Small modular reactors: How they differ from conventional nuclear plants
Small modular reactors are becoming an important part of India's nuclear power plans as the country looks to expand capacity
 "Small modular reactors: How they differ from conventional nuclear plants")
India plans to develop and operationalise at least five indigenous small modular reactors (SMRs) by 2033 as part of its Nuclear Energy Mission, the government told the Lok Sabha on Wednesday. The mission aims to raise the country's nuclear power capacity to 100 GWe by 2047.
But what exactly are SMRs, how much electricity can they generate, and how do they differ from conventional nuclear reactors?
What are small modular reactors?
SMRs are nuclear reactors with a smaller power output than conventional reactors. The International Atomic Energy Agency (IAEA) defines them as advanced nuclear reactors with a capacity of up to 300 MWe per unit.
The IAEA describes them as "small" because they are physically smaller than conventional reactors, and "modular" because their components can be manufactured or assembled in factories and transported to the site. Like conventional nuclear reactors, they also use nuclear fission to generate heat and produce energy.
The European Commission (EC) puts the typical capacity range at about 20 MWe to 300 MWe. It has estimated that an SMR can produce up to 7.2 million kWh of electricity a day.
The smallest reactors, generally below 20 MWe, are sometimes classified as microreactors, according to the World Nuclear Association (WNA).
How are SMRs different from conventional reactors?
The main difference is scale and the way the reactor is designed and built.
Conventional nuclear reactors generally produce around 1,000 MWe or more per unit. SMRs have a much lower electrical output, generally up to 300 MWe. This smaller size allows them to be considered for locations where a large nuclear plant may not be practical, including smaller electricity grids, industrial sites and remote areas.
The "modular" element also relates to construction. SMR components, and in some cases complete reactor modules, can be manufactured in factories and transported to the site for assembly. The WNA says the approach is intended to support serial production and reduce on-site construction requirements.
SMRs can also be deployed incrementally. Additional modules can be added as electricity demand increases, depending on the reactor design.
How much power can an SMR produce?
The IAEA's upper limit for an SMR is 300 MWe per unit. This is roughly one-third of the generating capacity of a traditional nuclear reactor, according to the agency.
According to the European Commission, SMRs typically have a capacity of around 20 MWe to 300 Mwe. It said a 300-MWe SMR can produce up to 7.2 million kWh per day, compared with up to 24 million kWh a day for a large nuclear power plant with an output of more than 1,000 MWe.
There is no single reactor design for SMRs. The technology includes light-water reactors, fast neutron reactors, graphite-moderated high-temperature reactors and molten salt reactors, according to WNA.
Where are SMRs being developed?
The global SMR pipeline includes designs at different stages, from early development to construction and operation.
The OECD Nuclear Energy Agency's (NEA) digital dashboard currently tracks 129 SMR designs worldwide, although 79 are included in the dashboard's detailed assessments. The remaining designs include projects that have asked not to be included for now, as well as technologies that are not under active development or have been cancelled or paused.
The NEA's 2025 dashboard assessment covered 74 SMR designs. Seven designs were either operating or under construction at the time of that assessment.
The United States has the largest number of SMR siting announcements, with 28, according to data sourced from the NEA. Canada had nine and the United Kingdom seven.
| Rank | Country | SMR siting announcements |
| 1 | United States | 28 |
| 2 | Canada | 9 |
| 3 | United Kingdom | 7 |
| 4 | Russia | 5 |
| 5 | China | 4 |
| 6 | Finland | 4 |
| 7 | France | 4 |
| 8 | Poland | 4 |
| 9 | Indonesia | 3 |
| 10 | Sweden | 3 |
Which countries have operating SMRs?
Russia and China are among the countries furthest ahead in deploying SMRs.
Russia's KLT-40S units are used at the Akademik Lomonosov floating nuclear power plant, which began commercial operation in 2020. The two units have a combined electrical capacity of 70 MWe.
China's HTR-PM is another operating SMR project. The NEA's 2025 dashboard also listed China's HTR-PM, Japan's HTTR and Russia's KLT-40S among three SMR designs already in operation, while several other designs were under construction.
Why are countries developing SMRs?
The smaller size of SMRs allows them to be considered for applications beyond conventional large-scale nuclear power plants.
The IAEA lists industrial applications, remote locations and areas with limited grid capacity among other potential uses. SMRs can also be used for electricity generation, heating, desalination and industrial steam, depending on the design.
India is considering SMRs for three specific applications. According to the government, they could be used to repurpose retiring fossil-fuel power plants, supply captive power to energy-intensive industries and provide electricity to remote, off-grid locations.
What is India's SMR plan?
India's Nuclear Energy Mission was announced in the Union Budget 2025-26. The government is pursuing large nuclear reactors at greenfield sites alongside SMRs for brownfield locations and specialised applications.
The Bhabha Atomic Research Centre is developing three indigenous designs: the 220-MWe Bharat Small Modular Reactor, the 55-MWe SMR-55 and a high-temperature gas-cooled reactor of up to 5 MWth. The government has set a target of at least five indigenous SMRs by 2033.