Small Modular Reactor (SMR)

A small modular reactor, or SMR, is a nuclear reactor of roughly 300 MWe or less, built from factory-made modules rather than constructed entirely on site. Smaller than conventional reactors of 1,000 MWe or more, SMRs aim to cut cost and build time, which has made them central to powering AI data centers.

What is a small modular reactor?

The defining traits are size and assembly. The World Nuclear Association describes SMRs as reactors generally 300 MWe or less, designed with modular technology so that components can be factory-fabricated and shipped to site, pursuing economies of series production and shorter construction (World Nuclear Association). That contrasts with conventional plants of 1,000 MWe or more, which are largely built on site over a decade. The US Nuclear Regulatory Commission reserves “SMR” for light-water designs under 300 MWe and labels non-light-water designs “advanced reactors,” though the terms are often used together in the market.

The International Atomic Energy Agency frames the category around the same threshold and the same factory-first logic:

“Small modular reactors are defined as advanced reactors that produce electricity of up to 300 MW(e) per module. These reactors have advanced engineered features, are deployable either as a single or multi-module plant, and are designed to be built in factories and shipped to utilities for installation as demand arises.” — International Atomic Energy Agency, What are Small Modular Reactors?

The word “modular” is doing the work. A conventional reactor is a one-off megaproject poured in place. An SMR is meant to be a product: the same module rolling off a line many times, so that learning and volume cut the cost of each copy rather than every plant starting from zero. That ambition is still mostly ahead of the industry. The IAEA counts more than 80 SMR designs and concepts under development worldwide, yet as of 2025 only two SMR-based plants are in commercial operation and four reactors are in advanced construction, in Argentina, China, and Russia (IAEA). In April 2025, GE Vernova’s BWRX-300 received a construction licence for Canada’s Darlington site, targeting 300 MWe by 2030.

How are SMRs used to power AI data centers?

SMRs can be sited close to demand and deliver firm, carbon-free baseload, which fits the around-the-clock load of AI compute. Google contracted to buy up to roughly 500 MW from a fleet of Kairos Power SMRs, with the first reactor expected around 2030 (DatacenterDynamics). Many advanced designs require high-assay low-enriched uranium (HALEU), and Centrus runs the first US-licensed HALEU enrichment facility, having produced the nation’s first such fuel in over 70 years (U.S. Department of Energy). The public developers and fuel suppliers sit inside the AI Electricity & Nuclear SMRs theme.

Related terms & concepts

FAQ

How is an SMR different from a conventional reactor?

An SMR generates roughly 300 MWe or less, while conventional reactors run 1,000 MWe or more. SMRs are built from factory-fabricated modules shipped to site, which is meant to shorten construction and lower upfront cost through series production (World Nuclear Association).

Why do SMRs matter for AI data centers?

AI data centers need firm, carbon-free power, and SMRs can be sited near demand to deliver baseload electricity. Google contracted for up to roughly 500 MW from Kairos Power SMRs, with the first reactor expected around 2030 (DatacenterDynamics).

Which companies are building SMRs?

US-listed developers include NuScale Power and Oklo, while X-energy (backed by Amazon) and Kairos Power (contracted by Google) are private. GE Vernova is developing the BWRX-300 SMR. Many advanced designs need HALEU fuel, which Centrus is the first US-licensed producer of (U.S. Department of Energy).

Sources & references

  1. Small Modular Reactors · World Nuclear Association, 2025-09-01
  2. Google signs nuclear SMR deal with Kairos for data center power · DatacenterDynamics, 2024-10-15
  3. Centrus Produces Nation's First Amounts of HALEU · U.S. Department of Energy, 2023-11-07
  4. What are Small Modular Reactors (SMRs)? · International Atomic Energy Agency, 2024-09-01