Small, modular reactors have long been viewed by many in the nuclear power industry as the most promising technology—indeed, as the only realistic path forward—for nuclear power in the United States. In a possible step forward for next-generation nuclear power, the Tennessee Valley Authority is applying for a permit to build one such reactor. Although the specific reactor technology has yet to be determined, the utility could have it running by the mid-2020s.

As the name implies, the modular reactors are smaller than traditional nuclear power plants. They’re 300 megawatts or less in generation capacity, as opposed to 1,000 megawatts and up for a traditional plant. They can be manufactured in a factory and assembled on-site, potentially avoiding the huge upfront capital costs and the overruns that have plagued many nuclear plants. They are theoretically safer, reducing the need for huge containment vessels and other expensive protections. And they can be installed singly or in combination to meet a variety of power-generation requirements.

As with most nuclear power technology, the promise of small modular reactors is the subject of some dispute, and none have been deployed to date. A 2013 report from the Union of Concerned Scientists concluded that “unless a number of optimistic assumptions are realized, SMRs are not likely to be a viable solution to the economic and safety problems faced by nuclear power.”

Nonetheless, the U.S. government has long supported the development of small modular reactors: beginning in 2012, the Department of Energy launched a $452 million cost-sharing program to support the design and licensing of small modular reactors from two companies, Babcock & Wilcox and NuScale. The Babcock & Wilcox program was scaled back in 2014 as cheap natural gas reduced demand for new nuclear plants. But the technology still has high-level support. Last year the White House issued an executive order that requires all federal agencies to get 25 percent of their electricity by 2025 from “alternative energy” sources, specifically including small modular reactors.

The Tennessee Valley Authority, which supplies power to nine million people in seven southeastern states, was expected to file its application for a small modular reactor to the Nuclear Regulatory Commission on Thursday. That marks the first step in a years-long licensing process.

The site chosen for the project, on the Clinch River, is notable in the checkered history of nuclear power in this country: it was to be the site of the Clinch River Breeder Reactor, on which more than $1 billion was spent in the 1970s and early 1980s. The project was finally killed by Congress in 1983, and many date the decline of the U.S. nuclear industry to its demise.

The small modular reactor project notwithstanding, the Tennessee Valley Authority is not abandoning older nuclear technology. This summer, Unit 2 at the 1,100-megawatt Watts Bar nuclear plant is scheduled to finally start up. Construction on the reactor began in 1973 but was halted in 1988 in the wake of the nuclear disaster at Chernobyl.