SMR (Small Modular Reactor)
A nuclear reactor of up to about 300 MWe per module, designed for factory fabrication and modular deployment to cut construction time and financing risk.
Small modular reactors aim to replace bespoke gigawatt-scale megaprojects with standardised units built in series. The IAEA defines small as up to 300 MWe; microreactors are below about 10–20 MWe. The IAEA tracked more than 80 designs in 2024. Main families:
- Light-water SMRs: NuScale VOYGR (77 MWe modules, the first SMR design certified by the US NRC, uprated version approved 2025), GE Hitachi BWRX-300, Holtec SMR-300, Rolls-Royce SMR (about 470 MWe).
- Advanced non-water designs: high-temperature gas reactors (China's HTR-PM, operating since 2021; X-energy Xe-100), sodium-cooled fast reactors (TerraPower Natrium, 345 MWe), molten salt reactors.
Operating examples are few: Russia's floating Akademik Lomonosov (2 × 35 MWe) and China's HTR-PM; China's Linglong One ACP100 was close to operation in 2025–2026. Ontario Power Generation began building the first BWRX-300 at Darlington in 2025, targeting about 2030.
Whether SMRs reach competitive costs is unproven. NuScale's Utah project was cancelled in 2023 after its estimated power price rose to USD 89/MWh even with subsidies. Many advanced designs also need HALEU fuel enriched to 5–20%, for which supply outside Russia is still limited.
Related terms
All terms →- Pressurised water reactor (PWR)
The most common nuclear reactor type, in which water under high pressure cools the core without boiling and transfers heat to a separate steam circuit.
- Boiling water reactor (BWR)
A light-water nuclear reactor in which coolant boils in the core and the resulting steam drives the turbine directly, without steam generators.
- Uranium enrichment
The process of increasing the share of fissile U-235 in uranium above its natural 0.711%, to make reactor fuel or, at very high levels, weapons material.
- Nuclear fission
The splitting of a heavy atomic nucleus such as uranium-235 or plutonium-239 into lighter nuclei after absorbing a neutron, releasing about 200 MeV of energy and further neutrons.
- Learning rate (Swanson's law)
The percentage cost reduction of a technology for every doubling of cumulative production; for solar modules, Swanson’s law puts it near 20%.
- Load following
Adjusting a power plant’s output over minutes to hours to track changes in electricity demand or in variable renewable generation.