Canada Approves First Grid-Scale SMR Construction at Darlington
The Canadian Nuclear Safety Commission (CNSC) has given Ontario Power Generation (OPG) the green light to begin building a 300-MW GE-Hitachi BWRX-300 small modular reactor (SMR) at the Darlington New Nuclear Project (DNNP) site in Clarington, Ontario. The historic approval marks the first time Canada has approved the construction of a grid-scale SMR.
The federal nuclear safety body issued its decision on April 4 following a two-part public hearing on OPG’s application, which concluded in January 2025. OPG submitted the application to construct a BWRX-300 reactor in October 2022, and in April 2024, the CNSC determined that the existing environmental assessment for the Darlington New Nuclear Project (DNNP) remained applicable to the selected SMR technology. The resulting Licence to Construct, which is valid until March 31, 2035, includes four site-specific conditions that, alongside standard licensing requirements, enable effective regulatory oversight.
The conditions require OPG to implement mitigation measures and commitments identified during the Darlington Joint Review Panel process, maintain an environmental assessment follow-up program, obtain regulatory approval before removing established hold points, and continue Indigenous engagement activities throughout the license term. The CNSC also accepted OPG’s proposed financial guarantee—a CA$167.18 million letter of credit—to cover future decommissioning and waste management responsibilities.
The current license, however, only permits construction. A separate CNSC authorization—a License to Operate—will be required to operate the reactor, including a future licensing hearing and public process.
Setting the Stage for the First BWRX-300 Construction in North AmericaOPG, 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 competivie 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.
CNSC originally granted OPG a site preparation licence in 2012, allowing the utility to begin work on necessary infrastructure while awaiting a future licence to construct. That site preparation licence was renewed in 2021 and remains valid through 2031.
So far, DNNP is “currently in the definition phase, which includes activities such as progressing detailed engineering, completing construction planning, procuring long-lead items and completing site preparation activities,” OPG said in its March 2025–released annual report. “In June 2024 and November 2024, respectively, the project completed the tunnel boring machine launch shaft retaining wall for the condenser cooling water system and the reactor building shaft retaining wall.”
Site preparation activities necessary for “the start of construction for the first SMR have been substantially completed,” it noted. OPG, for now, is continuing to progress with “planning and procurement of long-lead items such as the fabrication of the reactor pressure vessel (RPV),” the unit’s largest component, which acts as the primary pressure vessel and integrated steam generator. In January 2025, OPG awarded GE Hitachi a contract to manufacture the RPV.
As POWER has reported, the project is also 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.
OPG views the DNNP as a cornerstone of a strategy to ensure long-term energy security and support electrification amid surging demand in Ontario. “With electricity demand projected to grow by as much as 75% between now and 2050 we know there will be a need for new generation,” noted CEO Nicolle Butcher in the company’s latest annual report. As a first-mover, OPG has set out to lay the groundwork for a domestic SMR supply chain, stating the project will “build a foundation for further growing Ontario and Canada’s nuclear supply chains,” the report suggests.
OPG is notably spearheading several major nuclear projects, including the Darlington Refurbishment, a massive, multi-unit nuclear modernization project to refurbish the 3.5-GW Darlington Nuclear Generating Station. Three of the station’s four CANDU units—Units 2, 3, and 1—have now returned to service, with Unit 1 completed five months ahead of schedule in November 2024, and Unit 4 refurbishment underway and on track for completion in 2026.
OPG is also advancing plans to refurbish the Pickering Generating Station, with the project now in its definition phase and supported by a CA$6.2 billion Board-approved budget. If approved, the mid-2030s in-service timeline could preserve more than 2,000 MW of reliable baseload capacity. In parallel, the company is undertaking extensive hydroelectric upgrades, including a 25-unit overhaul at Sir Adam Beck, 16-unit work at R.H. Saunders, and redevelopment across eight stations along the Madawaska and Ottawa Rivers involving 45 units in total.
In January 2025, Ontario directed OPG to explore more new nuclear generation at the Wesleyville site. “Based on OPG’s early assessment, the Wesleyville site could host up to 10,000 MW of new nuclear energy generation, which could power the equivalent of approximately ten million homes. OPG will work with local communities and First Nations to determine their support for a potential project as part of the exploration process.” OPG is also engaging Indigenous and municipal partners at Nanticoke and Lambton—sites with pre-existing infrastructure and zoning.
—Sonal Patel is a POWER senior editor (@sonalcpatel, @POWERmagazine).
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