While studying materials science at the University of Oxford in the United Kingdom, Charles Hirst had an a-ha moment that led him on a path to investigating nuclear materials for both fission and fusion reactors.
“In my materials science training, we learned a lot about the aerospace industry and alloys used inside jet engines,” he says. “But if you put one of these specialized alloys into a nuclear reactor, the neutron radiation would rearrange the atoms inside the material and turn the exquisitely designed microstructure into scrambled eggs. That material couldn’t survive such a demanding radiation environment. And I thought, ‘Wow, that’s the ultimate challenge,’ which is why I’m a nuclear materials scientist.”
Hirst joined the University of Wisconsin-Madison Department of Nuclear Engineering and Engineering Physics as an assistant professor in August 2024.
In his research, Hirst explores the interplay between radiation damage, temperature and stress to determine how materials will behave in harsh irradiation environments. He uses various microscopy and characterization techniques to understand what’s happening inside a material at the atomic level and to investigate how defects in the material evolve as a function of time, temperature and applied load. “Once we understand the mechanisms behind those processes, we can design better, more resilient materials for the next generation of fission and fusion reactors,” he says. “And we can design mitigation strategies for existing materials that are currently in nuclear reactors.”
For example, Hirst says one strategy for extending the lifetime of current reactors could be to heat up the reactor materials. This would rearrange the materials’ atoms, which could “heal” some of the radiation damage and recover the materials’ original properties. Through his research, Hirst could provide reactor operators the details—like what temperature to heat the materials at, and for how long.
Hirst aims to create “maps” to describe the relationship between temperature and mechanical load to establish safe zones for current and future nuclear materials. “Designers could use these maps to, for instance, know that they could safely operate a reactor at a higher temperature if they reduce the mechanical load on the material,” he says. “So, ultimately this materials science knowledge could inform operational practices for reactors.”
Hirst will conduct research in the UW-Madison Ion Beam Laboratory, where he will lead development of several in situ ion irradiation experiments, including both mechanical testing and differential scanning calorimetry, to explore a wide variety of loading and annealing scenarios.
After earning his master’s degree in materials science at the University of Oxford, Hirst received his PhD in nuclear science and engineering from MIT in 2022. Prior to joining UW-Madison, he was a postdoctoral research fellow in the Department of Nuclear Engineering and Radiological Sciences at the University of Michigan. His postdoctoral research involved irradiation creep testing and developing gas implantation gradients to emulate fusion irradiation environments.
Hirst was drawn to UW-Madison because of the Department of Nuclear Engineering and Engineering Physics’ outstanding reputation, as well as the university’s nuclear reactor and ion beam laboratory, both of which are used for research and education.
“Having a nuclear reactor on campus is fantastic because we can put materials into the core and expose them to neutrons,” Hirst says. “Also in the Ion Beam Lab, ion accelerators can be used to emulate neutron irradiation by shooting ions into materials. So, at UW-Madison we can do both kinds of tests and compare the results, which is super interesting. I’m very excited to leverage the facilities at UW-Madison. It’s a pretty unique place, as there aren’t many universities with both a nuclear reactor and an accelerator lab on campus.”
Photo of Charles Hirst by Joel Hallberg