Ontario has completed the refurbishment of the fourth and final reactor at the Darlington Nuclear Generating Station months ahead of schedule and under budget, marking a major milestone for the province’s energy system and industrial base.
Energy and Mines Minister Stephen Lecce announced on Monday that construction work on Darlington Unit 4 is finished, clearing the way for the reactor to return to service four months earlier than planned. The broader refurbishment program, which involved all four units at the site, was delivered $150 million under budget, according to the province.
The Canadian Nuclear Safety Commission has approved the unit to begin initial power testing, expected to start on February 12. Full power is anticipated shortly after, well ahead of the original August 2026 return-to-service date.
“Ontario is proving to the world that we can deliver major nuclear energy projects on-time and on-budget,” Lecce said. “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 $90 billion in economic benefits and supporting 14,200 good-paying jobs.”
The Darlington refurbishment extends the operating life of the nuclear station to at least 2055 and completes what the province describes as the world’s largest nuclear refurbishment project to date. Once all four units are fully back online, the station will provide more than 3,500 megawatts of emission-free electricity—enough to power about 3.5 million homes—for the next three decades.
The long-term economic impact is significant. Ontario estimates the refurbishment and continued operation of Darlington over the next 30 years will generate up to $90 billion in economic benefits and support approximately 14,200 jobs across the province.
More than 6,000 Ontario workers were involved in the refurbishment, including skilled tradespeople, project managers and support staff. Work included replacing thousands of fuel channels, feeder tubes and other major components, as well as modernizing systems to meet current regulatory requirements. During the construction phase alone, the project contributed an estimated $14.9 billion to Ontario’s gross domestic product.
The province says 96 per cent of project spending remained in Ontario, with every dollar invested generating an average $1.30 increase in provincial GDP. Officials argue this local retention highlights the strength of Ontario’s nuclear supply chain and workforce.
Nuclear energy continues to anchor Ontario’s electricity system, providing roughly half of the province’s power supply. With electricity demand expected to rise sharply by 2050, nuclear generation is seen as critical to supporting population growth, housing construction and advanced manufacturing.
Ontario Power Generation president and chief executive Nicolle Butcher said the Darlington project demonstrates the province’s capacity to execute complex nuclear work while preparing for future expansion.
“Bringing the Darlington refurbishment in ahead of schedule and under budget will clearly demonstrate our team’s ability to deliver large and complex nuclear projects,” Butcher said. “The skills we developed and lessons we learned during this project are invaluable as we proceed with refurbishing Pickering Nuclear Generating Station, continue construction on the G7’s first Small Modular Reactor at the Darlington New Nuclear Project, and study the potential for up to 10,000 MW of new nuclear at Wesleyville.”
Ontario is positioning itself as a global leader in nuclear energy, with three operating nuclear stations and the first grid-scale small modular reactor under construction in the G7. The province has emphasized its track record of completing large-scale refurbishments on time and on budget as it looks to attract investment and maintain energy security.
The Darlington refurbishment is a cornerstone of Energy for Generations, Ontario’s first integrated long-term energy plan. The government says the strategy is designed to provide certainty for Indigenous communities, municipalities, businesses and industry partners while supporting economic growth and job creation.
With Unit 4 nearing full power, the Darlington station is set to resume its role as a key supplier of clean, reliable electricity to Ontario households and businesses. Provincial officials argue the project’s early completion strengthens confidence in the province’s ability to meet rising demand while maintaining affordability and emissions-free generation.
As Ontario prepares for a new phase of nuclear development, including refurbishments and new builds, the Darlington experience is being held up as a benchmark for future projects—one that supporters say underscores the province’s industrial capability and long-term energy resilience.
