Ni Doping in FeCrAl Introduces Competing Passivation and Dissolution Mechanisms in BWR Environments

Abstract The objective of this study is to understand how noble Ni additions affect FeCrAl corrosion in both oxidizing and reducing environments. FeCrAl alloys are promising accident-tolerant fuel candidates to replace Zr-based cladding, which exhibits poor high-temperature oxidation resistance. But in the Boiling Water Reactor (BWR) Hydrogen Water Chemistry (HWC) used across much of the commercial BWR fleet, FeCrAl cladding must withstand normal operation in a reducing environment, as well as survive accident scenarios in oxidizing environments. This study evaluates Fe-17.5Cr-5.5Al alloys doped with 0, 1, and 3 wt.% Ni under BWR HWC as well as Normal Water Chemistry (NWC) for six months at 288°C. Higher-nobility Ni enables passivation and improves oxidation resistance in NWC, but can adversely affect corrosion rates in HWC. Specifically, analytical transmission electron microscopy suggests a hydrogen-assisted oxidative dissolution mechanism is driven by Al 2 O 3 hydration into boehmite (AlOOH), facilitating H 2 entrapment and localized oxide failure. Because the kinetics of Ni diffusion and oxidation are sluggish, low Ni alloying concentrations (1 wt.%) exacerbate mass loss whereas higher Ni alloying concentrations (3 wt.%) allow for sufficient passivation before excessive dissolution can cause severe mass loss. Although minor Ni alloying additions can improve high-temperature oxidation resistance of FeCrAl, they may be detrimental in reducing environments. The impact of these findings reveals that designing Ni alloying additions in FeCrAl must consider competing mechanisms for accident conditions (i.e., high-temperature oxidation resistance) compared to normal operation (i.e., hydrothermal corrosion resistance) in BWRs.