Small modular reactor

These are small power plants. They make electricity for us. They are built in a factory. Then they are moved to a new home.

This helps us have power. Some of these plants can even make heat. They can also make fresh water. People can add more parts to make more power. These small plants help us keep the air clean. They are a new way to help our world.

Small modular reactors, or SMRs, are a new kind of nuclear power plant. Most big reactors are built in one spot. SMRs are different. They are built in a factory as modules. These modules are parts that fit together.

This makes building them faster and easier. You can even add more modules to make more power.

SMRs use nuclear fission to make energy. Fission is a way to split atoms to get power.

Many SMRs use water to stay cool. Other designs use gas or even liquid metal. Some SMRs make electricity. Others make heat or fresh water.

Only China and Russia use SMRs right now. Russia uses a floating plant on the water. China has a plant that uses gas to stay cool. Experts say SMRs can help keep our air clean. They could help us reach net zero emissions by 2050. This means stopping the rise of harmful gases in our air. Many people are working to make these plants even safer.

Small modular reactors, or SMRs, are a special kind of nuclear power plant. These reactors produce 300 megawatts of electricity or less. Most nuclear plants are huge and built on-site. SMRs are different because they are factory-made. They are built as prefabricated modules in a factory. These parts are then sent to a site for installation. This way of working makes construction much faster. It also lets people add more modules to get more power.

SMRs work using a process called nuclear fission.

In fission, atoms split to release energy. Many SMR designs use light-water reactors. These use water to cool the reactor and slow down neutrons. Other designs use different cooling methods. Some use helium gas to stay efficient. Others use liquid metals like sodium or lead. Some even use molten salt to stay cool. These reactors can make electricity for homes. They can also make heat or fresh water through desalination.

People have used small reactors for a long time. The military used them for ships since the 1950s. These naval reactors are very strong and stay powered for years. The US Navy has a great safety record with them. They have not had a meltdown in 60 years. In 2003, Admiral Frank Bowman testified about this safety. The term "small modular reactor" became common in the late 1970s. In 2010, Steven Chu called them a new nuclear option for America. He said they could be "plug and play" when they arrive.

Right now, only two countries have operational SMRs. Russia operates a floating plant called Akademik Lomonosov. It has been working in Pevek since 2020. China has a gas-cooled reactor called HTR-PM. It connected to the power grid in 2021. As of 2025, there are 127 different modular reactor designs. Seven of these are already operating or being built. Many more are in the process of getting licenses. China also plans to start a land-based reactor called ACP100 by 2026.

SMRs might help the world reach net zero emissions by 2050. This means stopping the rise of harmful gases in our air. The European Commission views SMRs as a way to help the planet. Some experts say we may need thousands of these reactors. They could power big things like data centers. However, some people worry about the cost of moving fuel. Others worry about making more radioactive waste. Scientists are still working to make sure new designs stay safe.

A small modular reactor, or SMR, is a specialized type of nuclear fission reactor. These reactors are defined by their electrical power capacity of 300 megawatts electrical (MWe) or less. Unlike traditional nuclear plants, SMRs are designed for modular construction. This means they are factory-fabricated as prefabricated modules. These modules are then transported to a specific installation site. This approach allows for streamlined construction and enhanced scalability.

Customers can also integrate multiple units into large configurations to meet specific energy needs.

The core mechanism of an SMR relies on nuclear fission.

In this process, atoms split to release massive amounts of energy. Most current SMR designs are light-water reactors (LWRs). These use water as both a coolant and a moderator. A moderator is a substance, such as water or graphite, that slows down neutrons. Some advanced SMR concepts use different cooling methods to improve efficiency. For example, helium gas can be used as a coolant to provide high thermal efficiency. Other designs explore liquid metals, such as sodium or lead, to manage heat. Some even utilize molten salt as a cooling medium.

There are several distinct types of reactor technologies within the SMR category. Thermal-neutron reactors are the most common and rely on a moderator to slow neutrons. In contrast, fast-neutron reactors do not use moderators. Instead, they rely on highly enriched uranium (HEU) fuel to absorb fast neutrons. Fast reactors can also function as breeder reactors. These reactors release enough neutrons to transmute non-fissionable elements into fissionable ones. This often involves surrounding the core with a "blanket" of uranium-238. When the uranium-238 absorbs a neutron, it becomes plutonium-239, which can then be used as fuel.

The history of small reactors begins with military applications in the 1950s. The military has long used small reactors for nuclear marine propulsion. These naval reactors require high power density because submarine spaces are very constrained. Because of these constraints, naval reactors often use highly enriched uranium (HEU). This differs from the low-enriched uranium (LEU) used in most civilian SMRs. The US Navy's Naval Reactors program has a strong safety record. Admiral Frank Bowman testified in 2003 that the program had no meltdowns or radioactive releases in 60 years. While the US Army experimented with land-based reactors between 1954 and 1977, they did not use modern modular designs.

As of 2025, the SMR landscape is growing rapidly. There are 127 modular reactor designs currently in existence. Of these, seven designs are either operating or under construction. Fifty-one designs are in the licensing or pre-licensing process. Another 85 designers are in discussions with potential site owners. Currently, only China and Russia have successfully built operational SMRs. Russia has operated the floating Akademik Lomonosov plant in Pevek since 2020. China connected its pebble-bed modular high-temperature gas-cooled reactor, the HTR-PM, to the grid in 2021. China also expects to start the 125 MWe ACP100 land-based reactor by the end of 2026.

SMRs are considered significant for global decarbonization efforts. The European Commission recognizes them as contributors to the EU Green Deal. To reach global net zero emissions by 2050, the International Energy Agency suggests doubling nuclear power. Some experts, like Antonio Vaya Soler, agree that nuclear capacity must at least double. However, the scale required is immense. The German Federal Office for the Safety of Nuclear Waste Management warns that several thousand to tens of thousands of SMRs might be needed. This would be necessary to match the electrical power produced by all current nuclear reactors combined. This massive deployment would aim to significantly reduce carbon emissions.

Despite the potential, SMRs face several engineering and economic challenges. Proponents argue that smaller size increases safety by reducing decay heat. Decay heat is the heat present after a reactor is shut down. However, critics worry that more reactors mean more transportation of nuclear fuel. They also note that more reactors could increase radioactive waste production. There is also an engineering risk of corrosion in systems using liquid metals or molten salts. Economically, some studies suggest SMR costs are comparable to large conventional reactors. To be cost-effective, a high market share of identical modules is likely required. This remains a central topic for technology corporations interested in powering data centers.