An advanced pebble-bed reactor will be built in Tennessee. It will be cooled by molten fluoride salts making the reactor simpler and cheaper to run. If it succeeds it will be a major advancement for pebble reactors.
Image by Markus Distelrath from Pixabay
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The growing pressure of climate politics and the opposition to fossil fuels lead to nuclear energy becoming more attractive. But as you probably know, it also has its own problems. One of the biggest ones is the fact that not many countries want the traditional large water-cooled reactors.
This is why some American organizations that run nuclear power plants such as the Tennessee Valley Authority (TVA) that is responsible for a large part of American nuclear energy is flirting with more advanced and unconventional designs of nuclear power plants. One such design is Hermes a pebble-bed reactor that is cooled with molten salts and made by Kairos power. TVA and Kairos decided to combine their powers and build a proof-of-concept reactor in Tennessee.
In a conventional reactor, the pellets with fuel in the form of uranium or plutonium are in fuel rods inside the reactor core alongside the control rods and fully covered in water. The fuel cells are close enough to each other that they start a fission reaction while the water slows down the neutrons, helps the fission reaction going and the control rods allow us to keep the reaction stable and prevent the reactor itself from melting.
On the other hand, pebble-bed reactors are quite different. The rods are replaced with balls the size of tennis balls known as pebbles. These are made from a layer of nuclear fuel and graphite built into a ceramic material. Thousands of these pebbles are put into the reactor and that’s where the fission reaction takes place without control rods. In the majority of concepts for pebble-bed reactors, the core is cooled with some secure gas such as helium, nitrogen, or carbon dioxide. And while the original design for a pebble-bed reactor goes back to early after World War II we never managed to get over all the hurdles and only experimental and prototype reactors were ever built.
The reactor Hermes is an advanced design of a pebble-bed reactor. Instead of using gas for cooling it uses molten fluoride salts. Compared to water that boils and changes into steam and 100° Celsius, giving us a lot of trouble, fluoride salts can reach more than 1000° Celsius without boiling, allowing us to transfer gigantic amounts of heat while keeping the pressure down. And these salts are also chemically stable and don’t require any large or expensive security structures to keep the core from melting even if the reactor fails. Once Hermes is online it should provide 140 MW of energy.
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