Laser Heating Study of the High-Temperature Interactions in Nanograined Uranium Carbides

Nanograined nuclear materials are expected to have a better performance as spallation targets and nuclear fuels than conventional materials, but many basic properties of these materials are still unknown. The present work aims to contribute to their better understanding by studying the effect of grain size on the melting and solid-solid transitions of nanograined UC_2-y. We laser-heated 4 nm-10 nm grain size samples with UC_2-y as the main phase (but containing graphite and UO₂ as impurities) under inert gas to temperatures above 3000 K, and their behavior was studied by thermal radiance spectroscopy. The UC_2-y solidification point (2713(30) K) and α-UC₂ to β-UC₂ solid-solid transition temperature (2038(10) K) were observed to remain unchanged when compared to bulk crystalline materials with micrometer grain sizes. After melting, the composite grain size persisted at the nanoscale, from around 10 nm to 20 nm, pointing to an effective role of carbon in preventing the rapid diffusion of uranium and grain growth.