Ontario Authorizes OPG to Start Construction of First Commercial Nuclear SMR

Ontario’s provincial government has given Ontario Power Generation (OPG) the green light to begin construction on the first of four BWRX-300 small modular reactors (SMRs) at its Darlington New Nuclear Project (DNNP) site in Clarington, Ontario. “This represents the first new nuclear build in Ontario in more than three decades,” the utility noted.

The province on May 8 formally authorized OPG to proceed with full-scale nuclear construction following the Canadian Nuclear Safety Commission’s April issuance of a Licence to Construct for the first unit. The Darlington project, now slated to begin commercial service by the end of 2030, remains the most advanced SMR build in North America and positions Ontario as a global first mover on commercial, grid-scale deployment of SMRs.

“This is truly a historic moment,” said Nicolle Butcher, OPG’s president and CEO. “This made-in-Ontario project will support provincial companies, create jobs for Ontarians, and spur growth for our economy. OPG is proud to be leading this first-of-a-kind project. With the province’s robust nuclear supply chain and our successful track record on nuclear projects, particularly our Darlington Refurbishment, we are confident we will be able to deliver the first SMR unit for Ontario, on time and on budget.”

A Major SMR Milestone

OPG, a crown corporation, first unveiled its selection of GE-Hitachi’s BWRX-300 boiling water reactor (BWR) design for the site in December 2021 following a competitive evaluation, and it anticipates, pending regulatory approval, that the first unit could commence operations by the end of 2029. In July 2023, it initiated planning and licensing for three additional SMRs at the DNNP site, bringing its potential capacity to about 1.2 GW. The projected in-service dates for the three additional SMRs are in the mid-2030s, between 2034 and 2036.

Ontario officials on Thursday noted the project will be the first grid-scale small modular reactor under construction in any G7 country. The province noted Ontario’s Independent Electricity System Operator (IESO) concluded the four planned units represent the least-cost, lowest-risk option to meet a projected 75% rise in electricity demand by 2050, compared with alternatives like wind, solar, and battery storage.

OPG said construction of the SMR fleet has so far been preceded by significant onsite activity. Since 2022, OPG’s DNNP team has completed extensive grading and utility installation, relocated clean fill, and advanced early infrastructure such as fire protection and water systems. Buildings for on-site fabrication and support services are also well into development.

Excavation is currently underway for the reactor building shaft—a major civil works milestone. Fabrication is also progressing on several long-lead components. BWXT, at its Cambridge, Ontario, facility, has begun cladding work for the reactor pressure vessel—the largest component of the SMR, a 550-tonne vessel that will house the reactor core, coolant, and support structures.

The generator rotor, a critical component of the turbine-generator system that converts nuclear heat into electricity, has also been forged and is undergoing pre-machining. OPG suggests the component is expected to arrive at the site by summer 2027.

Later this year, the project’s tunnel boring machine—nicknamed “Harriett Brooks” after Canada’s first female nuclear physicist—is set to arrive from Germany and will be assembled in 2026. The machine is expected to carve a 3.4-kilometer-long, 6-meter-diameter tunnel for condenser cooling water beneath the site.

OPG has indicated that roughly 80% of project spending will remain in Ontario, with more than 80 local companies expected to participate in the project’s supply chain. Annual economic activity from the SMR fleet could inject more than $500 million into Ontario’s economy during the construction phase, it said.

Cost Projected at C$7.7B

Ontario has pegged the total DNNP budget at C$20.9 billion, which includes site preparation, engineering, design, and construction of all four SMRs. The province said the project will sustain approximately 3,700 jobs annually for 65 years, and contribute an estimated C$38.5 billion to Canada’s GDP over that time. Ontario also said it is pursuing financial instruments to help reduce overall ratepayer costs and is working with OPG to explore potential equity partnerships with the Williams Treaties First Nations—an initiative that could mark a first-of-its-kind ownership structure in Canadian nuclear generation.

Although Ontario Power Generation (OPG) has not formally disclosed a detailed cost breakdown, Ontario Energy Minister Stephen Lecce told the Associated Press, as reported on May 8, that the first BWRX-300 unit will cost a combined C$7.7 billion—C$6.1 billion for the reactor itself, plus C$1.6 billion for systems and services common to all four planned units at the Darlington New Nuclear Project site. The news agency reported, citing Lecce, that the cost of subsequent units is expected to decline as efficiencies are gained through first-of-a-kind execution. OPG maintains that its early-stage work—including site preparation, long-lead procurement, and lessons learned from the Darlington Refurbishment—will help ensure the first SMR is delivered on time and on budget.

As POWER has reported, the project is backed by a six-year alliance among OPG, GE Hitachi Nuclear Energy, SNC-Lavalin, and Aecon—an industry-first integrated project delivery (IPD) model for a grid-scale SMR in North America. The agreement brings together reactor design, engineering, construction, and oversight under a single collaborative framework structured to reduce risk, streamline decisions, and prevent cost and schedule overruns. OPG leads the alliance as a license holder and operator; GEH supplies the BWRX-300 technology and key components; SNC-Lavalin serves as architect-engineer; and Aecon leads construction.

The Tennessee Valley Authority (TVA) in January 2025 formed a similar alliance with Bechtel, Sargent & Lundy, and GE Hitachi to spearhead the initial planning and design phases for a potential BWRX-300 SMR at its Clinch River Nuclear site in Oak Ridge, Tennessee. TVA in April submitted the first portion of its construction permit application to the U.S. Nuclear Regulatory Commission, including an environmental report and general administrative details. The utility plans to file a Preliminary Safety Analysis Report by June, and the NRC has initiated an acceptance review of the submittal.

—Sonal Patel is a POWER senior editor (@sonalcpatel, @POWERmagazine).