Graduate Thesis Or Dissertation


Microstructural Characterization of Porosity in U-Mo Low Enriched Uranium Plate Fuel Public Deposited

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  • New low enriched uranium (LEU) fuels are being developed for replacement of high enriched uranium (HEU) fuels in high power research reactors. U-Mo LEU plate fuels have been identified as a candidate for replacement of current HEU fuels. However, U-Mo fuels tend to exhibit accelerated swelling typically at fission densities exceeding 4.5 x 1021 fissions/cm3, that can cause break away swelling, delamination, and pillowing. Therefore, it is critical to identify a method to more effectively characterize porosity in irradiated U-Mo LEU plate fuel. This thesis compares two different sample preparation methods for U-Mo plate fuels, vibratory polishing and contemporary focused ion beam (FIB) preparation, in order to determine the most effective method. Micrographs, new and archived, of irradiated U-Mo fuels are analyzed using MatLab’s image processing toolbox, and the open source software ImageJ. Adaptive thresholding techniques are employed to segment images and identify pores that are counted and measured for size, and morphology, distributions, and overall porosity estimate. Verification and validation is conducted using the ASTM E562- 11 standard counting process to estimate porosity from 2D images. Size and morphology distributions for the samples are compared to identify any potential trends between porosity and fission density. This work demonstrates that, while significant improvements must be made, vibratory polishing has the potential to prepare much larger and higher surface quality surfaces, allowing for collection of more accurate, statistically significant porosity data in U-Mo fuels. Also, the results collected support the hypothesis that porosity increases with increasing fission density, up to a transition point, near 4.5 x 1021 fissions/cm3, where U-Mo fuels recrystallize and swelling grows exponentially.
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