The compatibility of Eu2O3, a potential control material for fast reactors, with the prototypic reference cladding alloy, Type 316 stainless steel, for the fast flux test facility and Clinch River Breeder Reactor Plant reactors is characterized at 1093°C. Metallographie examination of the reaction band shows that severe reaction occurred on the surface of the cladding alloy, particularly grain boundary penetration. X-ray diffraction analyses, electron microprobe analyses, and electron dispersive analysis of x rays were employed to identify the reaction product. The results show that the main reaction product is an europium silicate that contains little or no alloying components such as iron, chromium, and nickel of the Type 316 stainless steel. Consequently, it is recommended that low-silicon Type 316 stainless steel should be used for cladding purposes when Eu2O3 is used for neutron absorber in the fast reactors.