Multiple companies are looking at molten salt and liquid metals for fusion and advanced fission, because they are excellent heat-transfer fluids that promise high operating temperatures at lower pressures, leading to higher efficiency. However, molten salt and liquid metals create harsh environments that can degrade reactor materials, making corrosion research a critical area of inquiry.
Corrosion expertise: “Fission and fusion are critical technologies that are of great interest to researchers and industry,” said Rishi Pillai, who leads ORNL’s Corrosion Science and Technology Group. “A number of these new reactor concepts that are being pursued by industry use molten salts and liquid metals, which have been historical areas of expertise for ORNL.” From the molten salt research in the 1960s during the Molten Salt Reactor Experiment (MSRE) to the corrosion research to support the liquid-metal cooled Experimental Breeder Reactor-II in Idaho from the 1970s to 1994, ORNL has extensive history digging into the effects of corrosion.
The Corrosion Science and Technology Group specializes in studying individual and combined effects of corrosion stress and irradiation. Researchers expose a variety of materials to these types of stressors and then study them at the atomic level, aided by the expertise of technicians and insights from models run on high-performance computers.
“Our research blends state-of-the-art experimental observations of real-world conditions with high-fidelity modeling of material degradation, providing rapid engineering data on material performance while enabling deep mechanistic understanding of material-environment interactions,” said Pillai.
Fusion corrosion: While liquid metals and molten salts have long been of interest in fission energy, they have only recently taken on heightened importance for fusion energy. The predominant architectures for magnetic confinement fusion—donut-shaped tokamaks and cruller-shaped stellarators—create extremely high-temperature plasmas that can initiate the fusion of hydrogen isotopes and release kinetic energy.
One of the challenges facing companies building fusion devices is how to convert that energy to electricity while cooling the reactor—and even creating fuel on-site. These tasks are accomplished by a blanket that surrounds the plasma, absorbing heat and energy from neutrons exiting the plasma.
“Research has been focused for decades on how to create and sustain fusion in the plasma, but the blanket is also a formidable challenge due to its multipurpose nature and the complex material interactions that take place there,” Pillai said. “Incorporating molten salts into the blanket is a concept that needs more experimental investigation to explore its potential for resolving this challenge.”
ORNL researchers are working with colleagues at other national labs and several private companies to design blanket and fuel cycle systems. Pillai’s group is looking at a variety of alloys, both conventionally and additively manufactured, along with coating systems that could withstand liquid metals or molten salts over extended periods of time in the harsh fusion environment.
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