Darlington New Nuclear Project by Ontario Power Generation: status and timeline

Milestones

Next · First reactor building level complete (200+ modules)

Licence to construct from Canada's nuclear regulatorApr 2025Complete.
Ontario's final investment decision; unit 1 construction starts8 May 2025Complete.
Federal and Ontario funds take a 22.5% stake for C$3B23 Oct 2025Complete.
Operating licence application filed for unit 1Mar 2026Complete.
Unit 1 basemat set in the 35 m reactor shaft22 Apr 2026Complete.
Williams Treaties First Nations invest C$700M23 Jun 2026Complete.
First reactor building level complete (200+ modules)Target Q4 2026Current milestone.
Approval to proceed with units 2-4Target 2028Not yet reached.
Unit 1 connected to the gridTarget Q4 2030Not yet reached.
Units 2-4 in serviceNot yet reached.

Most important updates

Upcoming

Q4 2026First reactor building level complete (200+ modules) (next)
2028Approval to proceed with units 2-4
Q4 2030Unit 1 connected to the grid

Current obstacles

First-of-a-kind cost riskNo BWRX-300 has been finished anywhere; unit 1's C$6.1bn estimate rests on a design never built before.
Regulatory hold pointsTwo more regulator checkpoints remain for unit 1: before the reactor vessel goes in and before fuel is loaded.
Module supply chainOver 100 suppliers must deliver about 1,200 modules per unit on time; one late module stalls the build sequence.

Physics limits

Small reactors lose economies of scaleSteel, concrete and staff per megawatt rise as reactors shrink, so savings have to come from factory modules, simpler systems and building many identical units.

How it works

4 parts

Boiling water

Steam made in the reactor itself

Water boils in the core and the steam drives the turbine directly, so there are no separate steam generators to build.

Deep shaft

Reactor sits 35 m underground

The reactor building fills a 35 m deep shaft, 37 m across, which shields it and shrinks the structure above ground.

Modules

Built off site, stacked on site

About 1,200 prefabricated modules fill eight levels; the basemat itself is a steel-plate box later filled with concrete.

Repeat

Unit 1 alone, then copies

Unit 1 is built standalone so its lessons carry to units 2-4, which are estimated to cost about C$5bn falling to C$4.1bn.

Spec sheet

Spec	Darlington New Nuclear Project
Reactors	4 × BWRX-300^R (reported)
Power per unit	300 MW^R (reported)
Total power	1,200 MW^R (reported)
Total budget	C$20.9 billion^R (reported)
Unit 1 cost	C$6.1 billion^R (reported)
Shared site systems	C$1.6 billion^R (reported)
Unit 4 cost (estimate)	C$4.1 billion^R (reported)
Reactor shaft depth	35 m^R (reported)
Modules per reactor building	About 1,200 on 8 levels^R (reported)
Spending in Ontario	About 80%^R (reported)

^R reported by the company

Update log

3 updates

About Ontario Power Generation

The team behind Darlington New Nuclear Project

Ontario Power Generation

Nuclear and hydro utility, Darlington SMRs

Ontario's provincially owned utility, producing about half of the province's electricity. It runs the Darlington and Pickering nuclear stations and is building the G7's first small modular reactors at Darlington.

Wholly owned by the Government of Ontario; generates about half of Ontario's power.
Building four GE Vernova Hitachi BWRX-300s at Darlington: C$20.9 billion, 1,200 MW, first unit on the grid by end-2030.
Finished refurbishing Darlington's four CANDU units in early 2026, ahead of schedule and under budget.

opg.com (opens opg.com)Company profile →

Founded: 199927 yrs
Headquarters: Canada
Status: Government
Valuation: government
Works in: EnergySmall modular reactors
Coverage: 1 program · 3 updateslatest 23 Jun 2026checked 11 Oct
Investors: Canada Growth FundBuilding Ontario FundWilliams Treaties First Nations
Suppliers: GE Vernova HitachiAecon Kiewit Nuclear PartnersAtkinsRéalis
People: Nicolle ButcherPresident and CEOSubo SinnathambyChief Projects Officer

Darlington New Nuclear Project

Milestones

Most important updates

Upcoming

Current obstacles

Physics limits

How it works

Steam made in the reactor itself

Reactor sits 35 m underground

Built off site, stacked on site

Unit 1 alone, then copies

Spec sheet

Update log

Tue 23 Jun

Thu 23 Oct 2025

Thu 8 May 2025

About Ontario Power Generation

Current obstacles

Physics limits

How it works

Steam made in the reactor itself

Reactor sits 35 m underground

Built off site, stacked on site

Unit 1 alone, then copies

Spec sheet

Update log

Tue 23 Jun

Thu 23 Oct 2025

Thu 8 May 2025

About Ontario Power Generation