Three of the four reactors at Ontario’s Darlington Nuclear Generating Station are currently offline, leaving only Unit 1 supplying power to the grid. Unit 4 ceased generation on 1 August, marking its third unplanned shutdown since returning to service earlier this year, while Unit 2 stopped supplying electricity just two days later. Unit 3 has been out of service for several months due to scheduled maintenance.
Outage Details and Official Statements
Ontario Power Generation confirmed that Units 2 and 4 were taken offline “to complete required maintenance.” Spokesperson Neal Kelly said Unit 2 is expected to restart in September and Unit 4 in October. The Canadian Nuclear Safety Commission noted that the forced outages were reported to its staff, with inspectors maintaining regulatory oversight. Braeson Holland of the CNSC added that staff are satisfied the events pose no risk to health, safety or the environment.
Each Darlington reactor contributes roughly 900 megawatts, giving the station a total capacity of about 3,500 megawatts – the second‑largest in the province after the eight‑reactor Bruce Nuclear Generating Station. Meanwhile, OPG’s Pickering plant, with four operational reactors totalling 2,100 megawatts, is set to shut down next month for a £26.8‑billion refurbishment slated for completion in the mid‑2030s.
Financial and Grid Implications
Unplanned outages can cost a utility £1 million or more per day in lost revenue, and sudden swings in generation place additional stress on the power grid. David Novog, a professor of engineering at McMaster University who specialises in nuclear safety and maintenance, stressed that utilities invest heavily to avoid such disruptions because each reactor represents a high‑value asset on the system.
OPG’s July filing to the Ontario Energy Board projected 286 outage days at Darlington in 2026 – the highest total since at least 2008 – and warned that the recent forced outages are likely to push that figure even higher. For 2027, the utility forecasts 512 planned outage days, including a major steam‑generator overhaul on Unit 2, and expects the entire station to be offline for nearly 46 days next year while work proceeds on its vacuum building.
Expert Commentary and Future Outlook
Novog observed that repeatedly stopping and starting reactors is atypical of normal operations. He noted that both Bruce and Darlington experienced many unplanned outages in their early years, but Darlington’s units ran exceptionally well in the period leading up to the recent refurbishment. He urged OPG to publish more detailed information about outages, warning that a lack of transparency can fuel speculation and erode public confidence.
Provincial officials have reiterated that Ontario’s nuclear projects were delivered ahead of schedule and under budget, a point echoed by Energy Minister Stephen Lecce at a recent press conference in St Clair Township. As nuclear output has dipped due to refurbishments and outages, the province has increased reliance on natural‑gas‑fired plants. Gridwatch data showed that on a recent Thursday afternoon, the 11 operational reactors supplied 38.5 percent of Ontario’s electricity, compared with 31.5 percent from gas plants. For 2024 and 2025, nuclear generation has averaged roughly half of the province’s power, while gas has contributed less than 20 percent.
Why it Matters
The recurring shutdowns at Darlington underscore the fragility of Ontario’s nuclear backbone just as the province leans on atomic energy to meet climate goals and curb reliance on fossil fuels. With costly refurbishments underway at both Darlington and Pickering, any further erosion of reactor availability could drive up electricity prices, increase greenhouse‑gas emissions from gas‑filled generation, and shake investor confidence in Canada’s nuclear ambitions. Transparent, timely communication from OPG and rigorous regulatory oversight will be essential to maintain grid stability and public trust during this critical transition period.
