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TerraPower Natrium

The Fast Flux Test Facility, a sodium-cooled test reactor at the Hanford Site in Washington State, looking northwest.

The Fast Flux Test Facility, a sodium-cooled test reactor at the Hanford Site in Washington State, looking northwest.

Photo: U.S. Department of Energy, via Wikimedia Commons, public domain (work of the U.S. federal government).

Energy Pilot

What it is

Natrium is a nuclear power plant design from TerraPower, a U.S. company that develops nuclear technology. The plant has a 345-megawatt sodium-cooled fast reactor, meaning that liquid sodium carries the heat away from the core, joined to a molten salt energy storage system. TerraPower says the storage can lift output to 500 megawatts when demand peaks, which it equates to the power for around 400,000 homes, and that it is designed to keep base output steady. The reactor is a TerraPower and GE Vernova Hitachi Nuclear Energy technology. The first plant, Kemmerer Unit 1 in Lincoln County, Wyoming, is being developed through the U.S. Department of Energy’s Advanced Reactor Demonstration Program, a public-private partnership.

Why it matters

On 4 March 2026 TerraPower announced that the Commissioners of the U.S. Nuclear Regulatory Commission had voted to award Kemmerer Unit 1 a construction permit, which the company describes as the first for a commercial-scale advanced nuclear power plant. The Federal Register, the U.S. government’s official daily journal of public notices, records that the permit was issued on 9 March 2026 to US SFR Owner, LLC, the company that holds it, and that it authorizes construction of a power reactor facility in Lincoln County, Wyoming. TerraPower announced the official start of construction on 23 April 2026, with a workforce of roughly 1,600 workers being mobilized and about 250 full-time staff expected once the plant operates. The company says the project is expected to be completed in 2030, and that it would then be the first utility-scale advanced nuclear power plant in the United States.

How to read it

Three dates appear in the record: the Commission vote on 4 March 2026, the issue of the permit on 9 March 2026 and the start of construction on 23 April 2026. The construction permit is the government’s approval to build the reactor facility, and the Federal Register notice is the official record of it. Descriptions such as “first” come from TerraPower’s own announcements. The 500-megawatt figure is the peak output while the storage discharges, and the 345-megawatt figure is the reactor’s base output.

Limits

Kemmerer Unit 1 is under construction, and the completion year of 2030 is TerraPower’s expectation. TerraPower’s chief executive calls the plant a first-of-a-kind nuclear plant, so its final cost and schedule are still to be shown. TerraPower also says it has an agreement with Meta for up to eight Natrium plants by 2035. That is an agreement between companies, and the first plant has yet to be completed.

Sources