Atomic Structure in Metals Forms Corrosion Pathways in Nuclear Reactors

Scientists at Penn State have uncovered a critical factor influencing corrosion in molten salt nuclear reactors, a next-generation technology promising enhanced efficiency and safety. By delving into the atomic-scale structure of nichrome, a nickel-chromium alloy commonly employed in reactor components, researchers revealed how specific atomic arrangements create rapid corrosion pathways, jeopardizing reactor materials.

Traditional nuclear reactors rely on dense fuel rods submerged in water to manage the immense heat generated by fission reactions. Molten salt reactors, in contrast, use liquid fuel dissolved in a molten salt mixture, operating at temperatures exceeding 800 degrees Celsius. This design offers significant advantages, such as improved safety margins, continuous fuel processing, and enhanced thermal efficiency. However, the aggressive chemical environment posed by the molten salts accelerates corrosion in metals, threatening reactor integrity.

The Penn State team employed advanced reactive simulations on the ROAR supercomputer to model how different atomic structures within nichrome alloys respond when exposed to FLiNaK molten salt, a popular mixture used in these reactors. Crucially, they examined the impact of atomic ordering—the degree to which chromium and nickel atoms arrange themselves in short- or long-range patterns within the alloy.

Their simulations demonstrated that long-range atomic ordering forms interconnected “corrosion highways.” These pathways allow corrosive species to rapidly penetrate the metal from the surface inward, causing severe pitting and roughening of the alloy in mere nanoseconds. In contrast, alloys with short-range ordering or random atomic arrangements showed significantly better resistance to corrosion under identical conditions, maintaining smoother surfaces.

This breakthrough reveals that corrosion susceptibility is not merely a function of chemical composition but heavily influenced by microstructural atomic organization. “Understanding these percolation pathways gives us predictive power over corrosion behavior, enabling us to design alloys tailored to withstand molten salt environments,” explains Hamdy Arkoub, co-corresponding author and doctoral candidate in nuclear engineering.

The study addresses long-standing challenges in experimentally characterizing corrosion under extreme reactor conditions, such as intense radiation and high temperatures, by using high-fidelity computational modeling. This approach allows researchers to observe real-time atomic interactions during corrosion processes that unfold over billionths of a second, an impossible feat in laboratory settings.

This new atomic-level insight paves the way toward engineering more durable structural materials for molten salt reactors, advancing their commercialization potential. The work, to be published in Corrosion Science, represents a crucial step in overcoming one of the key hurdles in developing safer and more efficient nuclear power systems capable of meeting future energy demands.

Keywords

Corrosion, Chemical processes, Nuclear engineering, Molten salt reactors, Nickel-chromium alloys, Atomic ordering, Nuclear power safety