Nuclear fusion, the same process that fuels the sun and stars, has the potential to generate electricity on earth without producing carbon emissions and long-lasting nuclear waste. Central to nuclear fusion’s success is the development of new materials that can withstand the extreme temperature, mechanical stress and damage from intense neutrons. Novel metal alloys and ceramic composites are coming into view as potential game changers, with researchers now attempting to understand how these materials can benefit fusion reactor designs.
David Sprouster, assistant professor in the Department of Materials Science and Chemical Engineering at Stony Brook University, has a number of ongoing research projects that are tackling the materials science and engineering challenges associated with new materials for fusion energy.
“My research is really about stress testing these different materials to see how we can improve their function when exposed to different combinations of extremes,” said Sprouster. “It’s also fun to design them, to fabricate them in the lab, and then to break them.”
Sprouster and his team have received three multi-million dollar recent grants that focus on materials for fusion energy, with two from the Department of Energy, Office of Fusion Energy Sciences Fusion Innovation Research Engine (FIRE) Collaboratives.
In a recent study, Sprouster’s group compared two steels with similar alloy compositions, but fabricated in two different ways: one by traditional casting and the other through direct current sintering. In direct current sintering, both heat and pressure are used to rapidly convert powders into a solid monolithic material. As compared to conventional casting, this process allows the relatively complicated and graded structures of fusion chamber walls to be formed. Both fabricated steels are designed to resist deformation under heat and stress over time, a phenomenon known as “creep.”
“Creep is a very slow process — it happens over days, weeks, months and years — and depends on the applied stress and temperature,” said Sprouster. “It’s a tough moving target, but we have had success in designing the least ‘creepy’ materials, and to engineer the movement of dislocations, the defects within materials that allow plastic deformation to occur to improve our overall fundamental understanding of creep.”
Sprouster’s recent work concluded that both the conventionally cast and sintered materials showed equally good creep resistance. But they observed that when temperature increases, dislocations move more easily, which makes the material more prone to deformation. Equipped with this new knowledge, materials engineers can predict how these steels will perform under high-temperature service conditions, such as in fusion reactors.
In a second study, Sprouster’s group fabricated composites of steel with hafnium hydride through direct current sintering for neutron shielding applications within advanced nuclear fusion reactors. “The hydrogen is there to stop the neutrons. It has a very good cross-section for neutron absorption,” said Sprouster. “So, it basically takes most of the neutrons away so that you can shield the critical components that are close to the plasma.”
One of the key findings from this work was that upon heating, hafnium hydride breaks down and releases hydrogen, and the hafnium metal reacts with the iron to produce new intermetallic phases. However, due to the composite nature of this shield, the release is relatively show and at a much higher temperature than anticipated in the fusion reactor application.
These projects serve a shared purpose — to construct safer, more efficient and more durable materials for extreme nuclear environments for future fusion reactors.
“The fusion space has become an enormously attractive research area,” said Lance Snead, research professor in the Department of Materials Science and Chemical Engineering. “Historically, the Department of Energy was the primary agency funding this future energy source, but with the realization that fusion can be a near-term source of electricity, private investors now dominate the field.”
“Fusion is very exciting right now,” said Sprouster. “There’s a lot of activity and good collaborations across the universities, national labs and within industry. The community is very energetic and focused on materials science solutions to tough engineering problems.”
“Last year over 1.6 billion dollars in private research funding went into fusion, or three times that of the federal contribution,” said Snead. “As a key to the success of any of the current fusion concepts hinges on the ability to develop new and robust fusion chamber materials, Professor Sprouster has positioned his group in a very exciting growth area for research.”
Future work in the Department of Materials Science and Chemical Engineering at SBU will include the development of advanced materials that can withstand the extreme environments that are intrinsic to fusion.
— Angelina Livigni
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