapor pressure of these liquids eliminates the need for a pressure vessel and instead operates slightly below ambient pressure. A primary issue with the uses of these coolants is their compatibility with nuclear fuel, cladding and core structure materials at elevated temperatures more than 500oC. Therefore, in pile and out-of-pile test loops have been constructed or being considered for quantifying the …

Sensitivity And Uncertainty Analysis Of Inertial Confinement Fusion Experiments, Colin A. Weaver

Nuclear Engineering ETDs

Sandia National Laboratories conducts Magnetized Liner Inertial Fusion (MagLIF) experiments at the Z Pulsed Power Facility. Their objective is to study the burning plasma formed under magnetic direct drive Inertial Confinement Fusion (ICF) conditions and use the inferred information to reduce uncertainty in computational models and improve experimental designs. The Z machine has five neutron time-of-flight (nToF) detectors that measure the fusion neutron time spectrum from three lines-of-sight. Together, these signals are used to infer the ion temperature, target liner mass density, and the burn history of the MagLIF experiment from measured data. These parameters are a few used by …

Measurements Of Scintillation Light Quenching For Protons In Rare-Earth Inorganic Scintillators, Tatiana Nathaly Espinoza

Nuclear Engineering ETDs

Scintillator detectors have become a leading choice of radiation detectors for a variety of applications, including space science. Due to their intrinsic characteristics, rare-earth inorganic scintillators provide the capability to detect both gamma and charged particles in a small detector. The response of these detectors is typically characterized using isotropic gamma sources. However, the light output produced in the scintillator from an incident gamma of a particular energy differs from the light output produced from an incident charged particle of the same energy; a phenomenon known as quenching. Using two types of rare-earth inorganic scintillators, Y2SiO5(YSO:Ce), and Gd₃Al₂Ga₃O₁₂(GAGG:Ce), we measured …

Material Reliability For A Molten Chloride Salt System, Aaron A.H. Overacker

Nuclear Engineering ETDs

Energy efficiency and cost reduction can both be improved upon using overall higher temperatures for the working fluid. This interest is shared in both nuclear energy as well as concentrated solar power. To achieve higher temperatures would require industry to change working fluids. The United States Department of Energy set out a goal of operating concentrated solar to above 700℃. This would help reduce the cost by having more efficiency in the thermal energy storage, while not a concern for nuclear, these high temperatures can reduce the safety risk and pressure use with the implementation of molten salts. The National …

Understanding The Behavior Of Upper Subcritical Limit Calculations, Bobbi Riedel

Nuclear Engineering ETDs

This research consists of two comparison studies: the first study employed standard practices to characterize Upper Subcritical Limit (USL) estimation methods. A series of 33 neutronic systems that used standardized nuclear data and benchmark libraries were studied to compare the Whisper, TSURFER, and USLSTATS methods relative to a stochastic USL. USLs were also estimated for these 20 systems using the Whisper 1.1 code. Sensitivity data files were produced using MCNP6.2 and then used with the ORNL TSURFER and USLSTATS methods to estimate USLs for a cross-method USL comparison. The results show that USLs for each of the loosely coupled system …