<b>Corrosion of FeCrAl and Ni-doped FeCrAl in 400 – 900 °C Steam and Near Pressurized Water Reactor Conditions</b>

<p dir="ltr">Following the Fukushima Daiichi Nuclear Disaster, the need for accident tolerant fuel and cladding that could increase coping time in a loss-of-coolant-accident (LOCA) was clear. The candidate to replace the Zircaloy cladding currently used in most commercial light water reactors (LWRs) is the iron-chromium-aluminum (FeCrAl) alloy. FeCrAl offers superior corrosion resistance compared to Zircaloy in both accident conditions and normal operating conditions of LWRs. Less heat and less H₂ gas are generated in accident conditions on FeCrAl due to the protective Al₂O₃ oxide layers formed during these conditions. During normal operating conditions, Cr-based oxides prevent corrosion of the FeCrAl alloy and protect it from failure. Though the corrosion behavior of FeCrAl in steam conditions above 1000 °C and in unirradiated simulated LWR conditions is well-studied, the understanding of FeCrAl oxide layer formation in lower temperature steam and in irradiated simulated LWR conditions is less informed. Additionally, the addition of an Ni dopant to FeCrAl has been suggested to increase its corrosion resistance in irradiated environments, but the impact of Ni on FeCrAl in these conditions has not been studied. Four sets of experiments address this lack of knowledge. Six samples of a nuclear grade FeCrAl alloy, PM-C26M, were subjected to steam at temperatures ranging from 400 – 800 °C for 100 hours and 900 °C for 2 hours, separately. The results indicate that outer Fe-oxide and inner Cr/Al-oxide form on the alloy up to 600 °C, before the Al₂O₃ oxide protective layer is formed at 700 °C. The corrosion kinetics and mechanism for corrosion enhancement in Ni-doped FeCrAl (FeCrAl-Ni) was studied by submersing FeCrAl and FeCrAl-Ni alloys into simulated pressurized water reactor (PWR) water temperature and chemistry without B or Li for various timeframes to examine the evolution of oxide formation. The FeCrAl-Ni alloys displayed decreased mass loss and a thermodynamic effect for the enhanced corrosion resistance was postulated. Another set of experiments subjected pristine and pre-oxidized FeCrAl and FeCrAl-Ni to proton irradiation in near PWR conditions. The pristine alloy irradiation-assisted corrosion (IAC) experiment found that Ni accumulation at the metal-oxide interface facilitated Cr/Al-oxide growth in the oxide inner layer, increasing the rate at which protective oxides can form in irradiated conditions, which struggle to form without Ni influence. The pre-oxidized IAC experiment found that Ni dopant enhances Fe₃O₄ stability and prevents Fe₂O₃ from forming on the surface. This work elucidates the corrosion resistance of oxide layers on FeCrAl in 400 – 900 °C steam and on FeCrAl-Ni in near PWR conditions.</p>