X-energy, a Maryland-based company, uses uranium to make so-called TRISO fuel — inside what’s known as “pebbles.”

The Energy Department says it’s the most robust nuclear fuel on Earth because the particles cannot melt in a reactor.

Uranium powder, in the form of triuranium octoxide, gets added to nitric acid, said Dan Brown, vice president of fuel development for TRISO-X. Then carbon and an organic solution are added. They have two glass containers set up — one wears a heated jacket, looking almost like a little sweater, that helps the uranium dissolve into the acid solution. The second cools the acid solution while the carbon source is added, which turns the mix near-black, he said.

At another station, in a long clear tube, the cocktail solidifies into small black spheres with a jellybean-like consistency. Those black balls, about the size of poppyseeds, then travel through machines under temperatures as high as 1,800 degrees Celsius to get protective carbon coatings — like candy dipping — that make them look like very tiny BBs.

X-energy uses graphite and other cohesive materials to bind 18,000 kernels together into a larger sphere. That gets coated in a final layer of graphite to seal the final pebble. In the end, it’s strong enough to withstand the weight of an SUV.

The pebbles will eventually give up their energy in the high-temperature gas-cooled nuclear reactor X-energy is developing, with about 220,000 pebbles per reactor, like gumballs in a gumball machine. When they exit the bottom, if energy remains, the pebbles will return to the top for another pass. Each one could be used about six times. X-energy also plans to make fuel products for other advanced reactor designs.