Ontario Power Generation (OPG) said work has continued on the commercial, grid-scale small modular reactor (SMR) under construction at Darlington New Nuclear Project (DNNP). In June, Candu Energy, part of Canada’s AtkinsRéalis, was awarded a CAD450m ($327m) execution contract by OPG, for the first of four planned SMR units at DNNP. In May, Ontario and OPG approved construction of GE Vernova Hitachi Nuclear Energy’s (GVH’s) BWRX-300 SMR, clearing the way for construction to with completion of the first unit scheduled by the end of the decade. Early site preparation work at Darlington was completed and in April the Canadian Nuclear Safety Commission granted OPG a licence to construct the first unit.
OPG says that since May, the project has achieved several major milestones, including the arrival of all components for a massive tunnel boring machine. In July, after months of meticulous planning and coordination, the project’s tunnel excavating machine, named Harriet Brooks after Canada’s first female nuclear physicist, finished its journey from overseas to the project site. “Each piece of this big digger, from the massive cutterhead to the smallest bolt, will be safely stored until its assembly begins in early 2026.”
Once operational, the 6.97-metre-width Harriet Brooks tunnel boring machine will be used to bore and line a 3.4-kilometre-long tunnel for the project’s condenser cooling water system – a key operational feature critical to bringing the first SMR online.
Elsewhere, OPG and its partners, with the help of skilled trades from across Ontario, have been fabricating the structural components of the building that will house the reactor itself. Production of these components, called diaphragm plate steel composite (DPSC) modules, are progressing at an offsite fabrication shop, with the first assemblies that make up the Basemat module – the foundation of the reactor building – being delivered to site. Once the reactor building shaft is completely excavated, a heavy crane will lift the Basemat and place it at the bottom of the shaft, 35 metres in the ground.
Meanwhile, construction of the on-site pre-assembly building is now complete and ready for use. The facility will support the final assembly of reactor building structural components for the first SMR unit. The fabrication building, where final assembly of modular building components will take place, is also now complete, as is foundation work for the radiation waste building and control and service buildings.
Excavation work is continuing on the reactor building shaft, forebay shaft, and the condenser cooling water launch shaft, while site grading for three additional SMR units has officially been completed. In parallel to the on-site progress, OPG continues to advance planning and licensing activities for the subsequent SMR units in its planned fleet.
Deploying and operating four SMRs is expected to increase Canada’s GDP by CAD38.5bn over 65 years, according to the Conference Board of Canada. And over the next 65 years, OPG’s SMR fleet is expected to sustain, on average, about 3,700 jobs per year, including 18,000 jobs per year during construction.
OPG said about 80% of project spending will go to more than 80 companies across Ontario and construction of the SMR fleet is expected to drive CAD500m annually into the province’s supply chain. “To ensure a successful buildout, OPG will be leveraging more than 7,000 lessons learned from its Darlington Refurbishment project, which remains on track to be completed in early 2026. The company will also incorporate lessons learned from the construction of the first SMR to the rest of the fleet.”
Meanwhile, the DNPP has been named as one of five projects to be reviewed by Canada’s newly established Major Projects Office (MPO). The MPO was created under the Building Canada Act, which came into force in June 2025. It was launched on 29 August under the leadership of its first CEO Dawn Farrell.
The MPO said DNPP will make Canada the first G7 country to have an operational SMR, accelerating the commercialisation of a key technology that could support Canadian and global clean energy needs while driving CAD500m annually into Ontario’s nuclear supply chain. “Once complete, Darlington’s first of four planned SMR units will provide reliable, affordable, clean power to 300,000 homes, while sustaining 3,700 jobs annually, including 18,000 during construction, over the next 65 years. The project has the potential to position Canada as a global leader in the deployment of SMR technology for use across the country and worldwide.”
