A small modular reactor (SMR) is a new type of nuclear fission reactor that produces less than 300 megawatts (MW e) of electricity. These reactors use modular design principles, which make them easier and faster to build and allow them to grow in size more easily than large light-water reactors. Many SMR designs are built in factories as pre-made parts and then moved to their final locations. Others are designed to be flexible, allowing multiple units to be combined as needed.
The term SMR describes the reactor’s physical size, electrical power, and modular construction method. Different SMR designs use various reactor technologies. As of March 2026, most SMRs are light-water reactors (LWRs), but other types, such as Generation IV reactors, thermal-neutron reactors, fast-neutron reactors, molten salt reactors, and gas-cooled reactors, are also included in SMR concepts. Many SMRs include passive safety features that work without needing external power or human action during emergencies.
Commercial SMRs can produce as little as 10 MW e of electricity per module, up to 300 MW e. Reactors with less than 10 MW e are called nuclear microreactors. Some SMRs are designed to provide heat or desalination instead of electricity, and these are measured in megawatts thermal (MW t). Many SMR designs allow customers to add more modules to increase power output instead of building larger reactors. These reactors are expected to improve safety through passive systems and may reduce staffing costs because they are simpler to operate. They may also avoid some financial and safety challenges that affect traditional reactors.
SMRs have drawn interest from technology companies like Google and Microsoft for use in powering data centers, especially to meet energy needs from artificial intelligence (AI) development. Modular reactors are expected to lower construction costs and time compared to large light-water reactors. They also allow data centers to use power directly from an SMR instead of buying electricity from the grid.
Definition
According to the American Nuclear Society (ANS), small or modular reactor ideas were first developed in the 1950s. The term "small modular reactor," or SMR, became widely used in the late 1970s. However, the definition of an SMR has not always been clear or agreed upon.
In 2026, John Fabian wrote in Nuclear Newswire that until about 2011, the abbreviation "SMR" could refer to either "small modular reactor" or "small and medium sized reactor." Fabian noted that the use of "SMR" today is not always clear and depends on the design of the reactor. For example, as of 2026, the United States Nuclear Regulatory Commission (NRC) defines SMRs as only light-water reactors with power output under 300 MW e. Other reactor designs, such as those not using light-water technology, are called "advanced reactors" by the NRC. At the same time, the World Nuclear Association defines SMRs as any reactor under 300 MW e that uses modular technology. Fabian explained that the classification of reactors as SMRs based on power output has remained consistent, with reactors under 300 MW e always being called SMRs.
By 2023, most experts in the nuclear industry agreed that SMRs are reactors designed to produce low power (less than 300 MW e) and built with modular design, which can apply to individual parts or the whole reactor system.
Operational SMRs
As of 2024, only China and Russia have completed and are using small modular reactors (SMRs). Russia has been using a floating nuclear power plant called Akademik Lomonosov in the Far East of Russia (Pevek) for commercial purposes since 2020. China connected its pebble-bed modular high-temperature gas-cooled reactor, called HTR-PM, to the electrical grid in 2021.
As of 2025, there were 127 designs for small modular reactors. Of these, seven designs were already in use or being built, 51 were in the early stages of getting approval or were being licensed, and 85 designers were talking with people who might build the reactors.
Background
Small reactors have been used for military purposes since the 1950s for nuclear marine propulsion. The largest naval reactor as of 2025 produces about 700 MW of thermal energy (the A1B reactor), which is similar in size to some large small modular reactor (SMR) designs. Naval nuclear reactors have a strong safety record. Public information shows that the U.S. Navy’s Naval Reactors program has never experienced a meltdown or radioactive release during its 60 years of operation. In 2003, Admiral Frank Bowman supported the Navy’s claim by stating no such accident has ever occurred.
Lawrence R. Hafstad, Director of Reactor Development at the U.S. Atomic Energy Commission, suggested building small, inexpensive, and transportable nuclear power systems for use in remote areas. Alvin M. Weinberg, Director of Research at Oak Ridge National Laboratory (ORNL), supported Hafstad’s idea in 1952, noting that naval reactors could help develop these systems. He believed that building many small reactors for remote locations would reduce financial risks for the nuclear industry:
— Alvin Weinberg, "Wanted: Smaller and More Reactors," Nucleonics (November 1952)
Between 1954 and 1977, the U.S. Army tested small land-based reactors to power military bases during the Army Nuclear Power Program. ORNL designed one of these reactors under Weinberg’s leadership. One reactor, PM-2A, used prefabricated parts to lower construction costs.
Military small reactors differ from commercial SMRs in design, safety, and fuel type. Customers can increase the power of an SMR plant by adding more modules. Historically, the military used highly enriched uranium (HEU) instead of the low-enriched uranium (LEU) used in SMRs. This is because submarine reactors require more power in smaller spaces. Many naval reactors also operate for over a decade without refueling.
The term "small modular reactors" (SMRs) became widely used in 2010 when U.S. Energy Secretary Steven Chu called SMRs "America’s new nuclear option" in a Wall Street Journal article. He said SMRs would be easy to install and more affordable. President Barack Obama requested $39 million for a new SMR design and licensing program.
Economic factors often make nuclear reactors large, as size affects costs. The 1986 Chernobyl disaster caused major setbacks for the nuclear industry, including pauses in development, reduced funding, and closures of reactors.
Supporters say SMRs could be cheaper because standardized modules can be made in factories off-site. However, studies show SMR costs may be similar to large reactors. Limited information about transporting SMR modules is available. Critics argue that modular construction is only cost-effective if many of the same SMR type are produced, requiring high market demand.
In February 2024, the European Commission recognized SMR technology as important for reducing carbon emissions under the EU Green Deal.
The International Energy Agency (IEA) says nuclear power should double worldwide by 2050 to meet global net zero emissions goals. Antonio Vaya Soler, an expert from the Nuclear Energy Agency (NEA), agrees that while renewable energy is important, nuclear energy must also grow significantly to achieve net zero CO₂ emissions.
To produce the same electricity as the 400 large nuclear reactors in use today, Germany’s Federal Office for Nuclear Waste Safety (BASE) says thousands to tens of thousands of SMRs would need to be built.
Many identical SMRs, produced in large numbers, must be deployed globally to reduce CO₂ emissions. The NEA launched an initiative called "Accelerating SMRs for Net Zero" at COP 28 to encourage collaboration among researchers, the nuclear industry, safety groups, and governments to reach net zero emissions by 2050.
Supporters say proven nuclear technology can be safer, and the industry claims SMRs may be safer than large reactors due to their smaller size. This is because SMRs produce less heat after shutdown, reducing the risk of meltdowns. Critics argue that more small reactors could increase risks, such as transporting nuclear fuel and managing radioactive waste. New SMR designs need to be tested for safety.
SMRs face risks of corrosion in systems using liquid metals or molten salts for cooling. Limited licensing and safety rules make it difficult to assess corrosion risks in different SMR designs.
Until 2020, no truly modular SMRs had been used commercially. In May 2020, the first prototype of a floating nuclear power plant with two 30 MW reactors (KLT-40) began operating in Pevek, Russia. This design is based on nuclear icebreaker technology. A 125 MW demonstration reactor (Linglong One) in China is expected to start operating by the end of 2026.
The introduction of SMRs has raised concerns about social and institutional challenges. Nuclear projects often involve centralized planning, leading to criticism about risks to communities affected by limited energy flexibility. As with other energy sources, communities must be included in decisions, and environmental impacts must be studied as SMR use expands.
Designs
Small Modular Reactors (SMRs) come in many different designs. Some are simpler versions of current reactors, while others use completely new technologies. All SMRs use nuclear fission, and their designs include thermal-neutron reactors and fast-neutron reactors.
Thermal-neutron reactors use a moderator, such as water, graphite, or beryllium, to slow down neutrons. These reactors typically use uranium (U) as the fissile material. Most traditional reactors in use today are of this type.
Fast reactors do not use moderators. Instead, they use highly enriched uranium (HEU) fuel to absorb fast neutrons. This often requires changing how fuel is arranged in the reactor core or using different types of fuel. For example, plutonium (Pu) is more likely to absorb fast neutrons than uranium.
Fast reactors can also be breeder reactors. These reactors produce enough neutrons to change non-fissionable elements into fissionable ones. A common method involves surrounding the reactor core with a "blanket" of uranium-238 (U-238), which is the most available isotope. When U-238 absorbs a neutron, it becomes plutonium-239 (Pu-239). This plutonium can be removed during refueling, reprocessed, and used as fuel later.
Technologies
Conventional light-water reactors use water to cool the reactor and slow down neutrons. Small modular reactors (SMRs) can use water, liquid metal, gas, or molten salt as coolants. The choice of coolant depends on the reactor type, design, and intended use. Large reactors often use light water as a coolant, which can also be used in SMRs. Helium is commonly used as a gas coolant in SMRs because it increases the efficiency of the reactor and provides enough heat. Liquid metal coolants like sodium, lead, and lead-bismuth eutectic (LBE) are being studied for fourth-generation SMRs. Sodium was widely used in early large reactors and remains a popular choice for SMRs. SMRs require less cooling water, making them suitable for building in remote areas where mining or desalination might occur.
Some gas-cooled reactor designs can use thermal energy directly to power gas turbines instead of boiling water. This energy can also be used for producing hydrogen or supporting industrial processes like desalination and extracting oil from oil sands or coal.
SMRs are typically designed to provide steady electrical power. Some designs can adjust their power output based on electricity demand. For SMRs that produce high-temperature heat, cogeneration can be used to maintain consistent heat output while redirecting unused heat for other purposes. Examples of cogeneration include district heating, desalination, and hydrogen production.
Desalination requires storage for freshwater to be available when needed. The two main methods for seawater desalination are reverse osmosis membranes and thermal evaporators. Reverse osmosis uses electricity to power water pumps and is the most common method. Thermal desalination uses heat to evaporate water in stages with decreasing pressure. This method avoids converting thermal energy into electricity and is divided into two types: multi-stage flash distillation (MSF) and multi-effect desalination (MED).
Nuclear safety
A report from the German Federal Office for the Safety of Nuclear Waste Management (BASE) examined 136 historical and current reactors and small modular reactor (SMR) designs. It noted that SMRs may have safety benefits compared to larger reactors because they have less radioactive material per unit and use simpler designs and passive safety systems. However, some SMR designs suggest lower regulatory standards, such as fewer backup systems or reduced planning for emergency responses. Since reactor safety depends on all these factors, the report concluded that it is not clear if SMRs are inherently safer than larger reactors based on current knowledge.
SMRs use negative temperature coefficients in their moderators and fuel to control fission reactions. As temperature rises, the reaction slows, helping to maintain stability. After a reactor is shut down, it must be cooled continuously to remove decay heat. If emergency cooling fails, as happened in the Fukushima and Three Mile Island accidents, the reactor can overheat, leading to a meltdown. Because SMRs operate at lower power levels, they produce less decay heat, which makes cooling easier and improves safety.
Some SMR designs use natural convection, or thermoconvection, to cool the reactor without pumps, reducing the risk of mechanical failure. Natural convection can remove decay heat after shutdown. However, some SMRs may still require active cooling systems as backup, which can increase costs.
Some SMR designs integrate the reactor core, steam generator, and pressurizer into a single sealed vessel. This design reduces the risk of accidents by limiting the spread of contamination. Compared to larger reactors with many components outside the vessel, this integration lowers the chance of uncontrolled accidents. Some SMR designs also plan to place reactors and spent-fuel storage underground.
Molten salt reactors are being developed as SMRs, though they are not new. These reactors operated as research and test facilities since the 1950s. One early experiment, the Molten Salt Reactor Experiment at Oak Ridge, ran for four years but was shut down in 1969 after a critical event. While the experiment was considered a success, later studies found it only operated about 40% of the time and had 171 unplanned shutdowns. These issues included pipe clogging, blower failures, and leaks in the freeze-valve system. Modern materials have not yet proven effective in resisting the corrosive effects of molten salt over long periods.
Fluoride-Salt-Cooled High-Temperature Reactors (FHRs) also face challenges, such as buildup of fission products that can clog cooling and safety systems. A method called reductive extraction can remove uranium fuel before fission products form, but the gas produced from fluoride is highly corrosive and damages metal parts. Nitrogen trifluoride is being studied as an alternative, but research has not yet confirmed its effectiveness.
Radioactive waste
New technology for recycling nuclear waste offers safer and less expensive ways to handle waste compared to current methods. This process, called partitioning and transmutation (P&T), reduces the amount of waste produced and lowers the harmful radiation in the waste.
P&T uses a chemical process to separate plutonium and other radioactive elements from spent nuclear fuel. A special reactor then changes these elements into less dangerous materials. Finally, a process called fission is used to safely break down the remaining radioactive parts. P&T helps reduce the total amount of waste and its harmful effects.
Even reactors that use highly enriched uranium now recycle important radioactive elements without needing complicated purification steps. This method is already used in fast reactors in countries like France, India, Japan, and Russia. These reactors do not need to separate plutonium from other elements in the waste. A process called pyroprocessing is being developed for these reactors and is already used in India, Russia, and the European Union. However, because small modular reactors (SMRs) are still new, P&T has not yet been used on their waste. As SMR technology improves, P&T may become an important way to recycle their waste.
The waste management process for SMRs is complex and debated. The amount and harmfulness of waste from SMRs depend on their design and how they handle fuel. SMRs can include different types of reactors, such as third-generation light water reactors and fourth-generation fast neutron reactors.
Some companies developing SMRs claim their designs reduce waste and may eliminate the need for deep underground storage for radioactive waste. This is especially true for companies working on fourth-generation fast neutron reactors, like molten salt reactors and sodium-cooled fast reactors.
Fast breeder reactors use uranium-235 (a small part of natural uranium) as fuel and convert uranium-238 (the majority of natural uranium) into plutonium-239, which can be used as fuel. A reactor called the traveling wave reactor, developed by TerraPower, is designed to use the plutonium it produces without removing it from the reactor or reprocessing it.
Some SMRs use thorium instead of uranium as fuel. Supporters say this reduces the long-term harmfulness of waste compared to uranium. However, using thorium also creates challenges because it produces uranium-232 and uranium-233, which emit strong gamma rays. These materials make it harder to protect workers and safely store waste.
A 2022 study by Krall, Macfarlane, and Ewing found that some SMRs might create more waste per unit of energy than traditional reactors. In some cases, they could produce up to five times more spent fuel or thirty-five times more waste from materials like steel and graphite. The study linked this to "neutron leakage," which happens more often in SMRs because they have a higher surface-area-to-volume ratio. Neutrons escape the reactor core more easily, making materials used for shielding radioactive.
The study also noted that SMRs may use less of their fuel, leaving more radioactive material in their waste. To keep reactors running in smaller cores, some SMRs might use fuel with higher concentrations of uranium-235. This could increase risks of nuclear weapons development and require stricter safety measures.
If more fissile material remains in spent fuel, it becomes easier to create a nuclear chain reaction, which could be dangerous if waste is stored improperly. This means more waste canisters and storage containers may be needed to prevent accidents.
SMRs are important for providing clean energy to reduce climate change, but managing their waste safely is a major challenge. The 2022 study by Krall et al. has sparked debates about how to handle SMR waste and has raised questions for scientists and policymakers.
Some SMR designs produce waste or coolants that are chemically reactive and hard to store safely. For example, uranium fluoride from molten salt reactors or sodium from fast reactors can react with underground materials, making deep disposal risky.
Scientists stress that future SMR projects must address these challenges to reduce waste and gain public and government support. Managing waste from many different types of SMRs may be more difficult than handling waste from traditional reactors.
Nuclear proliferation
Nuclear proliferation, or the spread of nuclear materials used to make weapons, is a concern for small modular reactors (SMRs). Because SMRs are smaller and produce less power, they are planned to be placed in more locations than traditional power plants. SMRs are expected to need fewer workers. This setup raises concerns about security and protection.
SMRs can be built to use different types of fuel, which allows the fuel to last longer and reduces the need for refueling. Longer time between refueling may lower the risk of nuclear materials being used for weapons. After fuel is used in a reactor, the mixture of materials created during nuclear reactions becomes highly radioactive and must be handled carefully. This makes it harder for people to steal the fuel.
Unlike large traditional reactors, SMRs can be built in sealed underground areas. This helps protect them from attacks or natural disasters. Some SMR designs, like those made by Gen4, improve resistance to nuclear proliferation by being sealed underground for their entire lifespan.
Some SMR designs use fuel only once. This reduces the risk of nuclear materials being handled on-site because the fuel is sealed inside the reactor. However, this design requires a large amount of fuel, which could make the reactor a bigger target. A reactor with a power output of 200 MWe and a 30-year lifespan might contain about 2.5 tonnes of plutonium when it stops operating.
Many SMRs can operate for more than 10 years without needing refueling. This improves their resistance to nuclear proliferation compared to large reactors, which need refueling every 18–24 months.
Light-water reactors that use thorium instead of uranium are safer against nuclear proliferation than traditional uranium-based reactors. However, molten salt reactors may have higher risks.
SMRs are shipped from factories without fuel, as they are filled with fuel at their final location, except for some small reactors. This means fuel must be transported separately, which could increase the risk of nuclear materials spreading. At the same time, millions of tons of nuclear waste are moved across the United States each year, and there is no record of nuclear fuel or waste being stolen during these shipments.
Licensing process
Licensing is a necessary step to ensure the safety, security, and protection of new nuclear power plants. As of 2025, only NuScale Power’s VOYGR, VOYGR-4, and VOYGR-6 small modular reactors (SMRs) are fully licensed for use in the United States. However, not all countries follow the same licensing rules as the U.S. Nuclear Regulatory Commission (NRC) or the International Atomic Energy Agency (IAEA). In the United States and countries that follow IAEA standards, licensing involves a detailed and independent review of all structures, systems, and components that are important for nuclear safety during normal and emergency situations throughout the entire life of the installation, including the long-term management of radioactive waste. Licensing requires the evaluation of risk studies and safety documents prepared by the manufacturer and operator of the SMR as part of their application to the regulatory body for permission to build and operate the facility. For NRC and IAEA licensing, safety and feasibility plans must address all aspects of operational safety, security (such as access control), nuclear safeguards (to prevent the spread of nuclear materials), the proper handling of radioactive waste in stable forms, and the long-term safety of waste disposal, including waste from dismantling the installation after it stops operating. A key concern is avoiding the creation of poorly managed waste or waste types that lack safe disposal options, which could lead to unexpected costs.
The most common licensing process used for existing nuclear reactors applies to light water reactors, such as pressurized water reactors (PWRs) and boiling water reactors (BWRs). Early designs for large reactors were developed in the 1960s and 1970s, and many of these reactors are still in use today. Some changes to the original licensing process by the NRC have been made to better fit the needs of SMRs. The NRC’s current licensing process focuses mainly on traditional large reactors, with design and safety rules, staffing requirements, and other factors developed for reactors producing more than 700 megawatts of electricity (MWe).
To support nuclear safety and improve the licensing process, the IAEA has encouraged the development of a central licensing system for SMRs. Workshops in 2009 and 2010, along with a U.S. congressional hearing in 2010, discussed this topic. The NRC and the U.S. Department of Energy are working to define licensing rules for SMRs. A challenge is ensuring that safety regulations are not weakened, as faster adoption of less strict rules could reduce the safety of SMRs. While manufacturing SMRs in controlled plants with improved quality control is an advantage, SMRs still have high energy density and their smaller size does not automatically mean better safety. A serious accident involving radioactive material release could have severe consequences similar to those of a large reactor and might lead to public rejection of nuclear energy. The variety of SMR designs and the potential for many SMRs to be deployed also complicate the licensing process. Nuclear safety must not be compromised for economic or industrial reasons, as the risk of accidents increases with the number of reactors, regardless of their size.
The U.S. Advanced Reactor Demonstration Program was planned to help license and build two prototype SMRs during the 2020s, with up to $4 billion in government funding. In July 2024, the ADVANCE Act required the NRC to create a process for licensing and regulating microreactor designs. This law aims to speed up the deployment of microreactors and other nuclear technologies.
Flexibility
Small nuclear reactors, compared to traditional nuclear power plants, can be built in smaller, modular sections. This allows for adding more units to the power grid as electricity demand increases. The modular design of small modular reactors (SMRs) also makes it possible to build them more quickly and at lower costs after the first reactor is completed.
SMRs can be added to existing power plants to increase their electricity generation capacity. At a single site, multiple SMRs can operate together, with one reactor temporarily shut down for refueling while others continue to produce power, similar to how larger conventional reactors function.
SMRs can work with renewable energy sources like wind and solar power in hybrid systems. These systems can improve energy efficiency in areas where electricity is hard to use, such as in industries or transportation.
In hybrid systems, SMRs can provide thermal energy directly instead of just electricity. This thermal energy can be used for tasks like desalination (removing salt from seawater), heating homes and buildings, industrial processes, and producing hydrogen fuel.
The flexibility of SMRs allows nuclear energy to be used in larger energy systems, helping to reduce emissions in various ways.
SMRs are being considered for use in remote areas with micro-grids. Their ability to provide steady power output can support communities that rely on wind and solar energy, which are not always reliable. This helps make these communities more energy-independent and resilient.
When electricity is not needed, some SMR designs can use thermal energy directly, reducing energy waste. This includes uses like desalination, industrial processes, hydrogen production, shale oil recovery, and heating homes or buildings. These tasks are not typically handled by larger conventional reactors.
Economics
A small modular reactor (SMR) factory would need a large amount of money to start. The cost per unit would only become cheaper when about 40 to 70 units are made.
One possible benefit is that a future power station using SMRs can begin with one unit and add more units as electricity demand increases. This reduces the high initial costs of traditional power plants. Some SMRs are designed to produce less electricity when demand is low.
A 2014 study about electricity in small, local power systems found that using SMRs would cost much less than using offshore wind power, solar thermal energy, biomass, or solar photovoltaic power plants.
In 2016, it was reported that building costs for each SMR reactor were less than for a traditional nuclear plant. However, operating costs for SMRs might be higher because they are smaller and require more reactors. The cost to operate SMRs per unit of electricity can be up to 190% more than for larger reactors. Building SMRs in modules is a complex process, and a 2019 report noted there is very little information about how to transport these modules.
A 2014 study by the German Federal Office for the Safety of Nuclear Waste Management (BASE) estimated that about 3,000 SMRs would need to be built before production would be cost-effective. This is because SMRs are more expensive to build than large nuclear plants due to their smaller electricity output.
In 2017, a study by the Energy Innovation Reform Project (EIRP) looked at eight companies with reactor designs ranging from 47.5 MWe to 1,648 MWe. The study found an average capital cost of $3,782 per kilowatt, average operating costs of $21 per megawatt-hour, and a levelized cost of electricity (LCOE) of $60 per megawatt-hour.
In 2020, Bret Kugelmass, founder of the Energy Impact Center, said that building thousands of SMRs at the same time could lower costs by reducing the time needed for long-term loans and lowering risks for large projects. Jon Ball, an executive from GE Vernova Hitachi Nuclear Energy, agreed, noting that SMR modules could also reduce costs linked to long construction times.
In October 2023, an academic paper published in Energy analyzed the economic data of 19 SMR designs and compared their costs. A Monte Carlo simulation showed that none of the designs were profitable or economically competitive. For SMRs closer to being built, the median LCOE ranged from $218/MWh to $614/MWh (in 2020 US dollars). Three high-temperature gas-cooled reactor designs, which needed more development, had lower median LCOEs from $116/MWh to $137/MWh.
The first SMR project in the United States was the Carbon Free Power Project, which planned to build six 77 MWe NuScale reactors (originally 12). The estimated electricity cost after subsidies was $89/MWh in 2023, up from $58/MWh in 2021. The higher cost led to the project being canceled in November 2023. Before cancellation, the project received a $1.355 billion cost-share award from the US government in 2020 and an estimated $30/MWh subsidy from the Inflation Reduction Act of 2022. Unsubsidized costs at cancellation were $20,139 per kilowatt for capital and $119/MWe for electricity generation. This raised concerns about the future of other SMR designs in the US.
In 2024, Australia’s CSIRO estimated that electricity from an SMR built in 2023 would cost about 2.5 times more than from a traditional large nuclear plant. This cost would decrease to about 1.6 times by 2030.
In 2025, a final decision was made to build a BWRX-300 SMR in Canada, based on a forecast cost of Canadian dollars (CA$) 7.7 billion (US$5.6 billion) for one unit. The estimated cost for three additional units was CA$13.2 billion (US$9.6 billion). These costs include financing and some extra expenses for unexpected issues.
List of reactor designs
Many reactor designs have been suggested. Important SMR designs include:
The power listed refers to the capacity of a single reactor unless stated otherwise.
Siting/infrastructure
Small modular reactors (SMRs) are expected to need less land than traditional power plants. For example, a 470 MWe 3-loop Rolls-Royce SMR reactor would require 40,000 m (430,000 sq ft) of space, which is about 10% of the area needed for a traditional plant. However, this unit is larger than the International Atomic Energy Agency's definition of an SMR, which specifies a maximum size of 300 MWe. Because of its size, it may require more construction work at the site, which raises questions about the benefits of SMRs. The company aims to build this unit in 500 days.
Electricity demand in remote areas is often small and changes frequently, making these locations well-suited for smaller power plants. Smaller plants may also not need to connect to a large power grid to share their electricity.
Proposed sites
In February 2014, the CAREM SMR project began in Argentina with the construction of the containment building for a prototype reactor. The name CAREM stands for Central Argentina de Elementos Modulares. The National Atomic Energy Commission (CNEA), Argentina’s nuclear energy research agency, and Nucleoeléctrica Argentina, the country’s nuclear energy company, are working together to complete the project.
CAREM-25 is a 25 MWe prototype reactor, the first nuclear power plant fully designed and built in Argentina. The project was paused multiple times before continuing. In October 2022, CNEA expected the construction to finish by 2024. If the plan stays on track, the first test of the reactor, called criticality, is expected by the end of 2027.
In 2018, the Canadian province of New Brunswick announced it would invest $10 million in a demonstration project at the Point Lepreau Nuclear Generating Station. Later, SMR companies Advanced Reactor Concepts and Moltex opened offices there. A unit was scheduled to be built at Point Lepreau in July 2018. Both Moltex and ARC Nuclear are competing for the contract.
On December 1, 2019, the leaders of Ontario, New Brunswick, and Saskatchewan signed an agreement to work together on developing small modular reactors (SMRs). Alberta joined the agreement in August 2020. Continued support from citizens and government officials led to the selection of an SMR project at the Canadian Nuclear Laboratory.
In 2021, Ontario Power Generation announced plans to build a BWRX-300 SMR at their Darlington site, with completion expected by 2028. A construction license still needed to be applied for.
On August 11, 2022, Invest Alberta, a government-owned company, signed an agreement with Terrestrial Energy to develop an SMR called IMSR in Western Canada.
In July 2019, China National Nuclear Corporation announced plans to build an ACP100 SMR near the Changjiang Nuclear Power Plant in Hainan province by the end of the year. In June 2021, the project, named Linglong One, received approval from China’s National Development and Reform Commission. Construction began in July 2021, and the bottom part of the containment vessel for the first unit was installed in October 2021. This project is the world’s first commercial land-based SMR prototype.
In August 2023, the core module of the reactor was installed. The core includes a pressure vessel, steam generator, and primary pump receiver. The reactor is planned to produce 125 MWe of electricity.
At the start of 2023, Électricité de France (EDF) created a new company to develop an SMR called Nuward. The design includes two reactors, each producing 170 MWe, housed in a single containment building. In August 2023, EDF submitted a safety report to the French nuclear safety authority.
In July 2024, EDF announced it would stop the Nuward project and instead develop an SMR based on existing technology. In January 2025, EDF said the new design would be completed by mid-2026 and ready for use in the 2030s, producing about 400 MWe of electricity and 100 MWt of heat.
A Polish chemical company, Synthos, announced plans to build a Hitachi BWRX-300 reactor (300 MWe) in Poland by 2030. A feasibility study was completed in December 2020, and the licensing process began with Poland’s nuclear energy agency.
In February 2022, NuScale Power and KGHM Polska Miedź, a large mining company, signed a contract to build the first operational reactor in Poland by 2029.
At the 2021 United Nations Climate Change Conference, Romania’s state-owned nuclear company, Nuclearelectrica, and NuScale Power signed an agreement to build a power plant with six small reactors at the Doicești power station, near Bucharest. The plant is expected to be completed by 2026–2027 and will produce 462 MWe of electricity, enough to power about 46,000 homes. It will also prevent the release of 4 million tons of CO₂ annually.
Russia has started using small nuclear reactors on icebreakers along its Arctic coast. In May 2020, the first floating nuclear power plant with two 30 MWe reactors, called KLT-40, began operating in Pevek, Russia. This design is based on nuclear icebreaker technology.
In 2016, the UK government studied potential SMR sites, including the former Trawsfynydd nuclear power station and former coal plants in Northern England. Existing nuclear sites like Bradwell, Hartlepool, and Sellafield were also considered. The target cost for a 470 MWe Rolls-Royce SMR unit is £1.8 billion for the fifth unit built. In 2020, Rolls-Royce announced plans to build up to 16 SMRs in the UK. In 2019, the company received £18 million to design the system, and in 2021, the UK government gave £210 million, with £195 million from private companies. In November 2022, Rolls-Royce said it would focus on sites like Trawsfynydd, Wylfa, Sellafield, and Oldbury for SMR projects.
The UK government launched Great British Nuclear in July 2023 to oversee SMR development and fund viable projects.
In 2007, researchers at Oregon State University, led by José N. Reyes Jr., designed a prototype SMR. Their work formed the basis for NuScale Power’s commercial SMR design. In 2013, NuScale and OSU built the first full-scale SMR prototype. In 2022, NuScale received approval from the US Nuclear Regulatory Commission for its SMR design. In 2025, NuScale received approval for two additional SMR designs, VOYGR-4 and VOYGR-6. The US Department of Energy had expected NuScale to complete its first SMR by 2030, but the project was canceled due to rising costs. In 2024, the US had nearly 4 gigawatts of announced SMR projects and about 3 gigawatts in early development stages.
SM