Nuclear startup X-energy announced Monday that it had been given the go-ahead from federal officials to build its first four commercial reactors.

The Nuclear Regulatory Commission (NRC) approved the construction permit application for four of X-energy’s Xe-100 reactors at a Dow chemical plant in Texas. Each reactor will be capable of generating 80 megawatts of electricity and 200 megawatts of heat. X-energy says the approval is the first for an advanced nuclear reactor at an industrial site in the United States.

The U.S. nuclear industry has pinned its hopes on small modular reactors — or SMRs — like those being developed by X-energy. By shrinking the reactor, proponents say it will speed construction and reduce costs, though those advantages have yet to be proven. No SMR is currently in operation in the U.S., and X-energy says Dow’s reactors won’t be operational until the early 2030s.

X-energy claims that its reactor design, which flows helium gas over uranium-containing fuel pellets, is safer than many existing reactors, but the Union of Concerned Scientists questioned the claim and the speed with which X-energy received the permit. 

“The NRC only accomplished this feat by pushing consideration of critical safety questions to a later date—issues the NRC should’ve fully resolved before green lighting construction,” Edwin Lyman, director of nuclear power safety for the organization, said in a statement.

The nuclear industry has benefited from strong interest from hyperscalers and data center developers, who are desperate for any and all sources of electricity. Amazon’s Climate Pledge Fund led X-energy’s $500 million Series C-1, and the big tech company has also committed to buying 5 gigawatts of capacity from the nuclear startup.

X-energy rode that wave of excitement earlier this year when its April initial public offering raised $1 billion. But since then, investors’ optimism has tempered.

The hesitancy isn’t surprising: Nuclear power plants are expensive to build and can take years to complete. Eventually, X-energy hopes to rein in both time and cost, but its first reactors are likely to be pricey. 

The new permit approval gave X-energy a small jolt yesterday, though it was only enough to recover last week’s losses. The company’s shares are trading at less than half their initial offering price.