On Wednesday, the US Nuclear Regulatory Commission announced that it had issued its first construction approval in nearly a decade. The approval will allow work to begin on a site in Kemmerer, Wyoming, by a company called TerraPower. That company is most widely recognized as being financially backed by Bill Gates, but it’s attempting to build a radically new reactor, one that is sodium-cooled and incorporates energy storage as part of its design.
This doesn’t necessarily mean it will gain approval to operate the reactor, but it’s a critical step for the company.
The TerraPower design, which it calls Natrium and has been developed jointly with GE Hitachi, has several novel features. Probably the most notable of these is the use of liquid sodium for cooling and heat transfer. This allows the primary coolant to remain liquid, avoiding any of the challenges posed by the high-pressure steam used in water-cooled reactors. But it carries the risk that sodium is highly reactive when exposed to air or water. Natrium is also a fast-neutron reactor, which could allow it to consume some isotopes that would otherwise end up as radioactive waste in more traditional reactor designs.
The reactor is also relatively small compared to most current nuclear plants (245 megawatts versus roughly one gigawatt), and incorporates energy storage. Rather than using the heat extracted by the sodium to boil water, the plant will put the heat into a salt-based storage material that can either be used to generate electricity or stored for later use. This will allow the plant to operate around renewable power, which would otherwise undercut it on price. The storage system will also allow it to temporarily output up to 500 MW of electricity.
Globally, only about 25 significant reactors have been built using sodium cooling, and most of them weren’t used to generate power; the US hasn’t built one since the 1960s and hasn’t operated one since the 1990s. This is a radical design, and the company could still face many hurdles before getting approval to operate it.
That said, building it is a critical first step. The company chose the site in 2021 and submitted the construction application to the NRC in early 2024. That was shortly before the passage of the ADVANCE Act in June 2024, which sought to streamline the approval of nuclear projects and promote new generations of reactor designs. That may explain why the NRC completed its evaluation of TerraPower’s filing nearly 10 months ahead of its initial prediction.
The Kemmerer plant is being built as a joint public-private partnership as part of the Department of Energy’s Advanced Reactor Demonstration Program. Right now, the project is expected to be completed in 2030, and so will arrive far too late to help with the expected surge in datacenter demand over the next several years. As a first-of-its-kind project, it should also be expected to experience construction delays. And while the Trump administration has been enthusiastic about simplifying the approval process for operating reactors, a 2030 timeline may delay the Kemmerer plant’s approval well into the next administration.
