On April 22, 2026, one of the world’s largest crawler cranes lowered a 953-tonne module with millimetre precision into a 35-metre-deep excavation at the Darlington site in Ontario. That single piece of steel and concrete is the reactor basemat — the physical foundation of the Western world’s first grid-scale SMR. The project belongs to provincial utility Ontario Power Generation, and the reactor is the BWRX-300 developed by GE Vernova Hitachi Nuclear Energy.
Known as the Basemat, the structure measures 37 metres in diameter and serves as the shared foundation for both the reactor building and the containment structure. It was assembled as a single unit before being lifted into place, using a steel-concrete composite diaphragm construction method. This marks the first time in Canada that a reactor building foundation has been built using modular construction — a milestone OPG described as “putting the M in SMR.” Under international convention, the placement of a reactor foundation officially marks the moment a project becomes a nuclear unit under construction. From that day forward, Darlington is no longer a project: it is a reactor.
The construction licence had been issued by the Canadian Nuclear Safety Commission in April 2025, followed within days by final approval from the Province of Ontario. The total approved budget for all four planned units stands at CAD 20.9 billion (approximately USD 15 billion), with the first reactor estimated at CAD 6.1 billion. The federal government contributed CAD 2 billion through the Canada Growth Fund, while Ontario added CAD 1 billion via the Building Ontario Fund. OPG has already filed an operating licence application with the CNSC — a prerequisite for loading fuel and connecting the unit to the grid. The target is to bring the first reactor online by 2030.
The BWRX-300 is a 300-megawatt natural-circulation boiling water reactor equipped with passive safety systems. It derives its technical and licensing basis from the ESBWR, a design certified by the U.S. Nuclear Regulatory Commission. Each unit will generate enough electricity to power approximately 300,000 homes and is roughly one-tenth the size of a conventional boiling water reactor. Four units combined would bring the site’s total capacity to 1,200 megawatts. The fuel is standard low-enriched uranium, the same type used by the majority of reactors worldwide. Each unit’s construction footprint is comparable to a football pitch. More than 100 Canadian companies have already secured supply chain contracts, with 80% of spending directed toward Ontario-based firms.
Darlington is only the starting point. The Tennessee Valley Authority has filed a construction permit application with the U.S. NRC for a BWRX-300 at the Clinch River site, backed by a USD 400 million federal grant. In Poland, ORLEN Synthos Green Energy is targeting a fleet of around 24 units across six sites. Sweden, Estonia, Hungary, and the Canadian province of Saskatchewan are pursuing the same path. The economic case for SMRs hinges on standardisation: build the same machine repeatedly to drive down costs. Darlington is the reference unit. If construction stays on schedule, every subsequent project will have real-world data to underpin its forecasts — and the entire sector will shift to a new scale.
