A. James Clark School of Engineering

Permanent URI for this communityhttp://hdl.handle.net/1903/1654

The collections in this community comprise faculty research works, as well as graduate theses and dissertations.

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Subject: search.filters.subject.Nuclear physics and radiation

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    NEUTRON SHIELDING DESIGN FOR CENTRIFUGALLY CONFINED SPACE PROPULSION SYSTEM
    (2023) Parsons, Jennifer; Sedwick, Raymond J; Aerospace Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    This thesis presents a preliminary neutron shielding design for the HTS coils of a centrifugally confined fusion space propulsion system, which is a promising technology for future space travel. The design process involved a comprehensive study of neutron transport, material selection, and shielding optimization using MCNP and MATLAB simulations. First, the neutron attenuating properties of reflector, moderator, and absorber candidate materials were compared in MCNP. The thickness and composition of the shield were optimized from the resulting MCNP data. Next, two overall reactor and shielding geometry models were developed in MATLAB to estimate the total mass of the HTS shielding for both coils. The first model assumed a point neutron source and uniform thickness across the surface area of the shield. The second model improved upon the first by considering a source distribution and the varying distance between the source and surface of the shield. Both D-T and D-D fuel cases were run with the model and the resulting mass estimates were used to compare the specific mass to the state-of-the-art technology.
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    RADIATION SYNTHESIS OF IONIC LIQUID POLYMER ELECTROLYTE MEMBRANE FOR HIGH TEMPERATURE FUEL CELL APPLICATIONS
    (2020) Mecadon, Kevin; Al-Sheikhly, Mohamad; Material Science and Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    The purpose of this thesis was to design, synthesize and analyze innovative anhydrous fuel cell membranes that can operate at temperatures above 100°C. Operating at this higher temperature region improves performance and reliability of fuel cells: increasing proton mobility, enhancing reaction kinetics, increasing catalysis activity and reducing carbon monoxide poisoning. Traditional polymer electrolyte membrane fuel cells (PEMFCs) do not operate efficiently above 100°C because water is used as a proton conductive medium though the Grotthuss hopping mechanism. Through substituting water with protic ionic liquids and grafting onto fluorocarbon films, a new proton conductive network solid state PEM has been developed. These membranes can perform at high temperature above 100°C. Polymers were selected for grafting based on the following properties: high proton conductivity, low electrical conductivity, high mechanical properties, high chemical resistance, and high temperature and humidity stability. The method used to synthesize these anhydrous polymer electrolyte membranes (PEMs) was radiation grafting using heterocyclic protic ionic liquid monomers and fluorocarbon substrates. PEMs were prepared at the Medical Industrial Radiation Facilities (MIRF) at the National Institute of Standards and Technology (NIST). MIRF is a 10.5 MeV electron beam accelerator, which was used to radiate the fluorocarbon substrate and then indirectly graft heterocyclic protic ionic liquids to create PEMs. After synthesis, the extent and uniformity of PEM composition was analyzed using FTIR microscopy, SEM/EDS, SANS and their proton conductivity as measured by EIS. Through this research, indirect radiation grafting was shown to covalently bond ionic liquids onto fluorocarbon substrates to synthesize PEMs. The resulting ionic liquid PEMs showed proton conductivities greater than 10-3 S/cm above 100°C that behaved independent of humidity. The ionic liquid PEMs also demonstrated a positive correlation of increasing proton conductivity with increasing temperatures above 100°C even after the PEMs are dehydrated. The chemical properties and structure of the grafted ionic liquids greatly affects the proton conductive mechanisms present in the PEMs. These trends found through the course of this research will help the development of future anhydrous PEM with higher proton conductivity, performance, and reliability.