# Darlington New Nuclear Project by Ontario Power Generation

Canonical page: https://technooptimist.io/energy/darlington-new-nuclear
Frontier: [Energy](https://technooptimist.io/energy.md) · Field: Small modular reactors · Company: [Ontario Power Generation](https://technooptimist.io/companies/ontario-power-generation.md)
Stage: Pilot (3 of 5: Research → Proto → Pilot → Deploy → Scaling)
Updated: last update 2026-06-23, facts checked 2026-10-11
Goal: Prove that small reactors can be built on budget in a Western country, then repeat the design so each unit gets cheaper: from C$6.1 billion for the first to about C$4.1 billion for the fourth.
Status: Unit 1 basemat set April 2026; grid target end-2030; go-ahead for units 2-4 expected 2028.
Next milestone: First reactor building level complete (200+ modules), target Q4 2026

## Milestones

| Status | Milestone | Date | Slip |
| --- | --- | --- | --- |
| Done | Licence to construct from Canada's nuclear regulator | Apr 2025 |   |
| Done | Ontario's final investment decision; unit 1 construction starts | 8 May 2025 |   |
| Done | Federal and Ontario funds take a 22.5% stake for C$3B | 23 Oct 2025 |   |
| Done | Operating licence application filed for unit 1 | Mar 2026 |   |
| Done | Unit 1 basemat set in the 35 m reactor shaft | 22 Apr 2026 |   |
| Done | Williams Treaties First Nations invest C$700M | 23 Jun 2026 |   |
| Current | First reactor building level complete (200+ modules) | Q4 2026 |   |
| Planned | Approval to proceed with units 2-4 | 2028 |   |
| Planned | Unit 1 connected to the grid | Q4 2030 |   |
| Planned | Units 2-4 in service |   |   |

## Upcoming events

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

## Most important updates

- **23 Jun 2026**: Williams Treaties First Nations invest C$700 million in OPG's Darlington SMR project. Seven Williams Treaties First Nations, through a joint partnership, are investing C$700 million in the Darlington New Nuclear Project, the largest collective First Nations investment in Canadian nuclear power. ([our story](https://technooptimist.io/stories/williams-treaties-first-nations-invest-c-700-million-in-opg-s-d2d6ea59.md) · [original source](https://www.bnnbloomberg.ca/press-releases/2026/06/23/williams-treaties-first-nations-announce-historic-700-million-investment-in-darlington-new-nuclear-project/))
- **23 Oct 2025**: Canada Growth Fund and Building Ontario Fund commit C$3 billion for 22.5% of the Darlington SMR project. The federal Canada Growth Fund will put in up to C$2 billion for a 15% stake and Ontario's Building Ontario Fund up to C$1 billion for 7.5%, with OPG remaining majority owner and operator. ([our story](https://technooptimist.io/stories/canada-growth-fund-and-building-ontario-fund-commit-c-3-billion-for-22-33c45dd2.md) · [original source](https://www.renewcanada.net/feds-ontario-to-invest-3b-in-darlington-small-modular-reactor-project/))
- **8 May 2025**: Ontario approves construction of the first of four BWRX-300 small reactors at Darlington. Ontario's government cleared OPG to build the first of four 300 MW BWRX-300 reactors at Darlington, after the nuclear regulator issued a licence to construct in April. ([our story](https://technooptimist.io/stories/ontario-approves-construction-of-the-first-of-four-bwrx-300-small-d03a3cbc.md) · [original source](https://world-nuclear-news.org/articles/opg-gets-go-ahead-to-build-first-smr-in-canada))

## Current obstacles

- **First-of-a-kind cost risk**: No BWRX-300 has been finished anywhere; unit 1's C$6.1bn estimate rests on a design never built before.
- **Regulatory hold points**: Two more regulator checkpoints remain for unit 1: before the reactor vessel goes in and before fuel is loaded.
- **Module supply chain**: Over 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 scale**: Steel, 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

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

Provenance: reported = stated by the company; estimated = our estimate; sample = a sample figure.

## About Ontario Power Generation

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.

- Founded: 1999
- Headquarters: CA
- Status: government
- Website: https://www.opg.com
- People: Nicolle Butcher (President and CEO); Subo Sinnathamby (Chief Projects Officer)
- Partners, customers, investors: GE Vernova Hitachi (supplier); Aecon Kiewit Nuclear Partners (supplier); AtkinsRéalis (supplier); Canada Growth Fund (investor); Building Ontario Fund (investor); Williams Treaties First Nations (investor)

Company page: https://technooptimist.io/companies/ontario-power-generation.md

## Related programs

Everything in Energy: https://technooptimist.io/energy.md

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