The Liquid Salt Cooled Reactor (LSCR) provides several potential benefits compared to pressurized water-cooled reactor systems. These include low operating pressure of the liquid salt coolant, the high burnup tolerance of the fuel, and the high operating temperatures which leads to increases in efficiency. However, due to inherently low heavy metal loading, the fuel cycle design presents specific challenges. In order to study options for optimizing the fuel design and fuel cycle, SCALE6.1 was used to create simplified models of the reactor and look at various parameters. The primary parameters of interest included packing factor and fuel enrichment. An economic analysis was performed on these results by developing a simple fuel cycle cost (FCC) model that could be used to compare the different options from an economic standpoint. The lithium enrichment of the FLiBe coolant was also investigated. The main focus was to understand the practical limitations associated with the Li-7 enrichment and whether it could be used for beneficial purposes. The main idea was to determine whether a lower-than-equilibrium enrichment could be used at reactor start up so that the Li-6 isotope acts as a burnable absorber. The results for the lithium enrichment study showed that the enrichment converges over time, but the amount of time required to reach steady state is much too long and the FLiBe coolant could not be utilized for reactivity control as a burnable absorber. The results found through this research provide reasonable guidelines for expected costs and narrow down the types of configurations that should be considered as fuel design options for the LSCR. Additionally, knowledge was gained on methods for modeling the system not only accurately but also efficiently to reduce the required computing power and time.

Thesis (MTech (Electrical Engineering))--Cape Peninsula University of Technology, 2017. / Fuel cell (FC) technology is one of the most sought-after renewable energy technology. However, the output voltage of FC stacks is inherently unstable; as such, it is of little or no use for most power supply applications. In addition to the unstable output voltage, FC stacks are susceptible to high current ripple, which can reduce the system’s life expectancy. The work carried out in order to stabilise the output voltage, and to reduce the current ripple of FC stacks involves a review of some existing converter topologies used for power conditioning units (PCUs), modelling, design, control and simulation of different converter topologies and the experiment of the prototype circuit for the interleaved boost voltage multiplier (IBVM) converter topology. In the process to stabilise the stack output voltage and to reduce the stack output current ripple, it is also required to improve the system response to load changes. This work presents results that show that system works, with the voltage stabilised, the stack output current ripple reduced and the response time reduced. A relative evaluation of the dynamic behaviour of four converter topologies in power conditioning units is carried out, and these are the isolated current-fed full-bridge (ICFFB) converter, the boost converter, the sepic converter and the IBVM converter. The simulation results of the four topologies show that the output voltage of a PEMFC stack was stabilised, and that the IBVM topology is a better topology compared to the others, especially when it comes to reducing the stack current ripple.

The present dissertation covers three research topics on catalytic environmental emissions control, including (1) aging and regeneration mechanisms of Rh- and Pd- model three-way catalysts (TWC) for gasoline automotive emission control, (2) catalytic methane emissions abatement from natural gas vehicles, and (3) scale-up of CO₂ capture and methanation using dual functional catalytic materials. The study resulted in two peer-reviewed publications, two future papers and one patent application which is currently under review. Modern TWC use supported two separate catalyst layers on a monolith containing one Pd and the other Rh for the emissions control of CO, HC and NOₓ. The rhodium (Rh) metallic component (active for NOₓ reduction) experiences the most severe oxidative thermal deactivation (forming inactive Rh³⁺) during fuel cutoff, an engine mode (e.g., at downhill coasting) used for enhancing fuel economy. In a subsequent switch to a slightly fuel rich condition, in situ catalyst regeneration is accomplished by the reduction of the Rh³⁺ with H₂ generated through steam reforming catalyzed by residual Rh⁰ sites. The present thesis reports the effects of the deactivation and regeneration processes on the activity, stability and structural properties of 0.5% Rh/Al₂O₃ and 0.5% Rh/Ce_xO_y-ZrO₂ (CZO) as model catalysts. Both materials are used to varying extents in modern TWC. A very brief introduction of three-way catalysis and system considerations will be presented. During simulated fuel cutoff, catalyst deactivation is accelerated with increasing aging temperature from 800 °C to 1050 °C. Rh on a CZO support experiences less deactivation and faster regeneration than Rh on Al₂O₃. Catalyst characterization techniques including BET surface area, CO chemisorption, temperature programmed reduction, and x-ray photoelectron spectroscopy, transmission electron microscopy, scanning-electron microscopy, and x-ray diffraction measurements were applied to examine the role of metal-support interactions in each catalyst system. For Rh/Al₂O₃, strong metal-support interactions leading to the formation of a stable rhodium aluminate (Rh(AlO₂)_y) complex dominates during fuel cutoff, resulting in more difficult catalyst regeneration (reduction). For Rh/CZO, Rh sites were partially oxidized to Rh₂O₃ and were relatively easy to be reduced to active Rh⁰ during regeneration. Moderate Pd and support sintering of Pd-Ce_xO_y is experienced upon aging, but with a minimal effect on the catalyst activity. Cooling in air, following aging, was not able to reverse the metallic Pd sintering by re-dispersing to PdO. Unlike the aged Rh-TWCs, reduction via in situ steam reforming (SR) of exhaust HCs was not effective in reversing the deactivation of aged Pd/Al₂O₃, but did show a slight recovery of the Pd activity when CZO was the carrier. The Pd⁺/Pd⁰ and Ce³⁺/Ce⁴⁺ couples in Pd/CZO are reported to promote the catalytic SR by improving the redox efficiency during the regeneration, while no such promoting effect was observed for Pd/Al₂O₃. A suggestion is made for improving the catalyst performance. The use of natural gas for vehicle applications is growing in popularity due to advanced fracking technology. Exhaust methane has been excluded from regulations since it does not participate in photochemical reactions. New vehicle environmental regulations are expected for controlling methane emissions given their contribution to the greenhouse gas effects. Methane is extremely resistant to oxidation when the natural gas-fueled engine operates in the stoichiometric mode with a supported Rh-Pd three-way catalyst (TWC). Furthermore, vehicles will still operate with fuel cutoff (for enhanced fuel economy), resulting in thermal oxidative deactivation (1050 °C) of the Rh metal in TWC to inactive Rh³⁺, resulting in a loss of both NOₓ and methane abatement activity. When the engine returns to the slightly rich mode, H₂ generated by methane steam reforming does not readily occur to reduce and regenerate the Rh. We report a solution to methane emissions abatement by catalytic reforming of an injected aqueous solution of ethanol into the simulated exhaust stream in TWC mode, which generates sufficient H₂ to regenerate especially Rh by reducing Rh³⁺ to its metallic active state. Conventional CO₂ capture and sequestration (CCS) in aqueous alkaline solutions is a very energy-intensive process with relative unstable performance and low efficiency especially for power plant effluents, and therefore there is a need for new approaches to control green house gas emissions of CO₂. Here we report on progress with an advanced technology involving CO₂ adsorption from flue gas and synthetic natural gas production, via methanation, both performed at the same temperature with the addition of renewable H₂ and by using a dual functional material (DFM). The stored H₂ used is produced by water electrolysis during those times when solar, wind, and other alternative energies generate excess power out of phase with the direct use of the electricity. The DFM is composed of nano-dispersed CaO (or Na₂CO₃) and Ru metal supported on γAl₂O₃ carrier, respectively functioning as the CO₂ adsorbent and methanation catalyst. The present paper focuses on a laboratory scale-up study by using a simulated flue gas and 5%Ru,10%CaO/Al₂O₃ and 5% Ru,10%Na₂CO₃/Al₂O₃ DFM samples. The effects of DFM preparation methods, Al₂O₃ carrier materials (with different shapes and properties), and adsorption and methanation conditions (feed compositions, flow rates, reaction temperatures) on the DFM performance were examined. Samples were prepared using chloride precursor salts and showed stable performance under pseudo scale-up conditions, with SASOL TH100 Al₂O₃ (with the highest BET surface area and pore volume/radius among the support materials) exhibiting the best performance. Compared to Ru-CaO, Ru-Na₂CO₃ based DFM materials showed improved CO₂ utilization and methanation production. Reaction conditions were explored to find optimized CO₂ adsorption and methanation.