Experts chip away at corrosion for the future of fusion

Practical fusion energy is not just a dream at the Department of Energy’s Oak Ridge National Laboratory. Experts in fusion and material science are working together to develop solutions that will make a fusion pilot plant — and ultimately carbon-free, abundant fusion electricity — possible.

As head of the lab’s Fusion Nuclear Science, Technology and Engineering Section, Chuck Kessel is familiar with the materials challenges that must be addressed to build a power plant. Kessel needed to look no further than Bruce Pint, head of ORNL’s Corrosion Science and Technology Group, for a collaborator.

Pint has been studying corrosion-resistant, high-temperature materials for power generation applications for decades. His work has focused mostly on gas-metal or alloy corrosion and oxidation for coal, gas and nuclear power plants. Examining corrosive liquids in the context of fusion energy represents a different and tougher challenge.

“It's a little bit of science and a little bit of art that goes into the whole thing,” Pint said.

One critical challenge for fusion is how to produce and recover tritium, a heavy hydrogen isotope that, along with its lighter cousin deuterium, will serve as fuel for tomorrow’s fusion reactors.

In a fusion reaction, these isotopes are heated to Sun-like temperatures in a plasma where they collide to form helium and a neutron, releasing energy in the form of kinetic energy. By directing those speeding neutrons at the more common metal lithium, scientists can produce tritium within the reactor itself.

A promising strategy for producing tritium in a fusion reactor involves channeling liquid lead-lithium through the reactor “blanket” — the inner walls that are made of specialized steel with silicon carbide flow channel inserts. However, there’s a catch: The ongoing flow of lead-lithium will gradually eat away at the steel. Minimizing that corrosion is a crucial step for a viable fusion power plant.

“This type of blanket, with a liquid breeder flowing through it and corroding these materials, is fundamentally limited by this corrosion mechanism,” Kessel said.

Marie Romedenne, who studied liquid metals for her doctorate and joined ORNL in 2019, is helping Pint and learning more about the ORNL liquid metal experimental methods that have been used since the 1950s.

Many factors contribute to corrosion rates, including the composition of the exposed materials; how long it is exposed; how fast the liquid flows; the strong magnetic fields used to control and confine the plasma; the temperature; and impurities in the system. This corrosion challenge gave Pint and Romedenne the chance to chart out several experiments designed to detangle these factors while edging closer to the conditions of an actual fusion reactor.