Part 2 of 3 Parts (Please read Part 1 first)
     Jordan Tiarks is another scientist at Ames Lab who is working on the project led by PNNL. He is focused on a different aspect of this reactor research. His team is relying on Ames Lab’s thirty-five 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 in a fusion reactor.
     Tiarks said, “The first wall structural material is the part that holds it all together. It requires more complexity and more structural strength. Things like cooling channels 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 reactors. ODS steel contains very small ceramic particles (nanoparticles) that are distributed throughout the steel. These particles improve the metal’s mechanical properties and assist in the ability to withstand high irradiation.
     Tiarks said, “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.”
     The major challenge that Tiarks’s team now faces is how vanadium behaves differently from steel. Vanadium has a much higher melting point, and it is more reactive than steel. It cannot be contained with ceramic. Instead, his team must use a similar but different process for creating vanadium-based powders.
     Tiarks explained, “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. 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 a liquid stream pours through, and we use supersonic gas jets to attack that liquid stream.”
     There are some significant challenges with the method Tiarks described. The first problem is that it is less efficient than other methods that rely on ceramics. The second problem is that due to the high melting point of vanadium, it is harder to add more heat during the pouring process. This would provide more time to break up the liquid into droplets. The third problem is that vanadium tends to be reactive.
     Tiarks added that “Powders are reactive. If you aerosolize them, they will 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. It’s kind of like an M&M. It’s the candy coating on the outside that protects the rest of the powder particle from further oxidizing.”
     Tiarks continued that, “A lot of the research we’ve done in the Ames lab is actually figuring out how 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 went on to explain that discovering a powder processing method for vanadium-based materials should make them easier to form into the complicated geometric shapes that are necessary for the second layer to function properly. In addition, vanadium will not interfere with the powerful magnetic fields in the reactor core.
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Iowa State University

Part 1 of 3 Parts
     Researchers at the U. S. Department of Energy (DoE) Ames National Laboratory and Iowa State University are leading efforts to overcome material challenges to making commercial fusion a reality. The research teams are part of a DoE Advanced Research Projects Agency-Energy (ARPA-E) program referred to as “Creating Hardened And Durable fusion first Wall Incorporating Centralized Knowledge” (CHADWICK). They will research materials for the first wall of a fusion reactor. The first wall is the part of the reactor that surrounds the fusion reaction. It bears the brunt of the extreme heat and pressure in the fusion reactor core.
     ARPA-E recently selected thirteen projects under the CHADWICK program. Of those thirteen, Ames Lab leads one of the projects. It is also collaborating with Iowa State on another project, which is led by Pacific Northwest National Laboratory (PNNL).
     Nicolas Argibay is a scientist at the Ames Lab and the lead of one project. One of his key challenges in harnessing fusion-based power is containing the plasma core that generates the energy. The plasma is like a miniature sun that needs to be contained by materials that can survive a combination of extreme temperature, extreme pressure, 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 surrounds this environment. The first wall has two layers of material. One layer is closest to the strong magnetic and plasma environments. The other layer will help move the energy along to other parts of the system.
     The first layer material needs to be structurally sound, and able to resist cracking and erosion over time. Argibay also said that it cannot stay radioactive for very long because the reactor needs to be turned on and off for maintenance without endangering anyone working on it. The project that Argibay is leading is focused on the first layer material.
     Argibay said, “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. 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.”
     Special equipment is required to process and test refractory materials, which have extremely high melting temperatures. In Argibay’s lab, the first piece of equipment installed was a commercial, modular, customizable, open-architecture platform for making refractory materials. The lab will explore advanced and smart manufacturing methods to make the process more efficient and reliable.
     Argibay added, “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.”
     By spring of 2025, Argibay said that they intend to have two additional systems in place for creating these refractory materials at both lab-scale and pilot-scale quantities. He explained it is easier to make small quantities (lab-scale) than larger quantities (pilot-scale). However, larger quantities are important for collecting meaningful and useful data that can translate into a real-world application.
     Argibay’s team also has the ability to examine the mechanical properties of refractory materials at relevant temperatures. Systems able to make measurements well above eighteen hundred degrees Fahrenheit are rare. Ames Lab has one of the only commercial thermal testers in the country that can measure tensile properties of alloys at temperatures up to twenty-seven hundred degrees Fahrenheit. This puts the lab in a unique position to support process science and alloy design.
Please read Part 2 next

Ames National Laboratory