SerpApi.Org
Scientists at the Penn State University in the U.S. have found out why advanced nuclear reactors see ‘corrosion highways’ and how adjusting the atomic arrangement of their structural metals can affect the rate and extent of the corrosion.
Nuclear energy is poised for a major comeback as countries look for ways to meet their energy demands without increasing their carbon emissions. In a conventional fission reactor, a uranium fuel rods are submerged inside a large vat of water. As fission reactions occur, a large amount of heat is generated, which the water absorbs to keep the fuel rods cool.
At the same time, the absorbed heat converts water into steam, which is used to drive turbines and generate electricity. In the newly designed fission reactors, molten salt is used as a coolant and fuel, removing the need for a pool of water to pack fuel rods in. This allows fuel and nuclear waste to be cycled in and out of the reactor vessel, improving the reactor’s efficiency and safety. However, researchers have noticed corrosion issues in these reactors.
Corrosion Highways
When compared to conventional fission reactors, molten salt reactors run much hotter. Temperatures inside these reactors can reach 1,500 degrees Fahrenheit (800 degrees Celsius). At these temperatures, the molten salt remains chemically stable but begin corroding the metal used to build the reactor vessel, posing a major safety risk.
Scientists are aware of this, and previous research in 2024 sought to understand the cause of the corrosion using a chemical model. In that study, researcher Hamdy Arkoub used FLiNaK salt and sought to understand its interaction with nichromem, the nickel-chromium alloy used in reactor construction.
“The high temperatures and the presence of radiation in these reactors make it difficult to experimentally study how corrosion starts and propagates in nichrome,” explained Arkoub in a press release. “Our work aims to use modeling and simulation to fill in the gaps.”
The model has helped the team build detailed simulations of how chromium specifically corrodes when exposed to FLiNaK salt under different levels of mechanical stress and changes in the orientation of the metal surface.
Role of atomic ordering
In the studies, the researchers noticed that individual samples of nichrome were much more prone to corrosion than other alloys with the same chemical composition. This was earlier attributed to mechanical stress, but Arkoub and his team wanted to determine if the microscopic structure of the metal had a role to play.
In nichrome, the chromium atoms are scattered due to a process called atomic ordering, which determines how the atoms travel or percolate. This can manifest at short range or long range, but the research team did not understand the mechanisms at play in the process.
Using PennState’s ROAR Supercomputer, the team created several detailed simulations of the corrosion between the alloy and the molten salt. The depth of the simulations is evident be the fact that the supercomputer took a full day to process just one nanosecond of the corrosion reaction.
Through these simulations, the research team found that long-range atomic ordering creates a sort of highway for the corrosion process when compared to short-range random structuring.
“Using this new understanding, we are trying to build a high-length-scale model that allows us to see the real-time evolution of how certain alloy materials will behave when exposed to molten salt,” added Arkoub, which will eventually lead to building safer vessels for molten salt reactors.
The research findings have been published in the journal Corrosion Science.
