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.