When Alexander O’Brien sent in his application to graduate school in the Department of Nuclear Science and Engineering at MIT, he had the seed of a research idea that was already brewing. So when he received a phone call from Professor Mingda Li, he shared: The student from Arkansas wanted to explore designing materials that could hold nuclear reactors together.
Lee listened to him patiently and then said, “I think you would be a great fit for Professor Joe Lee,” O’Brien recalls. Joe Lee, a professor of nuclear engineering at Battelle Energy Alliance, wanted to explore 3D printing for nuclear reactors, and O’Brien seemed like the right candidate. “At that moment I decided I would go to MIT if they would accept me,” O’Brien recalls.
And they did.
Under the guidance of Gu Li, the fourth-year doctoral student is now exploring 3D printing of ceramic and metal composites, materials that can be used to build fusion power plants.
Early interest in science
O’Brien grew up in Springdale, Arkansas as a “band nerd”, and was particularly interested in chemistry and physics. It was one thing to mix baking soda and vinegar to make a “volcano” but quite another to understand why it happened. “I enjoyed understanding things on a deeper level, being able to understand how the world works,” he says.
At the same time, it was difficult to ignore the energy economics taking place in his backyard. When Arkansas, a place that rarely experiences earthquakes, began recording earthquakes following fracking in neighboring Oklahoma, it was a “lightbulb moment” for O’Brien. “I knew this would create problems in the future, and I knew there had to be a better way to get (the energy),” he says.
With the idea of energy alternatives simmering, O’Brien enrolled in undergraduate studies at the University of Arkansas. He participated in the school band – “You show up a week before everyone else and there are 400 people who automatically become your friends” – and enjoyed the social environment a large state school could provide.
O’Brien majored in chemical engineering and physics, and appreciated “the ability to put your hands on machines to make things work.” O’Brien decided to begin exploring his interests in energy alternatives, and researched transition metal dichalcogenides, whose layers could catalyze a hydrogen evolution reaction and more easily produce hydrogen gas, an alternative to green energy.
However, shortly after his sophomore year, O’Brien truly found his way into the field of energy alternatives—in nuclear engineering. The American Chemical Society was soliciting student applications for a summer study of nuclear chemistry in San Jose, California. O’Brien applied and was accepted. “After years of knowing I wanted to work in green energy, but not knowing what that looked like, I quickly fell in love with (nuclear engineering),” he says. That summer also solidified O’Brien’s decision to attend graduate school. “I had the idea that I needed to go to graduate school because I needed to learn more about this subject,” he says.
O’Brien particularly appreciated the independent project assigned as part of the summer program: he chose to research nuclear-powered spacecraft. Digging deeper, O’Brien discovered the challenges of powering spacecraft – nuclear power was the most viable alternative, but it had to work around extraneous radiation sources in space. Access to Exploration National Laboratories near San Jose sealed the deal. “I visited the National Ignition Facility, which is the big fusion center there, and to see this huge facility designed entirely around this fusion idea was amazing to me,” O’Brien says.
A new scheme for fusion power plants
Current research conducted by O’Brien in MIT’s Department of Nuclear Science and Engineering (NSE) is equally surprising.
As new fusion devices begin to be designed, it is becoming increasingly clear that the materials we use cannot withstand the high temperatures and radiation levels of operating environments, O’Brien says. Additive manufacturing, another term for 3D printing, “opens up a whole new world of possibilities for what you can do with metal, which is exactly what you’ll need[to build the next generation of fusion power plants].” He says.
Metals and ceramics by themselves may not be able to withstand high temperatures (target 750°C), pressures and radiation, but together they may get there. Although these metal matrix composites have been around for decades, they were not practical for use in reactors, because “they’re hard to make with any kind of uniformity, and they’re really limited in size,” O’Brien says. This is because when you try to put ceramic nanoparticles in a pool of molten metal, they will fall in any direction you want. “3D printing is completely changing this story so quickly that if you want to add these nanoparticles in very specific areas, you have the ability to do that,” O’Brien says.
O’Brien’s work, which forms the basis of his doctoral thesis and a journal paper Additive manufacturingIt involves implanting metals with ceramic nanoparticles. The end result is a metal matrix composite that is an ideal candidate for fusion devices, especially for the vacuum vessel component, which must be able to withstand high temperatures, highly corrosive molten salts, and the internal helium gas produced by nuclear conversion.
O’Brien’s work focuses on nickel superalloys such as Inconel 718, which are particularly strong candidates because they can withstand higher operating temperatures while retaining strength. Helium embrittlement, where helium bubbles resulting from neutron fusion lead to weakness and failure, is a problem with Inconel 718, but composite materials show the ability to overcome this challenge.
To create composite materials, a mechanical grinding process is first performed to coat ceramic over metal particles. Ceramic nanoparticles act as strengthening agents, especially at high temperatures, and make materials last longer. Nanoparticles also absorb helium defects and radiation when they are uniformly dispersed, preventing these damage agents from reaching grain boundaries.
The composite then goes through a 3D printing process called powder bed fusion (non-nuclear fusion), where a laser is passed over a layer of this powder to melt it into the desired shapes. “By coating these particles with ceramic and then melting only very specific areas, we keep the ceramic in the areas we want, so you can build and get a uniform structure,” O’Brien says.
Print an exciting future
3D printing of nuclear materials shows such great promise that O’Brien is looking forward to pursuing this possibility after his doctoral studies. “The concept of these metal matrix composites and how they can enhance material property is really interesting,” he says. Expanding his business through a startup is something on his radar.
For now, O’Brien enjoys research and attends a Broadway show with his wife from time to time. While the band nerd doesn’t pick up his saxophone much anymore, he enjoys driving to New Hampshire and backpacking. “This is my new hobby, since I started graduate school,” O’Brien says.
(Tags for translation) MIT Nuclear Science and Engineering
