Darlington SMR Project: Cost, Timeline and Plans

Ontario is building four 300 MW reactors at Darlington for $20.9 billion. Here is the timeline, the cost math and where Saskatchewan fits.

Ontario Power Generation is building four small modular reactors at its Darlington site in Bowmanville, Ontario, with a total budget of $20.9 billion and the first unit targeted to be complete by the end of 2030. It is the first grid-scale SMR project in Canada to reach construction. Saskatchewan has picked the same reactor design, and the project is now the reference case for what a small reactor costs in this country.

What a small modular reactor is

The Canadian Nuclear Association describes SMRs as reactors that generate between 10 and 300 megawatts of electricity. For comparison, Canada’s existing CANDU reactors average around 700 MWe each. The pitch is that smaller units built from repeatable designs can be added in steps, sited on smaller grids, and built faster once the first few are done.

Scale helps frame it. Four BWRX-300 units add up to 1,200 MW, which is roughly the output of 1.7 average CANDU reactors (1,200 divided by 700). The trade is fewer megawatts per unit in exchange for smaller, repeatable projects. Each new reactor in Canada needs three separate licences from the Canadian Nuclear Safety Commission: to prepare the site, to construct, and to operate.

Darlington will use the BWRX-300, a boiling water reactor from GE Hitachi rated at 300 MWe. OPG lists Aecon as the constructor. Each unit is expected to power about 300,000 homes, and all four about 1.2 million, according to OPG and the federal Major Projects Office.

Canada already relies on nuclear power. About 15% of the country’s electricity comes from nuclear, and Ontario drew roughly 48% of its electricity from nuclear in 2025, according to the World Nuclear Association. Canada has 17 commercial reactors, almost all CANDU units in Ontario, with one in New Brunswick.

The Darlington project, step by step

Date	Milestone
April 4, 2025	Canadian Nuclear Safety Commission issues the licence to construct
May 8, 2025	Final investment decision on four units, $20.9 billion total budget
September 11, 2025	Project referred to the federal Major Projects Office
October 24, 2025	Canada Growth Fund commits $2 billion for a 15% stake; Building Ontario Fund commits $1 billion for 7.5%
March 2026	CNSC clears the first regulatory hold point for foundation work; OPG applies for a licence to operate
June 23, 2026	Federal Indigenous loan guarantee of about $715 million announced for a Williams Treaties First Nations ownership stake
End of 2030	OPG’s goal for completing and connecting the first unit
Mid-2030s	Remaining three units expected

OPG keeps majority ownership and operational control. The two government funds described their role as temporarily sharing risks that limit private sector interest, with money for units two to four released as the project hits milestones. The federal government estimates 18,000 jobs a year during construction of all four units and 2,500 during operation, and says more than 80% of spending will go to Canadian companies.

What the $20.9 billion covers

OPG’s figure is an all-in budget. According to World Nuclear News, it includes licensing, engineering, procurement, construction, operations readiness, contingency, interest and escalation over the roughly 10-year build. Many international cost comparisons use “overnight” cost, which excludes financing and inflation, so the Darlington figure will look higher than those on a like-for-like basis.

First unit: $6.1 billion
Common infrastructure shared by all four: $1.6 billion
First unit plus common infrastructure: $7.7 billion
Fourth unit, projected: $4.1 billion, about a third less than the first

The math: cost per kilowatt

Dividing budget by capacity shows why the first unit matters so much. All figures are Canadian dollars and include financing and escalation.

Scope	Budget	Capacity	Cost per kW
First unit plus common infrastructure	$7.7 billion	300 MW	About $25,700
Fourth unit alone	$4.1 billion	300 MW	About $13,700
All four units	$20.9 billion	1,200 MW	About $17,400

The calculation: $7.7 billion divided by 300,000 kW is about $25,700 per kW. The drop to about $13,700 for the fourth unit is OPG’s own projection of learning and repetition, and it is the number the rest of the SMR plan depends on. Whether later units come in at that level is something the public record will show over the next decade.

The wider push across Canada

Darlington sits inside a policy framework that has been building since 2018.

2018: Natural Resources Canada publishes the SMR Roadmap after a 10-month national consultation, with more than 50 recommendations.
December 2019: Ontario, New Brunswick and Saskatchewan agree to work together on SMRs. Alberta joins in August 2020.
December 2020: Ottawa launches Canada’s SMR Action Plan to carry out the roadmap.

Saskatchewan is next in line. SaskPower selected the BWRX-300 after a four-year evaluation and is studying two potential sites near Estevan, one by the Boundary Dam Reservoir and one near the Rafferty Reservoir. SaskPower says it expects a final investment decision in 2029 and possible operation in the mid-2030s. It needs three separate CNSC licences: to prepare the site, to construct, and to operate.

New Brunswick has been pursuing advanced reactor designs at its Point Lepreau site, and smaller micro-reactor concepts are being studied for remote communities and mines. Those are at earlier stages than Darlington. For how SMR demand ties into fuel supply, see our piece on data centre power and uranium, and for the approvals side, how the Major Projects Office works.

What to watch

The CNSC public hearing schedule for Darlington’s licence to operate.
OPG quarterly and annual reports for spending against the $20.9 billion budget and schedule updates.
Construction milestones on the first unit, including remaining CNSC hold points.
SaskPower’s site selection near Estevan and its application for a licence to prepare a site.
Updates on the Major Projects Office page for the Darlington New Nuclear Project.

Sources

Frequently asked questions

How much does the Darlington SMR project cost?

Ontario Power Generation set a total budget of $20.9 billion for four BWRX-300 reactors at Darlington. The first unit costs $6.1 billion plus $1.6 billion for infrastructure shared by all four, or $7.7 billion together. OPG projects the fourth unit at $4.1 billion. The budget includes contingency, interest and escalation, not only construction costs.

When will the Darlington SMR be finished?

OPG’s goal is to complete the first 300 MW unit and connect it to the grid by the end of 2030. The remaining three units are expected in the mid-2030s. The CNSC issued the licence to construct on April 4, 2025, and OPG made its final investment decision on May 8, 2025, then applied for a licence to operate in March 2026.

What is a small modular reactor?

The Canadian Nuclear Association describes small modular reactors as reactors generating between 10 and 300 megawatts of electricity, compared with about 700 MWe for Canada’s average CANDU reactor. The Darlington project uses the BWRX-300, a 300 MWe boiling water reactor from GE Hitachi. Each unit is expected to power about 300,000 homes.

Small Modular Reactors in Canada: The Darlington SMR Project Explained