How to cool the nuclear reactors of the future?

Researchers at the Tokyo Institute of Technology are paving the way for cooling fusion reactors, following a historic breakthrough in nuclear fusion.

According to the IEA, nuclear power made up about 10% of global electricity generation in 2020. This share has declined from 18% in the late 1990s, but nuclear is still the second- largest source of low emissions electricity (i.e. non-fossil-based) after hydroelectricity. [1] 


Nuclear fusion and nuclear fission


A nuclear power plant generates electricity from the heat released by the fission of uranium atoms. Nuclear fusion, on the other hand, consists of bringing together two hydrogen atoms (deuterium and tritium). [2] Under the influence of extreme heat and pressure, gaseous hydrogen fuel becomes a plasma—a hot, electrically charged gas. In a star as in a fusion device, plasmas provide the environment in which light elements can fuse and yield energy. [3]  Nuclear fusion is a complex process that occurs naturally only in space, in the heart of our Sun. For a long time, nuclear fusion research has remained at the theoretical stage, but has recently taken a historic leap forward. On 5 December 2022, the Lawrence Livermore National Laboratory (LLNL) in California conducted the first nuclear fusion experiment with net energy production. [4] 

Fusion reactors are being actively developed throughout the world as a form of sustainable zero-carbon energies because their fuel can be extracted from an inexhaustible supply of seawater. Also, fusion differs from fission in that there is no nuclear waste. [4] In addition to the ITER project involving 35 nations (Japan, EU, United States, South Korea, China, Russia, and India) [3], fusion development by the private sector is also accelerating. 


Cooling fusion reactors 


The divertor is one of the most important components in a fusion reactor; it controls the exhaust of waste gas and impurities from the reactor and withstands the highest surface heat loads. [3] Researchers are working to develop a solid divertor in which a block of heat-resistant material such as tungsten is placed in contact with the plasma and cooled with water. For instance, the ITER project will be equipped with a cooling water system. [5] Conversely, researchers have also considered coating the structural material of the divertor with a liquid metal that possesses excellent cooling performance. For instance, liquid metal tin is an excellent coolant, but it has the drawback of corroding structural materials.


In December 2022, researchers at the Tokyo Institute of Technology and the National Institute for Fusion Science published a study clarifying the chemical compatibility between high temperature liquid metal tin (Sn) and reduced activation ferritic martensitic, a candidate structural material for fusion reactors. [6] The team believes that their discovery will contribute to promote the use of liquid metal tin not only for fusion energy but also for solar thermal power plants. [6] 




[1] IEA (2022), Nuclear Power and Secure Energy Transitions, IEA, Paris  





[6] Tokyo Institute of Technology. (2022, December 15). Mitigating corrosion by liquid tin could lead to better cooling in fusion reactors. ScienceDaily. Retrieved January 16, 2023 from