Choosing the Right Structural Materials for Fusion Reactors

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Do two promising structural materials corrode at very high temperatures when in contact with “liquid metal fuel breeder reactors” in fusion reactors? Researchers from Tokyo Institute of Technology (Tokyo Tech), National Institutes for Quantum Science and Technology (QST), and Yokohama National University (YNU) now have the answer. This high-temperature compatibility of the reactor structural materials with the liquid breeder reactor – a coating around the reactor core that absorbs and traps the high-energy neutrons produced in the plasma inside the reactor – is key to the success of a fusion reactor design.

Fusion reactors could be a powerful way to generate clean electricity, and currently several potential designs are being explored. In a fusion reactor, the fusion of two nuclei releases massive amounts of energy. This energy is trapped as heat in a “breeding blanket” (BB), usually a liquid lithium alloy, surrounding the reactor core. This heat is then used to run a turbine and generate electricity. The BB also has an essential fusion fuel breeder function, creating a closed fuel cycle for endless reactor operation without fuel depletion.

Operating a BB at extremely high temperatures above 1173 K performs the interesting function of producing hydrogen from water, which is a promising technology for realizing a carbon neutral society. This is possible because the BB heats up to over 1173 K by absorbing energy from the fusion reaction. At such temperatures, the structural materials in contact with the BB risk corroding, compromising the safety and stability of the reactors. It is therefore necessary to find structural materials that are chemically compatible with the BB material at these temperatures.

One type of BB currently being explored is liquid metal BB. A promising candidate for such BBs is liquid lithium lead alloy (LiPb). As candidates for structural materials compatible with ultra-high temperature liquid LiPb, some silicon carbide (SiC), CVD-SiC material, and air pre-oxidized iron-chromium-aluminum (FeCrAl) alloy are explored. But information on this compatibility is lacking beyond temperatures of 973 K.

Now, a team of scientists from Tokyo Tech, QST and YNU, Japan, led by Professor Masatoshi Kondo of Tokyo Tech, have demonstrated compatibility at much higher temperatures. Their findings are published in Corrosion Science. “Our study highlights the nuances of the corrosion resistance mechanism of CVD-SiC and FeCrAl alloys in liquid LiPb up to 1173 K,” says Professor Kondo.

The team first synthesized high-purity LiPb by melting and mixing Li and Pb pellets in a vacuum apparatus. They then heated the alloy to the aforementioned temperatures, at which it liquefied. Samples of CVD-SiC and two variants of the FeCrAl alloy – with and without pre-oxidation treatment to form an α-Al2O3 surface layer – were placed in this liquid LiPb for 250 hours for corrosion testing. Professor Kondo observes: “An interesting finding is that, unlike previous literature, the oxidation pretreatment to form an α-Al2O3 layer did not provide corrosion resistance beyond 1023 K.”

Cross-sections of the recovered samples showed that the CVD-SiC reacted with the impurities of the LiPb alloy to form a layer of complex oxides, which then gave it corrosion resistance. Untreated FeCrAl alloy formed γ-LiAlO oxide layer2 during the reaction with LiPb, which then acts as an anti-corrosion barrier. In the case of pretreated FeCrAl, the α-Al2O3 surface layer provided corrosion resistance at 873 K but transformed to γ-LiAlO2 at 1173 K, and it was γ-LiAlO2 which then offered corrosion resistance.


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More information:
Masatoshi Kondo et al, Corrosion resistant materials for liquid LiPb fusion blanket in high temperature operation, Corrosion Science (2021). DOI: 10.1016/j.corsci.2021.110070

Provided by Tokyo Institute of Technology


Quote: Selecting the Right Structural Materials for Fusion Reactors (2022, March 3) Retrieved March 3, 2022 from https://phys.org/news/2022-03-materials-fusion-reactors.html

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