Pickering, Darlington, Bruce and small modular reactors: Ontario's nuclear rebuild
Nuclear supplies about half of Ontario's power. Here's the timeline of retirements, refurbishments and new reactors.
Nuclear power is the backbone of Ontario's grid, supplying 48.5% of the province's electricity in 2025.1 Much of that fleet is decades old, so Ontario is retiring some reactors, rebuilding others and starting new ones.
Timeline
- 2024: Pickering units 1 and 4 retire.2
- Early 2026: Darlington's refurbishment finishes ahead of schedule and under budget, extending its reactors' lives by about 30 years.3
- September 2026: Pickering units 5 to 8 go offline ahead of a $26.8 billion refurbishment beginning in 2027 and running to the mid-2030s, securing about 2,100 MW for another 30-plus years.4
- Through the 2030s: Bruce Power's Major Component Replacement on Units 3 to 8 adds 30 to 35 years to each reactor.5
- End of 2030: the first of four BWRX-300 small modular reactors at Darlington is planned to be in service; the fleet would produce 1,200 MW.6
- Planning: OPG is exploring the Wesleyville site in Port Hope, which could host up to 10,000 MW.7
Why it affects supply
A reactor being rebuilt makes no power. With several offline at once, Ontario has relied more on natural gas: gas and other sources grew from 6% of transmission-connected output in 2018 to 16.6% of supply in 2025.81 The IESO counts these long outages among the reasons new supply is needed.9
What it means at home: while the big plants are rebuilt, reducing peak demand at home, with efficiency, batteries and off-peak use, eases pressure on the grid.
Sources
Figures are as reported by the sources listed, at the dates shown. Older figures are included for historical context. Canadian Energy Standard is an independent company, not affiliated with any government, utility, generator or energy retailer named here.
- Ontario Energy Board, Ontario's system-wide electricity supply mix: 2025 data
- Ontario Power Generation, Pickering Nuclear Generating Station
- NucNet, Darlington refurbishment construction completed ahead of schedule and under budget (February 2026)
- insauga, $26.8 billion nuclear refurbishment to begin in Pickering early next year (August 2026)
- Bruce Power, Life-Extension Program and Major Component Replacement
- Ontario Power Generation, Darlington small modular reactors
- Ontario Power Generation, Wesleyville new generation opportunity
- Financial Post, OPG's gas-plant purchases partly prompted by shifting nuclear landscape (August 2019)
- IESO, 2026 Annual Planning Outlook: Ontario's electricity system needs, 2027-2050 (March 2026)
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