The Nuclear Regulatory Commission (NRC) gave TerraPower the go-ahead this week to build a new nuclear reactor in the shadow of an aging coal power plant in Wyoming.

TerraPower’s permit is the first to be issued by the NRC in nearly a decade. The startup — founded by Bill Gates in 2015 and backed by Nvidia — has been designing its Natrium reactor with GE Vernova Hitachi. The final power plant will generate 345 megawatts, which is about two-thirds smaller than modern full-size reactors, but multiple times larger than many small modular reactor designs favored by other startups.

Natrium differs from other reactors not just in scale, but also in the details of its design. Where most nuclear reactors built in the last 50 years have been cooled by water, Natrium is cooled by molten sodium, which TerraPower says should be safer. This is the first time a commercial reactor that is not cooled by regular water has been approved by the NRC in more than 40 years.

The reactor will operate with an excess of molten sodium, which will be stored in large, insulated tanks. This allows atoms to keep splitting when demand is low, with the hot sodium saving that energy, which can be used to fill in any lulls in wind and solar output. Since nuclear power plants operate best near full capacity, storing excess energy as heat should help lower generating costs.

The NRC’s approval is notable because TerraPower followed the long-established permitting process, giving it permission to build on private property. The Department of Energy recently loosened its safety rules, but those regulations only apply to land owned by the agency.

TerraPower is one of nearly half a dozen nuclear startups backed by tech companies or their founders. As electricity demand from data centers grows, the Trump administration has come under pressure to boost generating capacity, including by building new nuclear reactors.

Investors have taken note of the two trends, and in recent months, they’ve showered nuclear startups with well over $1 billion in capital. TerraPower alone has raised a total of $1.7 billion, including a $650 million round that closed in June, according to PitchBook.

Despite the momentum, nuclear power still faces an uphill battle. To date, nuclear has been one of the most expensive forms of new generating capacity. Part of that is due to cost overruns at massive power plants, but it also reflects the tremendous strides that solar, wind, and batteries have made in bringing costs down over the years. 

Nuclear startups are hoping to leverage mass manufacturing to rein in capital expenditures, but the theory has yet to be proven. And while manufacturing can help cut costs, it often takes at least a decade for the savings to materialize.