Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Nuclear Science and Engineering, June 2010. / "June 2010." Cataloged from PDF version of thesis. / Includes bibliographical references (p. 35). / The proliferation resistance of a reprocessing facility can be improved by using a novel detection system that utilizes the nuclear resonance fluorescence (NRF) phenomenon to determine the isotopic composition of materials flowing through the plant. In an aqueous reprocessing facility, the waste stream was identified as a weak point for proliferation resistance. By identifying the isotopic composition of the waste stream and monitoring levels of plutonium and uranium, greater accountancy can be maintained. After the detection system was designed, a probabilistic risk assessment method was used to evaluate the added proliferation resistance afforded by the NRF detection system and the overall proliferation resistance of the reprocessing facility to a diversion of a small quantity of material from the waste stream by two individuals. The overall probability of success for a proliferator to divert materials from a reprocessing facility utilizing an NRF detection system is 8.73* 10-5. This is a decrease, from 3.39* 104 , over the probability of success for the proliferator if the NRF detection system is not present. This decrease in proliferator success probability demonstrates and increased proliferation resistance of the reprocessing facility. The NRF detection system is shown to increase the proliferation resistance of the reprocessing facility. / by David Ballin Smith. / S.B.

Thesis: S.M., Massachusetts Institute of Technology, Department of Nuclear Science and Engineering, September 2016. / Cataloged from PDF version of thesis. "August 2016." / Includes bibliographical references (pages 100-102). / Molten salts for nuclear reactor applications are not a new idea, as these were investigated at Oak Ridge National Lab in the 1960s. However, the past decade or so has seen a large increase in the interest of these, with a variety of designs proposed. The high volumetric heat capacity is of great appeal, as is the low pressure operation with a several hundred degree Celsius margin to boiling. A wide range of passive safety features have also been proposed. However, no matter what the design, there is a need to measure the flow rate of the salt during operation. The nature of the salt greatly complicates the use of a flow meter that must be submerged in the salt. Ultrasonic flow meters have been used for decades with a variety of fluids. These clamp on the outside of the pipe and send an ultrasonic pulse through the pipe from one transducer to another to measure the flow rate. Unfortunately, these have never been used in conjunction with molten salts at the temperatures necessary for nuclear reactor designs. The high temperature of the molten salt presents a problem, as the transducers must be kept cooler. To facilitate this, a thin metal sheet, known as a Wave Injector, was designed to keep the transducer away from the pipe wall and to carry the pulse from the transducer to the pipe. Prior to testing this system on a molten salt facility, it was tested on a water loop to characterize its behavior in a known environment and help inform future design and testing with the molten salt. The bulk of the testing was done in comparing the flow rate measured by the ultrasonic flow meter with that from a reference, electromagnetic flow meter. While the measurements from both agreed well overall, there was significantly better agreement above 7 GPM than below. The ultrasonic flow meter did exhibit good linearity, giving a predictable response for a known change in flow rate. Other testing related to the installation and set-up of the ultrasonic flow meter. Unlike a more traditional flow meter, the ultrasonic flow meter can be configured in a range of ways. It was determined that, as predicted, having the ultrasonic signal take more paths through the fluid produced more precise flow rate data. Additionally, silver was found to be material of choice to go between the piping and the Wave Injector on the molten salt facility, to promote transfer of the pulse from one to the other. These design and configure settings have helped to inform aspects of the molten salt facility, such as tank size. Additionally, testing with and without the Wave Injector provides an anticipation of the spread in data that will be seen on the molten salt facility. Going forward, some additional tests can be done with flowing water to further evaluate configuration options, however the bulk of testing will be with molten salt. Most tests will be similar to those done with the water loop in this study, with either a single path or multipath configuration. Other tests will need to be done to examine the impact of averaging flow rate data on the spread of measurements as well as the loss of temporal resolution. The intended reactor applications should help inform the acceptable resolution in time for safety purposes. Overall, the ultrasonic flow meter performed well and has shown promise with respect to its use as a flow meter for molten salt measurements. / by Michael Pantano. / 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. 161-167). / Low-frequency fluctuations of plasma density, floating potential, ion saturation current, visible light intensity, and edge magnetic field are routinely observed in the Levitated Dipole Experiment (LDX). For the purposes of this thesis, we define low-frequency as W << Wbe where Wbe is the electron bounce frequency. These fluctuations in a laboratory dipole confined plasma lead to turbulence mixing that maintain peaked density profiles. The relationship between the different types of low-frequency fluctuations and plasma density transport is considered. Two 16-channel photodiode arrays were designed and constructed to study the spatial and temporal structure of these fluctuations as part of this dissertation. In addition to the photodiode arrays, a four-channel microwave interferometer is used to estimate the density profile and to measure density fluctuations in the plasma. Several electrostatic probes, including a 24-channel floating probe array, measure fluctuations at the plasma edge and eight Mirnov coils measure magnetic fluctuations. The fluctuations fall into three general categories: broadband, turbulent fluctuations observed during nearly all plasma conditions; quasi-coherent fluctuations with low azimuthal mode numbers and peak frequencies on the order 1 kHz observed during discharges with low neutral pressure; and coherent fluctuations with zero toroidal mode number and peak frequencies on the order of 100 Hz, observed during discharges with moderate neutral fueling. The relationship between time-averaged fluctuation characteristics and plasma parameters are explored. The spatial structure of the fluctuations for several representative shots are discussed. The turbulent fluctuations and concurrent density profiles are compared to quasilinear diffusion of interchange mixing in dipolar plasmas for cases where the fluctuations are random. I show that the quasilinear diffusion equation agrees well with the experimental observations of random fluctuations, supporting the conclusion that interchange mixing is causing inward transport that results in peaked density profiles. For other cases, where nonlinear effects appear to dominate the plasma dynamics, the saturated fluctuation amplitudes are compared to the plasma density profiles. / by Jennifer L. Ellsworth. / Ph.D.

Thesis: Ph. D., Massachusetts Institute of Technology, Department of Nuclear Science and Engineering, 2013. / 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. Pages [228-229] blank. / Includes bibliographical references. / Progress towards a viable fusion reactor will require comprehensive understanding of boundary plasma physics. Knowledge in this area has been growing, yet there are critical gaps. Measurements of the sheath heat flux transmission coefficient-a fundamental physical quantity whose theoretical value is ~ 7-have varied from 2 to 20. Values below 5 are physically impossible and have challenged the understanding of this very basic theory. In addition, measurements of ion temperature are sparse and ion energy transport is poorly understood. To this end a set of new diagnostics, including a surface thermocouple, ion sensitive probe, and retarding field analyzer, have been developed that can tolerate the extreme heat fluxes in the Alcator C-Mod boundary plasma. These probes are used to asses issues of heat flux and ion energy transport. Systematic studies with these new tools reveal the following: A comparison of surface thermocouples and Langmuir probes confirms standard sheath heat flux theory in a tokamak for the first time. The measurement of unphysically low sheath heat flux transmission coefficients and an anomalous increase in measured divertor pressure by Langmuir probes, which is also unphysical, are found the be linked. Plasma-neutral simulations indicate that these artifacts are due to the Langmuir probe bias modifying the local plasma. Important space charge limits to measurements with ion sensitive probes are found experimentally and explored in depth with a 1D kinetic simulation. These results clarify the plasma conditions under which an ion sensitive probe may be used to measure ion temperature and/or plasma potential. The retarding field analyzer is demonstrated to be a viable ion temperature diagnostic up to the last closed flux surface in C-Mod. A ₁D fluid simulations is built to interpret edge ion heat transport. At high collisionality-where the fluid approximations are valid: the simulation reproduces the measured edge ion-to-electron temperature ratio (~ 2). However, at low collisionality-where fluid approximation is not valid-the simulation is not able to reproduce the experimental temperature ratio (~ 4). The addition of kinetic heat flux limiters can bring the simulated ratio into agreement with measurements. The value of heat flux limiter is found to be consistent with that expected from kinetic theory. / by Daniel Frederic Brunner. / Ph. D.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Nuclear Science and Engineering, 2011. / "June 2011." Cataloged from PDF version of thesis. / Includes bibliographical references (p. 66-67). / The recent serious reconsideration of nuclear power as a means for U.S. electric utilities to increase their generation capacity provokes many questions regarding the achievable success of future nuclear power plant construction projects. The troublesome nature characterizing much of the history of U.S. nuclear power plant commercialization provides impetus for an examination of the reasons behind the unanticipated outcomes of many nuclear power plant construction projects. An examination of the history of U.S. nuclear power provides for both an understanding of the historical context of the technology, in addition to an acknowledgement of the difficulties that have surrounded its commercialization. This thesis work identifies the factors that have contributed most significantly to the inability of U.S. electric utilities to successfully manage nuclear power plant construction projects. The historical record of these endeavors was used to create a causal-loop diagram. This diagram reflects a generalized decision-making process used by electric utilities when considering the pursuit of nuclear power plant construction. From the results of the diagram, policy changes are proposed that could reduce the susceptibility of the decision-making process to environmental instabilities and increase the overall attractiveness of the technology. / by Brittany L. Guyer. / S.M.

Thesis: Sc. D., Massachusetts Institute of Technology, Department of Nuclear Science and Engineering, 2014. / 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 143-147). / Monte Carlo (MC) methods for reactor analysis are most often employed as a benchmark tool for other transport and diffusion methods. In this work, we identify and resolve a few of the issues associated with using MC as a reactor design tool. It is widely thought that MC tallies converge at an ideal rate proportional to the inverse of the square root of the number of tally batches. This is true only if tally batches are independent from one another. For a high dominance ratio light water reactor such as the BEAVRS model, significant correlation is present and the convergence rate was much slower. This work developed a means for analytically predicting tally convergence rates when batches are correlated. Analyses supported these findings and confirmed less than ideal convergence rates. For highly correlated problems, it is recommended to reduce error by running additional independent simulations, rather than increasing the number of neutrons in each individual simulation through additional batches. Before tallies can be accumulated, the fission source must be stationary. For the BEAVRS model, this took approximately 200 fission source generations. This process can be accelerated by using coarse mesh finite difference (CMFD), a nonlinear diffusion acceleration method. CMFD was implemented in the continuous-energy MC code OpenMC. When employing this technique, the number of inactive generations was reduced by a factor of 10. Realistic reactor calculations also require thermal hydraulic (TH) feedback which was integrated into the source convergence process. The use of CMFD in addition to TH reduced the number of fission source generations by a factor of 3. Further reduction was achieved by performing nonlinear iterations between the low-order CMFD operator and TH model. Support vector regression, a machine learning algorithm, was used to construct coolant density and fuel temperature dependencies of diffusion parameters between each TH update using MC tallies. A framework was introduced to obtain relative pin power distributions with 95% confidence intervals to 1% with continuous-energy Monte Carlo coupled to thermal hydraulics using low-order CMFD iterations. / by Bryan Robert Herman. / Sc. D.

Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Nuclear Science and Engineering, 2007. / "June 2007." / Includes bibliographical references (p. 57-58). / One of the most interesting aspects of nuclear power is the perceived risk that the public infers from its existence. This paper explores the public's response to risk in general and specifically to nuclear power by reviewing behavioral studies examining how risk is perceived. The paper also discusses important themes relevant to nuclear power and risk perception, including trust, stigma, the difference between experts and the public, and ways of informing and educating the public. The current political status of nuclear power is discussed by examining the roles and opinions of three groups dealing with nuclear energy: 1) the Nuclear Regulatory Commission, 2) the nuclear energy industry, and 3) experts in the field of nuclear power and environmentalists who are concerned with the subject. Finally, conclusions are drawn based on the research into the public's perception of risk and the current status of nuclear energy in order to develop suggestions that may aide in the development of nuclear technology and a resurgence of nuclear power, while addressing the public's concerns and furthering the public's understanding of nuclear technology. / by Christopher Russell Waits. / S.B.

Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Nuclear Science and Engineering, 2013. / "June 2013." Cataloged from PDF version of thesis. / Includes bibliographical references (pages 24-25). / In February of 2013, North Korea conducted its third nuclear weapons test. Speculations are that this test was conducted to further develop a warhead small enough to fit on an intercontinental ballistic missile. This test further strained North Korea's relationship with the international community. North Korea has continued to make steps towards advancing its military capabilities using nuclear weapons, and has even threatened an attack on U.S. soil. The steps that North Korea are currently taking could have detrimental effects on the stability of the region. The role of enrichment technology in the production of nuclear weapons material and the history of North Korea's nuclear program is described. The effect of a nuclear weapons attack on the United States is presented and analyzed. The number of casualties could be or is estimated to be on the order of several thousand people, in addition to the destruction of infrastructure. Although a highly unlikely scenario, these calculations have implications for future policy decisions. This discussion shows the importance of verifying North Korea's nuclear program. Verification would facilitate a better relationship between North Korea and the international community. This could lead to economic support and security assurances for North Korea. Furthermore, it would help the United States avoid a potential attack. / by Ciara Sivels. / S.B.

Thesis: S.B., Massachusetts Institute of Technology, Department of Nuclear Science and Engineering, 2015. / "June 2015." Cataloged from PDF version of thesis. / Includes bibliographical references (page 29). / Renewable energies can reduce the dependence on fossil fuels. Solar thermal systems designed to use molten salts to directly absorb the solar heat are promising due to (1) potentially higher efficiency in capture of sunlight and (2) use of the salt to simultaneously capture sunlight and store heat in the salt. The optical properties of the molten salts are crucial for the design of such thermal systems because they determine the depth of the salt required to absorb sunlight and allow modeling of the performance of such systems. Molten salts are also being developed as coolants for high temperature reactors. Optical properties are also required to determine the radiative heat transfer of the coolant. The objectives of this thesis were to build a better system to measure these properties and measure the optical properties of the proposed salt for a direct absorption concentrated solar thermal system. The attenuation coefficient of light in a binary nitrate salt mixture (KNO 3-NaNO3 40-60 wt%) was measured over the wavelength range 833-2500 nm and the temperature range 300-400°C. This salt is the leading candidate for the first generation of a proposed concentrated solar power on demand (CSPonD) concept [3]. The relevant data was obtained using a FTIR spectrometer and an experimental apparatus designed for semitransparent liquids. The apparatus was validated using the published data for the attenuation of light in deionized water. The attenuation coefficients of the binary nitrate salt mixture for the lower wavelengths matched the data obtained by Passerini [1]. For the longer wavelengths, the attenuation coefficient peaked around 2.5 Pm as predicted by Drotning [2]. Since certain metallic components of solar and nuclear systems are exposed to the molten salt, it is important to characterize the behavior of their reflectivity in the presence of the molten salt. The reflectivity of 304L stainless steel was measured for the wavelength range 600-5000 nm at incident angles of light 10°, 40°, and 70° after an 8-day molten salt immersion test. The reflectivity was measured to be less than 10% for the solar spectrum. / by Shapagat Berdibek. / S.B.

Thesis: Ph. D. in Applied Plasma Physics, Massachusetts Institute of Technology, Department of Nuclear Science and Engineering, 2018. / 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 181-191). / In this thesis, a comprehensive study of Bernstein-Greene-Kruskal (BGK) mode electron holes in a collisionless plasma where strong kinetic effects are important is presented. Kinematic theory based on momentum conservation is derived treating the electron hole as a composite object to study the dynamics of electron holes. A novel 1-D Particle-In-Cell simulation code that can self-consistently track the electron hole motion has been developed for the purpose of this thesis work. Quantitative agreement is achieved between analytic theory and simulation observations. The thesis reports a new kind of instability for electron holes. Slow electron holes traveling slower than a few times the cold ion sound speed in the ion frame are observed to be unstable to the oscillatory velocity instability. A complete theoretical treatment for the instability is presented in this thesis. Numerical simulations yield quantitative agreement with the analytic theory in instability thresholds, frequencies and partially in instability growth rates. It is further shown that an electron hole can form a stable Coupled Hole Soliton (CHS) pair with an ion-acoustic soliton. A stable CHS travels slightly faster than the ion-acoustic velocity in the ion frame and is separated from a typical BGK mode electron hole in the velocity range by a gap, which is set by the oscillatory velocity instability. Transition between the two states is possible in both directions. A CHS exhibits a soliton-like behavior. The thesis sheds light on solving the ambiguity between an electron hole and a soliton. This thesis work also has important implications for interpreting space probes observations. / by Chuteng Zhou. / Ph. D. in Applied Plasma Physics