Initial oxidation behavior of Fe-Cr-Si alloys in 1200 degrees C steam

Abstract

Accident-tolerant fuel (ATF) cladding with high oxidation resistance during severe accidents is of critical importance to light water reactor safety and sustainability. One newly proposed ATF cladding concept, a multi-metallic layered composite (MMLC), hinges upon the oxidation resistance of an outer Fe-Cr-Si layer on top of a Zr-based alloy, separated by barrier layers to avoid Fe-Zr eutectic formation. The initial oxidation resistance of three potential Fe-Cr-Si alloys was evaluated by exposing them to 1200 degrees C oxidizing steam for up to one hundred seconds, along with a Zr-Nb-Sn alloy as a reference. The oxidation resistance of Fe12Cr2Si and Fe16Cr2Si was poor, exhibiting a porous, incomplete multilayer oxide composed mainly of mixed Fe/Cr/Si spinels. However, Fe20Cr2Si showed excellent oxidation resistance due to a continuous amorphous SiO2 layer formed at the metal-oxide interface, followed by almost fully dense Cr2O3. This motivates the consideration of Fe-Cr-Si alloys as an additional ATF design choice, similar to FeCrAl alloys in performance and oxidation resistance mechanism.