Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Nuclear Science and Engineering, 2012. / Cataloged from PDF version of thesis. / Includes bibliographical references (p. 89-97). / A compact cyclotron built with superconducting magnets could be a transformative solution to many scientific problems facing the defense, medical, and energy industries today. This thesis discusses three potential applications of compact cyclotrons: generation of ¹³ for medical imaging, active interrogation for counter-proliferation, and fast neutron imaging for Enhanced Stockpile Surveillance (ESS). The first two applications are broadly reviewed. The ESS imaging application extends from preliminary work performed by Lawrence Livermore National Laboratory, who proposed a linear accelerator-driven ²H(d,n)³He reaction, and a complex gas-handling target subsystem. Here, the entire source-side engineering is reconsidered by investigating the viability of 56 different neutron-producing reactions. It is found through Monte Carlo simulation that the ⁷Li(p,n)⁷Be reaction could improve image contrast by employing a superconducting cyclotron capable of 3.8 MeV, 414 [mu]A proton beam and liquid lithium target. / by Eric S. Marshall. / S.M.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Nuclear Science and Engineering, 2009. / Cataloged from PDF version of thesis. / Includes bibliographical references (p. 147-150). / The vertical position of elongated tokamak plasmas is unstable on the time scale of the eddy currents in the axisymmetric conducting structures. In the absence of feedback control, the plasma would drift vertically and quench on the wall, a situation known as Vertical Displacement Event (VDE), with serious consequences for machine integrity. As tokamaks approach reactor regimes, VDE's cannot be tolerated: vertical feedback control must be robust against system uncertainty and the occurrence of noise and disturbances. At the same time, adaptive routines should be in place to handle unexpected events. The problem of robust control of the vertical position can be formulated in terms of identifying which variables affect vertical stability and which ones are not directly controlled/controllable; identifying the physical region of these variables, and the corresponding most unstable equilibria; and designing the control system to stabilize all equilibria with sufficient margin. The margin should be enough to allow the system to tolerate realistic scenarios of noise and disturbances. A set of metrics is introduced to characterize the problem of vertical stability: the stability margin describes the plasma-wall interaction and the open-loop growth rate; the maximum controllable displacement looks at the vertical stabilization power supplies and their ability to handle noise and off-normal events; the gain and phase margins quantify the linear stability of the feedback control loop. / (cont.) The dependence of these metrics on relevant plasma parameters is proven with analytic calculations and numerical simulations: in particular, it is shown that the stability margin is a decreasing function of the plasma internal inductance, for a given plasma elongation. An upper bound of the value of the internal inductance is derived and validated with database analysis, which describes the most unstable equilibrium for given values of the external elongation and the edge safety factor. The stability metrics are evaluated for typical and ITER-like C-Mod plasmas to give an example of the C-Mod operational space and of feasible control conditions. The vertical stabilization system should be able to tolerate realistic scenarios of noise and disturbances. The main sources of noise and pick-ups in Alcator C-Mod are identified and their effects on the measurement and control of the vertical position are evaluated. Broadband noise may affect controllability of C-Mod plasmas at limit elongations and may become an issue with high-order controllers, therefore two applications of Kalman filters are investigated. A Kalman filter is compared to a state observer based on the pseudo-inverse of the measurement matrix and proves to be a better candidate for state reconstruction for vertical stabilization, provided adequate models of the system, the inputs, the intrinsic and measurement noise and an adequate set of diagnostic measurements are available. A single-input single-output application of the filter for the vertical observer rejects high frequency noise without destabilizing high-elongation plasmas, however does not match the performance of an optimized low-pass filter. / (cont.) Aggressive control targets and large off-normal events can cause a control current to rail. The magnetic topology is consequently perturbed and the plasma might become uncontrollable. An adaptive anti-saturation control routine is demonstrated which avoids an impending saturation by interpolating in real-time to a safe equilibrium. This approach becomes necessary when poor redundancy of control coils may require mid-shot pulse rescheduling, as opposed to an adaptation in control. / by Marco Ferrara. / Ph.D.

Thesis: Ph. D., Massachusetts Institute of Technology, Department of Nuclear Science and Engineering, 2016. / This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections. / Cataloged from student-submitted PDF version of thesis. / Includes bibliographical references (pages 327-331). / In this thesis, a general Methodology framework to characterize, assess and quantify the representativeness uncertainty in performance indicator measurements in thermal and nuclear plants is presented. The representativeness uncertainty arises from the inherent heterogeneity or the variability of the quantity being measured or from the inadequacy of the physical models used to simulate the measurement. The main objective of the Methodology is to gain a deeper physical understanding of the Representativeness uncertainty of the measurement by using numerical simulation tools such as Computational Fluid Dynamics (CFD) and to quantify various sources of representativeness uncertainty. First, the components of the Methodology are expressed using the normal probability distribution for the uncertainty sources. Second, a non-parametric formulation of the Methodology framework is developed and demonstrated. The use of non-parametric techniques allows the quantification and integration of uncertainties that are not expressed by the normal probability distribution. The Methodology is developed based on the analysis of four industrial Case Studies involving uncertainties in performance indicator measurements to structure the analysis. They are: Mass flow rate measurement by an orifice plate (Case Study 1), Steam Generator recirculation ratio measurement using chemical tracers (Case Study 2), The simulation of cooling tower deformation using a Photomodeler (Case Study 3) and the NOx emission measurement from a Combined Cycle Gas Turbine (Case Study 4). In Case Study 1, the non-parametric bootstrap method was used to quantify sampling, iterative and discretization uncertainties thus demonstrating its applicability to CFD uncertainty analysis. In Case Studies 2,3 and 4, the parametric formulation of the Methodology is used to structure the technical analysis. / by Uuganbayar Otgonbaatar. / Ph. D.

Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Nuclear Science and Engineering, 2007. / Includes bibliographical references (leaves 40-41). / This thesis analyzes a sample of 15 fuel-handling events from the past ten years at commercial nuclear reactors with significant human error contributions in order to detail the contribution of human error to fuel-handling activities, emphasizing how latent conditions can directly contribute to events. In particular, procedural inaccuracies often create conditions that lead to the development of errors related to maintenance work practices. This would be of significant concern for a pre-closure safety assessment for a geologic repository for spent nuclear fuel and high-level radioactive waste, where many fuel-handling work activities would be performed. Specific emphasis is placed on fuel movement activities and control of ventilation systems, which could significantly impact worker and public health and safety in the case of a fuel-handling accident. / by Bradley Sutton. / S.B.

Thesis: Ph. D., Massachusetts Institute of Technology, Department of Nuclear Science and Engineering, 2014. / Cataloged from PDF version of thesis. / Includes bibliographical references (pages 123-139). / This thesis studies radiation-induced mixing at interfaces between low solubility metals using molecular dynamics (MD) computer simulations. It provides original contributions on the fundamental mechanisms of radiation-induced mixing and morphological stability of multilayer nanocomposites under heavy ion or neutron radiation. An embedded atom method (EAM) interatomic potential is constructed to reproduce the main topological features of the experimental equilibrium phase diagram of the Cu-Nb system in both solid and liquid states. Compared with two previously available EAM Cu-Nb potentials, the phase diagram of the current potential shows better agreement with the experimental phase diagram. The newly constructed potential predicts that the Cu-Nb liquid phase at equilibrium is compositionally patterned over lengths of about 2.3 nm. All three Cu-Nb potentials have the same solid phase behavior but different liquid phase properties, serving as a convenient set of model systems to study the effect of liquid phase properties on radiation-induced mixing. To study radiation-induced intermixing, a specialized MD simulation is developed that models multiple 10 keV collision cascades sequentially up to a total dose of ~5 displacements per atom (dpa). These simulations are comparable to experiments conducted at cryogenic temperatures. Mixing is modeled using all three Cu-Nb potentials and found to be proportional to the square root of dose, independent of interface crystallography, and highly sensitive to liquid phase interdiffusivity. It occurs primarily by liquid phase interdiffusion in thermal spikes rather than by ballistic displacements. Partial de-mixing is also seen within thermal spikes, regardless of liquid phase solubility, which is explained by segregation of impurities into the liquid core of the thermal spikes. Additional MD and phase field simulations are carried out on Cu-Nb multilayered nanocomposites with individual layer thicknesses above 1 nm. These simulations demonstrate that Cu-Nb multilayers with individual layer thicknesses above 2-4 nm remain morphologically stable when subjected to 100 keV collision cascades, characteristic of neutron or heavy ion irradiation. The probability of morphological instability rapidly increases as the layer thickness decreases to 1 nm, which is due to overlap of zones of liquid-like interdiffusion inside radiation-induced thermal spikes at neighboring interfaces in the multilayer. This work shows that to design morphologically stable radiation-tolerant nanocomposites, it is desirable to a) choose low solubility metals with small liquid phase interdiffusivity as the constituents, and b) use a microstructural length scale larger than twice the size of the interdiffusion zone inside thermal spikes. / by Liang Zhang. / Ph. D.

Thesis: S.M., Massachusetts Institute of Technology, Department of Nuclear Science and Engineering, 2015. / Cataloged from PDF version of thesis. / Includes bibliographical references. / Nuclear Renewable Oil Shale Systems (NROSS) are a class of large Hybrid Energy Systems in which nuclear reactors provide the primary energy used to produce shale oil from kerogen deposits and also provide flexible, dispatchable electricity to the grid. Kerogen is solid organic matter trapped in sedimentary shale, and the formations of kerogen oil shale in the western United States are the largest and densest hydrocarbon resource on the planet. When heated above 300 °C, kerogen decomposes into oil, gas, and char. NROSS couples electricity and transportation fuel production in a single operation, reduces lifecycle carbon emissions from the fuel produced, improves economics for the nuclear plant, and enables a major shift toward a very-low-carbon electricity grid. The nuclear reactor driving an NROSS system would operate steadily at full power, providing steam for shale heating in closed steam lines when the price of electricity is low and electricity to the grid when the price of electricity is high. Because oil shale has low thermal conductivity, heat input to the shale can be cycled as needed without disrupting the steady increase in average temperature. The target average shale temperature of 350 °C would be reached over 2 years using two heating stages in the baseline configuration driven by light water reactors. First stage heating brings the shale to an intermediate temperature, assumed to be 210 °C in this study. The second heating stage isolates the steam delivery line from the reactor and uses electricity, purchased when prices are low, to increase steam temperature and bring the shale to 350 °C. This capacity to absorb low price electricity mitigates the tendency for electricity prices to collapse to zero, or potentially negative values, during periods of peak wind and solar output. The analysis herein shows that liquid fuels produced by a baseline NROSS would have the lowest life cycle greenhouse gas impact of any presently available fossil liquid fuels and that operation as part of an NROSS complex would increase reactor revenues by 41% over a stand-alone baseload reactor. The flexible, dispatchable electricity provided by NROSS could also enable the transition to a very-low-carbon grid in which renewables are widely deployed and the NROSS provides variable output to balance their uncontrolled output to meet demand. Fully deployed, NROSS could require tens or hundreds of reactors. Large fleet operations and local mass production of the necessary hardware could bring about substantial reductions in system cost as development proceeds, potentially offering a pathway to jump start and maximize the realization of the mass production cost savings envisioned for small modular reactors. The development pathway to achieve large scale NROSS deployment will be complicated, however, requiring involvement from many government agencies, a demonstration system, and a complex commercialization effort with partnered nuclear vendors, utilities, and petroleum system developers. / by Daniel Joseph Curtis. / S.M.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Nuclear Science and Engineering, 2010. / Cataloged from PDF version of thesis. / Includes bibliographical references (p. 399-417). / The dramatic change in the international security environment after the collapse of the bipolar system has had a negative impact on the effectiveness of the existing nuclear non-proliferation regime. Furthermore, the success of the Pakistani Gas Centrifuge Enrichment Technology (GCET)- based nuclear weapons program has imposed a great challenge on the Nuclear Nonproliferation Treaty (NPT) regime. In this context, this study tried to answer two questions: (a) what is the probability of proliferators successfully producing Highly Enriched Uranium (HEU) at Gas Centrifuge Enrichment Plants (GCEPs) and (b) how effective is the current NPT regime in dealing with this issue. In order to tackle these two questions, an integrated methodology is used that reflects all factors affecting the nuclear proliferation on the front-end of the nuclear fuel cycle. A quantitative assessment of the proliferation risks of producing HEU for multiple scenarios is presented using success tree models, uncertainty analysis, sensitivity analysis, importance measures, and expert opinion. This assessment identifies the factors that can reduce the proliferators' success of producing HEU, which will be helpful in prioritizing the use of the IAEA's limited resources. / (cont.) The study found that legal capabilities of the NPT regime are more problematic than technological capabilities in preventing proliferators from producing HEU at GCEPs, since the United Nations Security Council (UNSC) is the only NPT regime component that has compliance-enforcing resources. This study recommends three approaches as follows: First, the NPT regime should take a multi-faceted approach that incorporates all NPT regime components into each step of nuclear weapons program development. Second, the NPT regime should impose nuclear elements control via Multilateral Export Control Regimes (MECRs). Third, the NPT regime should develop an approach that challenges HEU production from both technological- and legal points of view. Since law governs technological capability, a multidimensional approach that includes this relationship would be more effective than an approach that focuses on either aspect individually. / by Taeshin Kwak. / Ph.D.

Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Nuclear Science and Engineering, 2013. / Cataloged from PDF version of thesis. / Includes bibliographical references (pages 37-38). / The Fluoride-salt-cooled High-temperature Test Reactor (FHTR) is a test reactor concept that aims to demonstrate the neutronics, thermal-hydraulics, materials, tritium management, and to address other reactor operational and maintenance issues before a commercial Fluoride-salt-cooled High-temperature Reactor (FHR) can be deployed. The MIT Nuclear Systems Design class proposed a design for a 100 MW FHTR that uses enriched- 7Li flibe (Li2BeF4), has both thermal and fast flux testing positions for fuel and materials testing, and provides a neutron flux greater than 3E14 n/cm2 -s for accelerated irradiation testing. One of the key technical issues of the FHR and FHTR is tritium generation from the flibe coolant and its radiological control. The objectives of this study are: 1) to provide an overview of tritium production in various types of nuclear systems, 2) to estimate the tritium source term in the FHTR using the ORIGEN-S computer code, and 3) to propose a tritium management strategy for the FHTR. A review of existing nuclear systems shows that tritium is the primary radionuclide in liquid and gaseous tritium release. Light water reactors release up to several hundred curies per year for which various tritium removal and control strategies have been developed and implemented. Using the ORIGEN-S code analysis, tritium production for the MIT FHTR design at 20 MW is estimated to be about 2600 Ci per year (based on a 70% capacity factor and-10 Ci/day), with 99.99% enriched- 7Li flibe. Using this source term, a tritium removal rate of >90% is proposed as a design target for the tritium control system of the FHTR in order to maintain tritium release within the limits of existing nuclear reactors. Proposed tritium management strategies for the FHTR include increasing the 7Li enrichment, carbon-based or metallic getters, and inert gas sparging with a high-temperature recombiner system. / by Judy N. Rodriguez. / S.B.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Nuclear Science and Engineering, 2007. / Includes bibliographical references (leaves 79-83). / Nanofluids are engineered colloidal suspensions of nanoparticles in water, and exhibit a very significant enhancement (up to 200%) of the boiling Critical Heat Flux (CHF) at modest nanoparticle concentrations (50.1% by volume). Since CHF is the upper limit of nucleate boiling, such enhancement offers the potential for major performance improvement in many practical applications that use nucleate boiling as their prevalent heat transfer mode. The nuclear applications considered are main reactor coolant for PWR, coolant for the Emergency Core Cooling System (ECCS) of both PWR and BWR, and coolant for in-vessel retention of the molten core during severe accidents in high-power-density LWR. To implement such applications it is necessary to understand the fundamental boiling heat transfer characteristics of nanofluids. The nanofluids considered in this study are dilute dispersions of alumina, zirconia, and silica nanoparticles in water. Several key parameters affecting heat transfer (i.e., boiling point, viscosity, thermal conductivity, and surface tension) were measured and, consistently with other nanofluid studies, were found to be similar to those of pure water. However, pool boiling experiments showed significant enhancements of CHF in the nanofluids. Scanning Electron Microscope (SEM) and Energy Dispersive Spectrometry (EDS) analyses revealed that buildup of a porous layer of nanoparticles on the heater surface occurred during nucleate boiling. This layer significantly improves the surface wettability, as shown by measured changes in the static contact angle on the nanofluid-boiled surfaces compared with the pure-water-boiled surfaces. It is hypothesized that surface wettability improvement may be responsible for the CHF enhancement. / by Sung Joong Kim. / S.M.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Nuclear Science and Engineering, 2009. / Cataloged from PDF version of thesis. / Includes bibliographical references (p. 100-104). / High temperature steam electrolysis is an efficient process and a promising technology to convert electricity and steam or a mixture of steam and CO₂, into H₂ or syn-gas (H₂2 + CO) respectively. It is carried out in Solid Oxide Electrolytic Cells (SOECs). At the high temperature of operation, above 8000[degree] C, loss in the rate of hydrogen (or syn gas) production by SOECs has been observed. This loss of performance has been a scientific and technological challenge. The goal of this thesis is to identify the mechanisms for the loss in the electrochemical performance of SOECs due to the oxygen electrode and bond layer degradation. Our specific research objectives were focused on two main mechanisms: 1) Cr transport into the oxygen electrode and bond layer, and 2) Long-range segregation of cations in the bond layer. For SOECs provided by Ceramatec Inc. for this analysis, La₀.₈Sr₀.₂CoO₃ (LSC) was the bond layer and A₀.₈Sr₀.₂MnO₃ (ASM*) was the oxygen electrode, both comprised of perovskite structure. The approach in thesis integrated complementary spectroscopy and microscopy techniques in a novel manner to carry out the 'post-mortem' analysis of SOECs from a high level to a high resolution. Raman spectroscopy was employed to identify secondary phases on the top surface of LSC near the interconnect interphase. Surface chemistry and microstructure of the air electrode and the bond layer was studied using scanning Auger Electron Spectroscopy (AES) with nano-probe capability. / (cont.) High-resolution analysis of the cation distribution in the bulk of the LSC bond layer was achieved by employing Energy Dispersive X-ray Analysis (EDX) coupled with Scanning Transmission Electron Microscopy (STEM). Electrochemical treatment and characterization was performed to isolate the mechanism(s) governing the long-range segregation of cations, leading to the dissociation of the LSC bond layer. Less-conducting, secondary phases of Cr₂O₃, LaCrO₃, La₂CrO₆ and Co₃0₄ were identified on the top surface of LSC bond layer. The bond layer exhibited: 1) presence of Cr, with average Cr-fraction of approximately 0.07 at the surface of its grains, and 2) surface composition variation locally, with La/Co ranging widely from 0.67 to 16.37 compared to the stoichiometric La/Co value of 0.8. Sr and Co cations migrated from the bond layer structure to the LSC/interconnect interface, over a distance of 10-20 microns. Furthermore, STEM/EDX results showed the presence of phase separated regions at the nano-scale rich in Cr and La but lacking Co, and vice-versa. This indicates the dissociation of bond layer bulk structure at nano-scale. Cr fraction in LSC bulk varied from 10 to 33%, which is higher than the average Cr-content at the surface of LSC grains. The maximum Sr fraction observed in LSC bulk was 4.16%, confirming the migration of Sr to LSC/interconnect interface. / (cont.) We hypothesize that the long-range transport of Sr, Co, and Cr cations can be caused by two primary mechanisms: 1) Driven by Cr-related thermodynamics, where the Crcontaning species (i.e. at the vicinity of the interconnect) could thermodynamically favor the presence of select cations (i.e. Sr and Co) at the region interfacing the interconnect. 2) Driven by the electronic or oxygen ion current. To test these hypotheses and to isolate the governing mechanism, we simulated controlled electrochemical conditions on reference cells having ASM electrodes coated with LSC, on both sides of SSZ electrolyte, without any Cr-containing layers on the LSC bond layer. The reference cells degraded even in the absence of Cr. AES results showed that the microstructure and surface composition of the reference cells stayed stable and uniform upon the electrochemical treatment, in spite of the degradation. Thus, this thesis concludes that the Cr-related thermodynamics could be the dominant mechanism driving the uneven dissociation and segregation of cations in LSC as observed in the stack cells. As a mechanism for Cr-deposition in the LSC bond layer, we suggest that a thermodynamically-favored reaction between the La-enriched phase (at the surface of the LSC grains) and the volatile Cr-species (Cr0₃ and CrO₂(OH)) is responsible for the formation of poorly-conducting secondary phases. This interaction is likely to be limited by the presence of the segregated La-O-species which can serve as a nucleation agent for this reaction. / by Vivek Inder Sharma. / S.M.