A small modular reactor (SMR) is a nuclear fission reactor that is smaller than a conventional plant and designed to be manufactured largely in a factory, then shipped and assembled on site. The International Atomic Energy Agency describes SMRs as reactors with an output of up to about 300 megawatts of electricity (MWe) per unit. Large reactors typically produce 1,000 MWe or more.
Why build them small
- Factory production. Building standard modules on an assembly line is meant to cut cost and construction time compared with one-off megaprojects.
- Lower upfront cost. Each unit needs less capital, and more units can be added as demand grows.
- More possible sites. Smaller units can fit sites where a large plant would not, including former coal power stations that already have grid connections.
The open questions
No SMR design has yet shown in commercial operation that factory production actually delivers the promised savings. Like all nuclear plants, SMRs need regulatory approval of each design, long-term waste management and secure fuel supply.
SMRs in the UK
The UK government ran a competition through Great British Nuclear to select an SMR technology for deployment. Rolls-Royce SMR’s design, at around 470 MWe, is larger than the IAEA’s 300 MWe threshold but is still built around factory-made modules.
Read more: Small modular reactors in the energy transition.