The insides of nuclear fusion reactors are violent and chaotic places. A new cold-spray coating can take the heat and also trap some rogue hydrogen particles at the same time, potentially making for smaller, better plasma chambers.
While nuclear fusion is still in a very experimental stage, the powering up of the world's largest and most advanced tokamak fusion reactor in Japan this month shows that the technology is constantly moving from theory towards reality.
In fusion reactions, an ionized hydrogen gas known as plasma is subjected to levels of pressure and heat that equal those at the center of the Sun. This causes the atomic nuclei to fuse and release a tremendous amount of clean energy.
Creating the chambers that hold the plasma needed for fusion has been a challenge due to the extreme levels of heat and pressure they need to reach. Another issue with the process is that sometimes hydrogen atoms can get neutralized and escape from the plasma, which weakens its potency.
“These hydrogen neutral particles cause power losses in the plasma, which makes it very challenging to sustain a hot plasma and have an effective small fusion reactor,” said Mykola Ialovega, a postdoctoral researcher in nuclear engineering and engineering physics at the University of Wisconsin-Madison (UW–Madison). Ialovega has led research on a coating that has demonstrated the ability to line fusion reactor chambers and capture this rogue hydrogen.
The coating is made from the metal tantalum, which can withstand extremely high temperatures. The tantalum was cold sprayed onto stainless steel and subject to fusion-like conditions in which it performed admirably.
In the cold-spraying process, particles of tantalum were blasted onto the stainless steel where they flattened like pancakes. Even when smooshed in this way though, there is still a small border between each particle which, the researchers found, was an ideal channel in which to capture errant hydrogen particles. When the sprayed steel was subjected to even higher temperatures, the trapped hydrogen particles were released, in effect renewing the material so that it could be reused repeatedly.
The research team touts not only the coating's ability to repeatedly grab and release hydrogen while withstanding punishing heat and pressure, but also its ease of use.
“Another big benefit of the cold spray method is that it allows us to repair reactor components on site by applying a new coating,” Ialovega said. “Currently, damaged reactor components often need to be removed and replaced with a completely new part, which is costly and time consuming.”
The team plans to use the coating on the Wisconsin HTS Axisymmetric Mirror (WHAM), an experimental device that may find its way into a next-gen fusion power plant being planned by Realta Fusion, a spinoff off UW-Madison.
“Creating a refractory metal composite with these features of well-controlled hydrogen handling combined with erosion resistance and general material resilience is a breakthrough for the design of plasma devices and fusion energy systems,” Oliver Schmitz said. “The prospect of changing the alloy and including other refractory metals to enhance the composite for nuclear applications is particularly exciting.”
Schmitz is a professor of nuclear engineering and engineering physics at UW-Madison and a co-author on a paper describing the findings that's been published in the journal Physica Scripta.
Source: University of Wisconsin-Madison