Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Nuclear Engineering, 1998. / Includes bibliographical references (leaves 89-90). / This thesis investigates alternate methods of controlling the vertical position of the plasma in the ALCATOR C-Mod Tokamak. The purpose of this work is to examine alternative methods of controlling the plasma position that can be adopted to improve performance over the current system, which uses a proportional-derivative (PD) control system actuated through a pair of outboard equilibrium field coils (EFC). The first part of this investigation examines the possibility of using inboard ohmic heating coils (OH2) as the controlling coils. A coupling transformer was designed to connect a large amperage/low bandwidth power supply to a small amperage/high bandwidth power supply, removing the need for an expensive large and fast power supply. Both PD control laws and full state feedback laws were also compared for performance. A rigid displacement model of the plasma motion was developed that took into account a model of induced currents in the vacuum vessel and coils. The results of the analysis concluded that there were moderate speed advantages to using state feedback on The OH2 coils, but these were outweighed by the robust operation of EFC PD control. No design achieved a decisive margin of improvement over the current control system. / by ENS George Hugh Miller, USN. / S.M.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Nuclear Engineering, 1998. / Includes bibliographical references (leaves 90-93). / by Shantel M. Utton. / S.M.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Nuclear Engineering, 1998. / Includes bibliographical references (leaves 62-65). / Use of the ⁹Be(d,n) nuclear reaction for accelerator-based boron neutron capture therapies (AB-BNCT) was investigated. The moderated neutron spectra produced at several deuteron bombarding energies were evaluated in terms of dose rates and dosimetric profiles in a water-filled brain phantom using an existing heavy water moderator and lead reflector assembly. Dosimetry results were obtained using the dual ionization chamber technique coupled with bare and cadmium-covered gold foils. Data have been taken with deuteron beams of 1.3 MeV to 1.8 MeV. As deuteron energy was increased, the tumor dose rate correspondingly improved due to the neutron yield increase. However, the data suggest that the advantage depth decreased, and the ratio of the fast neutron dose rate to the thermal neutron dose rate at a depth of I cm increased, although error bars are significant. All deuteron energies investigated produced a beam that, once moderated, appears viable for AB-BNCT. No conclusion was drawn about the best energy in terms of a high tumor dose rate, a significant advantage depth, and a low fast to thermal neutron dose rate ratio. Treatment times assuming 20 Gy to a tumor located 4 cm deep using a 4 mA accelerator ranged from 18 - 59 minutes, assuming a tumor boron concentration of 40 ppm and RBE values of 1.0 for photons, 3.2 for neutrons, and 3.8 for boron in tumor tissue. The average advantage depth was 6.4 ± 0.7 cm, so these moderated beams could be used to treat tumors near the brain centerline. The ⁹Be(d,n) nuclear reaction is exothermic, and is accessible to inexpensive, small particle accelerators. / by Susan Marie White. / S.M.

Thesis (S.B. and S.M.)--Massachusetts Institute of Technology, Dept. of Nuclear Engineering, 1998. / Includes bibliographical references (leaves 60-63). / A study was performed to develop a Monte Carlo method of modeling neutron shielding of proton therapy facilities in a complex, realistic environment. The bulk neutron shielding of the Northeast Proton Therapy Center (Massachusetts General Hospital, Boston, MA) was used as the basis of the design work. A geometrical model of the facility was simulated using the LAHET Code System, a set of Monte Carlo codes developed at Los Alamos National Laboratory. Additional software tools for reading and analyzing the simulation data that the model provides have been developed and tested. In order to verify the computer simulations, neutron detection and data acquisition systems have been assembled, modified, and thoroughly tested in order to monitor the neutron dose equivalent during proton beam operation at several locations on a continuous basis. Preliminary tests show that the geometry and physics models proposed in this work are valid. / by Michael R. Folkert. / S.B.and S.M.

Thesis (S.M. and Nucl.E.)--Massachusetts Institute of Technology, Dept. of Nuclear Engineering, 1998. / Includes bibliographical references (p. 157-162). / The goal of making nuclear plants more economically competitive with other sources of electricity has motivated research on extended operating cycles. By increasing cycle length in currently operating PWRs, the outage frequency is reduced, and the capacity factor is improved, providing an economic benefit. On the other hand, fuel with higher enrichment is required, and the fuel fabrication costs go up. A single-batch strategy is required if the current burnup licensing limit (60 GWD/MTU) is to be maintained. Previous work has shown the technical feasibility of single-batch cycles up to 44 calendar months in PWRs. Parametric studies indicated that the economically optimum length for a PWR, single-batch core is about 36 calendar months. The goal of this thesis is to design a PWR reload core for a 36-month cycle ready for implementation in current reactors and capable of appealing to utility managers. The core design includes physics, fuel performance and economics analysis. For the neutronics study, the core is modeled in 3 dimensions and in the steady-state using the codes CASMO-3/SIMULATE-3. Several steps are considered in the design process. First, the fuel enrichment required for the cycle and the most suitable burnable absorber are selected. Then, an optimum design is obtained for the peripheral assemblies that minimizes fuel costs. Finally, axial blankets that reduce neutron leakage are analyzed, as well as the benefits of axially grading the poison loading. The fuel performance --key to the technical feasibility of the core-- is analyzed with the code FROSSTEY-2, and simple models are developed for cladding corrosion and fission gas release. Core costs are calculated and the influence of operational and economics parameters is studied. A PWR reload core is presented that meets current physics and fuel performance design limits for a cycle of 33.9 EFPM or 36 calendar months when operating at a capacity factor of 94.1%. Fuel is enriched to 6.5% U-235 and selected pins use gadolinia as burnable absorber mixed with U0 2. By including pins with two different concentrations of gadolinia in the asssemblies, very good reactivity control is obtained, and the power is evenly distributed over a broad region of the core. Fuel costs are optimized by loading the core periphery with reused assemblies. The rest of the assemblies are discharged after one cycle in the core. The design criteria for peak pin exposure, axial enthalpy rise hot channel factor, and total peaking factors are met. The fuel performance analysis indicates that fuel centerline temperature, rod internal pressure, cladding oxide thickness, clad surface temperature and fission gas release are within acceptable limits, although in general slightly larger than for a contemporary reference 18- month cycle multibatch loading strategy. The 36-month core is economically competitive with an 18-month reference core under certain operational conditions. Considering a refueling outage of 30 days and 3% forced outage rate, the 36-month core is about $5M/yr more expensive than an 18-month reference core. However, if the outage length increases to 42 days, costs are similar for both cores. Furthermore, the reduction in enrichment costs expected with the development of AVLIS technology will make the 36-month cycle more economically attractive and potentially cost competitive with the 18-month reference cycle. / by Luis García-Delgado. / S.M.and Nucl.E.

Thesis (Sc.D.)--Massachusetts Institute of Technology, Dept. of Nuclear Engineering, 1998. / Includes bibliographical references (leaves 247-250). / This research broadens the prime concern of nuclear power plant operations from safe performance to both economic and safe performance through monitoring and advice. First, rotating machines such as turbine generators and reactor coolant pumps are identified as main contributors for the lost availability through the review of pressurized water reactor (PWR) forced outage records. The integrated architecture utilizes comprehensive sensor networks incorporating modern signal processing systems, advisory systems for sensor validation, and advisory systems for the intelligent diagnosis and maintenance (D&M). For the development of comprehensive sensor networks for complex target systems, an integrated method incorporating a structural system hierarchy and a functional system hierarchy, a fault-symptom matrix, sensor selection criteria, a sensor installation feasibility study, and advanced instrumentation techniques is formulated. Such advanced instrumentation techniques reflect the state of the art in advancement of data acquisition, data processing, and data integration techniques. Once the sensor types and locations are selected definitively, they are incorporated into drawings using a computer aided design tool (e.g. AutoCAD) program in order to make sure that it would be possible to install the comprehensive set of recommended sensors on each specific component studied. The second major part of this study is the development of an intelligent D&M advisory system integrating a comprehensive sensor network. This advisory system employs a Bayesian Belief Network (BBN) as a high level reasoning tool for incorporating inherent uncertainty for use in probabilistic inference. It is demonstrated that a rule-based knowledge representation is simply a special case of a general BBN by showing how the general BBN can be reduced to a rule-based representation. The presented major steps for constructing the BBN based generic inference algorithms are applied to systematic elicitation and synthesis of various levels of experts' knowledge. Prototype D&M algorithms are represented explicitly through topological symbols and links between them in a causal direction. This D&M advisory system is set up with an easy-to-learn, user-friendly, man-machine interface and modern graphics for efficient operator interactions. As new pieces of evidence from sensor networks developed are entered into this system, it provides operational advice concerning both availability and safety so that the operator is able to determine the likely failure modes, diagnose the system state, locate root causes, and take the most advantageous action. Thereby, the comprehensive monitoring supported advice improves operational availability. / bu Chang Woo Kang. / Sc.D.

Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Nuclear Engineering, 1998. / Includes bibliographical references (leaves 160-164). / In this thesis, we explore the use of RF gradients in NMR imaging. RF gradients have advantages over gradients of the static magnetic field in that they are non-secular and offer more experimental freedom (for example they permit amplitude, phase and frequency variations). In the case of pure NQR imaging, RF gradients preserve an undistorted line-shape. RF gradients also present significant new challenges in both the probe design and the spin dynamics. All of these issues are addressed in this thesis. Potential applications of RF gradients include NMR imaging and RF gradient spectroscopy (where the RF gradients are used to average internal Hamiltonians and to select a unique coherence pathway). Pure NQR imaging is also a potentially exciting application due to the large spectral changes that are observed with physical modifications, such as radiation dose, pressure and temperature. Additional complications arise in pure NQR as compared to high field NMR since the principle axis system is defined by the crystal orientation rather than an external field. The RF field breaks this symmetry and introduces another level of complexity to the spin dynamics. / by Guowang John Zhang. / Ph.D.

Thesis (M.Eng.)--Massachusetts Institute of Technology, Dept. of Nuclear Engineering, 1998. / Includes bibliographical references (leaves 51-52). / After thirty years of commercial nuclear plant operation, the nuclear industry has achieved dramatic improvements in the safe and reliable operation of its electrical generating stations. Recent indications, however, are that the rate of improvement may be slowing, particularly in the area of human performance. The nuclear industry has been and will be heavily dependent on rigid structure and centralized organization. Defense- in- depth is a key element in the prevention of human error or equipment malfunction and will continue to be so. The accident at Three Mile Island significantly increased the emphasis placed on procedures as a means of preventing human error. However, current reductions in the rate of human performance improvement have prompted reevaluation of the ability of improvement techniques, which have unquestionably achieved noteworthy success in the past, to enjoy similar success in the future. Years of adding more and more detail to procedures may in fact be becoming counterproductive. The majority of work on procedure use and procedure violations that has been performed to date deals primarily with the psychological aspects of human behavior. The ability of the procedure user to follow the procedure without becoming confused, however, has been left relatively unanalyzed. This paper attempts to characterize the recent slowdown in human performance improvement and the dynamics associated with human performance, to ascertain the significance of procedure complexity, and to put forward a technique to achieve an optimum balance of the critical factors that constitute human error defense-indepth. The embodiment of the technique, referred to as the A + B + C Method, is a mnemonic to allow workers and supervisors to balance the level of procedure detail, the worker's level of knowledge, and the amount of supervisory involvement required when executing work tasks. / by Alan B. Smith. / M.Eng.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Nuclear Engineering, 1998. / Includes bibliographical references. / Fuel cells are a promising new technology with the potential to benefit society through high energy conversion efficiencies, low environmental impact, and ability to deliver high quality electricity. After decades of development, the technology is on the verge of commercialization. However, fuel cell penetration of the electric power sector will be inhibited by a number of important market barriers, including high initial costs, lack of awareness, and undemonstrated operating performance. This thesis discusses the importance of developing a sound business strategy to ensure the market success of fuel cell technology. Two elements of marketing strategy are described as critical for commercialization initiatives: selecting the optimum target market for fuel cell products and designing an effective distribution strategy. A framework and criteria are proposed for choosing among alternative marketing strategies. Ongoing fuel cell commercializati0n efforts are examined in the context of this framework to derive lessons for the emerging fuel cell industry. / by Adam R. Cohn. / S.M.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Nuclear Engineering, 1998. / Includes bibliographical references (leaves 84-87). / During a postulated design basis accident at the MIT Research Reactor (MITR), radioactive fission products may be released from melted fuel plates into the con­tainment. To comply with regulations, the whole-body dose and thyroid dose at the boundary of the exclusion area as a result of this accident are determined. The fractions of the fission products contained in the fuel that are released through the reactor coolant system (RCS) into the containment are determined based on current regulations, experimental tests, and results from TMI-2 accident. After the fission products are released into the containment, a portion may be released to the outside through a containment crack or the stack. Also, the por­tion retained in the containment would contribute to the external gamma dose. The calculated dose due to atmospheric release depends on the source strength, the me­teorological conditions, and the dispersion model. For containment crack release and stack release, different dispersion models are used according to pertinent regulatory guides. The gamma dose through penetration or scattering depends on the struc­ture of the containment shielding and is determined analytically under appropriate approximations. Because the MITR is considering upgrading its power level, results at power levels from 5 to 10 MW are determined. At 5, 6, 7, 8, 9, 10 MW, the whole body doses at the back fence (8 meters away from the MITR) are 0.644, 0.764, 0.885, 1.00, 1.13, 1.25 rem respectively; the thyroid doses at the back fence are 0.112, 0.135, 0.157, 0.179, 0.202, 0.225 rem respectively; the whole body doses at the front fence (21 meters away from the MITR) are 0.887, 1.06, 1.22, 1.39, 1.56, 1. 72 rem respectively; and the thyroid doses at the front fence are 0.112, 0.134, 0.156, 0.179, 0.201, 0.224 rem respectively. The results show that even under conservative assumptions, the released doses for power levels from 5 MW to 10 MW are well below the regulatory limit - 25 rem for whole body and 300 rem for thyroid. / by Qing Li. / S.M.