Nuclear fusion presents a significant materials engineering challenge. In order to understand the scientific and technical innovations we’ll be discussing in this post, it’s important to review some basic concepts about nuclear fusion first.
In this respect, the plasma in the vacuum chamber of experimental nuclear fusion reactors contains deuterium and tritium nuclei, both of which are hydrogen isotopes. When this gas reaches temperatures of at least 270 million degrees Fahrenheit, the nuclei gain enough kinetic energy to overcome their natural repulsion (both with positive electric charges) and begin to fuse spontaneously. This fusion results in the creation of a helium-4 nucleus and a neutron with an average energy release of 14 MeV (megaelectronvolts).
The neutron is crucial for generating electricity using a fusion power reactor. However, due to their neutral electric charge, the neutrons can’t be confined by the magnetic field and escape, colliding with the inner lining of the vacuum chamber walls, which causes degradation.
The Lining of the Vacuum Chamber Is Exposed to Extreme Aggression
The vacuum chamber in a nuclear fusion reactor is the compartment where the fusion reactions between hydrogen isotopes occur. Its inner lining must be able to minimize the degradation caused by the action of high-energy neutrons, but this is by no means its only threat. In fact, the magnetic field responsible for confining the nuclei can’t retain all the particles.
When the particles are produced, they acquire widely varying energies, so some helium-4 nuclei escape magnetic confinement and accumulate next to the inner lining.
However powerful it may be, this magnetic field has a limit. As a result, it manages to retain the nuclei that don’t exceed a certain energy value. However, when the particles are produced, they acquire widely varying energies, and helium-4 nuclei escape the magnetic confinement and accumulate next to the inner lining of the vacuum chamber. This accumulation degrades the reactor walls and triggers the formation of cracks, which threaten the structural integrity of the reactor and lead to loss of vacuum.
To address this issue, it’s crucial to develop a material for the inner lining of the vacuum chamber that can minimize the degradation caused by high-energy neutrons and the accumulation of helium-4 nuclei. Several research groups are working on this, and a group led by professor Ju Li at Massachusetts Institute of Technology has developed a promising material, at least on paper.
The group of researchers examined over 50,000 materials with varying properties until they discovered one that could be ideal: iron silicate. When used to line the interior of the vacuum chamber, it effectively disperses accumulations of helium-4, as explained in an article published in Acta Materialia.
If this material lives up to its promise, it could significantly prolong the lifespan of fusion reactors. Furthermore, iron silicate is compatible with 3D printing, making it much easier to handle and administer. This gives us another reason to view the future of nuclear fusion with reasonable optimism.
Image | Galina Nelyubova (via Unsplash)
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