Fuels comprised of the element thorium have become increasingly popular with researchers and the public as the next generation fuel due to its ability to produce its own fissile element (U-233) and generate lower concentrations of heavy actinides. The use of thorium can possibly lead to a self-sustaining cycle whereby the addition of fissile material is not required and that the fuel can breed sufficient amounts of U-233 for a continuous supply. Research into thorium use in CANDU reactors has mainly been focused on using driver elements such as U-235 or Pu-239 to initiate the nuclear reaction by taking advantage of bundle design or by mixing the thorium and driver fuel together; however, these methods have added complexities and may not lead to a pure thorium fuel cycle, but extend the life of current nuclear fuels used. This thesis will investigate a simpler means of utilizing thorium for the intent of breeding U-233 through the use of pure thorium bundles in a once-through cycle by the ways of a heterogeneous core loading in a CANDU-6 reactor model. A 3x3 multi-cell model using DRAGON 3.06K will simulate the dual fuel model by having the centre lattice enclosing the thorium bundle and the outer eight lattices enclosing the enriched uranium bundles as the driver fuel. Next, the diffusion code DONJON 3.02E is used to produce time-average, instantaneous, and initial startup full-core simulations. As well, a brief look at the refuelling operations on the thorium channels will be done. The presence of a thorium bundle places a negative reactivity load on the multi-cell, but causes a positive insertion of reactivity for a coolant void and shutdown scenario. In the full-core modelling, the final core configuration chosen shows that thorium channels should be located in the inner core rather than in the most outer channels to produce a flattening effect on the radial profile. Thorium channels will require a combination of SEU and thorium bundles in an attempt to maintain channel power levels. Specifically, the use of 4, 6, or 8 Th bundles were investigated. The most optimal core performance shown has a radial form factor of 0.816, a total average core burnup of 18.32 GWd/t, and operates within designed power limits. It is possible to implement pure thorium bundles into a reactor set in a dual fuel mode. A careful consideration of where thorium bundles should be located in the core can help flatten the radial power distribution and help the reactor operate within the operating licensing parameters without the use of adjuster rods while breeding U-233 for a future thorium fuel cycle. / Thesis / Master of Applied Science (MASc)

Nuclear power plants provide about 11 percent of the world's electricity production. For fission process is uranium fuels used with varying percentage of enrichment 235U for most of nuclear reactors. Uranium reserves are reducing and their mining cost increases. Therefore, the thorium fuel is discussed as revolution fuel for current and future nuclear power plants. This diploma thesis deals with possibility of thorium fuel utilization at various types of nuclear reactors with a focus on light water reactors. The practical part of the thesis is focused on simulation and calculations of various uranium dioxide and thorium dioxide layers at the fuel rods. Model of WWER 440 reactor was developed for the calculations with the addition of thorium fuel. The model simulates burning out of fuel for 5 years, with monitoring of fuel behavior and tracking changes of each material. The thesis tries to define the suitable ratio and parameters of layers combination of uranium and thorium fuel. For these ratios and parameters the thesis tries to give sufficient amount of computational analyzes.

Global climate is controlled by two factors, the amount of heat energy received from the sun (solar insolation) and the way that heat is distributed Earth's surface. Solar insolation varies on timescales of 10s to 100s of thousands of years due to changes in the path of Earth's orbit about the sun (Milankovitch cycles). Earth's internal boundary conditions, such as paleogeography, the presence/absence of polar icecaps, atmospheric/oceanic chemistry and sea level, provide distribution and feedback mechanisms for the incoming heat. Variations in these internal boundary conditions may happen abruptly or, as in the case of plate tectonics, take millions of years. We use geochemical and sedimentological techniques to investigate the response of ocean chemistry, regional aridity and atmospheric and oceanic circulation patterns to climate change during both greenhouse and icehouse climates. To explore the connection between orbitally-forced changes in solar insolation, continental aridity and wind, we generated a high-resolution dust record for ~58 Myr old deep-sea sediments from Shatsky Rise. Our data provide the first evidence of a correlation between dust flux to the deep sea and orbital cycles during the Early Paleogene, indicating dust supply (regional aridity) responded to orbital forcing during the last major interval of greenhouse climate. The change in dust flux was comparable to that during icehouse climates implying subtle variations in solar insolation have a similar impact on climate during intervals of over-all warmth as they do during glacial-interglacial states. The Carboniferous Period (359-299 Ma) marks a critical time in Earth's history when a series of tectonic and biological events caused a shift in the mean climate state from a global "greenhouse" to an "icehouse". Geochemical records extracted from sedimentary rocks deposited in shallow epicontinental seaways are increasingly being used to infer relationships between tectonism, carbon cycling and climate and therefore are assumed to reflect global ocean processes. We analyzed radiogenic isotopes in biogenic apatite along a North American transect to constrain the degree of geochemical coupling between the epicontinental seas and the open ocean. Our results argue strongly for decoupling of North American seaways from the open ocean by latest Mississippian time.