OPG Sets Reactor Foundation at Darlington, Pushing the G7's First Commercial SMR Past Its First Regulatory Hold Point
Ontario Power Generation has placed the foundation module for the first BWRX-300 small modular reactor at Darlington, clearing the construction licence's first hold point and beginning above-ground reactor work on what is on track to be the G7's first commercial SMR.
Overview
Ontario Power Generation (OPG) has placed the reactor building foundation for the first GE Vernova Hitachi BWRX-300 small modular reactor at the Darlington New Nuclear Project site in Clarington, Ontario, clearing the first regulatory hold point in the project’s construction licence and beginning above-ground reactor structure work on what is set to be the first operating commercial SMR in any G7 country. The BWRX-300 deployment at Darlington is the most advanced commercial SMR project in North America, ahead of a Tennessee Valley Authority site in the United States that filed for a construction permit in May 2025.
What We Know
The Darlington SMR programme is a four-unit deployment of GE Vernova Hitachi Nuclear Energy’s BWRX-300, a 300-megawatt-electric water-cooled, natural-circulation boiling water reactor. According to Utility Dive, the project is the first commercial SMR contract in North America and assigns specific roles to each consortium member: OPG holds the operating licence and oversight responsibility, SNC-Lavalin is the architect-engineer, and Aecon Group leads construction services and project management. The BWRX-300 uses commercially available fuel rather than high-assay low-enriched uranium (HALEU), a deliberate design choice intended to keep its supply chain inside existing commercial nuclear channels.
The regulatory framework for the foundation work was set in April 2025. According to the Canadian Nuclear Safety Commission, the Commission issued OPG nuclear power reactor construction licence PRCL 32.00/2035 for one BWRX-300 reactor at the Darlington New Nuclear Project site, valid until March 31, 2035. The CNSC concluded that OPG was qualified to carry out the licensed activities and had adequate programs in place to protect workers, the public, and the environment, and that the licensee would maintain national security and Canada’s international obligations under the licence. The decision followed a two-part public hearing held virtually on October 2, 2024, and in person in Ajax, Ontario from January 8 to 14, 2025. The construction licence is gated by a series of regulatory hold points, of which the foundation hold point had to be cleared before the reactor building basemat could be installed.
When all four units are complete the Darlington SMR site is intended to deliver a combined 1,200 megawatts of electricity. According to Axios, Ontario officials gave final provincial approval in May 2025 to construct the first BWRX-300 adjacent to OPG’s existing Darlington Nuclear Station, and Ontario’s energy ministry stated that the unit would be the first SMR of its kind in the G7. The first reactor is sized to power roughly 300,000 homes, and early site preparation was already complete when provincial approval was granted, with construction expected to start soon and the reactor expected online by 2030.
The BWRX-300 is the most commercially advanced of the SMR designs currently being deployed in North America. As reported by Utility Dive, one BWRX-300 unit is under construction at Darlington with a target to come online by 2029, and in May 2025 the Tennessee Valley Authority became the first U.S. utility to submit a construction permit for a planned BWRX-300, with TVA targeting operation in the early 2030s. The same outlet describes the BWRX as a conventional boiling water reactor in which the core heats and partially boils pure water to produce steam for the main generator, a thermal cycle GE has built and operated commercially for decades, repackaged in a smaller, factory-friendlier form factor.
What We Don’t Know
The foundation milestone removes one regulatory hold point but does not by itself confirm the project will hit its 2030 in-service target. Two further CNSC hold points remain in the construction licence, and OPG has not yet received a separate licence to operate, which will require a further public hearing under the CNSC’s regulatory process before any reactor can produce power.
The schedule has also slipped at least once already. According to Utility Dive, the original commercial contract for the Darlington SMR targeted completion in the fourth quarter of 2028, an earlier date than current public statements that point to 2029-to-2030 grid connection. The gap between that initial target and present timelines underscores how SMR schedules have already moved once before reaching the foundation stage, and the gap may grow or shrink as construction proceeds.
The economics of the broader four-unit programme are also unresolved in the sources reviewed. Only the first unit is fully licensed for construction; the three remaining BWRX-300 units exist as planning intent rather than under regulatory authorization. The cost trajectory of the subsequent units, the timing of their CNSC submissions, and the degree to which lessons learned from Unit 1 will reduce schedules and capital costs for Units 2 through 4 have not been disclosed.
Finally, the wider commercial deployment story remains unproven. According to Utility Dive, the BWRX-300 has made significant progress toward commercialization, but no unit anywhere has yet generated grid power. Until Darlington Unit 1 completes hot functional testing, achieves first criticality, and connects to the Ontario grid, the BWRX-300 remains a paper-licensed design with one foundation poured rather than a demonstrated commercial product.
Why It Matters
The foundation lift is the first physical, irreversible step in turning the BWRX-300 from regulatory paperwork into a power-generating reactor. Most SMR projects worldwide remain in licensing, design, or site-preparation phases; Darlington Unit 1 is now past the line where capital is committed in steel and concrete rather than in studies. Whether the BWRX-300 ultimately delivers the cost and schedule advantages GE Hitachi has promised will be tested at Darlington first, and the outcome will shape decisions on the three follow-on Ontario units, on the Tennessee Valley Authority’s BWRX-300 plans, and on prospective deployments elsewhere.