The US has issued a permit to construct a different kind of nuclear reactor.
Known as a molten salt reactor, it could lead to smaller, easier-to-build nuclear power plants in the future that could end up powering ships and other off-the-grid locations.
What makes this reactor different is how it will cool its core, using molten salt instead of water.
Water vs. salt
High pressure is needed to keep the water liquid and prevent it from evaporating at high temperatures. This requires additional space and technology.
Some salts, on the other hand, have much higher boiling points, so they wouldn’t require the same expensive, high-pressure environments.
” You can use it at high temperatures and it won’t boil,” Nicholas V. Smith told Business Insider. “You don’t have to have big, thick pressure vessels to contain coolant.”
The first molten salt reactor tested in the 1950s, for example, was small enough to fit on a plane whereas the portion of the Diablo Canyon Nuclear Power Plant in California that generates energy takes up 12 acres of land, according to Berkeley Engineering.
That benefit, and others, is why the US Nuclear Regulatory Commission just issued the first permit to construct a non-water-cooled nuclear plant.
It will be the first since 1968, Mike Laufer, Kairos Power’s chief executive officer, told Bloomberg.
Kairos Power is the company that plans to build a test plant it calls Hermes, which will be cooled by molten fluoride salt in Oak Ridge, Tennessee by 2027.
The first version of the plant won’t provide electricity, but the company hopes its successor, Hermes 2, will by 2028.
Why should molten-salt reactors be explored again?
Molten salt reactors have been around since the 1950s but the US mostly abandoned them in the 1970s in favor of water-cooled reactors, many of which had already been built.
Recently, however, companies, including Kairos, and laboratories are looking into salt-cooled reactors again.
“Salt as a coolant is just superior to water, once you’ve got the engineering details hammered out,” Smith told BI.
Molten salt reactors do not require thick vessels that keep the water liquid even at very high temperatures. This allows for more flexibility in design, Smith explained.
Reactors can be smaller than water-cooled options and built in a wider variety of locations, for example.
“Molten salt sort of opens up a lot of design options that you simply can’t get to without it,” Smith said. “As you move into that low-pressure paradigm, manufacturing just gets a lot more straightforward.”
“I see molten salt reactors as being prolifically deployed in all areas,” from remote locations to shipping vessels to large power plants, he added.
How Hermes will operate
Hermes will operate at temperatures up to 1,200 degrees Fahrenheit. But its molten salt coolant — which is made of a mixture of lithium fluoride and beryllium fluoride known as FLiBe — boils at about 2,606 degrees Fahrenheit, well above the reactor core’s temperature.
Therefore, the FLiBe will remain a liquid at those high temperatures without additional pressure. Smith stated that this should reduce the cost and make it easier to construct reactors.
Kairos Power’s proposed fuel is also different from a typical nuclear reactor. The company plans to use TRISO, or TRi-structural ISOtropic particle fuel.
It can withstand extreme temperatures better than current fuels, making it less likely to release radioactive fission products, according to the US Office of Nuclear Energy.
Some challenges include limiting corrosion.
“Oxygen acts as a catalyst for corrosion when molten sal is exposed to oxygen,” Smith explained.
The challenge is to limit the salt’s exposure to oxygen. “It’s not the exact same processes, but it’s the same principles as any other coolant,” he said. “You’ve got to control the chemistry.”
Molten salt reactors do have drawbacks. For example, they “would produce several different waste streams, all of which would require extensive processing and would face disposal-related challenges,” physicist M.V. Ramana wrote in 2022.
One study suggested that the reactors could produce more nuclear waste than current systems and that they “will use highly corrosive and pyrophoric fuels and coolants that, following irradiation, will become highly radioactive.”