$1M DOE grant to explore three elements in used nuclear fuel

UNIVERSITY PARK, Pa. — Nuclear energy is a clean, low-carbon power source that can generate electricity 24 hours a day, according to the International Atomic Energy Agency. New reactor technologies, such as molten salt reactors — which use high-temperature liquid salts instead of water as the primary coolant — have the potential to improve fuel utilization and support more efficient fuel recycling, among other possible benefits, according to a team led by scientists in Penn State’s College of Earth and Mineral Sciences. But more research is needed to understand and manage the fission products present in molten salt reactor and nuclear fuel recycling systems, they said.

Supported by $1 million grant from the U.S. Department of Energy’s Nuclear Energy University Program (NEUP), the team will investigate how certain elements — samarium, europium and tellurium — behave in molten salt-based nuclear fuel recycling systems. Known as fission products, the elements are formed when heavy atoms such as uranium split after absorbing a neutron, releasing significant amounts of energy. Collaborators at the University of Nevada, Reno, and the Idaho National Laboratory will characterize and model the behavior of these elements, as well as perform complementary experiments in support of the project.

“We will study the oxidation states of these elements, which describe how many electrons an atom has gained or lost and strongly influence how they behaves chemically,” said Hojong Kim, professor of materials science and engineering and principal investigator of the grant. “We will also examine how these elements interact with other materials in nuclear systems and how they behave during nuclear fuel recycling processes known as pyroprocessing.”

Alok Pandey, a doctoral student in materials science and engineering, will apply electrical current to the three elements while they are dissolved in a molten salt solvent, studying their behavior under conditions relevant to molten salt reactors and recycling processes.

“This will allow us to understand the elements’ electrochemical properties and how their oxidation states change in molten salts, which could help improve strategies for their recovery and management during nuclear fuel recycling,” Pandey said.

Samarium and europium are unwanted in recycled fuel because they can interfere with reactor performance and fuel recycling processes, researchers explained. The elements can also interact with other materials in molten salt systems, making their recovery and management important for improving reactor performance and fuel recycling efficiency.

Tellurium, on the other hand, can react with metals used in molten salt reactors and fuel-recycling systems, contributing to corrosion and materials degradation.

While Kim and collaborators have studied some elements present in used nuclear fuel, particularly rare-earth elements, Kim explained, other elements haven’t been investigated due to their lower concentrations in used fuel. That is true for samarium, which was proposed to be studied as part of the group’s 2018 NEUP grant, but it could not be due to its low concentration in the molten salt and its different electrochemical behavior from that of other rare-earth fission products.

“Building on the accomplishments of that work, we now have a much better understanding of the key technical challenges and a clearer strategy for investigating samarium in this new project,” Kim said.

In addition to studying how the three elements behave electrochemically, the researchers will use a type of liquid metal, bismuth, to capture and remove certain fission products from molten salts. In past research, Kim’s group identified bismuth as an efficient liquid metal for recovering rare-earth elements from molten salt systems.

“If we are successful in our project goals, we could generate the scientific understanding needed to improve future molten salt reactor and fuel recycling technologies,” Kim said. “The knowledge gained could help recover valuable materials from used nuclear fuel and improve the efficiency and sustainability of advanced nuclear energy systems.”

In addition to Kim, Peyman Asghari-Rad, assistant research professor of materials science and engineering at Penn State, Dev Chidambaram of the University of Nevada, Reno, and Tae-Sic Yoo of the Idaho National Laboratory will serve as co-principal investigators on the grant.

This work is funded by the U.S. Department of Energy’s NEUP under award number DE-NE0009600. This content is the responsibility of the authors and does not necessarily reflect the views of the funders.