Nuclear Engineering Commons^™

Application Of An Empirical Density Law Via Python For Aqueous Plutonium Nitrate Systems, Tara L. Robertson

Nuclear Engineering ETDs

A predictive density tool has been developed to reduce bias and uncertainty in nuclear criticality safety calculations for aqueous plutonium nitrate systems. Multiple methods to calculate the density were reviewed and an empirical method was selected for use. The selected method was then implemented into a Python tool to calculate the solution density and the atom densities for an MCNP6.2 input file.

The Python tool has been validated and verified against the International Handbook of Evaluated Criticality Safety Benchmark Experiments to predict densities within ± 2.6%. The capability to calculate and utilize densities from this tool is a large improvement …

Computational Methods, Investigations, And Codes To Support Corrosion Experiments In Molten Lead And Transfer To Reactor Conditions, Khaled A. Talaat

Nuclear Engineering ETDs

Lead cooled fast reactors have many potential economic advantages over other Generation IV reactor designs due to the high boiling point of lead (~1750 °C) at atmospheric pressure and excellent neutronic properties which have made them attractive to the commercial energy sector in the recent years. They, however, remain hampered by challenges in cladding material compatibility with the heavy liquid metal coolant. A forced circulation loop was established at the University of New Mexico (“Lobo Lead Loop”) to prequalify materials for Versatile Test Reactor (VTR) testing and to improve the understanding of flow accelerated corrosion in molten lead environment. Corrosion …

Joining Of Candidate Materials For Lead-Cooled Fast Reactors, Brandon M. Bohanon

Nuclear Engineering ETDs

The lead-cooled fast reactor (LFR) is a fourth-generation reactor design characterized by high temperatures, neutron dosage, and highly corrosive and erosive environment due to high flow velocities. Therefore, materials testing must be performed to find structural and system components that withstand this harsh environment. These candidate alloys must have high-temperature creep strength, resistance to damage from fast-spectrum neutrons, and must grow protective oxide layers. FeCrAl alloys have been identified as possessing all these qualities, however, there are limitations due to erosion and the joining of these materials. In this work, mechanical and microstructural properties of base and conventionally joined FeCrAl-based …

The Effects Of A Power Iteration-Based K-Eigenvalue Solver For Various Subcritical Parameters And Calculations, Daniel H. Timmons

Nuclear Engineering ETDs

The need to simulate subcritical benchmark parameters quickly and accurately is becoming increasing important. When using Monte Carlo methods this is traditionally done using a fixed-source calculation where a particle and its progeny are tracked until their removal from the system. This method can be slow for near critical systems. The use of a k-eigenvalue solver could reduce the computational footprint and reduce the need to post process data.

This is done for four parameters from the ICSBEP benchmark values: R_1 , R_2 , M_L, and M_eff. These parameters are calculated in two new distinct ways. First, is directly …

Simulation Of Thermal Radiation Transport In Stochastic Media With Nonlinear Temperature Dependence, Corey Michael Skinner

Nuclear Engineering ETDs

Nonlinear gray thermal radiation transport (TRT) in binary statistical mixtures is investigated through Implicit Monte Carlo (IMC) simulation on one-dimensional planar Markovian geometries and two dimensional approximate Markovian or Poisson-Box geometries. A stochastic geometry option was implemented in the Los Alamos National Laboratory Branson IMC solver which yielded benchmark solutions by simulating thermal radiation and material energy transport over a large number of instantiations of the geometry followed by ensemble averaging to obtain conditionally averaged radiation intensity and material temperatures. A chord length sampling method was also implemented based on a heuristic generalization of the Levermore-Pomraning homogenized medium model to …

Experimental Investigations On Boiling Heat Transfer Characteristics Of Accident-Tolerant-Fuel And Traditional Claddings, Mingfu He Mr.

Nuclear Engineering ETDs

To make it more clear that how the materials’ thermal-physical properties and wall thickness have influential impacts on boiling heat transfer characteristics of cladding, this dissertation looks into the potential impacts of cladding materials on critical heat flux and heat transfer coefficients by a systematic experimental investigation across a wide range of pool/flow boiling conditions under the steady-state and power-transient heat inputs.

Recent thermal-hydraulics studies have demonstrated that iron-chromium-aluminium (FeCrAl) alloys have the thermal priorities over zircaloys and other commercial alloys including critical heat flux and heat transfer coefficient. However, it is found in our experimental results that FeCrAl-C26M, and …

Utilizing Sensitivity And Correlation Coefficients From Mcnp And Whisper To Guide Microreactor Experiment Design, Alexis Maldonado

Nuclear Engineering ETDs

When designing experiments for full-scale reactor systems, MCNP and Whisper can be used to create neutronic models and compare the similarity of two nuclear systems via correlation coefficients for 𝑘𝑒𝑓𝑓, effective multiplication factor. This thesis applies this framework to a conceptual heat-pipe, yttrium-hydride moderated microreactor system and experiments. The framework is intended as a supplement to other neutronics/thermal/multiphysics analyses and provides a concrete method to measure the neutronic similarity of two systems. By analyzing the shared nuclear data uncertainty, as well as sensitivity to nuclear data over all neutron energies, highly informative experiments can be designed to aid in the …

Monte Carlo Perturbation Analysis Of Dimension And Density Variations Of The Annular Core Research Reactor Model Fuel, Karissa Currie

Nuclear Engineering ETDs

This thesis assesses sources of uncertainty in the neutron energy spectrum of the Annular Core Research Reactor (ACRR) Monte Carlo N-Particle Transport Code (MCNP) model. Uncertainty evaluations have been performed on the ACRR core but were computationally intensive and could not isolate the uncertainties associated with discrete sources. Monte Carlo Perturbation Theory (MCPT) is used in MCNP to calculate 640-group neutron energy fluences and their associated uncertainties [1]. To understand the uncertainties associated with only the UO₂-BeO fuel, perturbations in densities and dimensions were evaluated. A 640 by 640 covariance and correlation matrices were produced and compared to …

Monte Carlo Perturbation Analysis Of Fuel Temperature Variations In The Mcnp Model Of The Annular Core Research Reactor, Melissa Andrea Moreno

Nuclear Engineering ETDs

The Annular Core Research Reactor (ACRR) Monte Carlo N-Particle (MCNP) model is used for a variety of computational calculations ranging from reactor kinetics metrics to safety analyses. To understand the dominant source of uncertainty within the model, perturbations in temperature were applied to individual ACRR MCNP fuel rods. Assigning random temperatures, selected uniformly, from the operational temperature ranges of the fuel enables a study of uncertainty effects based on temperature variations. Stochastic mixing was used to blend the cross-sections of the desired temperatures using the MCNP continuous and Thermal Neutron Scattering Treatment (S(α,β)) libraries in ENDF/B-VII.1. The uncertainty quantification process …

A Two-Dimensional Spherical-Polar Multigroup Discrete Ordinates Code For Atmospheric Particle Transport, Daniel T. Wakeford

Nuclear Engineering ETDs

A natural coordinate system for calculating neutral particle propagation in the atmosphere due to point sources is two-dimensional spherical-polar coordinates. Deterministic methods for solving the transport equation in this coordinate system require some interesting implementation details stemming from the two angular derivatives present in this form of the equation. In this dissertation, we present a bilinear discontinuous spatial discretization of the transport equation in this coordinate system. The weighted diamond difference discretization is applied to the angular derivative term in two angular dimensions, using zero-weighted starting directions to start the differencing. To our knowledge, the only previous deterministic code that …

Characterization Of Partial Charge Collection Induced By Neutron Damage In High-Purity Germanium Detectors, James W. Evans

Nuclear Engineering ETDs

This paper investigates the correlation of damage induced by neutron interactions and degradation in the spectra of HPGe detectors. As neutrons kinetically interact with germanium crystals, they create interstitial and vacancy defects within the lattice. These defects then interfere with the charge migration of electron-hole pairs and reduce resolution in the observed energy spectrum. The partial charge collection produces observable spectral changes by increasing the peak width and reducing resolution (full width half maximum). A detailed characterization using various check sources was performed before and after iterations of neutron exposure in order to observe the effects of the neutron damage. …

A Forward Analytic Model Of Neutron Time-Of-Flight Signals With Single Elastic Scattering And Beamline Attenuation For Inferring Ion Temperatures From Maglif Experiments, Colin A. Weaver

Nuclear Engineering ETDs

A forward analytic model is required to rapidly simulate the neutron time-of-flight (nToF) signals that result from magnetized liner inertial fusion (MagLIF) experiments at Sandia’s Z Pulsed Power Facility. Various experimental parameters, such as the burn-weighted fuel-ion temperature and liner areal density, determine the shape of the nToF signal and are important for characterizing any given MagLIF experiment. Extracting these parameters from measured nToF signals requires an appropriate analytic model that includes the primary DD neutron peak, once-scattered neutrons in the beryllium liner of the MagLIF target, and direct beamline attenuation. Mathematical expressions for this model were derived from the …

Modeling And Simulation Of Stochastic Neutron And Cumulative Deposited Fission Energy Distributions, Patrick O'Rourke

Nuclear Engineering ETDs

Methods of stochastic neutron transport are investigated and applied to novel formulations for the neutron number distribution and the cumulative fission energy deposition distribution. We utilize two Monte Carlo algorithms: the event-based Monte Carlo (EBMC) method and the Stochastic Simulation Algorithm (SSA) to benchmark and analyze systems. We show that the SSA outperforms the EBMC for the parameter space we are interested in. We then utilize the SSA to analyze systems composed of multiple spherical regions with fast and thermal neutrons with time-dependent reactivity insertions and determine whether group-dependent number distributions approach a gamma distribution. We develop two methods for …

Characterization Of Uranium Foil Irradiations At The Wsu Triga Reactor Using A New Reactor Model In Scale, Kimberly A. Hinrichs

Nuclear Engineering ETDs

A new reactor model of the Washington State University TRIGA was developed in the SCALE neutron transport code, and its fidelity was verified by comparison to MCNP and available data for several reactor parameters. The model was used to characterize irradiations designed to produce the short-lived actinides ²³⁷U and ²³⁹U, two key isotopes for nuclear forensics. These short-lived actinides, their decay daughters ²³⁷Np and ²³⁹Pu, and total fissions (via ⁹⁹Mo) were measured in irradiated foils at Los Alamos National Laboratory and other labs with good agreement among parent/daughter pairs and among labs. The laboratory-measured isotope …

Experimental Investigation Of Steady-State And Transient Flow Boiling Critical Heat Flux, Soon Kyu Lee

Nuclear Engineering ETDs

The Critical Heat Flux (CHF) causes a rapid reduction of heat transfer coefficient with a rapid increase of cladding temperature, which may induce physical failure of the heated material. Understanding CHF phenomena and reliable prediction of the boiling behavior are needed to design a heat transfer system including nuclear reactors. Due to the complex nature of CHF, it is still an active research topic of interest. With an increasing interest in Accident Tolerant Fuel (ATF), CHF of ATF is essential topic of study for the detailed design of the fuel – cladding element and for the reactor safety analysis.

In …

Neutronic And Cfd-Thermal Hydraulic Analyses Of Very-Small, Long-Life, Modular (Vsllim) Reactor, Luis M. Palomino

Nuclear Engineering ETDs

Neutronic and CFD-thermal hydraulic analyses are performed of the Very-Small, Long-LIfe, and Modular (VSLLIM) nuclear reactor. This reactor was developed at the University of New Mexico’s Institute for Space and Nuclear Power Studies (UNM-ISNPS) to generate 1.0 – 10 MW_th for extended periods without refueling. It offers passive operation and safety features and redundant control and would be fabricated, assembled and sealed in the factory. During nominal operation and after shutdown, the VSLLIM is cooled by natural circulation of in-vessel liquid sodium, with the aid of an in-vessel chimney and annular helically-coiled …

Interrogation Of Spent Nuclear Fuel Casks Using Cosmic-Ray Muon Computed Tomography, Daniel C. Poulson

Nuclear Engineering ETDs

Properly accounting and safeguarding spent nuclear fuel are key components in the International Atomic Energy Agency’s mission of non-proliferation. Currently, no instruments are deployed that are able to verify the spent nuclear fuel contents of dry storage casks. Cosmic-ray muons provide an ideal probe for the heavily shielded casks due to their ability to penetrate thick, dense materials. Coulombic scattering of the muons, to first order, is proportional to the Z2/A of the material; this makes it especially sensitive to actinides, such as uranium and plutonium. The combination of these traits allows muons to be used to image and verify …

Developing A Simulation Tool For Evaluating In-Motion Detector Systems (La-Ur-18-29139), Brian Jennings

Nuclear Engineering ETDs

Available simulation software lacks the ability to produce in-motion detector responses for detector systems that may be used to detect the illicit trafficking of nuclear materials. In this thesis, a simulation tool is developed that uses static measured data as a basis set for producing in-motion detector responses with the ability to vary many parameters in each simulated trial. Once the basis set is measured and loaded into the simulation tool, the user interface allows the user to enter variations to speed, source height, source-to-detector distance, background exposure rate, which source(s) are present, their relative strength and shielding configuration, and …

Development Of Wireless Pebble For Packed Bed Heat Transfer Measurements And Machine Learning-Aided Accident Diagnosis For Loss Of Flow Accident (Lofa), Dongjune Chang

Nuclear Engineering ETDs

In the first study, a novel wireless pebble for scale experiments is developed, and a simple heat transfer experiment is conducted to determine the difference in the local heat transfer coefficient. Based on the fact that the use of Dowtherm A between approximately 57–87 °C is an alternative to the normal use of the FliBe temperature range of 600–700°C, a new-concept wireless device in a scaled experiment is introduced. This device consists of a 63.5 mm diameter metal shell and contains a built-in customized circuit board and battery for driving temperature measurements and wireless data transfer. The circuit board used …

Application Of Machine Learning To Chf Modelling, Mingfu He Mr

Nuclear Engineering ETDs

Accurate prediction of CHF is still a challenging issue in the study of boiling heat transfer. Many factors contribute to the occurrence of CHF and the various trigger mechanisms are proposed to unravel physical phenomena behind CHF. However, those mechanisms cannot cover the multiple primary factors simultaneously and even some of them still remain controversially unresolved. In light of the complexity and difficulty of CHF modelling, hereby an ensemble-learning based framework is proposed to model and predict CHF based on the databank of CHF. Some prior trials have been done for three primary aspects of dominant factors, that is, surface …

An Experimental And Numerical Investigation Of Flow Accelerated Flibe Corrosion, David B. Weitzel

Nuclear Engineering ETDs

Renewed interest in molten salt reactor technology has brought to light the need for a better understanding of FLiBe corrosion. To this end a flowing FLiBe corrosion test loop was designed to test the flow effects of FLiBe corrosion. The loop consists of a pump, melt tank, and stainless-steel tubing assembly that heats the molten salt to high temperatures and circulates it over test specimens. The experiment has been constructed and has completed initial shakedown testing.

To support the flowing FLiBe experiment, a numerical corrosion model that couples FLiBe electrochemistry, solid metal diffusion, and mass transport was implemented. The model …

Development Of The University Of New Mexico Spectrometer For High-Resolution Fission Product Yield Data, Richard Emery Blakeley

Nuclear Engineering ETDs

Well-defined fission product yield data has been of increasing interest in various applications within the nuclear industry. With this need in mind, a fission fragment mass spectroscopy system was designed and developed at the University of New Mexico in collaboration with the Los Alamos National Laboratories with a stated goal of attaining a mass resolution of ≤ 1 % (FWHM/centroid) for light fragments and near 1 % for heavy fragments. The mass spectrometer utilized in this work consists of a transmission time-of-flight detection system to measure fission product velocity and an axial ionization chamber to measure the fission product energy, …

Investigating The Electrodeposition Of Plutonium And Curium For Safeguarding The Electrorefiner, Chantell L. Murphy

Nuclear Engineering ETDs

This research investigated the electrochemical deposition behavior of plutonium (Pu) and curium (Cm) for safeguarding the electrorefiner (ER) in a pyroprocessing facility. The main goal of this investigation was to evaluate the feasibility of using a safeguards concept called the neutron balance method to account for Pu in the ER. The neutron balance method relies on a known Pu/Cm ratio and measures neutrons from Cm-244 coming into and leaving a unit operation to track Pu. The application of the neutron balance approach for pyroprocessing facilities requires that Pu and Cm remain together in all extraction, product recovery, and waste streams. …

Investigation Of The Formation Of Γꞌꞌ Precipitates Under Ion Irradiation And Elevated Temperature Environments, James R. Pike

Nuclear Engineering ETDs

During a preventative maintenance at the Los Alamos Neutron Science Center (LANSCE) Isotope Production Facility (IPF), a beam window made of solution annealed Alloy 718 was replaced and the old beam window was analyzed. The old beam window underwent mechanical testing and microstructure analysis. During the microstructure analysis, the formation of γꞌꞌ precipitates was observed in Transmission Electron Microscopy (TEM) electron diffraction pattern. The formation of γꞌꞌ precipitates was not expected since they are not stable under irradiation. Furthermore, the formation of γꞌꞌ precipitates was observed only at a temperature of 33ºC, and a dose of 0.7 displacement per atom …

Radiation Effects In Metal Oxides And Carbides, Benjamin Jackson Cowen

Nuclear Engineering ETDs

MD simulations of SiO₂, TiO₂, Cr₂O₃, Al₂O₃, MgO, and SiC, are performed to: (a) calculate TDE probability distributions and dependence on crystallographic direction, and (b) determine the number and types of defects formed with low- and high-energy PKAs and projectiles. In addition, a qualitative comparison of the MD simulation results of radiation damage in TiO₂, MgO, and crystalline and amorphous SiC thin films are compared with those of in situ TEM ion beam irradiation experiments at the Sandia National Laboratories’ I³TEM facility.

The TDE …

Sonomechanical Enhanced Sparging Techniques For Advanced Reactor Applications, Floren V. Rubio

Nuclear Engineering ETDs

The fluoride salt cooled high temperature reactor (FHR) is a Generation IV advanced reactor design that has potential to produce efficient, low carbon, and safe energy. But, there are significant engineering challenges that need to be addressed before the deployment of this reactor. One of the key challenges is tritium release mitigation and sequestration. Because the FHR utilizes a eutectic LiF-BeF2 (flibe) salt as a coolant, the coolant is a significant source of tritium.

High-power ultrasonics have been used in many industrial process streams such as food processing, metal production, chemical production, and pharmaceutical manufacturing. Techniques and concepts from these …

Analysis Of Double-Wall And Twisted-Tube Heat Exchanger Concepts For Use In Fluoride Salt-Cooled High-Temperature Reactors, Bryan M. Wallace

Nuclear Engineering ETDs

Fluoride Salt-cooled High-temperature Reactors (FHRs) are an attractive fourth generation reactor concept. Like other fourth generation concept designs, FHRs offer characteristics such as a high-temperature low-pressure molten salt coolant allowing the reactor to be combined with a high-temperature high-efficiency power generation cycle such as an air-Brayton or supercritical carbon dioxide (SCO2). \par

Like most Gen IV reactor concepts, there are a few problems which need to be addressed with the design before it can be licensed. One particular design is the Mark 1 pebble bed FHR, a design put out by the University of California Berkeley. Two problems that need …

Design And Characterization Of Systems For Direct Spatial Imaging Of Low-Energy Gamma-Radiation Sources, Phoenix Baldez

Nuclear Engineering ETDs

This work describes the development of radiation detection systems to identify and image special nuclear material (SNM) using low energy gamma rays. The imaging of these materials is crucial for timely, in the field responses to potential threats to national security. Using a spectroscopy system, the sources can be identified while images can be produced concurrently for the sources which are present. Two systems were designed and characterized in this study, a collimated imager which used collimation in front of a small CdTe detector, and a pixelated pinhole imager, using a pinhole mask in front of a pixelated CZT detector. …

Patient Specific Radiation Doses From Projection Radiography Images: Improving The Accuracy Of Low Dose Radiation Calculations, Daniel J. Sandoval

Nuclear Engineering ETDs

Due to an increase in regulatory scrutiny and medical facility accreditation requirements to monitor patient radiation dose from diagnostic imaging procedures, there is a growing necessity to determine and record accurate patient radiation dose from diagnostic medical imaging procedures. Current methods of patient dosimetry in diagnostic imaging are both extremely difficult and time consuming, require large computing resources (such as Monte Carlo computations), or lack accuracy due to using data based on homogeneous materials and “standard-man sized” anthropomorphic models.

This dissertation provides an algorithm that calculates a more accurate dose using patient-specific projection radiographic images. The algorithm includes measurements acquired …

An Exploration Of The Optical Detection Of Ionizing Radiation Utilizing Modern Optics Technology, Sean D. Fournier, Adam Hecht, Cassiano De Oliveira, Jeffrey B. Martin, Richard K. Harrison, Charles Potter

Nuclear Engineering ETDs

Modern ultraviolet (UV) cameras, when combined with UV-transmitting lenses/filter arrangements, can be used to detect radiation dose in air. Ionizing radiation excites nitrogen molecules in ambient air, the resulting decay includes weak emission of ultraviolet photons. Previous work has proven this phenomenon is detectable using highly-sensitive electronically cooled cameras traditionally used in astronomy for low-background imaging. While the ability to detect the presence of radiation (i.e. qualitative measurement) has been demonstrated at Sandia National Laboratories, there are several challenges in correlating images to known dose-fields (quantitative measurement). These challenges include: a low signal to background ratio, interferences due to electronic …