Small modular reactors (SMRs) are advanced nuclear reactors that have a power capacity of up to 300 MWe per unit, which is about one-third of the generating capacity of traditional nuclear power reactors. SMRs, which can produce a large amount of low-carbon electricity, are:

• Small: physically a fraction of the size of a conventional nuclear power reactor.
• Modular: making it possible for systems and components to be factory-assembled and transported as a unit to a location for installation.
• Reactors: harnessing nuclear fission to generate heat to produce energy.

The World Nuclear Association (WNA) lists the unique features which include:

• Small power and compact architecture and usually (at least for nuclear steam supply system and associated safety systems) employment of passive concepts. Therefore there is less reliance on active safety systems and additional pumps, as well as AC power for accident mitigation.
• The compact architecture enables modularity of fabrication (in-factory), which can also facilitate the implementation of higher quality standards.
• Lower power leading to reduction of the source term as well as smaller radioactive inventory in a reactor (smaller reactors).
• Potential for sub-grade (underground or underwater) location of the reactor unit providing more protection from natural (e.g. seismic or tsunami according to the location) or man-made (e.g. aircraft impact) hazards.
• The modular design and small size lends itself to having multiple units on the same site.
• Lower requirement for access to cooling water – therefore suitable for remote regions and for specific applications such as mining or desalination.
• Ability to remove reactor module or in-situ decommissioning at the end of the lifetime.