The nuclear energy industry sees big promise in going small.

Earlier this year, NuScale Energy took a crucial step forward in its prolonged effort to build 12 scaled-down nuclear reactors on an empty parcel at the Idaho National Laboratory, a sprawling research campus on the outskirts of Idaho Falls (see “Shrinking Nuclear”). The U.S. Nuclear Regulatory Commission agreed to begin the formal process of reviewing the company’s designs for the 600-megawatt plant, which could power a city the size of Boise twice over.

That gives NuScale, based in Portland, Oregon, the inside track on building the country’s first commercial reactors of this type. Known as small modular reactors, or SMRs, they also represent the first substantially new reactor design of any kind to reach this NRC milestone in decades.

But many more SMR projects are coming or under way. There are around 50 designs or concepts in various development or planning stages around the world, according to the International Atomic Energy Agency. Four are already in advanced construction in Argentina, Russia, and China.

If the early projects are built and succeed, these smaller and potentially safer nuclear reactors raise the real possibility of mass-produced mini plants that can significantly reduce the industry’s up-front costs and risks. That, in turn, could make it far easier to add a source of carbon-free energy that many experts believe will be critical to lowering the risk of climate change.

On the other hand, we won’t know how economically the plants can really operate until they’re up and running. And a shift toward smaller but more numerous nuclear reactors could raise new kinds of proliferation dangers, some observers warn.

The grand promise of commercial SMRs is that they would be compact enough to prefabricate in factories and ship to their destination, where they could be stacked together to produce whatever level of energy generation is needed. Over time, the technology could introduce new levels of predictability, reliability, and economies of scale to an industry that’s become synonymous with billion-dollar cost overruns and years of delays. It also opens the possibility that nuclear power could serve smaller markets, and even military or industrial applications, where a full-scale reactor wouldn’t make economic sense.

The most immediate advantage, however, is that they might be cheap enough to get built at all. Raising the massive up-front capital to construct new full-scale reactors has become increasingly difficult in the United States, particularly after ballooning budgets for two plants in Georgia and South Carolina ended up tipping Westinghouse Electric into bankruptcy, nearly taking its parent company with it (see “Meltdown of Toshiba’s Nuclear Business Dooms New Construction in the U.S.”).

Small modular reactors like NuScale’s 50-megawatt module promise to be orders of magnitude cheaper. Even the company’s full-scale, 12-module configuration would cost around $3 billion, the company estimates. In contrast, Westinghouse’s Vogtle plant in Georgia, which includes two 1,200-megawatt reactors, was initially slated to cost $14 billion—and swelled to well over $20 billion.