http://hdl.handle.net/1721.1/7688 Sat, 18 May 2013 19:52:07 GMT 2013-05-18T19:52:07Z http://hdl.handle.net/1721.1/77067 Radial power flattening in sodium fast reactors Krentz-Wee, Rebecca (Rebecca Elizabeth) In order to improve a new design for a uranium startup sodium cooled fast reactor which was proposed at MIT, this thesis evaluated radial power flattening by varying the fuel volume fraction at a fixed U-235 enrichment of 18.5%. Of particular interest was how best to reduce the radial power peaking at the center of the reactor. Two cores were modeled: one with a uniform fuel volume fraction of 37% and one with fuel volume fractions which increased with the core radius. The ERANOS code was used to determine the power density, reactivity, and material values at the beginning and end of life. The varied fuel was shown to have a flatter radial power profile, but slightly lower reactivity and more mass. The power in each cell was normalized with respect to the average power; the peak power ratio in the uniform fuel volume core was 1.59, while the peak power ratio in the varied fuel volume core was 1.16, a significant improvement. The reactivity at beginning of life dropped from 12573.9 pcm to 11734.0 pcm, and stayed about 500pcm lower over the cycle, which is not a very large amount. The total mass of the heavy metals increased from the uniform core to the varied core by less than 0.9% and the mass of U-235 by 1.2%, so the varied fuel does not significantly impact the overall fuel cycle cost. Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Nuclear Science and Engineering, 2012.; "June 2012." Cataloged from PDF version of thesis.; Includes bibliographical references (p. 13). Sun, 01 Jan 2012 05:00:00 GMT http://hdl.handle.net/1721.1/77067 2012-01-01T05:00:00Z http://hdl.handle.net/1721.1/77065 Investigation into Greedy Exhaustive Dual Binary Swaps (GEDBS) for the optimization of core configuration in pressurized water reactors Hammond, Jessica L In order to promote nuclear power production as an attractive option for power generation, measures must be taken to ensure that the process is both safe and economical. One aspect of the nuclear fuel cycle that contributes significantly towards such goals is the management of the fuel. Proper fuel management within a reactor core requires an understanding of the trade-offs between maximizing the reactivity, while simultaneously minimizing the power peaking. To accomplish this, various algorithmic methods can be used to help determine the optimal arrangement of fuel bundles in the core. By exploiting innovative computational tools for the analyses of reactor cores, more accurate and precise calculations can be made, and nuclear power generation can continue to be safe and economical. While traditionally, heuristic algorithms have been used for these large optimization problems, more direct algorithms may have the potential to provide the most favorable configuration for the reactor core. The use of Greedy Exhaustive Dual Binary Swaps (GEDBS) was implemented for the optimization of the quarter-core of a reactor containing 193 fuel assemblies. The primary objective was to investigate the quality of the output from the GEDBS algorithm and to compare it to those of other algorithmic methods. In this way, conclusions could be made as to whether or not the end results from this exhaustive algorithm justified the added runtime associated with their use, and ultimately, help to determine its viability for future research. Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Nuclear Science and Engineering, 2012.; Cataloged from PDF version of thesis.; Includes bibliographical references (p. 38-40). Sun, 01 Jan 2012 05:00:00 GMT http://hdl.handle.net/1721.1/77065 2012-01-01T05:00:00Z http://hdl.handle.net/1721.1/77064 Critical assessment of thorium reactor technology Drenkhahn, Robert (Robert A.) Thorium-based fuels for nuclear reactors are being considered for use with current and future designs in both large and small-scale energy production. Thorium-232 is as abundant on Earth as lead, far more common than all isotopes of uranium, leading to its greatly reduced cost. Thorium itself offers a significantly greater neutron absorption cross-section than uranium at thermal energies, resulting in greater efficiency and smaller geometries. Certain thorium-based fuels can also significantly reduce proliferation by denaturing the thorium fuel cycle product U-233 (which is cause for proliferation concern) with U-236 and U-238. Several countries, including the USA, China, and India, are developing new conceptual designs which focus on the advantages offered by thorium. Thorium reactor technology today, as well as its practicality in the near-future, was surveyed to determine its potential for a major role in the nuclear power industry. Factors considered were economics, efficiency, waste, and proliferation. It is recommended that thorium-based fuels be further integrated in future reactor designs to take advantage of its numerous benefits in these areas. Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Nuclear Science and Engineering, 2012.; "June 2012." Cataloged from PDF version of thesis.; Includes bibliographical references (p. 31-32). Sun, 01 Jan 2012 05:00:00 GMT http://hdl.handle.net/1721.1/77064 2012-01-01T05:00:00Z http://hdl.handle.net/1721.1/76961 An evaluation of theories concerning the health effects of low-dose radiation exposures Wei, Elizabeth J. (Elizabeth Jay) The danger of high, acute doses of radiation is well documented, but the effects of low-dose radiation below 100 mSv is still heavily debated. Four theories concerning the effects of lowdose radiation are presented here: supra-linearity, linear-no-threshold (LNT), threshold, and hormesis. The available evidence for and against these theories, which falls into the categories of either epidemiological studies, in vitro cell experiments, or in vivo animal experiments, includes studies which support each of the four theories. Currently, all radiation risk estimates are based on an LNT interpretation of the life span study (LSS) of atomic bomb survivors in Japan. However, while this pattern is undisputed at high doses, this linear extrapolation of risk to low doses is challenged by many recent experiments involving cell mechanisms and animal models, and there is also high uncertainty involved in estimating risk using only epidemiological studies.. Variations have also been observed depending on dose-rate, the organ at risk, and other factors for which the current data cannot adequately account. While the evidence is still inconclusive, the existence of a threshold in human responses to low-dose radiation would drastically alter current guidelines, such as those currently restricting many people from returning to their hometowna in Fukushima, Japan. Thus, it is important to further investigate these low*dose responses in order to more fully describe the risks and to create more accurate radiation guidelines. Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Nuclear Science and Engineering, 2012.; "June 2012." Cataloged from PDF version of thesis.; Includes bibliographical references (p. 50-55). Sun, 01 Jan 2012 05:00:00 GMT http://hdl.handle.net/1721.1/76961 2012-01-01T05:00:00Z