A High-Throughput Investigation of Fe-Cr-Al As a Novel High-Temperature Coating for Nuclear Cladding Applications

During a reactor cooling system failure in a nuclear power plant, the reactor temperature rapidly rises. This results in the production of high-temperature and high-pressure steam within the reactor, which is periodically vented to prevent a failure of the nuclear containment vessel. At temperatures exceeding 1473 K, current generation Zircalloy claddings can undergo multiple structural phase transformations or react with steam to form ZrO₂ and hydrogen gas. The explosion of hydrogen gas during venting was one of the key contributing factors to the magnitude of the Fukushima disaster, as it damaged multiple containment vessels for units 1 and 3. A number of recent metallurgical studies have focused on the validation of Fe-Cr-Al alloys as possible replacements for Zircalloy due to its superior resistance to oxidation in steam environments. Unfortunately, the certification process for new cladding materials is time consuming. Conversely, coating technologies for existing cladding materials could potentially be more rapidly deployed while permitting for full replacements is completed. However, it is well known that deposited coatings can exhibit substantially different oxidation properties from their bulk counterparts. The coating composition is particularly problematic as subatomic percent variation in Al content can mark the difference between forming a passivating versus non-passivating oxide.

Here, I will describe the use of a MGI-based framework to investigate the role of synthesis and processing on Fe-Cr-Al thin films. Using computationally guided synthesis, high-throughput structural characterization and large scale data analytics we have systematically investigated oxidation resistance for the region of the phase diagram identified by the bulk community to resist oxidation. A primary screen, consisting of in-situ glancing incidence synchrotron diffraction during air oxidation, revealed that alloys containing greater than 3.08 at% Al and between 20.0 at% and 32.9at% Cr showed reduced formation of non-passivating oxides. Subsequent secondary screens revealed the formation of a passivating oxide for time periods in excess of 6 hours.