TerraPower, the nuclear startup founded and backed by Bill Gates, announced a new $650 million funding round this week. The investment will help the company build its first commercial power plant.

Like other nuclear startups, TerraPower has been riding a wave of interest from hyperscalers, data center developers, and, now, chip designers. Nvidia’s venture arm, NVentures, participated in the round, marking its first energy investment.

Bill Gates and HD Hyundai, both already on the cap table, also invested.

TerraPower started building its first power plant in Wyoming in June 2024. The company doesn’t have approval for the reactor itself, though it expects to receive permits sometime next year. Given the Trump administration’s benign attitude toward nuclear, that timeline seems reasonable.

When complete, TerraPower’s first reactor will generate 345 megawatts of electricity, striking a middle ground between today’s massive conventional reactors and tomorrow’s promised small modular reactors.

TerraPower’s Natrium reactors are cooled not by water but by molten sodium. The Natrium design uses far more sodium than is required to cool the reactor. That’s by design: when demand is low, the reactor can continue operating, heating sodium that is then stored in large tanks. 

When demand rises again, the steam turbines can draw heat from the stored sodium. Because nuclear power plants don’t easily ramp up and down, this allows the Natrium reactors to continue operating at a steady state.

The storage system is designed to produce up to 500 megawatts of electricity for more than five hours, helping to fill gaps in solar and wind generation.

The startup previously pursued a different reactor design, which it hoped to complete by the mid-2020s. But after uncertainties mounted, it changed course to pursue the current Natrium design.

TerraPower claims it can complete a reactor within three years after the first batch of concrete is poured for the reactor. Still, considerable site preparation and construction needs to happen before that occurs. 

And while there are signs that the first Natrium reactor will be cheaper than recent U.S. reactors, it won’t be cheap: the Associated Press reported last year that the bill could reach $4 billion, half of which could be shouldered by the Department of Energy.