In-Situ Transmission Electron Microscopy Microcantilever and Nanoindentation Testing of UO₂

Uranium dioxide is the standard fuel of the current nuclear reactor fleet and a potential fuel for future generation IV reactors. Enhancing the performance of uranium dioxide fuels necessitates a broader understanding of the fuel pellet/cladding mechanical interaction; this can be achieved through further study of the mechanical behavior of UO₂. Small-scale mechanical testing can be used to evaluate the mechanical properties of materials while reducing the total volume of material required for testing. This is beneficial when studying nuclear materials because small test samples reduce the dose to the researcher and can reduce costs by permitting mechanical testing to be performed outside of hot cells. In this work in situ transmission electron microscopy microcantilever and nanoindentation testing was used to evaluate the deformation of UO₂ at room temperature. The in situ testing was also used along with an innovative helium implantation technique to evaluate the effect of helium bubbles on the low temperature deformation of UO₂. It was found that, under similar testing conditions, the unimplanted material formed a single critical crack while material containing helium bubbles at a dose of 10¹⁸ ions/cm² responded with a large number of nanocracks, enhancing the toughness of the material.