Governments and tech companies around the world are betting on small modular reactors to supply clean, round-the-clock electricity. The United States, the United Kingdom, Canada and India all have SMR programmes. Here is what they are, how they differ from traditional nuclear plants and the engineering challenges still ahead.
What makes a reactor "small" and "modular"
The International Atomic Energy Agency describes SMRs as reactors producing up to about 300 megawatts of electricity per unit, roughly a third of a typical large reactor or less. "Modular" means major parts are built in a factory and shipped to site, rather than being constructed piece by piece on location. Several modules can be installed together to add capacity in steps.
How they generate power
Like any nuclear plant, an SMR splits uranium atoms in a controlled chain reaction. The heat produces steam, which spins a turbine connected to a generator. The physics is the same as in large reactors. What changes is the size, the construction method and, in many designs, the safety systems.
The engineering advantages
- Passive safety. Many designs can cool themselves after shutdown using natural circulation and gravity, without pumps or operator action.
- Factory quality. Building in a factory can improve quality control and, in theory, reduce delays that have plagued large projects.
- Flexible siting. Smaller units can replace retiring coal plants, using their existing grid connections, or power industrial sites and data centres.
- Smaller upfront cost per unit, so utilities can add capacity gradually.
The open questions
- Cost. The economics depend on building many identical units. The first few are expensive, and some early projects have been cancelled over rising costs.
- Licensing. Each new design must pass a lengthy safety review by national regulators.
- Fuel. Some advanced designs need higher-enriched fuel that is in short supply.
- Waste. Spent fuel still needs safe long-term storage, as with any reactor.
Where SMRs stand now
A handful of small reactors already operate, including floating units in Russia and a demonstration plant in China. Several Western designs are moving through licensing and early construction, and large technology companies have signed agreements to buy power from future SMRs for their data centres. India has announced plans for small reactors to help decarbonise industry. Most observers expect the first wave of commercial Western units around the end of this decade, with timelines that could still slip.
Frequently asked questions
Are SMRs safer than large reactors?
Many designs have extra passive safety features and smaller amounts of fuel, which limits the consequences of an accident. Safety still depends on design, construction quality and regulation.
How long does an SMR run before refuelling?
It varies by design, from about one and a half years to several years, and some microreactor concepts aim for a decade or more.