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Abstract Climate change has garnered attention of communities world-wide. The carbon-free thermal energy systems such as nuclear benefit from compact and highly efficient heat exchanger technologies. The plate-type compact heat exchangers such as the Printed Circuit Heat Exchanger (PCHE) holds promise to fulfil these requirements. The chemical etching and diffusion bonding technology expands PCHE application for several different nuclear technologies. This work presents the thermal-hydraulic and structural analysis of PCHE for molten salt application with thermal energy storage. In this study, three different types of geometry are chosen for the analysis i.e., the zigzag channel type, the airfoil fin type, and the slotted fin type. For the working fluid, FLiBe (Li2BeF4) and Solar Salt (60% NaNO3 and 40% KNO3) are chosen for hot side and cold side respectively. Titanium grade 5 is chosen as the structural material. The study is conducted by Computational Fluid Dynamics (CFD) and Finite Element Method (FEM) analysis. The thermomechanical behavior including pressure drop, fluid temperature, velocity profile, stress, and deformation of the flow channel were considered in this work. From the results, the zigzag channel geometry gives the best thermal hydraulic performance in terms of heat transfer and pressure drop. The structural analysis shows that the stress intensity of all three geometries can exceed the maximum allowable stress (MAS) under certain conditions. Overall, the zigzag channel PCHE is still the most suitable geometry for this application.

Thesis: Ph. D., 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 408-431)., According to the future of the nuclear fuel cycle study at MIT, a reactor with a conversion ratio around one can achieve desired objectives in the long-term sustainability of uranium and reduction of transuranic wastes. This finding relaxes the need for sodium fast reactors (SFR) in a closed-loop nuclear fuel cycle and enables high-conversion light water reactors (HC-LWR) to be used as an alternative. HC-LWRs have two major advantages over SFRs. First, apart from the reactor core, the remaining reactor system can be based on existing LWR technology. Second, extensive operating experience and a proven record of high reliability of LWRs would ease licensing and commercialization processes. Therefore, operating HC-LWRs instead of SFRs may be more economically and technically viable with lower capital and development cost for the near term. This type of reactor is being developed by Hitachi Ltd. under the name of resource-renewable boiling water reactor (RBWR). This study focuses on RBWR-TB2, transuranic burning version of RBWR. To demonstrate that the RBWR-TB2 can operate safely within design constraints and regulatory limits, the thermomechanical behavior of this reactor has been analyzed through fuel performance modeling. Due to its unique design characteristics, several physical phenomena at high temperature and high burnup typically ignored in most LWR fuel performance codes can potentially become active under RBWR's operating conditions. These phenomena involve migration of fuel constituents and fission products, the evolution of O/M ratio with burnup, high burnup structure (HBS) formation, accelerated corrosion, hot pressing, gaseous fuel swelling, hydride precipitation and hydrogen migration in the cladding. Semi-empirical models describing porosity and cesium migration behaviors have been replaced with mechanistic models. All of these phenomena have been successfully implemented in a modified version of FRAPCON-3.5 known as FRAPCON-3.5 EP where EP stands for en, by Yanin Sukjai., Ph. D.

Thesis: S.M., Massachusetts Institute of Technology, Department of Nuclear Science and Engineering, 2014., Cataloged from PDF version of thesis., Includes bibliographical references (pages 285-288)., There has been an ongoing interest in replacing the fuel cladding zirconium-based alloys by other materials to reduce if not eliminate the autocatalytic and exothermic chemical reaction with water and steam at above 1,200 °C. The search for an accident tolerant cladding intensified after the Fukushima events of 2011. Silicon carbide (SiC) possesses several desirable characteristics as fuel cladding in light water reactors (LWRs). Compared to zirconium, SiC has higher melting point, higher strength at elevated temperature, and better dimensional stability when exposed to radiation, as well as lower thermal expansion, creep rate, and neutron absorption cross-section. However, under irradiation, the thermal conductivity of SiC is degraded considerably. Furthermore, lack of creep down towards the fuel causes the fuel-cladding gap and gap thermal resistance to stay relatively large during in-core service. This leads to higher fuel temperature during irradiation. In order to reduce the high fuel temperature during operation, the following fuel design options were investigated in this study: using beryllium oxide (BeO) additive to enhance fuel thermal conductivity, changing the gap bond material from helium to lead-bismuth eutectic (LBE) and adding a central void in the fuel pellet. In addition, the consequences of using thorium oxide (ThO₂) as host matrix for plutonium oxide (PuO₂) were covered. The effects of cladding thickness on fuel performance were also analyzed. A steady-state fuel performance modeling code, FRAPCON 3.4, was used as a primary tool in this study. Since the official version of the code does not include the options mentioned above, modifications of the source code were necessary. All of these options have been modeled and integrated into a single version of the code called FRAPCON 3.4-MIT. Moreover, material properties including thermal conductivity, swelling rate, and helium production/release rate of BeO have been updated. Material properties of ThO₂, by Yanin Sukjai., S.M.