Global Landscape of Small Modular Reactors (SMRs)

What are SMRs, and How Do They Differ from Conventional Reactors

Small Modular Reactors (SMRs) are a class of advanced nuclear fission reactors with a capacity up to about 300 MWe per unit – roughly one-third or less the output of a typical modern nuclear plant. They operate on the same fundamental principle as conventional reactors (splitting atomic nuclei to produce heat, which generates steam to drive turbines and produce electricity). However, SMRs are "small" in physical size and power output and "modular" in design. This means most of their components can be factory-fabricated as modules and then transported to the plant site for assembly.

SMRs differ from conventional reactors in several important ways:

• Size and Footprint: An SMR may occupy only a fraction of the area of a large plant – some designs tout a footprint of only a few acres. Multiple SMR units can be clustered to scale up output if needed, but even a single unit can be deployed to serve smaller grids or remote regions where a giant reactor wouldn't be feasible.
• Factory Construction: Unlike traditional reactors built mostly on-site, SMR components can be mass-produced in factories. This factory fabrication allows for standardization and learning-curve benefits (akin to assembly-line production) which can potentially lower costs and construction times over successive builds. By shipping modular sections by truck, rail, or barge, on-site construction is faster and less complex.
• Passive Safety: SMRs often incorporate advanced safety features that make them less reliant on active controls or external power for emergency cooling. Many designs are intended to be installed underground or underwater, adding an extra barrier against external events.

Another key difference is economic scale. Large nuclear plants benefit from economies of scale (a single 1000 MWe reactor can produce power relatively cheaply once running), whereas a single SMR produces less power. The SMR concept instead pursues economies of series – building many standardized units to drive down per-unit costs. By 2025, there are over 80 SMR designs in various stages of development around the world, with a handful already in operation or under construction.

Key Technological Advances Enabling SMRs

Passive and Inherent Safety

A major innovation in many SMR designs is the use of passive safety systems. Traditional reactors rely on engineered active systems (pumps, diesel generators, operator actions) to respond to accidents, which can fail if power is lost (as occurred at Fukushima). In contrast, SMRs are being designed to shut down and self-cool without human intervention or external power.

For example, an SMR's cooling system might use natural convection: heat drives coolant circulation without pumps, and gravity-fed water tanks can provide emergency cooling. The reactor vessel is often inside a containment that can passively remove heat. The inherent safety of SMRs is bolstered by their smaller cores and lower operating pressure in some designs.

A smaller reactor has less residual heat to manage after shutdown, simplifying safe cooling. These features greatly reduce the risk of core damage or radioactive releases. Simply put, SMRs are often engineered to be "walk-away safe," capable of withstanding extreme events by design.

Modular, Factory-Built Systems

The "M" in SMR, modularity, is not just about physical size but about how the plants are constructed. SMR designs take advantage of factory fabrication for major components or entire reactor modules. This is a significant shift from the one-off on-site construction of traditional reactors.

Factory building can improve quality control and allow parallel production of multiple units. It also means deployment can be incremental – a utility could install one or two modules first and add more later as demand grows, rather than building a gigantic single-unit plant all at once.

The modular approach echoes how industries like aviation or shipbuilding spread fixed costs over a series of identical units. For SMRs, the hope is that mass production will drive costs down over time, something large reactors have struggled to achieve. Additionally, modular construction means shorter project timelines – some SMR vendors claim a module can be installed in 2–3 years once site prep is done, versus 5–10 years for a big reactor.

Advanced Cooling and Reactor Types

While many first-generation SMRs use established light-water reactor (LWR) technology (just scaled down), others employ advanced cooling methods and reactor types that differ from today's large reactors. Broadly, SMR designs span four categories:

1. Light-water reactors (LWRs) – small pressurized or boiling water reactors that use ordinary water for cooling and moderation (examples: NuScale's module, Rolls-Royce SMR, GE Hitachi's BWRX-300, Argentina's CAREM). These are the lowest technological risk since they're based on familiar reactor tech.
2. High-temperature gas-cooled reactors (HTGRs) – these use a gas (often helium) as coolant and graphite as a neutron moderator. They run at much higher outlet temperatures (750°C or more) than LWRs. A prime example is China's HTR-PM pebble-bed reactor, which uses helium to cool uranium fuel pebbles and reached first power in 2021.
3. Molten Salt Reactors (MSRs): These come in two sub-types – some have solid fuel with molten fluoride salt as a coolant (e.g. Kairos Power's FHR), while others dissolve the fuel in the molten salt itself. Molten salt reactors run at low pressure and high temperature, offering passive safety.
4. Fast Neutron Reactors: These SMRs forego a moderator and use fast fission of fuel, usually cooled by liquid metal like sodium or lead. Fast SMRs can potentially use recycled fuel or even consume nuclear waste.

Advanced Fuels (TRISO and HALEU)

Along with new coolants, many SMRs use innovative nuclear fuels to achieve their performance and safety goals. Two notable fuel advancements are TRISO particles and HALEU uranium fuel:

• TRISO Fuel: Several SMRs (especially gas-cooled and microreactors) use TRISO fuel, short for Tri-structural Isotropic fuel. TRISO fuel particles are often called "poppy-seed sized" microspheres – each particle has a tiny kernel of uranium fuel surrounded by three concentric layers of carbon and ceramic (silicon carbide). These layers are like a built-in containment for each particle, trapping fission products even at extreme temperatures.
• HALEU (High-Assay Low-Enriched Uranium): Many advanced SMRs plan to use uranium fuel enriched to between 5% and 20% U-235, which is termed HALEU. (By contrast, today's large reactors use <5% enrichment). HALEU fuel allows smaller reactors to pack more energy into a compact core, enabling longer periods between refueling and higher burn-up of fuel.

Global SMR Deployment Status

As of 2025, only a few SMRs have been deployed in practice, but many projects are in the pipeline worldwide. The IAEA reports that four SMRs are in advanced stages of construction (in Argentina, China, and Russia) and that the first operational units are expected around 2030 for many countries' programs.

Operational SMRs

Two pioneer SMR projects have already delivered electricity:

• Russia's floating nuclear power plant "Akademik Lomonosov" became the world's first commercial SMR deployment in 2019. It consists of two small PWR reactors (35 MWe each) mounted on a barge, supplying ~70 MWe to the remote Arctic town of Pevek and replacing an aging land reactor.
• China's HTR-PM is another milestone – it's a demonstration high-temperature gas-cooled pebble-bed SMR at Shidao Bay. The plant has two reactor modules (each ~100 MW thermal) driving one 210 MWe turbine. The first reactor module reached criticality in 2021 and was connected to the grid in December 2021.

SMRs Under Construction

Several countries have flagship SMRs being built:

• Argentina's CAREM-25 (a 25 MWe integral pressurized water reactor) is under construction near Buenos Aires. It began construction back in 2014 as one of the first SMR prototypes, but progress has been slow with some delays.
• In China, the ACP100 "Linglong One" is a 125 MWe multi-purpose SMR being constructed at Changjiang, Hainan Island. First concrete was poured in July 2021, with a planned construction period of 58 months, putting completion around 2026.
• In Russia, aside from the operating floating plant, a significant SMR project is the BREST-OD-300 fast reactor. It's a 300 MWe lead-cooled fast reactor being built at the Siberian Chemical Combine site in Seversk.

Licensed or Ready to Build

A few SMR designs have reached major regulatory milestones:

• In January 2023, NuScale's 50 MWe module design became the first SMR to be certified by the U.S. Nuclear Regulatory Commission (NRC).
• In Canada, the regulator CNSC is in the advanced stages of reviewing several SMR designs (such as GE Hitachi BWRX-300 and Terrestrial's IMSR), and granted site preparation license for an SMR at Ontario's Darlington site.
• In the UK, Rolls-Royce's 470 MWe SMR design is undergoing a Generic Design Assessment (GDA) by regulators as of 2023, and in 2024 the design was short-listed for government support with hopes of siting the first unit in the early 2030s.

National and Company Initiatives in SMR Development

Russia

Russia has been a leader in early SMR deployment, leveraging its long experience with small reactors in icebreakers and remote power. The Akademik Lomonosov floating plant is operational, making Russia the first to bring an SMR to market. Building on this success, Rosatom plans a fleet of improved floating SMRs and land-based units for hard-to-reach regions.

China

China sees SMRs as a complement to its massive nuclear build-out and also as a potential export product along the Belt and Road Initiative. It has two prominent SMR projects: HTR-PM and ACP100. The HTR-PM is a demonstration Generation IV reactor that has entered commercial operation, making China the first to operate a pebble-bed modular reactor.

United States

The United States has a vibrant private-sector driven SMR industry supported by federal funding. NuScale Power's SMR is the front-runner in licensing: it is a 77 MWe light-water reactor module, and a plant (called VOYGR) can have up to 12 modules (924 MWe). NuScale's design received NRC certification in 2023 – the first SMR to do so.

Alongside NuScale, the U.S. Department of Energy's Advanced Reactor Demonstration Program (ARDP) is funding two first-of-a-kind SMR demonstrations to be operational by around 2028: TerraPower's Natrium and X-energy's Xe-100.

Canada

Canada is moving assertively to be among the first adopters of SMRs in the West, with strong federal and provincial backing. The flagship project is at the Darlington Nuclear site in Ontario, where Ontario Power Generation (OPG) is building a 300 MWe GE Hitachi BWRX-300 SMR. This is slated to be Canada's first grid-scale SMR, operational by 2028.

United Kingdom

The UK is pursuing SMRs as part of its plan to rejuvenate nuclear power. The centerpiece is the Rolls-Royce SMR, a factory-fabricated 470 MWe pressurized water reactor. Although 470 MWe is on the upper end of "small", it's still about half the size of the latest large reactors, and Rolls-Royce's concept emphasizes modular construction of multiple large components.

Other Countries

Several other nations have significant SMR initiatives, including Argentina (CAREM-25), Poland (planning BWRX-300 units), South Korea (SMART reactor), France (Nuward), and Japan (restarting nuclear development post-Fukushima).

Applications of SMRs

One of the advantages of SMRs is their flexibility in deployment and applications. Because of their smaller size, enhanced safety, and often higher temperature output, SMRs can serve in roles beyond what large nuclear plants typically do. Key application areas include:

Grid Electricity Generation

This is the main focus of most SMRs – providing baseload or load-following power to electrical grids. SMRs can be connected to a grid either as a single unit or as a multi-module plant, depending on the needed capacity. For countries with large grids, SMRs offer a way to incrementally add clean generation in smaller chunks rather than building a gigawatt at a time.

Remote and Off-Grid Power

A transformative application of very small reactors (vSMRs or microreactors) is providing energy to remote locations that currently rely on diesel generators or have no reliable power. Examples are Arctic or island communities, mining operations in far-off areas, military bases, or research stations.

Desalination (Water Production)

SMRs are very well-suited to cogenerate fresh water through desalination. Nuclear reactors have long been considered for desalination because they produce heat (and power) that can drive desalination processes, and their steady operation pairs well with the continuous need for water.

Industrial Process Heat

Many industries require large amounts of heat (in the form of steam or high-temperature air/gas) – for example, refineries, petrochemical plants, steel mills, cement factories, and fertilizer plants. SMRs, especially advanced designs that reach higher temperatures, can supply carbon-free process heat for industries.

Hydrogen and Synthetic Fuel Production

With the push for green hydrogen (hydrogen made without fossil fuels), SMRs present an attractive production method. Electrolyzers need electricity – SMRs can provide continuous, carbon-free power for electrolysis of water to produce hydrogen gas.

Key Barriers to SMR Adoption

Despite their promise, SMRs face several barriers and challenges that need to be addressed for widespread adoption:

Regulatory and Licensing Challenges

Nuclear regulation is understandably rigorous, and most regulations were written with large reactors in mind. Certifying a novel SMR design can be time-consuming and costly. For example, in the U.S., NuScale spent over $500 million and ~5 years to get design approval for its SMR.

Financing and Economics

Building the first few SMRs will be expensive on a per-kW basis. While the modular approach should eventually lower costs, early units won't have volume discounts. Private investors may be hesitant given the history of nuclear cost overruns and the relatively unproven market for SMRs.

Fuel Supply Chain

As noted, several SMRs need HALEU fuel (enriched >5% U-235). Right now, the world's capacity to produce HALEU is very limited. Until a reliable supply is in place, reactor developers like TerraPower and X-energy face potential fuel delays.

Public Acceptance and Policy Support

Public perception of nuclear power can be a barrier, especially when introducing a lot of small reactors instead of one big plant. Some members of the public might be concerned that having multiple SMR sites increases the number of "nuclear locations" (even if each is very safe).

Forecasts and Outlook for SMRs

The outlook for SMRs is cautiously optimistic, with numerous projections suggesting they will become a significant part of the energy landscape by mid-century, especially as the world strives for net-zero emissions.

Market Size and Growth Projections

Various market research reports have sized the SMR market in the coming decades. One estimate suggests that by 2030, the global SMR market could be on the order of $70 billion, growing rapidly thereafter as deployments accelerate. By 2040, the OECD NEA sees a potential for 380 GW of SMR capacity worldwide if conditions are favorable.

Role in Net-Zero Emissions Goals

SMRs are often cited as a crucial tool for achieving net-zero carbon emissions by 2050. The logic is that certain sectors and loads cannot be fully served by intermittent renewables alone – and SMRs provide firm, dispatchable clean power and heat to fill that gap.

Complementing Renewables

As grids get dominated by wind and solar, maintaining stability and meeting peak demand on calm nights becomes a challenge. SMRs, especially load-following ones or those with integrated storage (like Natrium's molten salt heat storage), can ramp up output when renewables dip, ensuring supply matches demand.

Conclusion

The trajectory for SMRs is very promising but hinges on the next decade of demonstration and deployment. If early projects meet expectations, SMRs could usher in a new era where nuclear power is more accessible, flexible, and integrated than ever before – truly a "global landscape" change for nuclear energy.

They could light up remote corners of the world, desalinate oceans into drinking water, power factories and propel ships, all while working hand-in-hand with renewable energy to mitigate climate change. The coming years will test whether the substantial promise of small modular reactors can be realized in practice.