Forensic Signatures of Chemical Process History in Uranium Oxides

This dissertation comprehensively explores and develops new tools for nuclear forensic science to facilitate the identification of chemical process history in uranium oxides. Nuclear forensics is an emerging discipline motivated by the need to prevent and combat malevolent acts involving nuclear and radiological materials. This dissertation examined process signatures in uranium oxide powders, precursors, and sintered fuel pellets. Signatures were investigated on set of powder and pellet exemplars synthesized in the laboratory and a set of real‐world samples with process information obtained from the literature or manufacturer. The examined techniques included morphology as revealed by scanning electron microscopy, near‐infrared reflectance (NIR) spectroscopy, thermogravimetric analysis, powder x‐ray diffraction, specific surface area, and oxygen isotope composition. Overall, this dissertation identified promising process signatures related to powder morphology, NIR, and thermogravimetric analysis. Additional results provide insights on the direction of future research in the area of process signatures

Natural Fracture Evolution: Investigations into the Middle Devonian Marcellus Shale, Appalachian Basin, USA

Optimizing recovery from unconventional shale reservoirs has generated considerable research into optimal recovery methods through hydraulic fracturing design and shale reservoir characterization in the development of long-term hydrocarbon producers. Permeability at multiple scales from nanometer-scale pore sizes and nano-darcy permeability to completion-induced fractures defining a 100’s of meter stimulated reservoir volume plays a significant role in hydrocarbon flow during production in shale reservoirs. Preexisting cemented fractures in unconventional shale reservoirs are abundant and preferentially reactivate during induced hydraulic fracturing treatment to create necessary large-scale permeability. While previous investigations have significantly improved our knowledge of shale reservoirs, it has also highlighted the need for increased understanding of the geologic evolution and effect on hydraulic stimulation of pre-existing cemented fractures. This three-part dissertation examines natural fractures from four middle Devonian Marcellus Shale wells across the Appalachian basin through integration of visual core observation, thin section petrography, spectral gamma ray logs, borehole image logs, petrophysical logs, elemental data, and X-ray computed tomography cores. The research goals are: (1) to establish clues to assess natural fracture development in source rocks from kerogen maturation, relative timing, and hydrocarbon migration; (2) to investigate the relationship of natural fractures in wells of varying thermal maturity levels, and preferential fracture distribution in various clay types and redox environments; and (3) to characterize mineralized natural fractures in 3D using a medical CT-scan core to quantify volume and assess connectivity. This research indicates that overpressure from kerogen expulsion of hydrocarbon creates numerous cemented fractures filled with calcite and bitumen that achieve orientations related to the geologic burial stresses during their evolution, predominant in clay-rich units of certain redox conditions, cluster at geomechanical boundaries, and have inconsistent 3D volume changes within the core

Use of X-ray Computed Microtomography to Measure the Leaching Behaviour of Metal Sulphide Ores

Heap leaching is an important hydrometallurgical method to extract valuable metals from ores, especially low grade ores. The main disadvantages of heap leaching are the long processing time and low extraction efficiencies. Currently, a major barrier in fully understanding the leaching process is the study of the mass transport and surface chemistry at individual ore particle and mineral grain scale. This thesis describes a combined experimental and modelling approach to visualise, quantify and predict the leach behaviour based on X-ray Computed Microtomography (XMT, or micro-CT). An automatic image processing package was developed to process the 3D volume data. Individual ore particles as well as individual mineral grains can be tracked using a centroid tracking algorithm and a novel fast tracking algorithm respectively. The systematic and random errors and uncertainties in the image volume measurements were quantified. It was found that both the systematic and random errors are a strong function of the grain size relative to the voxel size. The random error can be reduced by combining the results from either multiple scans of the same object or scans of multiple similar objects while the systematic error can be eliminated by using volume standards. The leach performance for a leaching column was quantified at different scales and it was found that the leach behaviour and its variability were difficult to quantify at large scales (column and individual ore particle scale), but can be quantified at mineral grain scale by using a novel statistical analysis method. The tracked grains were divided into different size-distance categories to analyse the average leach performance and the variation for each category. Both grain size and distance dependencies were observed. The size dependency is more dominant at the early stage of leaching whereas the distance dependency can significantly influence the ultimate recovery. A method for using the data to estimate the variability in the in-situ surface kinetics was also developed. A model for simulating the grain dissolution and the resultant kinetics based directly on XMT based 3D volume is introduced. The simulations were able to accurately predict both the overall leaching trends, as well as the leaching behaviour of mineral grains in classes based on their size and distance to the particle surface.Open Acces

Multi-scale multi-dimensional imaging and characterization of oil shale pyrolysis

In recent years, oil shale has attracted renewed attention as an unconventional energy resource, with vast and largely untapped reserves. Oil shale is a fine-grained sedimentary rock containing a sufficiently high content of immature organic matter from which shale oil and combustible gas can be extracted through pyrolysis. Several complex physical and chemical changes occur during the pyrolysis of oil shale where macromolecular network structures of kerogen are thermally decomposed. The pyrolysis of oil shale leads to the formation of a microscopic pore network in which the oil and gas products flow. The pore structure and the connectivity are significant characteristics which determine fluid flow and ultimate hydrocarbon recovery. In this thesis, a state-of-the-art multi-scale multi-dimensional workflow was applied to image and quantify the Lacustrine Eocene Green River (Mahogany Zone) formation, the world’s largest oil shale deposit. Samples were imaged before, during and after pyrolysis using laboratory and synchrotron-based X-ray Micro-tomography (µCT), Optical Microscopy, Automated Ultra-High Resolution Scanning Electron Microscopy (SEM), MAPS Mineralogy (Modular Automated Processing System) and Focused Ion Beam Scanning Electron Microscopy (FIB-SEM). Results of image analysis using optical (2-D), SEM (2-D), and µCT (3-D) reveal a complex fine-grained microstructure dominated by organic-rich parallel laminations in a tightly bound heterogeneous mineral matrix. MAPS Mineralogy combined with ultrafast measurements highlighted mineralogic textures dominated by dolomite, calcite, K-feldspar, quartz, pyrite and illitic clays. From high resolution backscattered electron (BSE) images, intra-organic, inter-organic-mineral, intra and inter-mineral pores were characterised with varying sizes and geometries. A detailed X-ray µCT study with increasing pyrolysis temperature (300-500°C) at 12 µm, 2 µm and 0.8 µm voxel sizes illuminated the evolution of pore structure, which is shown to be a strong function of the spatial distribution of organic content. In addition, FIB-SEM 3-D visualisations showed an unconnected pore space of 0.5% with pores sizes between 15 nm and 22 nm for the un-pyrolysed sample and a well-connected pore space of 18.2% largely with pores of equivalent radius between 1.6 µm and 2.0 µm for the pyrolysed sample. Synchrotron 4-D results at a time resolution of 160 seconds and a voxel size of 2 µm revealed a dramatic change in porosity accompanying pyrolysis between 390-400°C with the formation of micron-scale heterogeneous pores followed by interconnected fracture networks predominantly along the organic-rich laminations. Combining these techniques provides a powerful tool for quantifying petrophysical properties before, during and after oil shale pyrolysis. Quantitative 2-D, 3-D and 4-D imaging datasets across nm-µm-mm length scales are of great value to better understand, predict and model dynamics of pore structure change and hydrocarbon transport and production during oil shale pyrolysis.Open Acces

Application of HPGR and X-Ray CT to investigate the potential of Witwatersrand gold ore for heap leaching : a process mineralogy approach

Includes bibliographical references.Auriferous conglomerates of the Archaean Witwatersrand Basin in South Africa host one of the largest known gold resources and rate as the world’s most outstanding example of a fossil megaplacer deposit. For the past 40 years, Witwatersrand gold production in South Africa has been progressively declining due to problems related to high energy costs, decreasing grade, accessibility to greater depths, health and safety issues, labour union unrest and economic uncertainties: thus the overall viability of current gold production is questionable. Ultimately, the future of Witwatersrand gold mining relies on devising smarter strategies across the entire industry, but in particular critical areas such as comminution and extraction. With the continuous increase in mining depth, dominance of low-grade gold ores and strict safety regulations, metallurgical processing options have become limited. Heap leaching is a well-established technology which continues to grow in use and provides several benefits to solve some of these problems. High pressure grinding rolls (HPGR) is another technology with significant potential, especially for its application in coarse particle heap leaching due to its ability to induce micro-cracks as well as its high grinding efficiency and low energy requirements. This study explores the use of these two technologies in a process mineralogical framework using novel 3D X-ray computed tomography mineralogical analysis in order to assess a potential of the Witwatersrand gold ore for heap leaching

Исследование влияния хромовых покрытий на эксплуатационные параметры реактора

Объектом исследования является ядерный реактор с покрытиями из соединений хрома на корпусе активной зоны. Цель работы: изучить влияние наличия покрытий из соединений хрома на нейтронно-физические параметры реактора.The object of research is a nuclear reactor with chromium compounds coatings on casing of the core. The purpose of the work: to study the influence of presence of chromium compounds coatings on neutron-physical parameters of the reactor

Investigation of ZrN Non-Reactively Sputtered Diffusion Barrier Coating for U-Mo Dispersion Fuel

Department of Nuclear EngineeringZirconium nitride (ZrN) coating as a diffusion barrier layer has been applied to a U-7wt.% Mo (U-7Mo)/Al dispersion fuel plate owing to its high melting point, high thermodynamic stability against U-Mo and Al, high hardness, and low absorption cross section for thermal neutrons. However, it has been experimentally revealed that a ZrN coating layer adopted in a U-Mo/Al dispersion fuel plate experiences a functional failure locally, and hence undesirably extensive fission-induced interaction layers (ILs) between U-7Mo fuel powders and the surrounding Al matrix reaction layer are locally produced when irradiated. It is believed that the local coating damage generated during the dispersion-fuel-plate fabrication process accelerates the U-Mo/Al interdiffusion by acting as a fast diffusion path of solid materials. Unfortunately, there have been no studies scientifically identifying the causes of, or presenting solutions to, the problem of ZrN coating damage. Accordingly, based on comprehensive microstructural studies, the aim of this research is to experimentally and numerically investigate ZrN coating fracturing as a function of several variables at a high heat-treatment temperature during dispersion-fuel-plate fabrication. This research will help present appropriate solutions for preventing the occurrence of coating fracturing at the heat-treatment temperature, taking into account a realistic coating microstructure. ZrN coating was deposited onto U-7Mo powders using a direct-current magnetron non-reactive sputtering machine equipped with a turnable mixing drum. Microstructural studies on the as-fabricated ZrN coatings were conducted using a scanning electron microscope (SEM), energy-dispersive X-ray spectroscopy (EDS), and X-ray diffractometer (XRD). This research is composed of the following three parts: First, the microstructural properties and residual stress of as-deposited ZrN coatings were measured as a function of the coating thickness ranging from 0.1 to 2.6 ??m. SEM and XRD results show that the microstructural characteristics (e.g., compact density and crystallographic properties) of the ZrN coating varied depending on the coating thickness. In addition, interlaminar delamination occurred when the coating thickness grew to greater than 2.2 ??m. Therefore, the thickness of the ZrN coating is considered to be an important factor influencing its microstructure, and thus its fracture resistance. Second, the effects of the U-7Mo substrate size on the thickness and microstructure of as-fabricated ZrN coatings with a mean thickness of 0.9 ??m deposited on 45???90-??m sized U-7Mo powders were investigated. With an increase in the U-7Mo substrate size, the ZrN coatings showed an increase in the coating thickness and grain size, and a decrease in the compact density owing to the increased macroscopic defects. Based on the measured coating thickness, a semi-empirical model expressing the relationship between the coating thickness and substrate size was newly developed. Based on the experimental results, it can be predicted that the U-7Mo substrate size, as well as the ZrN coating thickness, also affects the fracture resistance of the ZrN coating. Based on the above parametric studies on the ZrN coating microstructure, the structural integrity of ZrN coating was investigated at a high fabrication temperature as a function of the coating thickness, U-7Mo substrate size, and annealing temperature. To theoretically assess whether a mechanical failure of the ZrN coatings occurs at a given coating thickness, U-7Mo substrate size, and annealing temperature, a finite element simulation (FES) was conducted. The FES results show that the coating fracture is dependent on the given coating thickness, U-7Mo powder size, and annealing temperature, which affect the fracture criteria or induced tensile-hoop-stress of the corresponding coating. The thicker the coating, the larger the U-Mo substrate size, whereas the higher the heat-treatment temperature, the more likely a coating fracturing is to occur. The FES results are in good accordance with the corresponding experimental results.ope