Refurbishment of the four-unit Darlington Nuclear Generating Station (DNGS) has been completed four months ahead of schedule and CAD150m ($110m) under budget. DNGS comprises four Candu reactors with a total output of 3,512 MWe. Candu units are pressurised heavy water reactors designed to operate for 30 years before refurbishment. Units 1-3 are currently operating and refurbished with unit 4 expected to restart operation in the coming weeks. Ontario Power Generation (OPG) said station staff are now completing final testing ahead of the unit returning to full commercial operation.
In September 2025, the Canadian Nuclear Safety Commission (CNSC) granted OPG a 20-year licence for the Darlington Nuclear Generating Station, authorising OPG to operate the station until 30 November 2045, which is the longest nuclear operating licence granted to date in Canada.
The CAD12.8bn Darlington Refurbishment Project, which began in 2016, will extend the plant’s operating life to at least 2055. Unit 2, the first to be refurbished, returned to service in June 2020 followed by unit 3 in July 2023 and unit 1 in November 2024.
Refurbishment work included replacing a total of 1,920 fuel channels, 3,840 feeder pipes, calandria tubes, and end fittings, as well as rehabilitating other critical components. The project also included system improvements and plant upgrades to meet current regulatory requirements. OPG said that, with approximately 8,000 lessons learned, it will continue to leverage this experience to execute future projects, including the CAD 26.8bn Pickering Nuclear Generating Station refurbishment, the deployment of four small modular reactors (SMRs) at the Darlington site, and a proposed large nuclear development in Port Hope.
“This is a momentous achievement for OPG, Ontario, and Canada,” said Nicolle Butcher, OPG’s President and CEO. “Through this project, we have demonstrated to the world that complex nuclear projects can be completed successfully, ahead of schedule and under budget. Our experience on this refurbishment, and the thousands of lessons we have learned, will serve as our foundation as we advance nuclear’s future. Darlington’s refurbishment has given us the confidence, the tools, and the skills to forge ahead.”
The project’s success reflects a decade of meticulous planning and preparation, all of which took place before any work began. This included the construction of the world’s first full-scale reactor mock-up, which helped to train and prepare workers before they stepped into the reactor vault.
“Ontario is proving to the world that we can deliver major nuclear energy projects on-time and on-budget,” said Stephen Lecce, Ontario’s Minister of Energy and Mines. “Last year we returned another refurbished unit at Darlington four months ahead of schedule, and today we’ve done it again. Completing the full Darlington refurbishment on-time and under-budget is a made-in-Canada win for our economy, generating CAD90bn in economic benefits and supporting 14,200 good-paying jobs.”
He added “In a world of uncertainty, our government is doubling down on Canadian nuclear technology and workers, with 96% of investment benefiting Ontario’s supply chain. It is a tremendous industrial advantage that Canada is among only six nations that own civilian nuclear technology, yet we stand alone as number one in building, operating, and refurbishing projects on-time and on-budget.”
