Small modular reactors are gaining steam globally. Will any get built?

The nuclear energy industry is seeing a resurgence in global interest as governments, utilities, and tech giants seek to meet soaring electricity demand with around-the-clock, carbon-free power.

That’s true for not only conventional nuclear power plants but also a suite of alternative technologies known as ​“small modular reactors,” or SMRs, which proponents say could deliver nuclear energy at far lower costs and on faster timescales.

Broadly defined, SMRs include designs ranging in capacity from 1 megawatt to several hundred megawatts. They encompass reactors using the same light-water technology that’s inside most existing nuclear plants, as well as projects with gas-cooled reactors or that use emerging nuclear fuels like high-assay low-enriched uranium.

Seventy-four SMR designs are actively being developed worldwide, according to newly released data from the Nuclear Energy Agency (NEA), an intergovernmental agency within the Organisation for Economic Co-operation and Development.

Of that group, 51 designs are involved in pre-licensing or licensing activities with nuclear safety regulators in 15 countries — including the United States — marking a 65% increase in such efforts since 2023. The NEA said this growth reflects significant progress in bringing paper concepts closer to real-world projects, though only two commercial SMRs are actually operating today.

There’s ​“a real momentum behind this class of technologies,” William D. Magwood IV, the director-general of NEA, told reporters last week ahead of the July 22 launch of the agency’s updated SMR-tracking report.

At least $15 billion in public and private financing is now flowing into the SMR space, by the agency’s count. 

The idea for small-scale reactors isn’t new: Nuclear scientists have been exploring SMRs for over half a century, ever since the first fission power plants went critical in the 1950s. Previous attempts to quickly and cheaply build smaller plants have failed, though nuclear advocates say the technology is finally ready to launch — as long as the industry can overcome the high technical and regulatory barriers that ensnared earlier generations.

“I’ve seen small reactors come and go over the years,” said Magwood. ​“The economics and other issues have always held them back. But what’s really different this time is that the need for [SMRs] is very clearly there.”

A growing list of hopeful SMR projects 

Proponents envision SMRs as a more nimble alternative to the giant power plants that currently provide just over 9% of global electricity today.

Large-scale reactors can deliver gigawatts of baseload electricity, but they require a staggering amount of time and resources to build. In Georgia, Plant Vogtle’s 2.2 GW expansion took 15 years and cost $36.8 billion by the time the project was completed in April 2024. The challenging economics — plus the complications of handling radioactive waste and the risk of catastrophic accidents — help explain why nuclear power has stagnated over the years and is used in only 31 countries.

With SMRs, the thinking goes, relatively smaller plants can be plopped down wherever energy is needed in the world, with factory-fabricated components used to cut down on supply chain and construction costs. The designs being developed today aim to do everything from powering merchant ships and off-grid mining operations to supplying baseload power for data centers and producing high-temperature heat for manufacturing.

“SMR is not one thing — it’s a wide range of sizes, a wide range of temperatures,” said Diane Cameron, who leads NEA’s division of nuclear technology development and economics.

“This is both an opportunity and a challenge,” she said on the press call. ​“There’s a lot going on, and sometimes financiers or regulators and policymakers are wondering where to focus their efforts first.” That includes figuring out how to handle new types of nuclear-fuel waste streams from cutting-edge SMR designs, in addition to the mounting waste from conventional reactors.

So far, however, SMRs have yet to reach their potential.

Cameron noted that the only commercial reactors generating electricity today include a project at China’s Shidaowan Bay nuclear plant — in which two small units drive a single 210 MW steam turbine — and a 70 MW floating reactor on a barge in Russia. A test reactor in Japan is operating inside a laboratory. Meanwhile, in Argentina, the CAREM-25 reactor has been under construction for over a decade, though work was halted last year due to funding shortfalls.

In the U.S., the startup NuScale Power is the only SMR developer to have its designs approved by the Nuclear Regulatory Commission, though plans to build a 77 MW unit in Idaho fell apart in late 2023 after NuScale nearly doubled its cost estimates because of high interest rates and inflation.

But a handful of other first-of-a-kind projects in North America have received key approvals to start laying the early groundwork.

In Ontario, Canada, regulators recently gave Ontario Power Generation the green light to begin building a four-unit SMR project at the Darlington nuclear site. The project will use the light-water BWRX-300 reactor from GE Vernova Hitachi Nuclear Energy — a design that stretches the meaning of the word ​“small.” A single reactor building will reach an estimated 220 feet above ground and nearly 112 feet below grade.

The BWRX-300 units will each be capable of generating 300 MW, or enough to power about 300,000 homes, with the first unit expected to be in service by the end of 2030. The total 1.2 GW Darlington project could cost around $15 billion to complete.

In May, the Tennessee Valley Authority became the first U.S. utility to submit a construction permit application — for the BWRX-300 — with the Nuclear Regulatory Commission, which accepted the application on July 10. After regulatory approval, which is expected by the end of 2026, the TVA plans to install the design at its Clinch River site near Oak Ridge, Tennessee, and to commission the plant by 2032.

The startup Kairos Power is also developing an SMR project in Oak Ridge, but at a much smaller scale and with a less conventional design: a molten fluoride salt coolant and a higher-concentration uranium fuel recipe.

The company aims to start operating a 35 MW thermal Hermes reactor as early as 2026, with a commercial version to be deployed in the 2030s. On July 16, the company said it had installed the reactor vessel for its third engineering test unit, which will inform the design of its first reactor. The Department of Energy (DOE) has agreed to provide up to $303 million for the $629 million project through its Advanced Reactor Demonstration Program.