There are a few reasons, but the biggest one is that ceramics and composites also react with the molten salts. One study from 2015 (1) showed that even testing the corrosion resistance of metals was difficult because the type of crucible used had a large effect on the results.

These systems need pumps at a minimum. Sensors (temp, ph, flow rate, chemical composition, etc.) are also very important for prolonged, low maintenance use. These cannot be made of ceramics (that I know of)

The container will also need to safely hold a dense pool of molten salt. The linked $88k test reactor has a capacity of 350 liters, which at 1.94 g/cc is ~680kg/1500lbs of Li2BeF4.

Another important reason is that heat transfer is the whole point of the reactor, and most metal alternatives have poor thermal properties.

1. https://www.researchgate.net/publication/282433901_Impact_of...

I know on boats they use a piece of sacrificial metal (Anodes) that corrodes more readily than what the boat is made of. This prolongs the life of the boat. Maybe they can use something like that in this situation too.

no, because you would have to let the molten salt react with the sacrificial metal, introducing a lot of complicated impurities into your salt bath that may influence your reactor in numerous ways.

...unless the sacrificial material is a component of the salt anyway, like Beryllium.

ORNL proposed to have a Beryllium rod in contact with the fuel salt. It isn't needed to prevent corrosion of Hastelloy N in clean fuel salt, but it was intended to scavenge the fission product Tellurium, which was found to otherwise cause corrosion.

Doesn't quite work. It's also used in water boilers and most of them corrode after 10 years with the anode in good shape.

Furnaces use stone because it is not very sensitive to heat. Stone generally remains sensitive to acid.

Plastics would be great to withstand the acid, but they're sensitive to heat.

Ultra-high-temperature polymers might get there. There are polymers used in specialized industrial applications that can handle ~500° C.

Granite, for instance, has a 1200c melting point which sounds good. Its large grainy structure might cause porosity issues. And it's main constituents are silicon and aluminum, both of which do transmute under neutron bombardment. (An expert could say if they transmute to anything you really don't want around, and how long it'll be there.)

I think ceramics are an answer to the porosity and similar issues. Consistent structure, no inclusions or other weaknesses. But they would face the same transmutation and induced radioactivity problems as stone of the same material.

Ceramics used in water boilers crack. You don't want that in a nuclear reactor.

You mean ceramics?

There are so many to chose from, and most are unusable for one reason or another. The leading candidate being investigated is carborundum (silicon carbide). It doesn't corrode in molten salt, it low appetite for neutrons, is reasonably easy to manufacture, conducts heat fairly well. It's even mentioned in the video.