What are SMRs?

Most nuclear reactors in operation today have a capacity of around 800-1200 Mwe, enough electricity for up to one million homes. SMRs, by contrast, are defined by their modest electrical output – typically less than 300 MWe.

The smaller size of SMRs means they have significantly lower capital outlay per unit than large-scale reactors, lowering the financial risk. The size also makes siting, and deployment easier in settings where large plants may not be practical – such as remote communities, industrial clusters, or regions with small electricity grids.

Fission Fact: About 110 reactors of 300 MWe capacity or less have been built, of which over 20 are currently in operation.

‘Modular’ refers to both the design and construction approach.

Both large and small nuclear reactors increasingly make use of modular construction techniques that allow components to be fabricated in factories or specialized facilities before transporting them to site. This approach can streamline processes and improve quality control, as well as lower onsite construction times and reduce costs.

However, SMRs take modularity several steps further, with modular designs offering incremental deployment to allow capacity to be scaled over time to match demand, reducing financial risk and providing flexible solutions for customers.

This approach can become a series production of repeat units, like those achieved in the aerospace industry, lowering costs through assembly-line efficiency, shorter installation times, and replicated supply chains, rather than through traditional economies of scale.

Fission Fact: There are over 100 SMR designs at various stages of development. For more information on SMR designs, please visit our Small Modular Reactor Design Database.

SMRs encompass a range of reactor types, all of which are evolutions of existing designs rather than entirely new technologies.

Most SMRs that are candidates for near-term deployment are based on proven water-cooled reactor technologies (e.g. pressurized water reactor). Advanced SMR designs (e.g. high-temperature or molten salt reactors) are mostly at the development stage.

Fission Fact: The current fleet of nuclear reactors runs primarily on uranium fuel enriched up to 5% of the uranium-235 isotope. Fuel with uranium enriched to greater than 5% and less than 20% U-235 will be needed for many advanced power reactor fuels, and more than half of the SMR designs in development.

SMRs offer greater flexibility in how and where nuclear energy can be used. Some designs are intended to provide both electricity and heat, which can broaden nuclear’s role beyond grid supply to include industrial processes, district heating, desalination, and hydrogen production.

Their smaller size also makes SMRs suitable for a wider range of sites, including smaller grids, remote locations, or existing industrial or retired fossil fuel sites where a large reactor may not be practical. SMRs could also work alongside variable renewables by providing reliable, dispatchable output when needed.

Fission Fact: SMRs are being developed for more than electricity alone: more than 65% of SMR designs have potential for high-temperature heat or off-grid applications.

There are several SMRs already operating and under construction, as well as numerous projects at various stages of deployment. Find out more information on SMR progress in our SMR Global Tracker.

Fission Fact: There is a floating SMR currently in operation, Rosatom’s Akademik Lomonosov, which is located at the Russian port of Pevek in northeast Russia, where its two reactors provide electricity and heat to the region.