<p> The unique features of the Interrupted Thorium Cycle owing to Pa-233 have been examined including possible implications for practical implementation of the cycle. Generalized trajectories for the fuel inventories of fusion-fission symbionts are derived through a comprehensive parametric analysis. The resultant formulations are then applied to a specific example. It is concluded that this formulation and analysis leads to more exact fissile and fusile fuel characterizations than suggested by conventional procedures. </p> / Thesis / Master of Engineering (MEngr)

<p>A study was conducted to scope the relative merits of various thorium fuel cycles in CANDU reactors. It was determined that, due to the very large reprocessing demands of the self-sustaining equilibrium thorium fuel cycle, an additional fissile driver fuel is required for a practical thorium fuel cycle. The driver fuels considered were PWR- and CANDU- derived plutonium, PWR-derived MOX fuel, and low-enriched uranium. The addition a RU-fuelled CANDU reactor with possible americium, curium, and lanthanides recycling was also considered. The fuel cycles were evaluated for natural uranium consumption and reprocessing demands as well as spent fuel characteristics such as: thermal and gamma power, radioactivity, and ingestion and inhalation hazards.</p> <p>The two-dimensional multigroup code, WIMS-AECL, was used to calculate the burnup and some controllability properties of the CANDU reactors. ORIGEN, a depletion and decay module, was used to evaluate the spent fuel characteristics and the systems code, DESAE, was used to simulate the introduction of the thorium fuel cycle to a growing global reactor park.</p> <p>It was determined that ²³³U production in the thorium fuels is optimized at lower exit burnups. Therefore, less external fissile driver material is required for the operation of the thorium reactors and natural uranium savings of the overall fuel cycle are increased. Furthermore, it was determined that driving the thorium fuel cycle with low-enriched uranium is the most efficient way to minimize natural uranium consumption. Assuming that a 40 MWd/kg exit burnup was achieved in the CANDU reactors, the fuel cycle yielded an 82% savings of natural uranium, compared to a scenario in which all power came from PWRs, while a 20 MWd/kg exit burnup increased the savings to 94%. The savings ranged over those exit burnups from 55%-69% for the variant with PWR-derived plutonium, 60%-73% for PWR-derived MOX fuel, and 78%-87% for CANDU-derived plutonium. The thermal power, radioactivity, and health hazards of the spent fuel were the highest for the case with MOX fuel driver but americium recycling proved effective for decreasing the long term dangers. In a global reactor park, the introduction of the thorium fuel cycle was hampered by the availability of fissile resources and, for a PWR-derived driver, natural uranium consumption was only reduced by 22% over 100 years relative to the PWR only scenario.</p> / Master of Applied Science (MASc)

The purpose of this research is to develop a methodology for a thorium fuel recycling analysis that provides results for isotopics and radio-toxicity evaluation and analysis. This research is motivated by the need to reduce the long term radiological hazard in spent nuclear fuel, which mitigates the mixing hazard (radiotoxicity and chemical toxicity) and decay heat load on the repository. The first part of the thesis presents comparison of several once-through cases with uranium and thorium fuels to show how transuranics build up as fuel is depleted. The once-through analysis is performed for the following pairs of comparison cases: low enriched uranium dioxide (UOX) vs. thorium dioxide with 233UOX (233U-ThOX), natural uranium dioxide mixed with transuranic oxides (U-TRUOX) vs. thorium dioxide mixed with transuranic oxides (Th-TRUOX), natural uranium dioxide mixed with weapons grade plutonium dioxide (U-WGPuOX) vs. thorium dioxide mixed with weapons grade plutonium dioxide (Th-WGPuOX), natural uranium dioxide mixed with reactor grade plutonium dioxide (U-RGPuOX) vs. thorium mixed with reactor grade plutonium dioxide (Th-RGPuOX). The second part of the research evaluates the thorium fuel equilibrium cycle in a pressurized water reactor (PWR) and compares several recycling cases with different partitioning schemes. Radio-toxicity results of the once-through cycle and multi-recycle calculations demonstrate advantages for thorium fuel and reprocessing with respect to long term nuclear waste management.

One of the proposed solutions to the issue of nuclear waste volume is to transition from once through nuclear fuel cycle to advanced fuel cycles with used fuel recycling option. In any advanced fuel cycles with recycling options, the type and amount of separation technology deployed play a crucial role in the overall performance of the fuel cycle. In this work, a scenario study involving two advanced fuel cycles in addition to the once through fuel cycle were evaluated using VISION nuclear fuel cycle simulation code. The advanced fuel cycles were setup to transition completely to full recycling without any light water reactor by assuming all LWR currently in operation will have 20 years of operating life extension and no new LWR will be constructed thereafter. Several different separation capacities (1kT/yr, 2kT/yr and 4 kT/yr) were deployed and the overall impact of these capacities was analyzed in terms of resources utilization, used fuel and waste material generated and the amount of storage space required. Economic parameter (LCOE, LFCC, etc) analysis was also performed using VISION.ECON. Results presented in this work suggest that the need for LWR-UNF storage can be minimized if sufficient separation capacity is deployed early in the fuel cycle. It can also be concluded that a FuRe system without LEU will not be feasible, thus SFRs must be designed for optional use of LEU fuel. Otherwise LWRs must continue to be part of the mix to keep the near term cost of generating electricity competitive. It was observed that the higher amount of separation capacity deployed in the advanced fuel cycles led to higher LFCC and LCOE, but also translates into less environmental impact on both front and back end of the fuel cycle.

This Master’s thesis deals with optimization of loading patterns of nuclear reactors VVER. In the thesis is described the process of both types of fuel cycle – the closed and the open one. The middle part of fuel cycle containing the optimization process represents the crucial part of the thesis. The thesis is focused on the fuel cycles of the nuclear power plant Dukovany. The problem of the optimization is solved by using different programs. In the final part of the thesis, the program Athena for the loading patterns optimation is explained by a practical calculation for different versions of Moby-Dick macrocode and the calculated values for the optimization of the third unit of the nuclear power plant Dukovany are compared.