Thesis: S.B., Massachusetts Institute of Technology, Department of Nuclear Science and Engineering, 2018 / Cataloged from PDF version of thesis. / Includes bibliographical references (pages 48-53). / Proton therapy has yet to implement an in-vivo, real-time, fault-tolerant integral dosimeter. Proposed in this thesis is a conceptual dosimeter to meet such requirements, relying on the radiation-stimulated production of F-centers in alkali halide salts. F-centers are optically active vacancies in the cation-anion lattice filled with a lone electron. These vacancies cause dimming bands in broad-band illumination of the crystal, and the vacancies increase in number in a proportional fashion to the dose received. The experiment proposed here will serve both to measure the dimming quality of various alkali halide salts as well as their decay rate in the dark at room temperature. Once performed, this experiment will demonstrate the feasibility of correlating dose to a real-time color measurement of an implanted alkali halide crystal in a patient undergoing proton radiotherapy. Thus far no such experiments have been performed, however the experimental assembly outlined herein is nearly fully constructed and nearly ready for experimentation upon time of completing this thesis. / by Daniel Schumaker. / S.B. / S.B. Massachusetts Institute of Technology, Department of Nuclear Science and Engineering

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 157-163). / While many ex situ measurements exist to measure plasma-facing component (PFC) surfaces of materials extracted from tokamaks, developing a deeper understanding of the dynamics of erosion, redeposition, and fuel retention in these surfaces will require in situ measurements. A first-of-a-kind technique, Accelerator-Based In-Situ Materials Surveillance (AIMS), was developed for this purpose and first demonstrated on Alcator C-Mod to study divertor surfaces with shot-by-shot resolution [1]. However, the original AIMS methods are not applicable to studying the erosion of bulk, high-Z PFCs like molybdenum and tungsten. Thus, a new method of ion beam analysis (IBA) has been developed to expand the capabilities of AIMS to directly measure this high-Z bulk erosion. This new method, called DEA (Depth markers for Evaluating high-Z materials with AIMS), combines the traditional IBA technique of particle-induced gamma emission (PIGE) with implanted depth markers. / The implanted markers enable the study of bulk material by providing a reference to the surface that can be monitored for erosion and redeposition. Implanting the marker eliminates the need for specially-manufactured "marker tiles" formed by deposited layers that can delaminate and otherwise fail under operational conditions. Two variations of this method were developed: ex situ DEA (eDEA) and in situ DEA (iDEA). Both use PIGE spectroscopy with implanted markers, but they take advantage of different features in gamma production cross sections to analyze data. eDEA, which has shown promising results in ex situ analysis of materials exposed in a tokamak, can also be used to validate the use of depth markers. iDEA provides AIMS with the ability to measure in situ high-Z bulk erosion. As part of this thesis, the following ex situ experiments have been carried out to assess the viability of these techniques. / eDEA samples with implanted depth markers have been studied after plasma exposure on the Material and Plasma Evaluation System (MAPES) in the Experimental Advanced Superconducting Tokamak (EAST). Stability of the marker to temperature excursions was studied by exposing samples to temperatures from 200 to 1000C for times from 1 to 24 hours. iDEA samples were implanted at different depths to determine the sensitivity of the technique to depth. Two simulations were developed to allow interpretation of the experimental data and to test the sensitivity, with initial studies showing a match between predicted and experimental results. eDEA measured erosion of 42.0 23.5 nm on one sample exposed in EAST, and iDEA depth markers were located with 40 nm of accuracy. These results show that DEA, as a part of an AIMS experiment, has the appropriate resolution to monitor surfaces inside a tokamak for time-resolved bulk erosion. / by Leigh A. Kesler. / Ph. D. / Ph.D. Massachusetts Institute of Technology, Department of Nuclear Science and Engineering

This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections. / Thesis: S.M., Massachusetts Institute of Technology, Department of Nuclear Science and Engineering, 2019 / Cataloged student-submitted from PDF version of thesis. / Includes bibliographical references (pages 93-96). / Nuclear regulation lies at the nexus of public policy, business, and engineering. While current regulatory processes have become fairly effective for the regulation of existing nuclear power plants, the use of prescriptive technology-specific requirements may present a challenge for the licensing and deployment of advanced nuclear power plants. These advanced nuclear power plants can utilize passive systems, new fuel forms or coolants, or other new design features to accomplish their safety and security functions. Advanced reactors may not comply with existing requirements for nuclear power plant licensing due to their departure from the design philosophies and reactor technologies used in existing nuclear power plants. The challenge of licensing advanced nuclear power plants using existing regulatory requirements could increase the time and costs associated with licensing new plants, and jeopardize the commercial viability of the industry. / In this work, the principles of nuclear regulation are presented and discussed in the historical context and evolution of licensing and regulating nuclear power plants in the United States and abroad. The current licensing system for commercial nuclear power plants in the United States is then discussed in detail. Existing and proposed processes for advanced nuclear reactor licensing are presented, and challenges of advanced reactor licensing are discussed. Finally, a methodology is developed and presented for selecting an appropriate licensing pathway for a proposed advanced reactor. Answers to ten characterization questions are used to recommend which existing regulatory tools and pathways available in the United States could enable the most effective licensing of an advanced reactor. The proposed methodology could prove a valuable tool for companies seeking to develop new reactor technologies while minimizing licensing costs, schedules, and related uncertainties. / The methodology is accessible for users with limited experience with (or knowledge of) existing nuclear regulations. The recommendations for policy changes and the advanced reactor pathway selection methodology presented in this work could enable the more efficient licensing and deployment of advanced nuclear reactors. / by Robert Patrick White. / S.M. / S.M. Massachusetts Institute of Technology, Department of Nuclear Science and Engineering

This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections. / Thesis: S.M., Massachusetts Institute of Technology, Department of Nuclear Science and Engineering, 2018 / Cataloged from student-submitted PDF version of thesis. Page 123 blank. / Includes bibliographical references (pages 106-116). / Development of accident tolerant fuels (ATF) for light water reactors (LWRs) came into focus for the nuclear engineering community after the accidents at Fukushima-Daiichi. The primary focus of the ATF program is to identify alternative fuel and cladding technologies that may provide enhanced safety, competitiveness, and economics. The new fuel design must also be compatible with present-day LWR design. For near-term applications, coatings on the nominal Zirconium-based cladding material and other metallic materials are being considered to improve the corrosion resistance and reduce the generation of hydrogen at high temperatures. Major ATF coating choices under consideration include chromium as a coating, iron-chromium-aluminum alloys (FeCrAl) as cladding and molybdenum as a coating, which have demonstrated better mechanical and oxidation behavior during the experimental testing. / Thermal-fluids characteristics are pivotal for a robust testing of ATF concepts as the proposed candidates may have an entirely different thermal-hydraulic behavior when compared to Zircaloy-4. ATF coatings may display very different boiling characteristics as a result of different microstructures and surface characteristics. In the present work, transient boiling heat transfer during quenching of the candidate ATF claddings on vertical rodlets is studied experimentally. The candidate ATF material (chromium, FeCrAl, and molybdenum) are applied on Zircaloy-4 rodlets. The vertical solid rodlets are heated to temperatures up to 1000 °C and are quenched in a saturated pool of water at atmospheric pressure. The temperature variation during the quenching of rodlets was recorded insitu with synchronized visualization of boiling regimes over the test specimen using a high-speed video camera. / The quench performance of the ATF coatings was analyzed based on the examination of various surface parameters such as wettability, roughness, emissivity and capillary wicking. In order to obtain a more realistic picture of the candidate performance during the emergency cooling reflood phase in a nuclear reactor, the coated rodlets are also oxidized in an autoclave before quenching. The performance of the candidate claddings is evaluated after oxidation and the surface characterized. It was observed from the post-test analysis that the surface characteristics and oxidation had a significant impact on the quench performance of ATF coatings, which varied between different coating materials. In order to better understand the thermal margins in a reactor specific environment, an analysis was performed on samples after exposing them to gamma rays. The gamma rays tend to change the surface wettability through a phenomenon called Radiation Induced Surface Activation. / A Gammacell 220E irradiator that uses 12 cobalt-60 pencil sources, arranged axially in a sample chamber at MIT, was used to irradiated the samples. The results of water quenching and contact angle studies showed a higher Leidenfrost temperature and wettability in both samples exposed to gamma irradiation. The detailed microscopic analysis attributed the enhanced wettability to oxidation of the surface under gamma irradiation. / by Arunkumar Seshadri. / S.M. / S.M. Massachusetts Institute of Technology, Department of Nuclear Science and Engineering

This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections. / Thesis: S.M., Massachusetts Institute of Technology, Department of Nuclear Science and Engineering, 2019 / Cataloged from student-submitted PDF version of thesis. / Includes bibliographical references (pages 235-238). / The goal of fusion energy research is to build an economically competitive reactor. This is difficult due to the complicated system composing a reactor and the nonlinearities it entails. Practically, to even get to the neighborhood of an economic reactor requires hundreds of simulations - which in turn necessitate quick running fusion systems codes. Moving towards these economic reactors then involves finding what design parameters provide the most leverage in lowering reactor costs. As highlighted by the difference between European and American designs, however, the most important decision for tokamaks is whether to run them as pulsed or steady-state. This paper aims to fairly compare the two modes of operation using a single, comprehensive model. Benchmarked against other codes, this model actually shows that no fusion reactor is achievable without some technological advancements. This can be seen through every referenced design using nonstandard values of H and N[subscript G]. The interesting result this paper shows is that developing high-temperature super-conducting (HTS) tape could actually make both steady-state and pulsed tokamaks economically competitive against solar and coal. Further, this HTS tape actually has different best uses for the two modes of operation, appearing in the magnet structures of: TF coils for steady state and the central solenoid for pulsed. Developments in this technology should produce economic reactors within the coming decade. / by Daniel Joseph Segal. / S.M. / S.M. Massachusetts Institute of Technology, Department of Nuclear Science and Engineering

Thesis: S.B., Massachusetts Institute of Technology, Department of Nuclear Science and Engineering, 2018. / Cataloged from PDF version of thesis. / Includes bibliographical references (page 21). / The nature of deregulated energy markets in the United States has forced several nuclear reactors into early retirement over the next few years subjecting the energy market and economy as a whole to uncalculated risk. The unforeseen implications of early retirements of nuclear assets has inspired a cause for concern in Spain where nuclear power faces similar problems. In order to assess the danger that Spain's current market structure incentivizes a premature retirement of nuclear assets and suggest possible implications for carbon emissions, this thesis research project analyzed the economic performance of nuclear power generators in Spain and identified the underlying factors driving it. This was done by calculating the short run profitability of each nuclear reactor. Historical data on the generation, operating costs, and marginal price from the Spanish electricity market was gathered to develop a net profit model. The model was then applied looking forward into the future and revealed an average profitability of +32.24523 E/MWh for the nuclear reactors in Spain. These results point to a positive future for nuclear power in Spain and an incentive to extend the licenses of soon-to-be-retired reactors. / by Fabrice A. Fils-Aime. / S.B.

Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Nuclear Science and Engineering, 2007. / "June 2007." Leaf numbering handwritten. / Includes bibliographical references (leaf 21). / In the confectionery industry, there is considerable interest in understanding the mechanisms of liquid lipid migration inside chocolates as it relates to combating fat-bloom defects in confectionery products. [1] This thesis investigates the ability of MAS NMR spectroscopy to adequately resolve chocolate spectra and deliver diffusion data specific to individual chemical species. Using a Bruker 300 MHz spectrometer equipped with liquid state and hr-MAS probes various spectroscopic characteristics of a milk chocolate sample were recorded. The MAS spectrometer resolved the chocolate spectrum into individual chemical signals and demonstrated multi-compartment diffusion behavior. / by Dwight McCoy Chambers. / S.B.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Nuclear Science and Engineering, February 2009. / Cataloged from PDF version of thesis. / Includes bibliographical references. / Phase Contrast Imaging (PCI) was studied with the goal of understanding its relevance and its requirements. Current literature does not provide insight on the effect of a relaxation in coherence requirements on the PCI capabilities of an imaging system. This problem is all the more important since coherent X-ray and Neutron sources are mostly unavailable. We develop a model for PCI contribution to imaging for partially incoherent systems, and develop a methodology to identify a minimum and an optimum coherence length 4min and opt. We propose a figure-of-merit KPcI that quantifies the PCI capabilities of an imaging system. Our calculations show that X-ray PCI systems based on free space propagation using microfocus X-ray tubes have little PCI capabilities. We develop a model to explain the edge enhancement observed with those systems; our results suggest that scatter reduction is the process responsible for the observed edge enhancement. We performed experiments that show good agreement with the model. Coded Source Imaging (CSI) is proposed as a tool to produce highly coherent sources. The general theory of CSI is developed. We propose two possible systems: Fluorescent Coded Sources (FCS) and the AEB Encoded X-ray tube. / by Antonio Leonardo Damato. / Ph.D.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Nuclear Science and Engineering, February 2010. / Cataloged from PDF version of thesis. / Includes bibliographical references (p. 94-97). / In order to support the increasing demand for clean sustainable electricity production and for nuclear waste management, the Sodium-Cooled Fast Reactor (SFR) is being developed. The main drawback has been its high capital and operating costs in comparison with traditional light water reactors. In order to compete, the SFR must be shown to be economically competitive. This study makes use of the proposed Technology Neutral Framework (TNF) being developed by the U.S. NRC. By applying this risk-based approach to safety, rather than the traditional approach of applying deterministic requirements, it will be shown that significant savings can be realized without compromising fundamental safety. A methodology was developed using the Technology Neutral Framework to judge design alternatives based on risk significance that provide acceptable safety within the framework at less cost. The key probabilistic metrics of Risk Achievement Worth and Limit Exceedence Factor will be used to assess whether a system or component plays an important safety function. If not the system, structure or component either can be eliminated, modified or its safety grade can be reduced resulting in cost savings. In addition, assessments were made to determine how to improve thermal efficiency by raising reactor exit temperature and by applying other design alternatives to reduce costs as evaluated on a safety, reliability and economic basis. / (cont.) This methodology was applied in a series of case studies demonstrating the value of the approach in design. The probabilistic risk assessment, the reference economic model and the Technology Neutral Framework tools required for this methodology are described. A reference economic model for a pool-type SFR was developed using the G4-ECONS model since it is an acceptable standard model for economic analysis. Since cost predictions for sodium cooled fast reactors are highly uncertain, the results of the economic analysis are used to estimate the relative improvement in cost as a function of the design alternatives proposed by the TNF methodology approach. This study used generic and comparative numbers for the ALMR and SPRISM reactors for cost of components of the SFR, to identify capital cost drivers for further study and cost reduction. For comparative purposes, the light water reactor (LWR) economic model in the G4-ECONS model was used and benchmarked to current LWR data. As a result of the case studies in which the methodology was applied, it was shown that the capital cost of the SFR could be reduced by almost 18% ($336 million) over the reference design and the levelized generating costs could be reduced by over 10% (almost 1 cent/kw-hr). These savings come largely from improvements in thermal efficiency, elimination of the energetic core disruptive accident as a design basis event and simplification of the reactor shutdown system based on risk analysis and safety significance. Should this methodology be applied to the entire plant design, it is expected that significant additional savings could be identified. / by Christopher C. Nitta. / S.M.

Thesis: Ph. D., Massachusetts Institute of Technology, Department of Nuclear Science and Engineering, 2015. / Cataloged from PDF version of thesis. / Includes bibliographical references (pages 229-234). / This research demonstrates that multiple mono-energetic gamma lines produced from low threshold, high-Q nuclear reactions can be used to detect the presence of high-Z material shielded in low- and medium-Z cargo. Specifically, this work establishes a research foundation to inform the eventual development and optimization of a new type of low-dose, rapid-scan, transmission radiography imaging system designed to detect the presence of special nuclear material in cargo. This thesis explores the processes, reactions, and detection methods that may be used to develop a transmission imaging system significantly different from existing interrogation methods and major systems currently deployed in the field. This thesis introduces the nuclear smuggling issue, provides relevant background information, and defines the high-Z material detection problem. It also provides a brief overview of SNM detection efforts, to include both passive and active detection, and shows why active detection methods are needed to detect shielded SNM. The thesis then explains the underlying physics important to multiple monoenergetic gamma line imaging and defines key concepts to the characterization of cargo. An overview of the experimental concept and setup, to include development of a theoretical model to predict imaging counts, simulations conducted in support of the experiment, the presence and mitigation of neutrons in the beam line, major equipment and materials used, and the data acquisition and analysis software programs employed is then provided. This work considers and explains the difficulties of scanning of homogeneous and non-homogeneous cargoes, potential scanning system vulnerabilities to high-Z material smuggling, and suggests future efforts to address these vulnerabilities. The purpose, conduct, and results of 161 individual tests are provided. Finally, this thesis provides conclusions and recommendations for future work that could lead to development of a better cargo scanning system. Key achievements of this thesis included development of a simple attenuation model to predict the theoretical ratio of two monoenergetic gamma lines transmitted through complex cargo, exploration of the ability to discriminate between medium and high-Z materials both as pure cargo and when embedded in Fe, and the This research demonstrates that multiple mono-energetic gamma lines produced from low threshold, high-Q nuclear reactions can be used to detect the presence of high-Z material shielded in low- and medium-Z cargo. Specifically, this work establishes a research foundation to inform the eventual development and optimization of a new type of low-dose, rapid-scan, transmission radiography imaging system designed to detect the presence of special nuclear material in cargo. This thesis explores the processes, reactions, and detection methods that may be used to develop a transmission imaging system significantly different from existing interrogation methods and major systems currently deployed in the field. This thesis introduces the nuclear smuggling issue, provides relevant background information, and defines the high-Z material detection problem. It also provides a brief overview of SNM detection efforts, to include both passive and active detection, and shows why active detection methods are needed to detect shielded SNM. The thesis then explains the underlying physics important to multiple monoenergetic gamma line imaging and defines key concepts to the characterization of cargo. An overview of the experimental concept and setup, to include development of a theoretical model to predict imaging counts, simulations conducted in support of the experiment, the presence and mitigation of neutrons in the beam line, major equipment and materials used, and the data acquisition and analysis software programs employed is then provided. This work considers and explains the difficulties of scanning of homogeneous and non-homogeneous cargoes, potential scanning system vulnerabilities to high-Z material smuggling, and suggests future efforts to address these vulnerabilities. The purpose, conduct, and results of 161 individual tests are provided. Finally, this thesis provides conclusions and recommendations for future work that could lead to development of a better cargo scanning system. Key achievements of this thesis included development of a simple attenuation model to predict the theoretical ratio of two monoenergetic gamma lines transmitted through complex cargo, exploration of the ability to discriminate between medium and high-Z materials both as pure cargo and when embedded in Fe, and the / by Buckley E. O'Day, III. / Ph. D.