UNIVERSITY PARK, Pa. — FeiFei Shi, assistant professor in the John and Willie Leone Family Department of Energy and Mineral Engineering, received a $400,000 research and development award from the Nuclear Energy University Program (NEUP) in the U.S Department of Energy (DOE) to develop foundational research on the corrosive damage caused by molten salt in nuclear salt reactors (MSRs).
Nuclear salt reactors have many benefits, including higher efficiencies and less waste, compared to traditional reactors that require solid fuel. The International Atomic Energy Agency, a leading intergovernmental forum for scientific and technical cooperation in the nuclear field, has spotlighted growing international interest in the process as a potential key player in the sustainable clean energy transition. Despite the benefits, the corrosiveness caused by the molten salts affects reactor reliability and comes with high maintenance costs. Overcoming the corrosive effect of molten salt is one of the primary challenges preventing further adoption of the potential energy source.
"Corrosion is always happening or initiating on the surface, and in this extreme, harsh environment, the all-chloride-based assault makes the problem more severe," said Shi. "We need a better understanding of the whole process to develop informed preventative strategies that stop the corrosion from happening in the first place."
Most corrosion observed in our daily lives involves moisture and oxygen. However, the MSR environment contains little moisture, and the primary oxidizer comes from the chloride, or chlorine, inside the molten salt. According to Shi, the inhospitable conditions and uncommon corrosive mechanisms pose a unique research challenge.
"Duplicating the very high temperature of a 700 degrees Celsius reactor is hard enough," said Shi. " We also can't just take out our experiment to check it because the ambient air will affect the electrochemical and thermodynamic properties and destroy the results."
The challenge Shi noted is intrinsic to the study of interfacial properties, how a surface interacts with a liquid. The research team will use a mixture of emerging electrochemistry models in combination with reviving methods used in the 1950s to observe the interfacial phenomena.
Even if the team has chosen the correct models, they still must determine many factors, including penetration depth and magnification level, to find what Shi calls the molecular "sweet spot."
"As researchers, we have a lot of tools, but not all are useful," said Shi. "When we have a liquid like molten salt, which is a very viscous, high-temperature liquid, traditional methods like ultra-high vacuum UV systems are very limited because the surface is buried."
Shi hopes their observations of the unpredictable, buried surface will lead to more accurate simulations. Today, the bulk properties of molten salts are well-known, but there is a knowledge gap on what is occurring on the atomic scale, making current predictive models unreliable. Shi foresees the foundational knowledge gained by this study will have a long-lasting impact, potentially leading to breakthroughs beyond nuclear energy applications.
"Currently, molten salts are like a black box," Shi said. "Sometimes it's hard to see the impact, or the benefits are unclear, when you shine a light on such an interesting phenomenon. But I think the accumulation of knowledge and pushing the frontier of science is significant and will fuel exciting collaborations at Penn State for the next 30 or 50 years."
Shi holds a bachelor's degree in chemistry from Fudan University, China, and a doctorate in mechanical engineering from the University of California, Berkeley in 2015. Before joining Penn State in August of 2019, Shi was a postdoctoral researcher in the Department of Material Science and Engineering at Stanford University.
In 2022, the DOE awarded more than $24.3 million through NEUP to support 38 university-led, nuclear energy research and development projects in 21 states. NEUP seeks to maintain U.S. leadership in nuclear research across the country by providing top science and engineering faculty and their students with opportunities to develop innovative technologies and solutions for civil nuclear capabilities.