small modular reactor (SMR)

basicexperimental

A nuclear reactor prefabricated in a factory from components, much smaller than a conventional one, assembled on site, and able to power even a single industrial plant or data center.

In plain terms

A traditional nuclear power plant is like a cathedral: built on-site according to a unique design, often taking a decade or more. A small modular reactor resembles a prefabricated house: its main components are manufactured in a factory, transported by truck, train, or ship, and only assembled on-site.

"Small" means that a unit produces at most around 300 megawatts of electricity, roughly one-third to one-quarter of a modern large power plant block. The boundary is not sharp: some plans called SMRs are larger. "Modular" means that multiple units can be placed next to each other, so the plant can be expanded according to demand.

The term entered the AI glossary because artificial intelligence data centers consume enormous amounts of electricity, day and night, without interruption. Major tech companies are therefore looking for a source that does not depend on the weather and does not emit carbon dioxide during operation. Several companies have already signed agreements with SMR developers.

For now, this is mostly a promise: only a few such reactors operate worldwide, and most plans are still awaiting approval or under construction.

How it works

The same thing happens in the reactor as in a large nuclear power plant: uranium nuclei split, generating heat.
The heat boils water or warms another coolant; the resulting steam drives a turbine, which in turn generates electricity.
Due to the smaller size, less heat needs to be dissipated, so many types rely on so-called passive safety: in an emergency, gravity and natural flow are designed to cool the reactor for a long time without pumps, external power sources, or human intervention.
Main equipment is mass-produced in factories and only assembled on-site; developers expect this to make construction faster and cheaper over time.
If more energy is needed, additional modules are installed alongside existing ones, allowing the investment to expand incrementally.

An everyday example

You read in the news that a major tech company would buy power from small modular reactors for its new AI data centers, or that installing such reactors was raised in Hungary. When you use a chatbot or an AI agent works for you, the server machines consume electricity; the SMR is one possible answer to where this power will come from in the next decade.

Who is affected

everyoneAI's power demand can affect the electricity grid and prices, and building a reactor nearby directly impacts local residents.

industrial worker, engineerManufacturing, construction, and operations may bring new professional tasks and jobs to the energy and machinery sectors. → Industry

bank customer, investorSMR company stocks are popular but risky investments because most such companies have not yet delivered a single reactor, and the share price reflects future hopes. → Money

entrepreneur, executivePlanning for long-term power supply for energy-intensive facilities and data centers increasingly considers this as an option.

A common misconception

MythThe SMR is a ready, off-the-shelf solution that will resolve AI power issues within a few years.

In realityOnly a few such reactors operate worldwide, and the first examples of Western types are still under construction or awaiting approval. Today, data center power demand is therefore covered mainly by other sources.

Limits and risks

The price remains uncertain: savings expected from mass production have not yet been confirmed by anyone, and there have been projects halted due to rising costs.
Permitting and construction take years, so agreements announced today will typically yield electricity only in the 2030s.
Even small reactors produce radioactive waste, whose long-term storage must be solved just as for large power plants.
Some types require special, higher-enrichment fuel, whose supply chain is still limited.

Similar, but not the same

conventional nuclear power plant – The large block being built today is a unique, on-site mega-investment, typically with a capacity of around 1000 megawatts or more; the SMR is much smaller and consists of factory-made components.
mikroreaktor – A microreactor is an even smaller unit, typically up to a few tens of megawatts, which can fit even in a container.
fusion reactor – Fusion would derive energy from the merging of atomic nuclei and is still in the research phase, while SMR uses the long-known process of nuclear fission.

Related concepts

Broader

atomenergia, AI infrastructure, energy supply

Narrower

mikroreaktor

On the edge

data center, AI energy demand, hyperscaler, power purchase agreement, computing capacity

A brief history

Small reactors have powered submarines and icebreakers since the 1950s, while the idea of factory-built, modular civilian power plants gained momentum in the 2000s. In 2020, the Russian floating nuclear power plant Akademik Lomonosov entered commercial operation, and at the end of 2023 a new type of gas-cooled small reactor (HTR-PM) did so in China. In 2024, several major tech companies, including Google and Amazon, announced SMR agreements to supply their data centers.

Where things stand

At the end of 2026, only a few small modular reactors are operating worldwide, mainly in Russia and China. The first Western units are under construction or in licensing, while reactors intended for AI data centers are still only plans and contracts.

Status: 2026 November

In the news

Appears in 8 Agent Age stories; the curve shows weekly occurrence in the news magazine.

Reactors under construction rise to 79 worldwide as AI demand grows; SMRs expected to spread fastOct 28, 2026 · Ipar
Amazon funds 12 small modular reactors at a former coal plant site in IndianaOct 27, 2026 · Ipar
Amazon plans nearly 1 GW small modular reactor project in IndianaOct 19, 2026 · Ipar
Nuclear power for data centers: big tech's SMR deals and the existing fleetOct 1, 2026 · Ipar
Nuclear power for AI: Alphabet investment, small modular reactors and a construction testSep 14, 2026 · Ipar
HD Hyundai Heavy to invest 1.07 trillion won in engines and small modular reactorsSep 10, 2026 · Ipar
Small modular reactors for data centres: construction permits, high costs and slipping timelinesAug 31, 2026 · Ipar
Small modular reactors: data centers hope for them, but the technology is unprovenAug 17, 2026 · Ipar

Also known as

SMR · small modular reactor · small modular nuclear reactor · small modular reactor · modular nuclear power plant · small modular reactor · small modular nuclear reactor · SMR technology

This entry was machine-edited and has undergone machine expert review; the “In the news” section updates automatically from Agent Age stories.