Researchers address material challenges to make commercial fusion power a reality

Imagine if we could take the energy of the sun, put it in a container, and use it to provide green, sustainable power for the world. Creating commercial fusion power plants would essentially make this idea a reality. However, there are several scientific challenges to overcome before we can successfully harness fusion power in this way.

Researchers from the U. S. Department of Energy (DOE) Ames National Laboratory and Iowa State University are leading efforts to overcome materials challenges that could make commercial fusion power a reality. The research teams are part of a DOE Advanced Research Projects Agency-Energy (ARPA-E) program called Creating Hardened And Durable fusion first Wall Incorporating Centralized Knowledge (CHADWICK). They will investigate materials for the first wall of a fusion reactor. The first wall is the structure that surrounds the fusion reaction, so it bears the brunt of the extreme environment in the fusion reactor core.

ARPA-E recently selected 13 projects under the CHADWICK program. Of those 13, Ames Lab leads one of the projects and is collaborating alongside Iowa State on another project, which is led by Pacific Northwest National Laboratory (PNNL).

According to Nicolas Argibay, a scientist at Ames Lab and lead of one project, one of the key challenges in harnessing fusion-based power is containing the plasma core that creates the energy. The plasma is like a miniature sun that needs to be contained by materials that can withstand a combination of extreme temperature, irradiation, and magnetic fields while efficiently extracting heat for conversion to electricity.

Argibay explained that in the reactor core, the plasma is contained by a strong magnetic field, and the first wall would surround this environment. The first wall has two layers of material, one that is closest to the strong magnetic and plasma environments, and one that will help move the energy along to other parts of the system.

The first layer material needs to be structurally sound, resisting cracking and erosion over time. Argibay also said that it cannot stay radioactive for very long, so that the reactor can be turned on and off for maintenance without endangering anyone working on it. The project he is leading is focused on the first layer material.

“I think one of the things we [at Ames Lab] bring is a unique capability for materials design, but also, very importantly, for processing them. It is hard to make and manage these materials,” said Argibay. “On the project I’m leading, we’re using tungsten as a major constituent, and, with the exception of some forms of carbon, like diamond, that’s the highest melting temperature element on the periodic table.”

The equipment necessary to process and test refractory materials, which have extremely high melting temperatures, has been made possible through recent investments by both ARPA-E and Ames Lab. In Argibay’s lab, the first piece of equipment they obtained is a commercial, modular, customizable, open-architecture platform for both making refractory materials and exploring advanced and smart manufacturing methods to make the process more efficient and reliable.

“Basically, we can make castings and powders of alloys up to and including pure tungsten, which is the highest melting temperature element other than diamond,” said Argibay.

By spring of 2025, Argibay said that they will have two additional systems in place for creating these refractory materials at both the lab-scale and pilot-scale quantities. He explained it is easier to make small quantities (lab-scale) than larger quantities (pilot-scale), but the larger quantities are important for collecting meaningful and useful data that can translate to a real-world application.

Additional investments by Ames Lab have provided Argibay with capabilities for measuring the mechanical properties of refractory materials at relevant temperatures. Systems capable of making measurements well above 1000°C (1832°F) are rare. Ames Lab now has one of the only commercial testers in the country that can measure tensile properties of alloys at temperatures up to 1500°C  (2732°F), which puts the Lab in a unique position to both support process science and alloy design.

Jordan Tiarks, another scientist at Ames Lab who is working on the project led by PNNL, is focused on a different aspect of this reactor research. His team is relying on Ames Lab’s 35 years of experience leading the field in gas atomization, powder metallurgy, and technology transfer to industry to develop materials for the first wall structural material.

“The first wall structural material is actually the part that holds it all together,” said Tiarks. “You need to have more complexity and more structural strength. You might have things like cooling channels that need to be integrated in the structural wall so that we can extract all of that heat, and don't just melt the first wall material.”

Tiarks’s team hopes to utilize over a decade of research focused on developing a unique way of creating oxide dispersion strengthened (ODS) steel for next generation nuclear fission. ODS steel contains very small ceramic particles (nanoparticles) that are dispersed throughout the steel. These particles improve the metal’s mechanical properties and ability to withstand high irradiation.

“What this project does is it takes all of our lessons learned on steels, and we’re going to apply them to a brand-new medium, a vanadium-based alloy that is well suited for nuclear fusion,” said Tiarks.

The major challenge Tiarks’ team faces is how vanadium behaves differently from steel. Vanadium has a much higher melting point, and it is more reactive than steel, so it cannot be contained with ceramic. Instead, his team must use a slightly different process for creating vanadium-based powders.

“We use high pressure gas to break up the molten material into tiny droplets which rapidly cool to create the powders we’re working with,” explained Tiarks. “And [in this case] we can’t use any sort of ceramic to be able to deliver the melt. So what we have to do is called ‘free fall gas atomization.’ It is essentially a big opening in a gas die where liquid stream pours through and we use supersonic gas jets to attack that liquid stream.”

There are some challenges with the method Tiarks described. First, he said that it is less efficient than other methods that rely on ceramics. Secondly, due to the high melting point of vanadium, it is harder to add more heat during the pouring process, which would provide more time to break up the liquid into droplets. Finally, vanadium tends to be reactive.

“Powders are reactive. If you aerosolize them, they like to explode! However, a fair number of metals will form a thin oxide shell on the outside layer that can help ‘passivate’ them from further reactions,” Tiarks explained. “It's kind of like an M&Mâ. It's the candy coating on the outside that protects the rest of the powder particle from further oxidizing. A lot of the research we've done in Ames lab is actually figuring out, how do we passivate these powders so you can handle them safely, so they won't further react, but without degrading too much of the performance of those powders by adding too much oxygen? If you oxidize them fully, all of a sudden, now we have a ceramic particle, and it's not a metal anymore, and so we have to be very careful to control the passivation process.”

Tiarks explained that discovering a powder processing method for vanadium-based materials will make them easier to form into the complicated geometric chapes that are necessary for the second layer to function properly. Additionally, vanadium will not interfere with the magnetic fields in the reactor core.

Sid Pathak, an assistant professor at Iowa State, is leading the group that will test the material samples for the second layer. When the material powder made by the Ames Lab group is ready, it will be formed into plates at PNNL by spraying the powder and friction stir processing onto a surface.

“Once you make that plate, we need to test its properties, particularly its response under the extreme radiation conditions present in a fusion reactor, and make sure that we got something better than what is currently available,” said Pathak. “That’s our claim, that our materials will be superior to what is used today.”

Pathak explained that it can take 10-20 years for radiation damage to show up on materials in a nuclear reactor. It would be impossible to recreate that timeline during a 3-year research project. Instead, his team uses ion irradiation to test how materials respond in extreme environments. For this process, his team uses a particle accelerator to bombard a material with ions available at University of Michigan’s Michigan Ion Beam Laboratory. The results simulate how a material is affected by radiation.

“Ion irradiation is a technique where you radiate [the material] with ions instead of neutrons. That can be done in a matter of hours,” said Pathak. “Also, the material does not become radioactive after ion irradiation, so you can handle it much more easily.”

Despite these benefits, there is one disadvantage to using ion irradiation. The damage only penetrates the material one or two micrometers deep, meaning that it can only be seen with a microscope. For reference, the average strand of human hair is about 70-100 micrometers thick. So testing materials at these very small depths requires specialized tools that work at the micro length scales, which are available at Pathak’s lab at Iowa State University.

“The pathway to commercial nuclear fusion power has some of the greatest technical challenges of our day but also has the potential for one of the greatest payoffs – harnessing the power of the sun to produce abundant, clean energy,” said Tiarks. “It's incredibly exciting to be able to have a tiny role in solving that greater problem.”

“I'm very excited at the prospect that we are kind of in uncharted water. So there is an opportunity for Ames to demonstrate why we're here,  why we should continue to fund and increase funding for national labs like ours, and why we are going to tackle some things that most companies and other national labs just can't or aren’t,” said Argibay. “We hope to be part of this next generation of solving fusion energy for the grid.”

Ames National Laboratory is a U.S. Department of Energy Office of Science National Laboratory operated by Iowa State University. Ames Laboratory creates innovative materials, technologies, and energy solutions. We use our expertise, unique capabilities, and interdisciplinary collaborations to solve global problems.

Ames National Laboratory is supported by the Office of Science of the U.S. Department of Energy. The Office of Science is the single largest supporter of basic research in the physical sciences in the United States and is working to address some of the most pressing challenges of our time. For more information, please visit https://energy.gov/science.