Doctor of Philosophy / Department of Mechanical and Nuclear Engineering / Douglas S. McGregor / Cadmium Zinc Telluride (CdZnTe) has been used for many applications, such as medical imaging and astrophysics, since its first demonstration as a room temperature operating gamma-ray detector in 1992. The wide band gap, high effective Z-number and high resistivity of CdZnTe make it a good candidate for use as a room temperature operated detector with good absorption efficiency, while maintaining a low bulk leakage current at high electric fields. Nevertheless, the low mobility lifetime products mu tau of holes in CdZnTe makes detectors position sensitive, unless advanced detector designs are employed. Among those designs is the Frisch collar technology which turns the detector into a single carrier device by negating the degrading effects of hole trapping and low mobility. The superiority of the Frisch collar technology over other methods include its inexpensive associated electronics and straight forward fabrication process. The main objective of this research study is to develop a large volume gamma-ray detector with an array of individual CdZnTe Frisch collar gamma-ray spectrometers while still using a single readout. Several goals were to be accomplished prior to the main objective. One goal is to develop a reliable low cost method to fabricate bulk CdZnTe crystals into Frisch collar detectors. Another goal was to investigate the limitations of crystal geometry and the crystal electrical properties to obtain the best spectroscopic performance from CdZnTe Frisch collar detectors. Still another goal was to study all other external parameters such as the collar length, anode to cathode ratio, the insulator thickness and applied voltage on performance of CdZnTe Frisch collar detectors. The final goal was to construct the CdZnTe Frisch collar devices into an array and to show its feasibility of being used for large volume detector.

Master of Science / Department of Mechanical and Nuclear Engineering / J. Kenneth Shultis / A program which calculates the radiation dosage to a predetermined set of components inside of a kill vehicle as a result of natural or artificial radiation sources has been developed for use within the confines of a parent external simulation. This dose can then be used to determine if a critical component has malfunctioned or failed completely, thereby rendering the interceptor unable to finish its mission. Knowledge of system and component performance as a function of incident high-energy particles leads to better battle management planning, CONOPS, and potentially a more efficient shielding design to achieve a higher probability of mission success.

Doctor of Philosophy / Department of Mechanical and Nuclear Engineering / Douglas S. McGregor / A Micro-Pocket Fission Detector (MPFD) is a miniaturized type of fission chamber developed for use inside a nuclear reactor. Their unique design allows them to be located between or even inside fuel pins while being built from materials which give them an operational lifetime comparable to or exceeding the life of the fuel. While other types of neutron detectors have been made for use inside a nuclear reactor, the MPFD is the first neutron detector which can survive sustained use inside a nuclear reactor while providing a real-time measurement of the neutron flux. This dissertation covers the deployment of MPFDs as a large three-dimensional array inside the Kansas State University TRIGA Mark-II Nuclear Reactor for real-time neutron flux measurements. This entails advancements in the design, construction, and packaging of the Micro-Pocket Fission Detector Triads with incorporated Thermocouple, or MPFD[superscript]3-T. Specialized electronics and software also had to be designed and built in order to make a functional system capable of collecting real-time data from up to 60 MPFD[superscript]3-Ts, or 180 individual MPFDs and 60 thermocouples. Design of the electronics required the development of detailed simulations and analysis for determining the theoretical response of the detectors and determination of their size. The results of this research shows that MPFDs can operate for extended times inside a nuclear reactor and can be utilized toward the use as distributed neutron detector arrays for advanced reactor control systems and power mapping. These functions are critical for continued gains in efficiency of nuclear power reactors while also improving safety through relatively inexpensive redundancy.

Master of Science / Department of Mechanical and Nuclear Engineering / William L. Dunn / The signature-based radiation-scanning (SBRS) technique relies on radiation detector responses, called “signatures,” and compares them to “templates”, to differentiate targets containing nitrogen-rich explosives from those that do not. This investigation utilizes nine signatures due to inelastic-scatter and prompt-capture gamma rays from hydrogen, carbon, nitrogen, and oxygen (HCNO) as well as two neutron signatures, produced when a target is interrogated with a 14.1 MeV neutron source beam. One hundred and forty three simulated experiments were conducted using MCNP5. Signatures of 42 targets containing explosive samples (21 of RDX and 21 of Urea Nitrate), and 21 containing inert samples were compared with the signatures of 80 artificial templates through figure-of-merit analysis. A density filter, comparing targets with templates of similar average density was investigated. Both high and low-density explosives (RDX-1.8 g cm-3 and Urea Nitrate-0.69 g cm-3) were shown to be differentiated from inert materials through use of neutron and gamma-ray signature templates with sensitivity of 90.5% and specificity of 76.2%. Density Groups were identified, in which neutron signature templates, gamma-ray signature templates or the combination of neutron and gamma-ray signature templates were capable of improving inert-explosive differentiation. figure-of -merit analysis, employing the best Density Group specific templates, differentiated explosive from inert targets with 90.5% sensitivity and specificity of over 85%.

Doctor of Philosophy / Department of Mechanical and Nuclear Engineering / Douglas McGregor / The effect of polyethylene addition on the growth of mercuric iodide (HgI[supscript]2) tetragonal prismatic crystals is examined. Three types of polyethylene powder are utilized: low molecular weight (¯Mw ~ 4 x 103), ultra high molecular weight (¯Mw ~ 3 x 6 106), and spectrophotometric grade polyethylenes. Among these types of polyethylene, the low molecular weight polyethylene produces the most significant change in HgI[supscript]2 morphology, with {110} being the most prominent crystal faces. Thermal desorption - gas chromatography/mass spectroscopy (TD-GC/MS) studies show that thermal desorption of the low molecular weight polyethylene at 100°C and 150°C produce isomers of alkynes, odd nalkanes, and methyl (even-n) alkyl ketones. HgI[supscript]2 growth runs with n-alkanes, with either neicosane, n-tetracosane, or n-hexatriacontane, cannot replicate the crystal shapes produced during growth with the low molecular weight polyethylene, whereas HgI[supscript]2 growth runs with ketones, with either 3-hexadecanone or 14-heptacosanone, produce HgI[supscript]2 tetragonal prismatic crystals, similar to the crystals grown with the low molecular weight polyethylene. C-O double bond contained in any ketone is a polar bond and this polar bond may be attracted to the mercury atoms on the top-most layer of the {110} faces through dipoledipole interaction. As a result, the growth of the {110} faces is impeded, with the crystals elongated in the [001] direction and bounded by the {001} faces along with large, prismatic {110} faces.

Master of Science / Mechanical and Nuclear Engineering / Hitesh Bindra / This thesis extends the application of Lattice Boltzmann Methods (LBM) to radiation transport problems in thermal sciences and nuclear engineering. LBM is used to solve the linear Boltzmann transport equation through discretization into Lattice Boltzmann Equations (LBE). The application of weighted summations for the scattering integral as set forth by Bindra and Patil are used in this work. Simplicity and localized discretization are the main advantages of using LBM with fixed lattice configurations for radiation transport problems. Coupled solutions to radiation transport and material energy transport are obtained using a single framework LBM. The resulting radiation field of a one dimensional participating and conducting media are in very good agreement with benchmark results using spherical harmonics, the P₁ method. Grid convergence studies were performed for this coupled conduction-radiation problem and results are found to be first-order accurate in space. In two dimensions, angular discretization for LBM is extended to higher resolution schemes such as D₂Q₈ and a generic formulation is adopted to derive the weights for Radiation Transport Equations (RTEs). Radiation transport in a two dimensional media is solved with LBM and the results are compared to those obtained from the commercial software COMSOL, which uses the Discrete Ordinates Method (DOM) with different angular resolution schemes. Results obtained from different lattice Boltzmann configurations such as D₂Q₄ and D₂Q₈ are compared with DOM and are found to be in good agreement. The verified LBM based radiation transport models are extended for their application into coupled multi-physics problems. A porous radiative burner is modeled as a homogeneous media with an analytical velocity field. Coupling is performed between the convection-diffusion energy transport equation with the analytical velocity field. Results show that radiative transport heats the participating media prior to its entering into the combustion chamber. The limitations of homogeneous models led to the development of a fully coupled LBM multi-physics model for a heterogeneous porous media. This multi-physics code solves three physics: fluid flow, conduction-convection and radiation transport in a single framework. The LBE models in one dimension are applied to solve one-group and two-group eigenvalue problems in bare and reflected slab geometries. The results are compared with existing criticality benchmark reports for different problems. It is found that results agree with benchmark reports for thick slabs (>4 mfp) but they tend to disagree when the critical slab dimensions are less than 3 mfp. The reason for this disagreement can be attributed to having only two angular directions in the one dimensional problems.

Master of Science / Department of Mechanical and Nuclear Engineering / J. Kenneth Shultis / Perforated neutron detectors suffer the unfortunate effect that their efficiency is a strong function of the direction of neutron incidence. It is found, by Monte Carlo simulation of many perforation shapes, that sinusoidal-type perforations greatly reduce the variation of detector efficiency. Detectors with rod-type perforations are modeled using a hybrid transport method linking the MCNP transport code and a specialized ion-transport code to calculate the probability that a neutron is detected. Channel, chevron, and sinusoidal perforations are modeled using other customized transport codes. Detector efficiency calculations are performed for neutrons incident at various polar and azimuthal angles. It is discovered that the efficiency losses of the detectors result from the decreasing solid angle subtended by the detector from the source and streaming through the detector at specific azimuthal angles. Detectors achieving an efficiency in excess of 10% and having a relatively flat ± 1% angular dependence in all azimuthal angles and polar angles between 0 and 60 degrees are predicted. Efficiencies up to 25% are achievable at the loss of directional independence. In addition to minimizing the directional dependence of the perforated detectors, the feasibility of developing a neutron detector for deployment in cargo containers to locate nuclear weapon pits is investigated using the MCNP transport code. The detector considered is a 7-mm diameter, 6LiF, rod-perforated detector surrounded in a cylinder of polyethylene. The optimum thicknesses of surrounding polyethylene, to maximize the response of the detector, is determined to be 10 cm of radial, 5 cm of front, and 5 cm of back polyethylene for end-on neutron incidence. Such a detector is predicted to produce a count rate between 12 and 15 cpm from a nuclear-weapon pit composed of 90% 239Pu and 10% 240Pu at a distance of 3 m. Side incidence is also considered, and the optimum moderator dimensions are 8 cm of radial, 10 cm of front, and 10 cm of back polyethylene that produce approximately the same count rate.

Master of Science / Department of Mechanical and Nuclear Engineering / Donald L. Fenton / Increase in demand for energy necessitates nuclear power units to increase their peak power limits. This increase implies significant changes in the design of the nuclear power unit core in order to provide better economy and safety in operations. A major hindrance to the increase of nuclear reactor performance especially in Pressurized Water Reactors (PWR) is the so called ‘Axial Offset Anomaly (AOA)’. An Axial Offset Anomaly (AOA) is the unexpected change in the core axial power distribution during the operation of a PWR from the predicted distribution. This problem is thought to be occurring because of precipitation and deposition of lithiated compounds such as lithium metaborate (LiBO[subscript]2) on the fuel rod. Due to its intrinsic property, the deposited boron absorbs neutrons thereby affecting the total power distribution in the reactor. AOA is thought to occur when there is sufficient build up of crud deposits on the cladding during subcooled nucleate boiling. Predicting AOA is difficult because there is little information regarding the heat and mass transfer during subcooled nucleate boiling. This thesis describes the experimental investigation that was conducted to study the heat transfer characteristics during subcooled nucleate boiling at prototypical PWR conditions. Pool boiling tests were conducted with varying concentrations of LiBO[subscript]2 and boric acid (H[subscript]2BO[subscript]3) solutions along with deionized water. The experimental data collected includes the effect of coolant concentration, degree of subcooling, system pressure and heat flux on pool boiling heat transfer coefficients. An analysis of deposits formed on the fuel rod during subcooled nucleate boiling is also included in the thesis. The experimental results reveal that the pool boiling heat transfer coefficient is degraded by the presence of boric acid and lithium metaborate in water. At concentration of 5000 ppm in water, the boric acid solution reduced the heat transfer coefficient by 23% and lithium metaborate solution reduced the heat transfer coefficient by 26%.

Master of Science / Department of Mechanical and Nuclear Engineering / Douglas S. McGregor / Purification of cadmium, zinc and tellurium was attempted to improve the quality of cadmium-zinc-telluride (CdZnTe) crystal growth. Specifically, vacuum distillation, zone refining and H[subscript]2 gas flow assisted zone refining were all investigated as methods to purify the constituent elements of CdZnTe. A unique multi-chamber ampoule was used to enable a purification sequence starting with double vacuum distillation followed by zone refining all without sample handling after the initial step. Modifications due to unique material properties of Cd and Zn were developed. Glow discharge mass spectroscopy (GDMS) analysis was used to measure impurity concentrations of 74 elements. Cd purification using vacuum distillation proved to be an effective method to reduce the impurity level of 5N starting material to a purity between the range of 6N5 and 7N5, as measured using GDMS and laser ablation mass spectroscopy. Combined Zn double vacuum distillation and zone refining in an enclosed Ar atmosphere using 5N starting material yielded material with a purity between the range of 5N8 to 6N8. Tellurium purification using combined double vacuum distillation followed by zone refining under continuous H[subscript]2 flow of 4N specified raw material resulted in high purity tellurium between the range of 6N3 and 7N4.

Flow instabilities occur at all scales in planetary systems. In this thesis we examine three cases of such instabilities, on three very different length scales. In the first part, we test the idea that Archean granite-greenstone belts (GGBs) form by crustal diapirism, or Rayleigh-Taylor instabilities. GGBs are characterized by large granitic domes (50-100 km in diameter) embedded in narrow keel-shaped greenstones. They are ubiquitous in Archean (> 2.5 Ga) terrains, but rare thereafter. We performed finite element calculations for a visco-elastic, temperature-dependent, non-Newtonian crust under conditions appropriate for the Archean, which show that dense low-viscosity volcanics overlying a felsic basement will overturn diapirically in as little as 10 Ma, displacing as much as 60 % of the volcanics to the lower crust. This surprisingly fast overturn rate suggests that diapiric overturn dominated crustal tectonics in the hot conditions of the Early Earth, becoming less important as the Earth cooled. Moreover, the deposition of large volumes of wet basaltic volcanics to the lower crust may provide the source for the formation of the distinctly Archean granitic rocks which dominate Earth's oldest continents. The second part examines the origin of Venusian coronae, circular volcanic features unique to Venus. Coronae are thought to result from small instabilities (diapirs) from the core-mantle boundary, which are typical of stagnant-lid convection. However, most young coronae are located in a region surrounded by long-lived hotspots, typical of a more active style of mantle convection. Using analogue experiments in corn syrup heated from below, we show that the co-existence of diapirs and long-lived mantle plumes are a direct consequence of the catastrophic overturn of the cold Venusian lithosphere thought to have occurred ~ 700 Ma ago. In the last part we analyze the thermal effect of fluid flow through a full-scale experiment testing clay and concrete tunnel seals in a Deep Geological Repository for nuclear was finite element software, we were able to show that the formation of fissures in the heated chamber between the two seals effectively limited heat flow, and could explain the discrepancy between the predicted and measured temperatures.