Graduate Thesis Or Dissertation
 

Nano-Recrystallized UO₂ Microcantilever Bending After Ion Irradiation

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https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/02871365j

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  • Idaho National Laboratories recently conducted micromechanical testing of nano-recrystallized UO₂ as a part of an ongoing investigation of High Burnup Structure (HBS). The goals of the test were to determine the fracture stress, and the elastic modulus of subdivided grains within UO₂ using ion irradiation rather than neutron irradiation to not only reduce the radioactivity of the samples, but also to isolate the microstructural features that are observed in HBS otherwise known as separate effects testing. In this study, Uranium Dioxide (UO₂) with 10 µm and 70 µm grains were irradiated using 84 MeV xenon ions at 300°C and 500°C respectively to induce radiation damage up to about ~1400 dpa. Nano-recrystallization and xenon bubble formation were observed. Refined grains ranged from 100-300 nm in diameter in both samples. It was observed that grain refinement occurred in the top layer of the UO₂ where Xe ion electronic stopping was the dominant energy deposition mechanism. The refined grain layer thickness was grain size dependent with a 2 µm and 0.5 µm layer thickness for the 10 µm and 70 µm grains respectively. Bubbles and cavities were observed in the peak ion distribution occurring just 6 µm below the surface of the sample. The 10 µm sample had faceted bubbles ranging from 10-50 nm while the 70 µm sample had spherical bubbles ranging from 3-5 nm in diameter. Refined grain microstructure fracture properties were determined using 2-point microcantilever bending. Fracture stress ranged from 1-7 GPa. 70 µm lowly irradiated samples had a notably higher fracture stress when compared to the rest of the sample sets. 10 µm samples had insignificant fracture stress changes between the highly and lowly irradiated samples. Theories and results are discussed.
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