Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Nuclear Science and Engineering, 2008. / Includes bibliographical references. / Passive cooling systems sometimes use natural circulation, and they are not dependent on emergency AC power or offsite power, which can make designs simpler through the reduction of emergency power supplying infrastructure. The passive system approach can lead to substantial simplification of the system as well as overall economic benefits, and passive systems are believed to be less vulnerable to accidents by component failures and human errors compared to active systems. The viewpoint that passive system design is more reliable and more economical than active system design has become generally accepted. However, passive systems have characteristics of a high level of uncertainty and low driving force for purposes of heat removal phenomena. These characteristics of passive systems can result in increasing system unreliability and may raise potential remedial costs during a system's lifetime. This study presents a comprehensive comparison of reliability and cost taking into account uncertainties and introduces the concept of flexibility using the example of active and passive residual heat removal systems in a PWR. The results show that the active system can have, for this particular application, greater reliability than the passive system. Because the passive system is economically optimized, its heat removal capacity is much smaller than that of the active system. Thus, functional failure probability of the passive system has a greater impact on overall system reliability than the active system. Moreover, considering the implications of flexibility upon remedial costs, the active system may more economical than the passive system because the active system has flexible design features for purposes of increasing heat removal capacity. / by Jiyong Oh. / Ph.D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Nuclear Science and Engineering, 2008. / Cataloged from PDF version of thesis. / Includes bibliographical references (p. 177-179). / The North Sea oil province, one of the world's major centers of petroleum and natural gas production, has been in play for four decades. Production rates have approached their peaks in recent years and are expected to decline continuously in the future. The economies of certain cities and regions bordering on the North Sea have become heavily dependent on the oil and gas industry. How these local economies will sustain themselves in the future as resource depletion continues is a critical question. To gain insight into this question, we selected a matched pair of city-regions, each of which is an important center of the oil and gas industry in the North Sea province: Aberdeen in Scotland and Stavanger in Norway. By studying the similarities and differences between the local innovation systems in the two regions, we can gain a general understanding of how local economies respond to changes in their environment. U.S. patenting data are used as a tool to describe the behavior and performance of the two local innovation systems. The patent data provide a means of systematically and consistently estimating knowledge flows. The use of U.S. patent and patent citation data provides evidence, references, and guidelines to the project from a quantitative perspective. Several indicators were developed to describe these knowledge flows, along with a model providing further insight into how knowledge was acquired and introduced into the two local innovation systems, how and to what extent local innovation capabilities were developed, and how knowledge created locally has spread elsewhere. / (cont.) Both Stavanger and Aberdeen have worked hard to strengthen their local innovation capabilities by learning from the world's most advanced firms, especially those from the U.S.,and by building capabilities of their own. At the same time, attracted by the extensive reserves of oil and gas, multinational firms, many from the U.S., moved into the North Sea region. The involvement of multinational firms helped reinforce local innovation capabilities. However, because of the different policy approaches pursued in the two regions, U.S. firms, the international leaders in oil and gas technology, have played more important roles in Aberdeen than in Stavanger. In the Stavanger area, local innovation activities have been led by national oil companies rather than by foreign firms. / by Wei Gao. / Ph.D.

Thesis: S.B., 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 (page 45). / Materials used in nuclear reactors, both fission and fusion, are continuously interacting with high energy ions. Tandem electrostatic accelerators, such as DANTE, are able to produce ions at high energies that can be used to simulate these interactions. In order to enhance the quality of experimental data taken using an accelerator, it is useful to ensure that the particles being accelerated are of the same species. Wien filters use electromagnetic forces to filter particles in an ion beam. Also referred to as mass selectors or velocity selectors, Wien filters operate on the principles of the Lorentz force in order to select ions of a certain mass while filtering out all others. The Wien filters in DANTE were modeled and tested in order to determine their effectiveness and ideal operating conditions. Experimental data was taken by varying the voltage applied to the Wien filters operating in DANTE. Preliminary results concluded that the Wien filters are able to steer the beam, as demonstrated by the impact of Wien filter voltage on the beam current through the accelerator. However, the experiment was inconclusive as to whether or not the Wien filters successfully filtered out unwanted ions. The settings applied during the experiment were then simulated with a model. For a deuterium beam, the model recommends voltage settings of 312 V and 341 V for the horizontal and vertical Wien filters, respectively. The model results are consistent with the experimental data. Recommendations for future work on this project are outlined following the results. / by Carolena Ruprecht. / S.B.

Thesis: S.B., Massachusetts Institute of Technology, Department of Nuclear Science and Engineering, 2017. / Cataloged from PDF version of thesis. / Includes bibliographical references (pages 55-58). / Radiation damage in materials can cause critical components in fission and fusion reactors to fail with potentially catastrophic consequences. Radiation damage quantification is essential for understanding, predicting, and preventing such failures. The current unit of radiation damage, displacements per atom (DPA), is not a measurable quantity, and it is known to be an inaccurate measure of radiation damage. This project aims to quantify radiation damage accurately and measurably by characterizing the storage of energy in radiation-induced material defects, known as Wigner energy storage. In order to gain an atomistic understanding of radiation damage, the irradiation and calorimetry of elemental copper were simulated using molecular dynamics code. A custom defect analysis script was used to determine the energy stored as a function of irradiation energy and defect type. Wigner energy peaks were clearly visible in the calorimetry data, indicating that Wigner energy measurement is a plausible technique for quantifying radiation damage. Future work should focus on achieving more realistic heating rates and measuring Wigner energy storage experimentally using fast scanning calorimetry. / by Ki-Jana Carter. / S.B.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Nuclear Science and Engineering, 2010. / Cataloged from PDF version of thesis. / Includes bibliographical references. / Previous studies conducted at MIT showed that power performance of typical pin geometry PWRs are limited by three main constraints: core pressure drop, critical heat flux (CHF) and fretting phenomena of the fuel rods against grid spacers. The present work investigates the possibility to reduce the limiting effect exerted by these constraints by radically changing the core geometry, rather than by only taking measures to address specific constraints. The geometry modification consists of inverting the relative position of fuel and coolant, thus generating the so-called inverted geometry. An inverted assembly consists of a fuel prism perforated with cylindrical, vertically oriented, cooling channels, arranged in a triangular lattice. A pin vs inverted comparison, performed at cell level, shows that an inverted geometry can attain the same fuel volume fraction of the pin geometry but with a much lower pressure drop and fuel temperature. Also, CHF performance can be enhanced, relative to the pin geometry, by inserting multiple short-length twisted tapes (MSLTTs) inside the cooling channels, and fretting concerns do not apply since spacer grids are not needed. When the pin vs inverted comparison is performed at whole-core level, the same conclusion on pressure drop and fuel temperature apply to reactor types in which, thanks to low operating pressure and/or fuel-coolant chemical compatibility, the inverted core can be designed as to closely resemble a modular repetition of the inverted unit cell, i.e. the so-called continuous inverted geometry. / (cont.) However, the high operating pressure characterizing a PWR, together with the need of avoiding fuel-water interaction, require the inverted PWR (IPWR) to be provided with particularly thick ducts enclosing the fuel prisms. These ducts, together with the wide inter-assembly water gaps needed for control rod insertion, cause the inverted geometry to become discontinuous, and to lose part of the pressure drop and fuel temperature advantages characterizing a continuous inverted geometry. A U-Th-Zr-hydride fuel was selected for the IPWR. The main reasons that led to its choice were the negligible fission gas release which is compatible with the need to enclose the fuel in a large duct, and the pre-hydriding metal structure of the fuel which allows an effective drilling. A detailed study was performed to maximize the performance of a hydride-fueled IPWR, accounting for structural mechanics, thermal hydraulics, neutronics and manufacturing-related constraints. The analysis was performed over a wide spectrum of lattice geometries, each characterized by specific values of the cooling channel diameter and pitch. Three cooling channel designs were examined: MSLTT-provided channels, channels provided with a long twisted tape inserted in the top half of the core, and empty channels. Two duct designs were examined: collapsible and non-collapsible. The former, about 210 mm wide and with ~9 mm thick walls, is designed to collapse onto the fuel prism upon primary system pressurization. / (cont.) The latter, about 100 mm wide and with -6 mm thick walls, is internally pressurized: its small size together with the reduced differential pressure across its walls, allow preventing duct-fuel contact, but significantly penalize the reactor power performance due to the reduced volume available for fuel and coolant. As a consequence of these design options, a total of six IPWR designs were examined. Because of the scarcity of pressure drop data referred to MSLTT designs, pressure drop tests were performed and results entered in the IPWR computational analysis model. Besides usefulness for the IPWR study, the wide range of MSLTT designs that were tested allowed supplementing the literature with valuable experimental data. It was found that pressure drop is the most limiting IPWR design constraint, followed by CHF and, only marginally, fuel temperature. The fuel web thickness, i.e. the minimum thickness of fuel meat between adjacent cooling channels, was also found to significantly affect the attainable power. Specifically, the smaller this thickness, the higher is the power. To allow fuel prism manufacturability, fuel web thicknesses as low as 2 mm were examined. The IPWR provided with collapsible ducts and empty cooling channels was verified to outperform all the other IPWR designs examined. / (cont.) Conclusions on the competitiveness, from the attainable power viewpoint, of this IPWR design against typical pin geometry PWRs depend on the IPWR considered (maximum powered, but provided with a very small web thickness, or a "selected design", having lower power but larger fuel web thickness) and on the PWR relative to which the comparison is performed (maximum powered, but with thin 6.5 mm OD fuel rods, or reference geometry 9.5 mm OD rods). If the maximum powered IPWR is considered, maximum power gains are of 13% and 48% with respect to the maximum powered PWR and to the reference PWR respectively. If the selected IPWR design is considered, no power gain is possible relative to the maximum powered PWR, while a power gain of 19% is achievable relative to the reference PWR. A comprehensive analysis, including LBLOCA modeling and neutronics, was performed on the selected IPWR design. This reactor was demonstrated to be able to deliver a thermal power of 4078 MW, corresponding to a 19% gain with respect to the reference PWR analyzed with the same pressure drop limit. Power density and specific power are 119 MW/m3 and 73.6 kW/kgHM respectively. Required fuel enrichment to achieve a 17.2 month fuel cycle is 15%. Although a net power gain was demonstrated, the economic competitiveness of the IPWR concept is penalized by the higher enrichment required and, eventually, by higher manufacture costs of the inverted assemblies relative to pin assemblies. A complete economic analysis, not performed in this work, would be needed to assess the benefits of the IPWR design. / by Paolo Ferroni. / Ph.D.

Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Nuclear Science and Engineering, 2010. / Cataloged from PDF version of thesis. / Includes bibliographical references (p. 33). / The behavior of TRISO fuel used in high temperature gas reactors in order to achieve high fuel performance is difficult to model using traditional lattice codes due to the double-heterogeneity effect created by the multi-coated fuel kernels in a graphite matrix. A simple volume-weighted homogenization does not accurately reduce the problem to one degree of heterogeneity as it does not properly account for the self shielding of the TRISO particles. The Reactivity-equivalent transformation (RPT) model, which condenses the TRISO fuel into a smaller fuel zone radius before homogenization, has been proposed as a possible solution to the problem of double-heterogeneity. The RPT method has been demonstrated to accurately model the reactivity of individual pin cells. While small, seven-cell RPT arrays are still highly accurate models of TRISO behavior, it is unclear if negligible error will extend to even larger arrays, especially in the presence of a B4C absorber. The validity of RPT array models was assessed by comparing the reactivity, thermal absorption, thermal utilization, resonance escape probability, fast fission factor, power, and neutron flux with reference values for an array containing all double-heterogeneous cells. / by Steven T. Lynch. / S.B.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Department of Nuclear Science and Engineering, 2013. / Cataloged from PDF version of thesis. / Includes bibliographical references (pages 127-146). / This thesis is a computational and theoretical investigation of the response of materials' mechanical properties to a wide range of environmental conditions, with a particular focus on the coupled effects of strain rate and temperature. The thesis provides original contributions to the fundamental understanding of how the materials mechanical properties change, as manifested by defect structure evolution, with temperature and strain rate conditions, as well as to the development of methodology used for enabling the investigation of dislocation-defect interactions over a much wider range of time scales than of reach to traditional techniques. This thesis advanced the capabilities of a recently developed activation-relaxation based atomistic method to enhance the accuracy of kinetic predictions, and to enable the investigation of dislocation-defect interactions dynamically at long time scales. We took the Autonomous Basin Climbing (ABC) method as a starting point, and incorporated the ability to sample multiple transition pathways associated with a given state. This new feature addresses the problem of overestimating the system evolution time due to the one-dimensional nature of the original ABC algorithm. The ABC method was further implemented in a dynamic framework, which makes it possible for the first time to directly simulate the dislocation-obstacle interactions at very low strain rates. This approach allows for a new way to connect the atomistic results to models at the meso-scale for simulating the plasticity of metals. We analytically derived how the applied strain rate couples with the thermal activation process, based on the framework of transition state theory informed by the atomistic approach described above. We demonstrated the coupling effect is a common mechanism behind many important phenomena, and provide three examples from the atomic level on the dislocation mobility and dislocation interactions with radiation induced defects. (i) A well-known universal flow stress upturn behavior in metals has been examined. We provide a simple physically based model to predict the flow stress at various strain rates, without invoking any assumed mechanisms or fitting parameters as in the traditional constitutional models. (ii) We implemented this new model in (i) to investigate the dislocation-obstacle interactions. The approach enabled us to map the interaction between an edge dislocation and a self interstitial atom (SIA) cluster in Zr in a two-parameter space consisting of temperature and strain rate. This approach allows the direct atomistic simulation of dislocation-obstacle interactions at experimental time scale, namely at low strain rates, which cannot be reached by traditional atomistic techniques. The dislocation is found to absorb the SIA cluster and climb at low strain rates and high temperatures, while it passes through the SIA cluster at high strain rates and low temperatures. The predicted mechanism map is able to reconcile the seeming controversy between previous experimental and computational findings. (iii) A dislocation-void interaction in bcc Fe at prescribed strain rate is also investigated. We demonstrated that different applied strain rates can affect the interaction mechanism and the defect microstructure, and eventually lead to a negative strain rate sensitivity (nSRS) of yield strength below a critical strain rate. This finding at the unit process level supplements the previous explanations of the nSRS with higher level constitutive relations. Beyond the specific cases analyzed in metals in this thesis, the insights gained on the coupling between strain rate and thermal activation can be used to explain the dependence on strain rate and temperature in other important classes of materials (e.g. colloids, cement) and phenomena (e.g. corrosion, creep). / by Yue Fan. / Ph.D.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Nuclear Science and Engineering, 2011. / Cataloged from PDF version of thesis. / Includes bibliographical references (p. 119-123). / The commercial nuclear power industry is continually looking for ways to improve reactor productivity and efficiency and to increase reactor safety. A concern that is closely regulated by the Nuclear Regulatory Commission is the exothermic zircaloy-steam oxidation reaction which can potentially occur during a loss of coolant accident (LOCA), and may become autocatalytic beyond 1,200 0C, thus generating a large amount of hydrogen. The concern for the zircaloy oxidation reaction has been heightened since the March 2011 events of Fukushima, Japan. One solution offering promising results is the use of silicon carbide (SiC) cladding in nuclear reactor fuel rod designs. SiC, a robust ceramic which reacts very slowly with water or steam, has many features that meet or exceed that of zircaloy including the ability to withstand higher temperatures due to a higher melting point and the ability to absorb fewer neutrons than zircaloy which would allow for increased safety margins and fuel burnup. An experimental investigation of the oxidation performance of a-SiC during a postulated LOCA event was performed. The test facility was designed and fabricated to test the oxidation rates of zircaloy and SiC in a high temperature, high-purity, flowing steam environment. Studies of zircaloy-4 oxidation were conducted to validate the test facility for this purpose. Thirty six zircaloy-4 tests lasting up to 30 minutes, at temperatures ranging from 800°C to 1,200°C, were completed and compared to existing models and literature data. Additionally, six longer duration a-SiC tests lasting from 8 hours to 48 hours, at temperatures of 1,140°C and 1,200°C, were completed. These tests clearly show that, from an oxidation perspective, SiC significantly outperforms zircaloy in high-flowing, superheated steam. For zircaloy, results from the most intense temperature/duration testing combination of 1,200°C for 30 minutes show 15.6 percent weight gain. For the most intense SiC tests at 1,200°C for eight hours, a weight loss of two orders of magnitude less occurred, a 0.077 percent weight loss. The four 24 hour and 48 hour SiC tests at 1,140°C also correlate well with the expected paralinear oxidation trend and further confirm that SiC is more resistant to oxidation in high temperature steam than zircaloy. / by Ramsey Paul Arnold. / S.M.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Nuclear Science and Engineering, 2013. / Cataloged from PDF version of thesis. / Includes bibliographical references (pages 191-200). / This thesis discusses a series of experimental studies that investigate the coherence properties of a superconducting persistent-current or flux qubit, a promising candidate for developing a scalable quantum processor. A collection of coherence characterization experiments and techniques that originate from the field of nuclear magnetic resonance (NMR) are implemented. In particular, one type of dynamical decoupling techniques that uses refocusing pulses to recover coherence is successfully realized for the first time. This technique is further utilized as a noise spectrum analyzer in the megahertz range, by which a 1/f-type dependence is observed for the flux noise. Then, a novel method of performing low-frequency noise spectroscopy is developed and successfully implemented. New techniques used in the readout scheme and data processing result in an improved spectral range and signal visibility over conventional methods. The observed power law dependence below kilohertz agrees with separate measurements at higher frequencies. Also, the noise is found to be temperature independent. Finally, a robust noise spectroscopy method is presented, where the spin-locking technique is employed to extract noise information by measuring the driven-evolution longitudinal relaxation. This technique shows improved accuracy over other methods, due to its insensitivity to low-frequency noise. Spectral signatures of coherent fluctuators are resolved, and further confirmed in a time-domain spin-echo experiment. / by Fei Yan. / Ph.D.

Thesis: S.B., Massachusetts Institute of Technology, Department of Nuclear Science and Engineering, 2017. / 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 43-44). / In the field of radiation oncology, while there are simulations and devices that allow users to be relatively confident that radiation to the tumor and sparing of healthy tissue is being maximized, the inability to reliably measure and control the dose during radiation treatment is a major source of uncertainty. This uncertainty is due to issues such as organ movement, a lack of precise and constant knowledge of beam current at the target site, and the inability to correctly register dose during hardware or software failures; all of which result in radiation treatments being measured after the procedure or in a fault susceptible manner during the procedure. The integrating feedback f-center dosimeter (IF2D) is a dosimeter that would address these challenges and enable feedback during radiotherapy procedures, which would give doctors and patients confidence that the correct dose was delivered to the target sites without exceeding allowable doses to healthy tissue. An in-situ irradiator will be designed and later used to quantify the relationship between dose and f-center absorption. This design will help guide the future experiment and further the development of the IF2D. / by Hadrick Alexis Green. / S.B.