Experimental assessment of antimony (Sb) in pure uranium for immobilizing fission product lanthanides

The use of fuel additives is one of the concepts to mitigate fuel cladding chemical interaction (FCCI) for metallic fuel because fission product lanthanides are expected to be immobilized by the additive. Antimony (Sb) has been found to be a good additive candidate for UZr fuel. The present study focuses on the immobilization mechanism in pure uranium. U–4Sb alloy was fabricated to understand the behavior of Sb, while U–4Sb–4Ce was fabricated to simulate the condition when lanthanides are generated. The as-cast alloys were characterized by Scanning Electron Microscope (SEM) and Energy Dispersive Spectrometer (EDS). U–Sb precipitates are formed in U–4Sb alloy, while U–Sb and Ce–Sb precipitates were found in U–4Sb–4Ce alloy. The alloys that were heated under 650 °C for 500 h were also characterized by SEM/EDS and the results shows that the thermal exposure does not change the morphologies or chemical composition of the Sb-precipitates (U–Sb and Ce–Sb precipitates). In addition, diffusion couple tests between those alloys and cladding materials (Fe or HT9) under 650 °C for 500 h were performed and the samples were then analyzed using SEM/EDS. The reactions between cladding and uranium were found, while there was no reaction between Sb-precipitates and cladding materials.