TerraPower begins construction of its 345 MW Natrium reactor project (US)

US nuclear company TerraPower has officially announced the launch of construction for its flagship Natrium plant, Kemmerer Unit 1 in Wyoming, United States. The start of construction follows authorization granted by the US Nuclear Regulatory Commission (NRC) for Unit 1 in March 2026. The project is expected to become the first utility-scale advanced nuclear power plant in the United States (Terra Power press release, 23/04/2026).

The facility will incorporate a 345 MW sodium-cooled fast reactor combined with an integrated molten salt-based energy storage system. This storage system enables the plant to increase its output to 500 MW when required. This energy storage feature is intended to maintain a stable base output, ensuring consistent reliability, while also allowing rapid increases in generation during peak demand periods. According to the company’s press release, this makes it the only advanced reactor design offering such a capability.

The first Natrium plant is being developed under the US Department of Energy’s Advanced Reactor Demonstration Program (ARDP), structured as a public-private partnership. Upon completion, it will represent both the first utility-scale advanced nuclear power plant in the US and the first-ever commercial nuclear generating station in Wyoming. 

TerraPower is accelerating the commercialization of its Natrium technology, including a partnership agreement with Meta covering up to eight Natrium plants by 2035.

Kemmerer Unit 1 is the first commercial reactor approved for construction by the agency in nearly a decade, and the first authorization for a commercial non–light water reactor design in over 40 years. This development comes as Vogtle Units 3 and 4, the first new large-scale US reactors completed since the 1980s, enter operation in Georgia, reigniting discussions about the pace at which nuclear energy can expand within the US power mix (Power magazine, 23/04/2026).