Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Nuclear Engineering, 1998. / Includes bibliographical references (leaves 88-92). / The first direct measurement of the rate of spin diffusion through a homogeneous sample was performed as an incoherent NMR scattering experiment. The experiment consists of a combination of pulsed gradient spin echo methods with multiple pulse/ pulsed gradient spatial encoding met.hods. The NMR scattering experiment involves the creation of an initial spatial magnetization grating, a period of spin evolution including the displacement of spin magnetization, followed by the detection of the residual magnetization grating. The essence of NMR scattering measurements is to record the extent of microscopic motion of spin magnetization through a sample by directly observing amplitude and phase changes of a well defined spin magnetization grating. The spin diffusion measurement records the rate of destruction of a magneti­zation grating by the random offset of spin magnetization associated with the flip-flop term of the homonuclear dipole-dipole interaction. Since the microscopic motion driven by di- polar coupling is very slow, only fine magnetization gratings are sensitive to the small spatial offsets. Strong pulsed mag­netic field gradient techniques were developed for these studies which generate switched gradients with strengths up to 103T /m (a factor of 100 stronger than those commer­cially available, and a factor of 25 stronger than the highest previously reported). These gradients are able to create a spatial magnetization grating with a pitch of from l[mu]m to 1nm for solid state NMR scattering experiments. Gradients on the order of 200T /m were applied in the spin diffusion measurement experiment. For single crystal CaF2, the measured parallel components of the spin diffusion rates are 7.1 x 10-12cm2 /s along the [0,0,1) direction and 5.3 x 10-12cm2/s along the [1,1,1) direction, in good agreement with theoretical predictions. Additional work has been done on flow measurement. A novel approach is intro­duced to measuring flow velocities using a probe with a spatially varying RF field, and without using other magnetic field gradients. The velocities of the spins are measured as a modulation of the NMR signal from the translatlation of a spatial mag­netization grating through a detection coil with a spatially periodic field profile. Since the same coil can be employed to create the initial magnetization grating, the overall measurement is as simple as recording the signal modulation frequency following a single excitation pulse. The design principles are discussed for a probe that has a spatially periodic field constructed from a series of lumped element x-circuits. Spa­tial modulation of the amplitude or the phase of the RF field can easily be achieved, and either of these may be used t.o characterize a flow field. Examples are shown of measurements of pipe flow using a probe with an amplitude modulated RF field. / by Wurong Zhang. / Ph.D.

Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Nuclear Engineering, 1998. / "September 1997." Vita. / Includes bibliographical references (p. 124-132). / A methodology for evaluating environmental management programs using integrated risk communication, assessment and management tools is developed. The main novelty of the methodology lies in the use of decision analysis methods to integrate the wide range of decision objectives which characterize environmental management problems, and risk assessment for impact evaluations under uncertainty, in a framework that emphasizes and incorporates input from stakeholders in all aspects of the process. The outcomes of the analysis are then used to guide the behavioural deliberative process that is engaged to reach a consensual, defensible decision. The first step of the methodology is that of identifying all consequences relevant to the implementation of the decision, i.e. the performance measures. These are identified through a decomposition process based on the use of conditional influence diagrams which allow to incorporate and structure the quantitative a1.1d qualitative issues of the decision problem. Aggregation of the evaluations of the performance measures is done by means of an additive utility function in which single-attribute utilities for the various performance measures are weighed by appropriate measures of their relative importance. The weights of the performance measures are assessed by the pairwise comparison method of the Analytic Hierarchy Process (AHP) applied to the hierarchical structure of the influence diagram. For the determination of the single-attribute utilities we employ a novel approach based on the AHP in which the comparisons are made not on the actual numerical values of the performance measures but, rather, on more intuitive concepts such as 'worst', 'moderate' and 'best'. Within this approach, the innovative introduction of elements of fuzzy logic allows us to account for linguistic imprecision in the expression of the stakeholders' preferences ... / by Enrico Zio. / Ph.D.

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This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections. / Thesis: Ph. D., Massachusetts Institute of Technology, Department of Nuclear Science and Engineering, 2019 / Cataloged from student-submitted PDF version of thesis. / Includes bibliographical references (pages 205-208). / During the Fukushima Daiichi and Daini accidents, the interactions of multiple units at the same site made accident mitigation more difficult compared to single unit sites. The accidents revealed important multiunit risk sources that are not identified by risk assessments for single-unit sites. Therefore, it's important to obtain an integrated risk evaluation for multiunit sites. However, multiunit accident scenarios are difficult to analyze due to the complexity of multiunit interactions. In the work reported here, a framework capable of analyzing multiunit accident scenarios involving inter-unit interactions is presented. Our framework provides a structured method to analyze accident propagation events, which are not being studied much currently. In addition, our framework is capable of providing accident mitigation and site improvement suggestions that can help improve site safety. / The accident scenarios and risk contributors analyzed in our framework are developed based upon our interviews with Tokyo Electric Power Company (TEPCO) engineers concerning their experiences during the 2011 Fukushima accidents. This first-hand information helps us to better understand multiunit accident scenarios and difficulties in multiunit accident mitigations. In this work, the major steps of our framework are first explained by a simplified two-unit site. The simplified site structure is constructed such that the distractions from overly complex systems are minimized. Additionally, analyses of more risk contributors are illustrated using a relatively complex two-unit site, which illustrates the capability of our framework to analyze complex sites. Even though only a limited number of accident scenarios and risk contributors are illustrated in our work, the capability of the framework goes beyond that. / With proper input information, our framework can be adapted to sites and accident scenarios more complex than those illustrated in our work. Analyzing multiunit risks using our framework can help sites to refine expertise and data and to identify hidden multiunit vulnerabilities and eliminate them in advance. In addition, the risk assessment groups developed during this process can support emergency trainings and risk communications as well as provide risk assessment leadership for utilities. / by Yinan Cai. / Ph. D. / Ph.D. Massachusetts Institute of Technology, Department of Nuclear Science and Engineering

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Nuclear Engineering, 1998. / Includes bibliographical references (p. 132-134). / The management of environmental programs affects a great variety of issues and involves several stakeholders with diverse, and often conflicting, concerns. Any methodology proposed for environmental decision making should, then, be capable of integrating technical and value-laden objectives in a framework which ensures process transparency. Furthermore, only a methodology simple and easy to implement can achieve public involvement at every level, and, with it, achieve a thoroughly informed decision. Classic decision making techniques have provided the tools to organize decision problems in a sound logical structure. Unfortunately, actual applications have shown that, when it comes to the practical quantification of stakeholder values, these tools may be too burdensome to apply. This is particularly so in cases where non-technical public is a fundamental part of the decision process. In this thesis, the focus is on a methodology developed to assess stakeholder preferences regarding a number of objectives of environmental restoration activities, such as the minimization of costs and the impact on human health and safety, and on its combination with the structural approach provided by classic methods. Stakeholder input is used to produce a first set of relative weights using the Analytic Hierarchy Process in combination with value trees. The set of preferences so obtained, as well as possible inconsistencies in their assessments, are discussed with the stakeholders to revise the weights and reduce inconsistency. The stakeholders always have the final word regarding the relative weights. The prioritization procedure is presented through a case study. Insights gained from this real life application are also presented. / by Roberto Accorsi. / S.M.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Nuclear Engineering, 1997. / Includes bibliographical references (leaves 66-69). / Cancer remains a major medical problem accounting for over 500,000 deaths in the US annually. A common feature of most human tumors is their ability to induce the proliferation of new blood vessels, i.e. angiogenesis. Considerable evidence now exists which demonstrates that these tumor vessels are associated with a distinct range of morphological and physiological properties which are not present in normal tissue vasculature. Several studies now document that in a wide variety of tumor models, average tumor vessels have diameters two times those of normal tissue vessels. NMR techniques based on magnetic susceptibility mechanisms are sensitive to varying sizes of blood vessels. By using gradient echo (GE) and spin echo (SE) pulse sequences and different concentrations of an exogenous contrast agent, it is possible to determine the signal contribution from small versus large vessels by examining the change in T2 and T2* rates ([delta]R2 and [delta]R2*), i.e. the ratio of [delta]R2* to [delta]R2 increases with vessel size. This ratio provides an index for the average size of vessels within a voxel. The central goal of this research was to utilize such a tool in order to obtain a regional picture of the tumor vascular bed. Rats, inoculated with C6 glial cells, underwent an MR imaging series nineteen days after implantation, which comprised conventional SE and GE images prior to and following serial injections of an equilibrium iron oxide contrast agent (MION). Regions within the tumor and in the contralateral normal gray matter were identified. The change in the T2 rate and T2* rate ([delta]R2 and [delta]R2*) were calculated for each region. Since susceptibility contrast mechanisms designed to study the distribution of vessel sizes rely entirely on the compartmentalization of the contrast agent within the vasculature, the first set of experiments was designed to demonstrate the stability of MION to remain within the vasculature, despite the disruption in the blood brain barrier. The second experiments measured [delta]R2 and [delta]R2* as a function of contrast agent concentration and TE. The MR measurements were compared with predicted values of [delta]R2 and [delta]R2* made from histological assessment of vessel sizes and theoretical Monte Carlo simulation results. The steady state measurements of [delta]R2 and [delta]R2* in the first experiments demonstrated that once the maximum contrast agent concentration had been reached, the values of [delta]R2 and [delta]R2* remained stable over 90 minutes, suggesting that MION remains within the vasculature. In the second experiments, significant differences were observed between the tumor and contralateral deep gray matter. Specifically, the ratio of ([delta] R2*/ ([delta]R2 was greater in the tumor than the normal brain, by a factor of 1.9 ± 0.2. From histologic sections and numerical simulations, the corresponding ratio was predicted to be 1.9 ± 0.1. These ratios are suggestive of a greater relative density of large vs small vessels. Maps of the ratio [delta]R2*/[delta]R2 were also produced on a pixel by pixel basis. Regions of high intensity on these maps (indicating a higher ratio of [delta]R2*/[delta]R2) corresponded well with the location of the tumor as determined using conventional images. / by Joëlle Dennie. / S.M.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Nuclear Engineering, 1997. / Includes bibliographical references (p. 75). / The photonuclear production of radioisotopes using electron LINAC bremsstrahlung sources offers an industry alternative to reactor and ion beam production methods. One such method under development is the utilization of the Giant Dipole Resonance in the (y,n) reaction cross-section. This method is being studied for use in the production of 99mTc from enriched 100Mo by electron beam induced bremsstrahlung photons. Of primary concern to any radioisotope production system is the specific activity it is able to create of the radioisotope. In a photoneutronic production system maximizing the number of GDR photons on a given target increases the specific activity. Proper design and optimization of the electron-to-photon converter maximizes the number of GDR photons. This study examines some alternative types of converter design. MCNP is used to predict isotope yields and energy deposition in the converter assemblies and an Excel Spreadsheet is used to analyze the heat-transfer capabilities of the systems. Optimized designs are presented for the different types of converters studied. A radiantly cooled converter is presented as a low-yield design, while a circulating loop of molten lead is analyzed for use in a high-yield system. / by Jess L. Iverson. / S.M.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Nuclear Engineering, 1998. / Includes bibliographical references (leaves 32-33). / NMR experiments implementing two-bit controlled-NOT logic gates on alanine (JAB = 35.1 Hz) and 2,3- dibromothiophene (JAB = 5.6 Hz) were performed. Spectra were collected at a variety of tip angles (angles between the spin and the axis of magnetization) by applying a selective RF pulse of constant power and variable duration. From this collection of spectra, the effective Hamiltonian of the spin system was derived and found to contain an internal Hamiltonian. In a spin system with weak coupling, the internal Hamiltonian contains spin-spin coupling terms. The effective Hamiltonian gives a more complete description than the currently used transition Hamiltonian. Understanding the dynamics of a spin system not only furthers the field of NMR but has application in the subject of quantum computing. NMR pulse sequences for four-, eight- and 16-spin controlled-NOT logic gates were developed. A pattern is evident and the pulse sequence for any number of spins can be derived. Disregarding the differences in the spin-spin coupling constants of different spin systems, these results suggest that the total time to implement a controlled-NOT logic gate in NMR does not increase exponentially with the number of spins in the system. / by aMy e dunlop. / S.M.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Nuclear Engineering, 1998. / Includes bibliographical references (leaves 53-54). / In an effort to provide an accurate real-time continuous emissions monitor (CEM) for hazardous air-pollution metals as a viable option to EPA Method 29, a Microwave Induced Plasma (MIP) system is under development for real-time atomic emission spectroscopy in stack exhaust. This MIP-CEM has a nebulizer calibration subsystem attached to the sample line for real-time span calibration of the monitored metal concentrations. In order to quantify the amount of metal mass measured in the effluent flow, it is necessary to determine the analyte metal mass transport efficiency of the nebulizer system. A novel new approach to determine the nebulizer efficiency during plasma operation was tested in this thesis. A 0.1-mm tungsten filament attached to a 4- mm diameter alumina rod was used to introduce a known amount of mass into a nitrogen plasma at 0.5-cfm sample line flow in 6 different positions relative to the end of the sample line. The tungsten filament was heated by plasma radiation. These signals, obtained from the direct rod insertions, were then correlated to masses of metals aspirated by the nebulizer and drawn into the plasma through a quartz "T". The mass transport efficiency as a function of rod insertion position was calculated by dividing the correlated mass by the total mass aspirated by the nebulizer to achieve an identical signal. In the 4- inch long drift distance between the end of the sample line and the plasma sustaining waveguide, measurements from 0.5 inches away from the end of the sample line to 1.75 inches away, in 0.25-inch increments, were repeated, and the results tabulated. The efficiencies generally decreased as the rod was inserted closer to the plasma, with the efficiency extrapolated to 0.644 ± 0.153 % at the end of the sample line. The extrapolated value is in fair agreement with the efficiency used in the most recent field test conducted at Research Triangle Park in Raleigh-Durham, North Carolina. Initial tests at one insertion location of 1.75 in. were also done for a different nitrogen flow of 1.0 cfm and for air at 0.5 cfm. These initial tests are inconclusive, and more measurements are needed. Also, further testing is warranted for the determination of other factors, such as moisture, and the impact on the efficiency. / by Guadalupe Jorge Flores III. / S.M.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Nuclear Engineering, 1998. / Includes bibliographical references (p. 193-198). / The purpose of this research was to use state-of-the-art nuclear and fuel performance design packages to develop extended cycle cores for existing Light Water Reactor (LWR) designs which respect current fuel burnup limits while considering the full range of practical design and economic considerations. The driving force behind this research was the desire to make nuclear power more economically competitive with fossil fuel options by permitting higher plant capacity factors. In this thesis, reference cores for a 38.8 Effective Full Power Month (EFPM) PWR cycle and a 45 EFPM BWR cycle were developed and evaluated. To achieve these cycle lengths the designs use a single batch reloading strategy and contain fuel with enrichments as high as 7.4W/0 U2 3 5 (exceeding the current licensing limit of 5W/). The PWR design uses gadolinium oxide (Gd20 3) and IFBA (Integral Fuel Burnable Absorbers - a thin fuel pellet surface coating of ZrB2) as burnable poisons to hold down excess reactivity and to control power peaking. The BWR employs only Gd203. Both core designs require higher worth control rods in order to meet shutdown safety requirements. Fuel performance issues were also investigated. The presence of high burnup fuel assemblies in areas of greater-than core-average power leads to fuel performance concerns which must be carefully addressed. The effects of waterside corrosion, increased fission gas pressure, and intensified cladding strain in these assemblies must be carefully quantified. Steady state-analyses of fuel pin internal pressure performed on the PWR design show acceptable fuel pin performance. Fuel performance areas requiring further research were highlighted. Economic calculations show that extended cycle, single batch loaded cores have a fuel cost that is $13 million to $17 million per year more expensive than an optimized multi-batch strategy. This deficit would have to be made up from the net benefits of a higher capacity factor (e.g., less replacement energy, fewer refueling outages) levelized over plant lifetime. / by Michael Vincent McMahon. / Ph.D.