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Update ·

Ontario Nuclear: The Dip Before the Surge

Darlington's refurbishment is done, Pickering B has just come offline, and Canada's first SMR is due on the grid by the end of 2030. The next five years are about rebuilding the fleet; the big new megawatts come in the 2030s.

Nuclear is the backbone of Ontario's grid. In 2025 it produced about 48% of the province's electricity from roughly 32% of its transmission-connected capacity. The province now plans to grow that fleet, not just keep it: its 2025 energy plan, Energy for Generations, expects demand to rise about 75% by 2050 and allows for up to 17,800 MW of new nuclear capacity.

The next five years are not about new megawatts arriving. They are about rebuilding the existing fleet, finishing the first small modular reactor, and getting two large new stations through licensing.

The fleet today

Before this fall, Ontario had about 12,000 MW of nuclear capacity, all CANDU pressurized heavy water reactors:

  • Bruce (Bruce Power, 8 units): about 6,550 MW peak.
  • Darlington (OPG, 4 units): about 3,500 MW.
  • Pickering B (OPG, units 5 to 8): about 2,000 MW. Pickering's last two A units closed in 2024.

Refurbishment: keeping 12 GW running into the 2060s

Darlington is finished. Unit 4 returned to full power in early 2026, completing a C$12.8 billion, four-unit refurbishment that began in 2016. OPG reports it came in C$150 million under budget and four months early. The station gains about 30 more years of operation.

Bruce is halfway through. Its Life-Extension Program replaces major components in units 3 to 8 through 2033:

  • Unit 6 was completed in 2023.
  • Unit 3 returned to service in June 2026, more than seven months ahead of schedule.
  • Unit 4 has been out since February 2025, with restart planned for 2027.
  • Unit 5 follows, starting in fall 2026.
  • Bruce Power aims to raise site output from 6,550 MW to more than 7,000 MW in the 2030s.

Pickering B has just come offline. Units 5 to 8 were removed from service at the end of September 2026:

  • Refurbishment begins in January 2027, subject to final CNSC approval. It replaces 1,520 fuel channels and 48 boilers and adds a new deep-water intake.
  • Unit 5 is expected back in 2031 and all four units by 2034, at up to 2,200 MW.
  • Ontario approved a C$26.8 billion budget, in 2024 dollars including interest, escalation and contingency.
  • The first C$3 billion in execution contracts went to Aecon with Candu Energy (reactor work) and with Siemens Energy (turbine generators).

New build

Darlington New Nuclear Project: Canada's first SMRs. OPG is building four GE Vernova Hitachi BWRX-300 boiling water reactors, about 300 MW each and 1,200 MW in total. It is the first grid-scale SMR project in the G7.

  • Budget: C$20.9 billion for all four units. Unit 1 is C$6.1 billion plus C$1.6 billion for infrastructure shared by all four.
  • Approvals: the CNSC issued the construction licence in April 2025 and Ontario approved the project in May 2025.
  • Progress: in May 2026 the 953-tonne reactor building basemat was set 35 m below grade, and the first regulatory hold point has been lifted. OPG applied for a 20-year operating licence in April 2026.
  • Schedule: Unit 1 is planned to connect to the grid by the end of 2030. No in-service dates have been published for units 2 to 4.
  • Financing: the Canada Growth Fund (up to C$2 billion, 15%) and the Building Ontario Fund (up to C$1 billion, 7.5%) have taken minority equity stakes. Their capital for units 2 to 4 is released as milestones are met.

Bruce C: up to 4,800 MW at the Bruce site. The federal impact assessment is in its impact statement phase and is expected to finish in 2028. In May 2026 Ontario directed the IESO to sign a cost-sharing agreement of about C$300 million for pre-development work: engagement, workforce and site-preparation planning through 2030. No reactor technology has been selected.

Wesleyville (Port Hope): up to 10,000 MW. OPG filed its Initial Project Description with the Impact Assessment Agency of Canada on January 12, 2026, which started the federal impact assessment. The current outline has site preparation beginning in 2030 and construction in 2033. No technology has been selected; OPG is using a plant parameter envelope for site licensing.

The next five years at a glance

  • June 2026: Bruce Unit 3 back in service.
  • October 2026: Pickering B (about 2,000 MW) offline for refurbishment, until 2031 to 2034.
  • Fall 2026: Bruce Unit 5 refurbishment starts, while Unit 4 is still out. Bruce units keep cycling through refurbishment until 2033.
  • 2027: Bruce Unit 4 restart planned.
  • 2028: Bruce C federal impact assessment expected to conclude.
  • End of 2030: Darlington SMR Unit 1 grid connection target, about 300 MW of new capacity.
  • 2030: Wesleyville site preparation planned, construction from 2033.
  • 2031: Pickering Unit 5 expected back, the first refurbished Pickering unit.

The honest reading: for the next few years Ontario will run with less nuclear capacity than in 2025. Pickering B is out, and at least one Bruce unit is always in refurbishment. The only genuinely new nuclear capacity due before 2031 is the first 300 MW SMR. The large additions come in the 2030s: the remaining SMRs (about 900 MW), Bruce's uprate to more than 7,000 MW, Pickering's return at 2,200 MW, and then Bruce C and Wesleyville.

Update, October 18, 2026: a first look at how the gap is being managed. On October 1 the IESO contracted 600 MW of capacity from U.S.-based Alpha Generation for six months starting November 1, citing facility maintenance and winter peak demand. The IESO called it normal system planning and did not name Pickering; the contract was announced just as Pickering B went offline (CBC).

The money

  • Darlington refurbishment (complete): C$12.8 billion.
  • Pickering B refurbishment: C$26.8 billion.
  • Darlington SMRs (4 units): C$20.9 billion.
  • Bruce C pre-development: about C$300 million.

The new large stations have no published construction estimates yet. Those will follow technology selection and the impact assessments.

What to watch

  • The CNSC hearing on the Darlington SMR operating licence.
  • Whether Unit 1 makes its end-2030 grid date. It is the reference plant for the BWRX-300 projects that follow it.
  • Technology choices for Bruce C and Wesleyville, which will set Ontario's large-reactor path for decades.
  • How the IESO covers the gap while Pickering B is out.

Sources

Cover photo: Darlington Nuclear Generating Station from Courtice Waterfront, August 18, 2026, by Dillan Payne, CC BY-SA 4.0, via Wikimedia Commons. Cropped.

nuclearontariosmrrefurbishmentgrid planning

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