http://hdl.handle.net/1721.1/7856 2013-06-19T16:58:35Z http://hdl.handle.net/1721.1/79032 Development of a core design optimization tool and analysis in support of the planned LEU conversion of the MIT Research Reactor (MITR-II) Connaway, Heather M. (Heather Moira) The MIT Research Reactor (MITR-II) is currently undergoing analysis for the planned conversion from high enriched uranium (HEU) to low enriched uranium (LEU), as part of a global effort to minimize the availability of weapons-grade uranium. In support of efficient fuel management analysis with the new LEU fuel, a core design optimization tool has been developed. Using a coarse model, the tool can quickly consider the large range of refueling options available, and identify a solution which minimizes power peaking with the least fuel shuffling possible. The selected scheme can then be examined in greater detail with a more robust simulation tool. The unique geometry of the MITR core makes it difficult to develop a model that both runs very quickly and provides detailed power distribution information. Therefore, a correlation-based approach has been employed. Relationships between burnup, critical control blade position, core Um mass, and power distribution are used to predict fuel element U²³⁵ depletion, critical control blade motion, and power peaking. The tool applies the correlations to identify an optimal loading pattern, defined as the core which has the lowest maximum radial peaking factor in the set of valid solutions with the minimum number of fuel shuffling actions. The correlations that are utilized by the optimization tool were developed using data from simulations with MCODE-FM, a fuel management wrapper for the MCNP-ORIGEN linkage code MCODE. The correlations have been verified with results from additional MCODE-FM runs, and the code logic has been verified with the core loading solutions for a variety of input parameters. The verification found that the code is able to predict radial peaking, core mass, and general control blade motion with sufficient accuracy to develop a good refueling scheme. The tool provides the output solution in an interactive format, which allows the user to quickly examine small perturbations on the identified loading pattern. In addition to the optimization tool development, loading patterns for the mixed HEU-LEU fuel transition cores have been evaluated. This analysis identified general behavioral trends of the mixed-fuel cores, which serve as an initial basis for future transition core analysis. Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Nuclear Science and Engineering, 2012.; Cataloged from PDF version of thesis.; Includes bibliographical references (p. 100-101). 2012-01-01T00:00:00Z http://hdl.handle.net/1721.1/79029 Design and testing of an electron cyclotron resonance heating ion source for use in high field compact superconducting cyclotrons Artz, Mark E The main goal of this project is to evaluate the feasibility of axial injection of a high brightness beam from an Electron Cyclotron Resonance ion source into a high magnetic field cyclotron. Axial injection from an ion source with high brightness is important to reduce particle losses in the first several turns of acceleration within the cyclotron. Beam brightness is a measure of the beam current and rate of spread of the beam. The ultimate goal in developing an ECR ion source is to enable reduced beam losses along the entire acceleration path from the ion source through the cyclotron, allowing for a high beam current accelerator. Cyclotrons with high beam current have the potential to improve the availability of proton radiation therapy. Proton radiation therapy is a precisely targeted treatment capable of providing an excellent non-invasive treatment option for tumors located deep within tissue. In order to model injection into high field it is necessary to measure the parameters of the beam extracted from the ion source. The two most important beam parameters are emittance and beam current. The emittance of the beam is a measurement of the rate of beam spread along the path of the beam and beam current is a measurement of the energy and quantity of particles within a charged particle beam. This thesis presents the design and analysis of an ECR Ion Source and the instruments used to measure the emittance and beam current. Based on the modeling of the ECR ion source beam and the data gathered during testing, the ECR ion source presented in this thesis has the potential to provide a high brightness beam capable of high field axial injection. Beam simulations provide insight into the performance of the ECR ion source in high magnetic field. Axial beam injection from an external ion source is promising with moderate refinements to the ECR ion source. Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Nuclear Science and Engineering, 2012.; Cataloged from PDF version of thesis.; Includes bibliographical references (p. 78-82). 2012-01-01T00:00:00Z http://hdl.handle.net/1721.1/78208 Separate effects of surface roughness, wettability and porosity on boiling heat transfer and critical heat flux and optimization of boiling surfaces O'Hanley, Harrison Fagan The separate effects of surface wettability, porosity, and roughness on critical heat flux (CHF) and heat transfer coefficient (HTC) were examined using carefully-engineered surfaces. All test surfaces were prepared on nanosmooth indium tin oxide - sapphire heaters and tested in a pool boiling facility in MIT's Reactor Thermal Hydraulics Laboratory. Roughness was controlled through fabrication of micro-posts of diameter 20[mu]m and height 15[mu]m; intrinsic wettability was controlled through deposition of thin compact coatings made of hydrophilic SiO₂ (typically, 20nm thick) and hydrophobic fluorosilane (monolayer thickness); porosity and pore size were controlled through deposition of layer-by-layer coatings made of SiO₂ nanoparticles. The ranges explored were: 0 - 15[mu] for roughness (Rz), 0 - 135 degrees for intrinsic wettability, and 0 - 50% and 50nm for porosity and pore size, respectively. During testing, the active heaters were imaged with an infrared camera to map the surface temperature profile and locate distinct nucleation sites. It was determined that wettability can play a large role on a porous surface, but has a limited effect on a smooth non-porous surface. Porosity had very pronounced effects on CHF. When coupled with hydrophilicity, a porous structure enhanced CHF by approximately 50% - 60%. However, when combined with a hydrophobic surface, porosity resulted in a reduction of CHF by 97% with respect to the reference surface. Surface roughness did not have an appreciable effect, regardless of the other surface parameters present. Hydrophilic porous surfaces realized a slight HTC enhancement, while the HTC of hydrophobic porous surfaces was greatly reduced. Roughness had little effect on HTC. A second investigation used spot patterning aimed at creating a surface with optimal characteristics for both CHF and HTC. Hydrophobic spots (meant to be preferential nucleation sites) were patterned on a porous hydrophilic surface. The spots indeed were activated as nucleation sites, as recognized via the IR signal. However, CHF and HTC were not enhanced by the spots. In some instances, CHF was actually decreased by the spots, when compared to a homogenous porous hydrophilic surface. Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Nuclear Science and Engineering; and, (S.B.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2012.; Cataloged from PDF version of thesis.; Includes bibliographical references (p. 157-161). 2012-01-01T00:00:00Z http://hdl.handle.net/1721.1/77084 Mitigation of RF sheaths through design and implementation of magnetic field-aligned ICRF antenna Garrett, Michael Lane In ITER and in eventual reactors, enhanced impurity confinement due to internal transport barriers (ITBs) and H-mode operation establishes a very low tolerance for high-Z impurities [1]. Experiments have shown that impurity accumulation increases as power in the ion cyclotron range of frequencies (ICRF) is increased [2]. As a result, one of the primary challenges of ICRF heating is the reduction or elimination of impurities introduced into the plasma during ICRF operation, particularly for tokamaks with high-Z plasma facing components (PFCs). Plasma impurities associated with ICRF auxiliary heating are universally observed [3, 4, 5, 6]. However, the underlying physics of ICRF-specific impurity generation is not well understood, and observations of impurity characteristics differ among various tokamak experiments. Several methods have been proposed to reduce ICRF-specific impurity characteristics: low-Z PFC coatings such as boronization [7]; toroidal phasing of antenna straps [3]; and alignment of antenna Faraday screen elements with the total magnetic field [8]. On Alcator C-Mod we have designed a new magnetic field-aligned ICRF antenna to minimize ICRF-specific impurity characteristics. The field-aligned antenna is rotated 100 from horizontal, such that the antenna straps are perpendicular to the total magnetic field at the edge for a typical plasma discharge (BT ~ 5.4 T, 1, ~ 1 MA). ICRFinduced E-parallel is a likely candidate for producing enhanced sheath voltages that lead to greatly increased sputtering of material surfaces and enhanced impurity edge transport. Initial simulations performed using both slab and cylindrical geometry suggested nearly complete cancellation of E-parallel in front of the antenna structure for certain toroidal phasings. Using toroidal models, the cancellation of E-parallel is more modest, suggesting 3-D geometrical effects are important. Multiple antenna phases were analyzed for the field-aligned antenna using finite element method with a 3-D toroidal cold plasma model. In each case, the field-aligned antenna had reduced integrated E-parallel relative to the existing non-aligned antenna geometry, with the greatest reduction for monopole [0, 0, 0, 0] phasing. Initial results suggest that the field-aligned antenna operation results in fewer impurities in the plasma than conventional antennas. Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Nuclear Science and Engineering, 2012.; Cataloged from PDF version of thesis.; Includes bibliographical references (p. 133-138). 2012-01-01T00:00:00Z