Small modular reactors (SMRs) are nuclear reactors that produce roughly 300 megawatts of electricity or less — about a third of a typical large reactor or smaller — and are designed to be built from standardized, partly factory-made components. Canada is building its first grid-scale SMR at Ontario Power Generation's Darlington site east of Toronto, with the first unit expected around 2030, and Saskatchewan is planning to follow in the 2030s.
Key takeaways
- SMRs are smaller nuclear reactors meant to be quicker and more predictable to build through standardized designs.
- Canada's first SMR, a 300 MW BWRX-300 at Darlington in Ontario, is under construction, with the first unit targeted to be in service around 2030.
- The full four-unit Darlington project has an announced budget of about $20.9 billion.
- Saskatchewan is studying a site near Estevan for potential SMR deployment in the mid-2030s.
- Cost, waste management and construction timelines remain the key open questions.
What makes a reactor "small" and "modular"?
Conventional Canadian reactors, such as the CANDU units at Darlington, Pickering and Bruce, each produce several hundred to more than 800 megawatts and were custom-built on site over many years. SMRs aim to change that model.
| Feature | Large conventional reactor | Small modular reactor |
|---|---|---|
| Output per unit | Roughly 600–1,000+ MW | Up to ~300 MW (micro-reactors under ~20 MW) |
| Construction | Largely custom, built on site | Standardized design, more factory fabrication |
| Upfront cost per unit | Very high | Lower per unit, though not necessarily per MW |
| Typical uses | Large grid baseload | Grid power, remote communities, industrial heat |
| Safety approach | Active and passive systems | Greater reliance on passive safety features |
"Passive safety" means the reactor can shut down and cool itself using natural forces such as gravity and convection, without relying on pumps or operator action for an extended period.
Grid-scale SMRs vs. micro-reactors
The term SMR covers a wide range. Grid-scale units like the BWRX-300 are designed to feed provincial power systems. Micro-reactors, producing just a few megawatts, are being explored for remote communities and mines that currently rely on diesel. Most micro-reactor proposals in Canada are still at the design and licensing stage.
How an SMR produces electricity
At its core, an SMR works like other nuclear plants. Uranium fuel undergoes fission, releasing heat. That heat produces steam, which spins a turbine connected to a generator. The BWRX-300 is a boiling water reactor: water boils directly in the reactor vessel, and the steam goes to the turbine. Nuclear plants emit no greenhouse gases while operating, which is why they're part of most Canadian clean-electricity plans. Our explainer on how the electric grid works shows where steady sources like nuclear fit alongside hydro, wind and solar.
Where Canada is building SMRs
Ontario: Darlington New Nuclear Project
Ontario Power Generation (OPG) received a construction licence from the Canadian Nuclear Safety Commission in April 2025 for the first of four BWRX-300 reactors at Darlington in Clarington. Ontario approved the project the following month. Key details:
- Size: four units of about 300 MW each, roughly 1,200 MW in total — enough for many hundreds of thousands of homes.
- Cost: about $20.9 billion for all four units, with the first unit and shared site infrastructure budgeted at about $7.7 billion.
- Timeline: first unit targeted to be in service around 2030, with subsequent units to follow. Only the first unit is licensed for construction so far, and a separate operating licence will be needed.
- Indigenous participation: in June 2026, federal and provincial loan guarantees were announced to help the Williams Treaties First Nations take an ownership stake. Our article on Indigenous-led clean energy has more on equity partnerships.
Because it's the first of its kind in North America, Darlington is being watched closely by utilities in Canada and abroad.
Saskatchewan
Saskatchewan has no nuclear power today and relies heavily on natural gas and coal for electricity. SaskPower previously selected the BWRX-300 for potential deployment in the mid-2030s and has narrowed its focus to a site near Estevan in the province's southeast. Detailed siting, community engagement and a business case are planned before any final investment decision.
Other provinces
New Brunswick has explored advanced reactor designs at its Point Lepreau site, and Alberta has studied nuclear for both grid power and industrial heat in the oil sands. These efforts are at earlier stages. Our province guides cover each province's electricity mix and plans.
The case for SMRs
- Firm, low-carbon power: SMRs can run around the clock regardless of weather, which complements variable sources like wind and solar.
- Replacing fossil plants: In coal- and gas-dependent provinces, SMRs could provide steady output from existing grid connection points.
- Smaller footprint: They need far less land per megawatt than most renewables.
- Industrial heat: Some designs could supply high-temperature heat for industry.
The open questions
- Cost: First-of-a-kind projects are expensive, and it isn't yet clear how quickly costs will fall on later units.
- Schedule risk: Nuclear projects worldwide have a history of delays. The Darlington timeline has already shifted from early targets.
- Waste: SMRs produce spent fuel that must be safely stored. Canada's Nuclear Waste Management Organization is advancing plans for a deep geological repository for long-term disposal.
- Competition from alternatives: Wind, solar, storage and transmission links between provinces are also getting cheaper. Our explainer on electricity interties looks at one of those alternatives.
Frequently asked questions
Are SMRs safe?
SMRs are regulated by the Canadian Nuclear Safety Commission, the same body that oversees Canada's existing reactors, and many designs rely heavily on passive safety features. As with any nuclear facility, safety depends on rigorous design, construction, operation and oversight.
When will SMRs supply power to Canadian homes?
The first Darlington unit is targeted to be in service around 2030. Projects in other provinces, such as Saskatchewan, are aiming for the mid-2030s, subject to planning and approvals.
Will SMRs lower my electricity bill?
It's too early to say. Their impact on rates will depend on final construction costs, how many units are built and how they compare with other new generation options.
The bottom line
Small modular reactors are Canada's bet that nuclear power can be built smaller, more predictably and in more places. The Darlington project will be the real test: if it comes in on time and on budget, SMRs could become a significant part of a cleaner grid, especially in provinces that still burn fossil fuels for power. If costs and schedules slip, other options may win out.
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