A 215,000-square-foot nuclear power plant has had its frame, walls and roof completed in Tennessee, built to press uranium into billiard balls at a rate of 700,000 per year for up to 11 reactors, and the machines that do the pressing have yet to be moved inside.

Last August, we covered a factory in Oak Ridge, Tennessee, built to press uranium into billiard ball-sized spheres called pebbles. At the time, most of the story was on paper. The building itself was a steel frame with a new license and a very long list of things to do.

This building is now completed. On September 24, TRISO-Xthe fuel subsidiary of X-energyannounced that it had completed vertical construction on TX-1the company name for the factory. That means the 215,000 square foot structure (frame, walls, roof, the whole envelope) is standing and everything that happens from here on out happens inside.

So, is this a major milestone or a run-of-the-mill build update?

A bit of both, frankly. “Core and shell” is the term used in the construction industry for exactly what it looks like: the supporting structure plus the skin that protects against the elements, without any hoses installed. Your average warehouse reaches this point and it’s pretty much finished. A nuclear power plant reaches this stage and the costly phase begins.

Joel Duling, president of TRISO-X, said in the announcement that the company was “moving from building the core and shell of the facility” to fitting utilities inside, installing manufacturing equipment and constructing the support buildings around the main plant.

And if you’re wondering if the building landed on schedule, not quite. When X-energy began vertical construction in November 2025, it expected this phase to be completed by mid-2026, and it was completed on September 24. Call it three months late, which by nuclear construction standards is pretty close to on-time.

So, what really remains to be done?

Three things, according to the company: indoor utilities, the fuel manufacturing line itself and the support buildings on campus.

This middle element is the piece I would look at. Making this fuel is not about assembling widgets. Each particle starts out as a core of uranium, carbon and oxygen, and machines then envelop it in layers of ceramic carbon and silicon carbide deposited from hot gases, a process that must happen on the scale of a poppy seed. A finished pebble contains more than 18,000 of these particles, and most fuel safety arguments rely on these coatings doing their job. We looked at what these coatings experience inside a reactor a few weeks ago, if you want the more in-depth version.

X-energy did not say when the first manufacturing machines will arrive or how long the interior design will take. What the company and the Department of Energy have both set a date for is the finish line: Fuel production at TX-1 is expected to begin in early 2028.

The permit is already in hand

One thing this factory doesn’t have to wait for is permission.

The Nuclear Regulatory Commission on Feb. 13 approved a 40-year operating license, covering fuel made with high-grade low-enriched uranium, the material enriched between 5 and 20 percent that the most advanced reactor designs require. The Department of Energy notes that NRC had not issued a new license of this type in about 50 years before this one, and that it also covers TX-2, the second, larger plant planned on the same campus. Tennessee added an $11 million grant in July to support campus construction, including that second factory and a research lab.

Which means the paperwork is ahead of the hardware. It’s a strange sentence to write about anything nuclear, and I don’t expect to write it often.

What will be released in 2028

Once the machines are running, TX-1 is designed to produce approximately 700,000 stones per year. The company counts that as 5 tons of uranium, or just over five and a half short tons, and says it’s enough to power up to 11 of its Xe-100 reactors. Around 500 people are expected to work there.

These rocks do not sit still in a reactor like fuel rods do. The Xe-100 loads the new ones from the top while the spent ones fall from the bottom, and the Department of Energy has likened the system to a gumball machine, which is the clearest description of a nuclear core I’ve read all year. Each pebble makes up to six trips through the core over about three years before being exhausted.

The first batches are for the Xe-100 units that X-energy wants to build at Dow’s Seadrift chemical site in Texas, a project that was still undergoing federal safety review when we covered it in August. So the fuel plant keeps running past the reactors it has to power, which is the same weird sequence we reported on two months ago, but with a roof on it now.

TRISO-X announced the completed structure on September 24, and the Department of Energy’s stated goal for the first fuel to be put into service remains early 2028. Between those two dates, there’s an awful lot of plumbing to install.