Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Nuclear Engineering, 1985. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND SCIENCE. / Bibliography: leaves 267-269. / by Mushtaq Ahmad Malik. / Ph.D.

Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Nuclear Engineering, 1983. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND SCIENCE / Includes bibliographical references. / by Hussein Shoukry Khalil. / Ph.D.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Nuclear Engineering, 2003. / Includes bibliographical references (119-121). / This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections. / Alfvén eigenmodes that exist in the shear Alfvén continuum of toroidal magnetic fusion devices may be important for the confinement of energetic particles, particularly fusion-born alpha particles in burning plasma experiments. Interaction between these energetic particles and weakly damped toroidal Alfvén eigenmodes (TAE's) may cause anomalous particle transport leading to incomplete thermalization and possible first wall damage. These consequences must be avoided in next step burning plasma devices and thus an investigation into the stability of TAE's in present machines un- der reactor-like conditions is essential. Measurement of the damping rate of TAE's will provide insight into this area of research. The investigation of TAE's on Alcator C-Mod is accomplished by employing the recently completed Active MHD Spectroscopy system. Antennas mounted inside the C-Mod vacuum vessel are driven by a high power amplifier in the TAE range of frequencies and excite modes inside the plasma. Magnetic fluctuation diagnostics provide the plasma response to this excitation. The damping rate is then calculated from the complex transfer function between the antenna current and plasma response signals. / by David Anthony Schmittdiel. / S.M.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Nuclear Engineering, 2003. / Includes bibliographical references. / It is widely recognized that the behavior of actinides in the environment is dictated by their speciation, or chemical form. It is therefore imperative to have a clear understanding of a waste form or environmental contaminant in order to effectively assess and treat the affected area. Current methodology utilizes the distribution coefficient (Kd), a rough measure of contaminant mobility in environmental systems, however neither the empirical nor theoretical determination of Kd is well defined. Although we understand the limitation of the Kd parameter, the reality is that the Kd is often the only parameter used in environmental fate and transport models to account for the mobile fraction of contaminate in predicting total risk. A fresh approach to the problem incorporating speciation that can be applied to a wide range of conditions is required. X-ray absorption spectroscopy (XAS), a nondestructive technique that is ideal for determining the molecular composition of materials in dilute quantities in solution and solid forms, was used to determine the speciation of actinides in various solid nuclear materials including nuclear fuel, environmental contaminants, and advanced nuclear materials. This data could then be applied to individual systems to evaluate the environmental impact of the material via empirical or theoretical modeling. The fuels examined include Th₃UO₈, UC and a mixture of UC and US. In addition, an actual contaminant, metallic uranium-bearing samples recovered from the environment several decades after their accidental formation, was evaluated. / (cont.) The technique was also used to determine the structure of actinide templated resins and evaluate their reusability, and to look at the mechanism of uranium sorption to the metal reducing bacteria Shezoanella oneidensis. The results show that current methods for evaluating actinide transport/solubility in the environment do not accurately predict the empirical results. Our speciation method is shown to produce equilibrium data that can be used to develop more accurate Kd determination and to validate environmental models. This combination of empirical laboratory methods and speciation modeling improves upon current environmental remediation methods, and provides an improvement over direct K determinations. The method can also be used with advanced remediation techniques to target the critical actinide chemical forms that require treatment. / by Virginia Curran. / Ph.D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Nuclear Engineering, 2004. / Includes bibliographical references (p. 122-125). / An in vivo boron-10 screening technique was developed to analyze the boron biodistribution in a rabbit knee for the pre-screening of compounds for Boron Neutron Capture Synovectomy (BNCS). Three approaches were investigated: emission computed tomography (ECT), transmission computed tomography (TCT) and in vivo prompt gamma neutron activation analysis (IVPGNAA). Each was first studied using simulation-generated projection data. Experimental data collection systems were then constructed for TCT and IVPGNAA, and phantom experiments were conducted at the MIT Research Reactor (MITR) to verify simulation results. While TCT was predicted to have superior performance in terms of spatial resolution, temporal resolution and boron quantification, IVPGNAA was chosen for further development given the readily available neutron sources at the MITR. Assuming an 8.5x105 cm-2s-1 incident neutron flux, a 3.5mmx20mm beam, and a knee injection of 1.05mg 10B, one projection data set can be collected within 12 minutes, for reconstruction of relative 10B distribution in eight 40mm2 regions. The estimated uncertainty associated with reconstructed results, assuming a regional 2000 ppm concentration, is [approx.] 25%. Phantom experiments demonstrated the overall feasibility of IVPGNAA as a means of conveniently evaluating spatial and temporal characteristics of 10B in a rabbit knee. / (cont.) Animal experiments were then conducted at the MITR using 3.5kg anesthetized arthritic rabbits. Three boronated compounds were investigated, each with widely different in vivo spatial and temporal characteristics, as determined previously via dissection studies. Good agreement in egression behavior between IVPGNAA predictions and dissection study results was found for 2 compounds. The third compound was not detectable under experimental conditions, suggesting the possibility that the compound was not taken up by the synovium. This finding was consistent with the dissection study results. IVPGNAA is an invaluable tool for early rejection of compounds with poor characteristics, and can provide guidance for dissection studies of promising compounds. / by Xuping Zhu. / Ph.D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Nuclear Engineering, 2002. / "September 2002." / Includes bibliographical references (p. 235-244). / Decision making as a part of nuclear power plant operations is a critical, but common, task. Plant management is forced to make decisions that may have safety and economic consequences. Formal decision theory offers the potential for a structured approach capable of taking into account risk-related aspects (plant and worker safety, for instance) and, at the same time, important factors like economics and regulatory requirements. Since power generation involves large capital and operational costs, making the decision process more efficient can lead to significant economical savings. With millions of dollars at stake, it is imperative that operational decisions be made in a logical and consistent fashion. In addition to the monetary concerns, a primary driver for this work is the desire to make defensible decisions. Within a structured organization like a nuclear power plant, a variety of interactions take place between groups of decision makers. These groups are asked to provide guidance on a variety of issues, ranging from complex regulatory requirements to planning maintenance activities of standby equipment. By providing an integrated package for decision making, it is believed that tools like the plant risk assessment can be used in a defensible manner as part of the day-to-day operation of the facility. The goal of this report is to describe a decision methodology for nuclear power plant incidents. Here, incidents are categorized as plant upsets that are not serious challenges to plant safety, but nonetheless require an appropriate response. / (cont.) As part of this decision methodology, risk assessment, worker safety, economics, preferences, and formal decision making models make up the foundation. We describe the construction, analysis heuristics, and inherent uncertainty of these models. From this methodological framework, we developed a prototypical on-line advisory tool that provides decisional advice relevant to incident management. The capabilities of this prototype are discussed along with a demonstration via case studies. / by Curtis Lee Smith. / Ph.D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Nuclear Engineering, 2002. / Includes bibliographical references (p. 157-171). / Fuel performance models have been developed to assess the performance of ThO₂-UO₂ fuels that can be operated to a high burnup up to 80-100MWd/kgHM in current and future Light Water Reactors (LWRs). Among the various issues raised in high burnup fuel applications, the pellet rim effect, fission gas release (FGR), and response to reactivity initiated accidents (RIA) were of special interest in this work. These phenomena were modeled by modifying the NRC licensing codes FRAPCON-3 for normal operation and FRAP-T6 for transient conditions. These models were verified and compared to the results of previous thorium fuel studies and high burnup uranium fuel evaluations. The buildup of plutonium in the outer rim of LWR UO2 pellets has been observed to create a region of high fuel burnup, fission gas buildup and high porosity at the fuel rim. The power distribution of the thoria and urania fuel was calculated using a neutronics code MOCUP. Due to the lower build-up of Pu-239 (less U-238 in ThO₂-UO₂ fuel) and flatter distribution of U-233 (less resonance capture in Th-232), thoria fuel experiences a much flatter power distribution and thus has a less severe rim effect than UO₂ fuel. To model this effect properly, a new model, THUPS (Thoria-Urania Power Shape), was developed, benchmarked with MOCUP and adapted into FRAPCON-3. Additionally a porosity model for the rim region was introduced at high burnup to account for the larger fuel swelling and degradation of the thermal conductivity. The mechanisms of fission gas release in ThO₂-UO₂ fuel have been found similar to those of U0₂ fuel. Therefore, the general formulations of the existing fission gas release models in FRAPCON-3 were retained. / (cont.) However, the gas diffusion coefficient in thoria was adjusted to a lower level to account for the smaller observed gas release fraction in the thoria-based fuel. To model accelerated fission gas release at high burnup properly, a new athermal fission gas release model was developed. Other modifications include the thoria fuel properties, fission gas production rate, and the corrosion model to treat advanced cladding materials. The modified version of FRAPCON-3 was calibrated using the measured fission gas release data from the Light Water Breeder Reactor (LWBR) program. Using the new model to calculate the gas release in typical PWR hot pins gives data that indicate that the ThO₂-UO₂ fuel will have considerably lower fission gas release beyond a burnup of 50 MWd/kgHM. Investigation of the fuel response to an RIA included: (1) reviewing industry simulation tests to understand the mechanisms involved, (2) modifying FRAP-T6 code to simulate the RIA tests and investigate the key contributors to fuel failure (thermal expansion, gaseous swelling, cladding burst stress), and (3) assessing thoria and urania performance during RIA event in typical LWR situations. ThO₂-UO₂ fuel has been found to have better performance than U0₂ fuel under RIA event conditions due to its lower thermal expansion and a flatter power distribution in the fuel pellet (less power and less fission gas in the rim region). Overall, thoria has been found to have better performance than urania in both normal and off-normal conditions. However, calculations using the modified FRAPCON-3 ... / by Yun Long. / Ph.D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Nuclear Engineering, 2003. / Includes bibliographical references (p. 166-179). / Hydrogenic resonance line radiation interacts with the high-density low-temperature plasma at the tokamak edge. As a result, there exists a significant nonlocal plasma energy transport channel, local atomic level populations are altered by global plasma properties, and plasma transport is affected. In this dissertation, new theoretical and computational models of partially ionized plasma transport, which include line radiation interactions, are developed and then applied to the study of plasma phenomena at the tokamak edge. First, to include the effects of an external magnetic field on nonlocal thermodynamic equilibrium (NLTE) mlodels, TotalB, a computationally efficient spectral line shape code that describes the broadening of radiative transitions due to an applied magnetic field, the ion microfield, and electron perturbers, is developed using standard line broadening theory. Second, to enable the study of plasma transport and line radiation interactions, PIP, a partially ionized plasma transport model that includes the charge-exchange coupling of ions with neutral atoms, the transport of potential energy, the effects of resonance line radiation interactions on atomic rates, and the transport of an arbitrary number of atomic levels, is developed and coupled with an existing NLTE radiation transport model. Finally, the combined capabilities model is applied to the simulation of a tokamak divertor and the significant effect of line radiation interactions on plasma transport at the tokamak edge is demonstrated. In addition, since the solution of the radiation field is an integral part of the calculation, several spectroscopic diagnostic techniques are developed. / by Mark Lloyd Adams. / Ph.D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Nuclear Engineering, 2002. / Includes bibliographical references. / The production of clinically sufficient dose rates in Accelerator-based Neutron Capture Therapies (ABNCT) requires targets that can withstand ion beams of 2-10 kW or higher. Designing such a target requires knowledge of the current density profile which can exceed 1 mA/cm². A method has been developed to quantify the two-dimensional current intensity by utilizing the positrons emitted from the products of either the ¹²C(d,n) or ¹¹B(p,n) reaction. A desktop scanner was used to convert the dose profile measured with MD-55-2 radiochromic film into a map of beam current intensity. Analytic calculations coupled with Monte Carlo methods determined the resolution of this technique to be 0.22±0.01 mm. Liquid gallium metal was investigated as a possible coolant. Qualitative and quantitative comparisons between single submerged impinging jets of liquid gallium and water at low flowrates were supplemented with computational fluid dynamics. Experiments using an array of submerged jets were conducted to determine area-averaged Nusselt number correlations for water and gallium over a Reynolds number range of 7000<Re<38000. The spreading factor, β[sub]max, was introduced into the gallium correlation to account for surface wetting effects. Area-averaged heat transfer coefficients, h, produced by an array of gallium jets were found to exceed those of water for Re>13500. At a Reynolds number of 35000 an h of 10⁵ W/m²K was measured with the gallium array compared to 5.5xlO⁴W/m²K for water. Simulations of the thermal and mechanical stresses found that a gallium-cooled beryllium target could withstand beam powers of up to 20.2 kW. / (cont.) Because of its low melting-point, lithium targets were able to achieve 10 kW only if the beam power density was kept below 11.6 MW/m². No significant difference in figures of merit used to characterize neutron beams for ABNCT were found when water was replaced by liquid gallium as the cooling fluid. / by Brandon William Blackburn. / Ph.D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Nuclear Engineering, 2002. / Includes bibliographical references (leaves 69-74). / This thesis reports on the first measurement of the spin diffusion rate of a two-spin correlated state, known as dipolar order, in a single crystal of calcium fluoride. The experimental results for the component of the spin diffusion rate parallel with the azimuthal axis are ... for the [001] direction and ... for the [111] direction. These rates are significantly faster than those for Zeeman order and are also faster than theories have predicted. The standard method of measuring diffusion in magnetic resonance is to encode a spatial modulation of magnetization in a sample and then measure it's attenuation over time. The difficulty in measuring spin diffusion in solid crystals by these scattering methods is that the spin diffusion rate is very slow (of order 1 x 10⁻¹² cm²/s) and hence the displacement of coherence is very small. The experimental challenge for probing these dynamics is that a modulation must be created with a wavelength on these length scales. To perform the measurement a special probe was developed with a gradient coil constant of 370±10.5[G/cmA]. A special holder was designed for holding the 1mm³ sample in addition to a gradient switcher for switching pulsed currents through the coil. The peak pulsed gradient strengths ranged from 28 to 85 T/m and the spatial wavelengths generated ranged from 1[mu] to 0.5 [mu]/tm. / (cont.) Additional work focuses on correcting for finite pulse widths effects, phase transients and other pulse errors in a time-reversal multiple-pulse cycle known as the magic-echo sequence. The highest resolution achieved was a line-width of 0.5 Hz in a single crystal of calcium fluoride whose natural line-width was approximately 45 kHz, a reduction by 5 orders of magnitude. A phase alternating scheme for generating and detecting high order n-spin azimuthal spin correlations ... was also investigated. The relaxation times of 2, 3 and 4 spin correlations were was found to be comparable to that of dipolar order. / by Gregory Steven Boutis. / Ph.D.