The materials used in nuclear reactors have a tough job. They must withstand extreme conditions, including high temperatures, intensive radiation and high stress.
Over time, these punishing conditions will take a toll on the materials, making them less reliable than when they were freshly made. And if a material in a reactor degrades to the point where it loses important properties, there’s often not an easy fix.
“It’s expensive and extremely difficult to replace or repair a piece of material in a nuclear reactor, and many times we can’t do so,” says Yongfeng Zhang, who joined the engineering physics department as an assistant professor in fall 2019. “Basically once a material is in a reactor, it’s likely there for years or even decades. So we have to understand how materials evolve, or degrade, and how their properties change as a function of the reactor’s operating time.”
With his research, Zhang aims to gain a better understanding of the fundamental mechanisms that cause materials to degrade in extreme conditions. This knowledge will allow him to assess if a piece of material is still reliable after a certain service time in current reactors, and also aid in developing new materials that can perform better in future reactors.
“Ultimately, our goal is to help make nuclear energy more affordable and even safer,” he says. “Nuclear energy produces nearly 20% of all the electricity in the United States and doesn’t emit greenhouses gas, so it is critical for our energy reliability in the future and for mitigating climate change.”
Zhang’s expertise is in multi-scale modeling and simulation of materials, and his research focuses on the microstructure—the fine structure of materials seen with a microscope.
“In extreme conditions, the microstructure of materials change, most of the time in an unfavorable way,” he says. “So I’m trying to figure out how the microstructure evolves under these conditions using multi-scale modeling and simulation.”
He uses computer simulations to create models of how a material’s individual atoms will move and interact with each other in response to the extreme environment. From these atomic-scale models, he draws out the fundamental physical mechanisms responsible for the material’s degradation.
“But we’re not just stopping there,” Zhang says. “Instead, we want to use the mechanisms extracted from the atomic scale to develop scientific models that can predict material behavior at applicable human scales, such as meters and seconds.”
Zhang earned his bachelor’s and master’s degrees from the University of Science and Technology of China and his PhD from Rensselaer Polytechnical Institute, all in mechanical engineering. After earning his PhD, he began working as a researcher at Idaho National Lab, which stoked his interest in nuclear materials.
“I really like working on nuclear materials because it is an area rich with fundamental science while also having a clear applied purpose,” he says. “It would make me very proud if some of my research ends up being used in nuclear reactors in the future.”
And the impact of his research could extend beyond nuclear energy. For example, it could be useful for predicting how materials will behave in other types of harsh conditions, such as in extremely cold or underwater environments.
At Idaho National Lab, Zhang advanced to a senior staff scientist position and led the computational microstructure science group in the lab’s fuel modeling and simulation department before joining UW-Madison.
He says the engineering physics department’s excellent reputation for research and training students attracted him to the university.
“UW-Madison has an outstanding research community and the students are very talented,” he says. “I’m excited by the opportunities to collaborate with EP faculty as well as faculty in the mechanical engineering and materials science and engineering departments to do impactful research in the nuclear energy field.”
In spring 2020, Zhang is teaching a course on engineering problem solving using Matlab, and says he’s especially enjoying the teaching aspects of his new role. “It’s very rewarding to interact with the students and to see them grow as engineers,” he says.