Kr implantation into heavy ion irradiated monolithic U-Mo/Al systems: SIMS and SEM investigations

Worldwide, high performance research and material test reactors are aiming to convert their fuel from high enriched uranium towards low enriched ones. High density U-Mo/Al based nuclear fuels are considered as a promising candidate for this conversion. However, during in-pile test irradiations, the formation of an interdiffusion layer (IDL) between the U-Mo and the Al matrix is observed, caused by irradiation enhanced U-Al interdiffusion processes. This IDL accumulates fission gases at the IDL/matrix interfaces. Together, these two effects strongly reduce the performance of this new fuel type. Recently, the out-of-pile technique of heavy ion irradiation (¹²⁷I) on U-Mo/Al layer systems proved to be an alternative to time-consuming in-pile test irradiations for certain fuel behaviour aspects. Here we present SIMS and SEM investigations of non-conventional ⁸²Kr implantation into previously heavy ion irradiated U-Mo/Al layer systems. It is shown that Kr accumulates inside μm large porosities at the IDL/matrix interfaces. This critical accumulation of μm-sized large gas bubbles is directly related to the presence of the irradiation induced IDL. Without IDL no critical accumulation of fission gas bubbles occurs.