For more than half a century, nuclear power has been built around large reactors, often producing more than 1,000 megawatts from a single unit. Small modular reactors, or SMRs, take a different approach, using lower-capacity reactor units and shifting more manufacturing from the construction site to factories.
The International Atomic Energy Agency (IAEA) defines SMRs as reactors producing up to 300 MW of electricity per unit. More than 80 designs are under development worldwide, ranging from familiar water-cooled reactors to systems using gas, molten salt and liquid metals.
But “small” needs some qualification.
A 300-MW reactor is small compared with a conventional nuclear unit, but it is not a small building. An SMR plant still needs the reactor and containment structure, cooling systems, turbines, electrical equipment, security facilities and other infrastructure. Stanford University’s Understand Energy program notes that an SMR power plant can occupy considerable land, using China’s 125-MW ACP100 as an example.
“Modular” does not mean a nuclear power plant that arrives in a shipping container, either. It refers mainly to the manufacture and assembly of the reactor and its components. Factory production can shift some construction away from the site, while individual modules can be installed separately or combined into a larger plant.
Transportable nuclear power plants one already exists in Russia, using designs intended to be manufactured and prepared at one location before being moved to their operating site. These are a specialized part of the SMR field, not the standard model.
The technologies vary considerably. South Korea’s Korea Hydro & Nuclear Power is developing the i-SMR, a pressurized water reactor with passive safety systems that use gravity and natural circulation to remove heat in certain accident conditions. KHNP recently signed a cooperation agreement with AboitizPower covering nuclear technology studies and technical cooperation for the Philippines.
NuScale Power is also developing a pressurized water reactor, with each proposed module producing 77 MW. GE Hitachi’s BWRX-300 is a simplified 300-MW boiling water reactor based on existing commercial technology. TerraPower’s Natrium uses liquid sodium as its coolant and molten salt for energy storage, allowing its 345-MW reactor to increase output to 500 MW during periods of high demand.
The proposed applications extend beyond conventional power generation. Developers are examining SMRs for industrial heat, desalination, hydrogen production, remote mining and other isolated industrial operations. Data centers have also emerged as a potential market as artificial intelligence drives demand for continuous electricity.
Only two SMR projects are operating commercially, according to Stanford and the IAEA. Russia’s floating Akademik Lomonosov began commercial operation in 2020. Its two 35-MW reactors supply electricity and heat to Pevek, an Arctic port in Chukotka. China’s HTR-PM entered commercial operation in 2023 and uses two high-temperature gas-cooled reactor modules connected to a single turbine, producing about 210 MW.
Both provide valuable operating experience, but neither has yet demonstrated the economics being promised for a much larger commercial market. Stanford notes that both projects took longer and cost more to develop than initially expected.
Other projects are now moving through construction and licensing. GE Hitachi’s BWRX-300 is being developed at Ontario Power Generation’s Darlington site in Canada, while TerraPower’s Natrium project is under construction in Wyoming.
Then there is nuclear waste.
SMRs produce spent nuclear fuel, which remains radioactive and generates heat after removal from the reactor. It is initially stored in water-filled pools for cooling and radiation shielding before being transferred to dry storage. Ultimately, it requires permanent disposal.
Making the reactor smaller does not eliminate that responsibility. Stanford notes that SMRs face the same basic safety, waste and security issues as conventional nuclear plants. Research has also found that some SMR designs could produce more radioactive waste per unit of electricity than conventional reactors.
Some advanced reactor concepts are being designed to use fuel more efficiently or recycle nuclear material, potentially changing the amount and characteristics of waste requiring disposal. Most have yet to reach commercial operation.
That leaves SMRs in an unusual position. There is no shortage of designs or proposed applications, but there is still limited commercial experience. SMRs may eventually offer a way to add nuclear generation in smaller increments and serve applications that do not justify a conventional gigawatt-scale reactor. But their promised advantages in cost, construction time and deployment still have to be demonstrated in commercial operation.
