Observations of ‘far from equilibrium’ phenomena under in reactor thermal conditions using in situ TEM

During nuclear fission, the in reactor thermal conditions results in large thermal gradients across the fuel pellet and cladding material. These extreme thermal gradients result in non-equilibrium phenomena such as redistribution of constituent elements and fission products along the thermal gradient. Currently, this information can only be observed through post-mortem characterization of fuel rod cross sections. In order to study the dynamic processes that govern the microstructural evolution under in reactor thermal conditions at high spatial resolution and correlate them to fuel properties and performance, the development of new in-situ heating stages is needed. Here, we discuss the development of a modified micro electro mechanical (MEMS) based TEM heating stage that allow us to study the effect of in reactor thermal gradients on the microstructural evolution in a lamella prepare from a U-Zr metallic fuel alloy. Additionally, the challenges and opportunities associated with this novel approach will be discussed.