Effects of Crystallite Size on the Response of CeO2, ThO2, and UO2 to Highly Ionizing Radiation
Résumé
Radiation response is often a key limiting factor to the extension of nuclear fuel lifetimes and the development of advanced fuel materials. Recently, it has been shown that the response of CeO2, ThO2, and UO3 to highly ionizing radiation is highly dependent on redox response [Tracy et al., Nature Communications (2015)]. When exposed to this radiation, cations in the material are subject to changes in valence which drives swelling and microstrain as irradiation-induced defects accumulate. In an effort to mitigate these effects, many have studied nanostructured materials because they incorporate high defect sink strengths [Rose et al., Nanostructured Materials (1995), Nita et al., Journal of Nuclear Materials (2004)]. In this work, we present new insights into how crystallite size affects irradiation-induced redox response and defect accumulation in of isostructural CeO2, ThO2, and UO2. Using highly ionizing swift heavy ions (946 MeV Au ions) at the UNILAC accelerator of the GSI Helmholtz Center, we irradiated microcrystalline and nanocrystalline materials of different compositions known to reduce (CeO2), remain stoichiometric (ThO2), and oxidize (UO2) under ionizing conditions. Irradiated samples were characterized by synchrotron X-ray diffraction, transmission electron microscopy, and Raman spectroscopy. Each composition exhibited a distinct response between microcrystalline and nanocrystalline forms, such as magnitude of volumetric swelling (Fig. 1), driven mainly by redox processes. Our findings imply that nanocrystallinity has negative effects on a materials response to highly ionizing radiation. These results have implications in engineering safer, more tolerant materials for current and future energy-related applications.