Nuclear Science and Engineering Institute electronic theses and dissertations (MU)
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The items in this collection are the theses and dissertations written by students of the Nuclear Science and Engineering Institute. Some items may be viewed only by members of the University of Missouri System and/or University of Missouri-Columbia. Click on one of the browse buttons above for a complete listing of the works.
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Item Development of a novel titanium thermal ionization cavity source for electromagnetic radioisotope separation of samarium and other lanthanide isotopes(University of Missouri--Columbia, 2022) Jeffries, Bradley D.; Gahl, JohnAn available supply of high specific activity radioisotopes was identified by the Department of Energy as a critical priority to the development and eventual deployment of next-generation medical diagnostic and cancer therapy tools. A radioisotope mass separator, located at the Missouri University Research Reactor (MURR) Center, was constructed to provide radioactive ion beams for the separation and production of high specific activity lanthanides used in radiopharmacology. A novel thermal ionization cavity (TIC) source capable of seamlessly integrating the irradiation of reactor produced targets with isotope separations was developed. Isotope separations of irradiated samples of samarium with low levels of radioactivity will be performed to assist in the design of an electromagnetic separator facility with commercial scale. To this end, experimental data has been acquired with a custom ionization source designed to operate inside of a constrained set of parameters. These experiments led to the first reported case of a lanthanide ion beam to have been produced from a TIC source constructed completely from titanium. Investigations of the working parameters driving the performance of the source are discussed. Initial experiments with samarium ion beams transmitted through the ion optics of the separator system are also discussed. This work demonstrates the applicability of titanium in the construction of a TIC source designed for separations of radioactive lanthanides.Item Novel methods of evaluating materials in extreme environments(University of Missouri--Columbia, 2022) O'Donnell, Valentina; Gahl, JohnThree novel experiments were completed to investigate the difference in radiation response between production methods of Inconel 625. Production methods explored were the laser-powder bed fusion additive manufacturing method and the more conventional production method where samples were cut from a plate of wrought material. The experiments carried out aimed to further the understanding of how samples of this alloy, produced by AM methods, differ in radiation resistance from samples produced by conventional methods. The first experiment looked at the differences when subjected to a proton beam, while the other two experiments looked at the differences that resulted from neutron radiation environments. Differences in the effects of the irradiations on the hardness and microstructure were compared between the different manufacturing methods. The first experiment used the ion beam of a cyclotron to impart damage onto a metal target, then located that damage using nanoindentation. The second experiment used fast neutrons from a PET isotope production machine to irradiate metals for damage studies, proving that the technique yields measurable results even at low fluence irradiations. The third experiment used the neutron field in the University of Missouri Research Reactor to irradiate nanogram-scale flakes of metal and compare them to samples approximately nine orders of magnitude larger, on the order of a gram. These smaller samples were able to be analyzed sooner and were safer to handle while showing similar radiation response as compared to the larger samples.Item Effects of beta radiation on nanostructured semiconductor devices for low energy radiation sensing(University of Missouri--Columbia, 2021) Acosta, Eric Milan; Kwon, Jae W.Beta radiation detection currently relies primarily on scintillation detectors. However, the construction of these detectors tends to be large which significantly limits their applicability for field-use. A nanostructured Pt/TiO2/Ti Schottky device was constructed for use as a compact, low energy radiation detector by making use of surface plasmon resonance which has been shown to enhance energy coupling in similar technologies. The fabrication of the device was done by first electrochemically anodizing a titanium substrate to create a nanoporous surface, followed by annealing to produce a crystalline, semiconducting TiO2 layer and finally the deposition of the Pt Schottky metal through atomic layer deposition. Modeling of the device using COMSOL software showed the formation of strong electric fields when nanostructures were present. Exposure of the device to low energy 63Ni beta radiation showed a 2-to-3-fold increase to the forward current during radiation exposure without any additional signal amplification. This increase in the current is a consequence of a 2 to 4 percent lowering of the Schottky barrier height during radiation exposure as well as the production of hot and secondary electrons in the semiconductor. Subsequent improvements to the device using rapid thermal annealing resulted in a nearly 6 percent decrease of the Schottky barrier height during radiation exposure and a consequent 5-fold increase to the forward bias current in the presence of radiation. Thus, in its current construction the device is capable of being used as a qualitative low energy beta radiation detector.Item Influence of inert gases on heat and mass transfer in next-generation nuclear reactors(University of Missouri--Columbia, 2021) Iasir, Abu Rafi Mohammad; Hammond, KarlInert gases cause some unique challenges in nuclear fuel development. In this dissertation, we study the impact of inert gases on the transport behavior in nextgeneration fission and fusion reactors. Uranium--molybdenum alloys are potential nuclear fuels that can replace highly-enriched uranium fuel in research and test reactors around the world. Developing a uranium fuel with low enrichment is an important step towards preventing nuclear proliferation and promoting the peaceful use of nuclear energy. We look into how fission gas (i.e., krypton and xenon) impacts the transport properties of U--Mo alloys. We start with an analysis of the impact of fission gas on the overall thermal conductivity of U--Mo. We find that the presence of fission gas inside the fuel significantly reduces the overall thermal conductivity. We then discuss the electronic structure of uranium using density functional theory (DFT) and introduce a new pseudopotential for uranium. This pseudopotential is then used to examine xenon migration in U--Mo alloys. Our results show that the presence of molybdenum in nearest-neighbor lattice positions increases the migration energy of xenon relative to pure g-uranium, meaning molybdenum impedes fission gas transport. Finally, we study the interaction of helium with lithium, which is a potential plasma-facing material for fusion reactors, using DFT. We find that helium behaves very differently in lithium than it does in other bcc materials. Our studies show that helium has very low migration energies inside lithium, indicating high mobility.Item Phonons and thermal neutron scattering in [gamma]-U and U-Mo alloys(University of Missouri--Columbia, 2020) Saltos, Andrea; Hammond, KarlElimination of high-enrichment uranium fuels in research and test reactors around the world is one of the many efforts that supports the goal of minimizing proliferation risks. These efforts have pushed for the development of low-enrichment, metallic uranium fuels such as U-Mo alloys. The development of these fuels requires accurate prediction of their neutron transport properties, which in turn may be affected by the distribution of scattered neutrons from bound nuclei at thermal energies. In order to estimate such a distribution in a reactor, thermal neutron scattering cross sections are needed. Calculations of these cross sections require knowledge of the phonon scattering properties of the medium. Due to the difficulty in measuring these properties, thermal neutron scattering data have not been measured for uranium, molybdenum, and their alloys, and phonon effects have consequently been omitted from neutron transport models. In this dissertation, thermal neutron scattering in [gamma]-U, Mo, and U-Mo alloys is studied. The fundamental quantities of interest, the cross sections, were calculated using the NJOY software. NJOY was modified to include the calculation of the coherent elastic cross sections for non-stoichiometric alloys. Such modifications allowed us to generate thermal scattering cross sections for U-10Mo and U-7Mo at different temperatures and enrichment levels. The phonon density of states, which is the main input needed to calculate the cross sections, was generated through molecular dynamics simulations. We find that the incorporation of phonon effects decreases the cross sections compared to free-atom models. The effects that this decrease has on neutron transport were studied using simple reactor models. We conclude that binding effects have a minor impact on criticality, but they might be important in the assessment of uncertainties in reactor configurations and models as well as in neutron scattering experiments.