Weighing in at close to 953 tonnes (2.1 million pounds) - more than the weight of three Airbus A380 aircraft - and with a diameter of 37 metres, the Basemat is the foundation for the integrated reactor building and containment structure. It was fabricated, welded, and put together in one piece before being lifted into place by one of the world's largest crawler cranes. This is the first time in Canada that a foundation for a reactor building has been assembled modularly, "putting the 'M' in SMR", according to Ontario Power Generation (OPG).
For conventional large-scale nuclear power plants, the pouring of the first concrete for the reactor's basemat is usually taken as marking the point at which a project becomes a nuclear power unit under construction.
The Basemat module features components made of Diaphragm Plate Steel Composite, an innovative and ground-breaking modular steel-concrete material, which were produced by OPG and its partners, with the help of skilled trades from across Ontario.
The Province of Ontario approved OPG to begin construction of the first of four GE Hitachi BWRX-300 small modular reactors (SMRs) planned at the Darlington New Nuclear Project site in May 2025, weeks after the Canadian Nuclear Safety Commission (CNSC) issued a construction licence. Early site preparation works began in the autumn of 2022 and were completed in early 2024, clearing the way for main preparation works to begin. The company recently submitted its application to the CNSC for a licence to operate the plant: it plans to connect the first unit to the grid by the end of 2030.
The basemat was lifted into place in a precision operation (Image: OPG)
Building the chain
Alongside the basemat lift, the Ontario government announced that more than 100 Canadian companies have now signed on to the supply chain to support SMR builds, with the recent addition of 16 new Ontario-based companies and six companies from Quebec and Alberta. Recently awarded contracts include Walters Group, which has been awarded a CAD44.5 million (USD32.8 million) contract for structural steel; Marmon Industrial Water, with a CAD17.8 million contract for a condensate purification package; Tractel, with a CAD9.9 million contract for the reactor building weather enclosure; and Hooper Welding, awarded a CAD8.8 million contract for sampling and collection tanks.
"Ontario just executed with great precision the first foundation of a new nuclear reactor in Ontario in over 30 years," Ontario Minister of Energy and Mines Stephen Lecce said. "This is a major achievement as the world turns to Ontario to refurbish and build large scale nuclear on-time and on-budget."
The SMR supply chain is "infusing" more than CAD500 million into Ontario's economy, Lecce added: "Our government is deeply committed to building more in Canada, which is why we are proud to invest at least 80 per cent of every dollar in the Canadian supply chain."
"With the foundation of the first small modular reactor at the Darlington New Nuclear Project in place, we are now able to begin building up, with the project team now advancing construction on the reactor building's structure, internal systems and components," said Nicolle Butcher, OPG President and CEO. "This was a milestone months in the making, requiring significant attention to detail and safety, as well as the hard work of dedicated trades and project partners from across Ontario."
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