Darlington Nuclear Refurbishment Project update

Updated Thursday, 16 May 2024

Reactor details

Location          Bowmanville, Ontario, Canada
Reactor type    Pressurized heavy water reactor (PHWR)
Owner       Ontario Power Generation
Operator Ontario Power Generation
Net capacity 4 x 878 MWe
Unit 1 construction/grid connection 1 April 1982 / 14 November 1992
Unit 2 construction/grid connection 1 September 1981 / 9 October 1990
Unit 3 construction/grid connection 1 September 1984 / 14 February 1993
Unit 4 construction/grid connection 1 July 1985 / 14 June 1993

The four CANDU 850 reactors at the Darlington nuclear power plant meet about 20% of Ontario’s electricity needs and have been in operation since the early 1990s. In 2016 OPG commenced a 10-year refurbishment project of all four units, beginning with unit 2, that would extend the operating lifetimes of the reactors by 30 years. Work on units 2&3 has been completed, while refurbishment of units 1&4 continues.

Beginning in 2007, OPG conducted thorough station equipment assessments followed by extensive programme planning and preparation. This upfront investment of time and attention to detail resulted in an integrated 10-year long execution schedule (all four units will be returned to service before the end of 2026) and a committed total budget of C$12.8 billion.

In October 2016, OPG’s team of project partners, industry experts, energy professionals, and skilled tradespeople shut down unit 2, the first of four Darlington reactors scheduled for refurbishment, and reconnected it to the power grid in June 2020 – an execution duration of 44 months. In addition to enabling unit 2 to operate for another 30 years, more than 4000 lessons learned were captured from the full evolution of the refurbishment of the reactor and associated unit systems.

Unit 3 refurbishment execution began in September 2020, incorporating the unit 2 lessons learned. Then in February 2022, execution commenced on unit 1 – the first time two units overlapped in execution during the refurbishment project.

Unit 3 was reconnected to the Ontario electricity grid on 17 July 2023 – after 34 months, 169 days ahead of OPG's commitment. On July 19, unit 4, the final of the four Darlington reactors to be refurbished, was taken offline to begin its refurbishment outage.

Interview Subo Sinnathamby, Senior Vice President, Nuclear Refurbishment


Four years later, has the project proceeded as expected?

The project has progressed better than expected. Executing a long-term mega construction project within an operating commercial nuclear station has required continued focus on safety and quality by the team to successfully drive the project forward. At more than halfway through the project execution phase (60% complete at the time of writing), it is the “OneTeam” culture within the OPG leaders and employees, our vendor partners and the tradespersons, focused on completing quality work that has kept this project ahead of schedule, with a far safer working environment than the average commercial construction site in Ontario.

A detailed schedule, effective implementation of lessons from the unit 2 refurbishment, along with strong risk mitigation plans, has allowed the team to overcome major challenges, including discovery and first of a kind execution.

In our 2019 case study, OPG identified many lessons learned from the execution of the unit 2 project. Has it been possible to apply these lessons learned in practice to the refurbishment of subsequent units?

As a learning organization, the Darlington refurbishment project team continuously gathers information throughout planning, tooling proofing, operation and maintenance, worker training, material management, work series execution and ultimately return-to-service evolutions. The information is assessed, lessons learned identified and then incorporated into the schedule of subsequent refurbishments. From the execution of unit 2, the team captured 4000 lessons learned to enhance the quality of work, safety to workers, and improve cost and schedule performance on subsequent units.

Effective implementation of these lessons learned through new execution strategies and innovation have resulted in greater than 20% performance improvement from unit 2 to unit 3 on safety, quality, and schedule. One key innovation for unit 3 based on lessons learned was modification of tooling to enable the pressure tubes and calandria tubes to be removed together, versus in series in unit 2, resulting in savings of 30 days and enhanced worker safety on each of the unit 3, 1 and 4 schedules.

Did the COVID-19 pandemic have any impact on the project and, if so, how were any challenges managed?

The Darlington refurbishment project was not immune to challenges brought on by the COVID-19 pandemic. The health and safety of all workers on OPG sites has and remains a top priority for us. The implementation of social distancing guidelines, enhanced disinfection and sanitizing of all work areas and enforcing screening protocols not only minimized the spread of the virus in our stations, but it also highlighted to our employees, workers, and community, OPG’s commitment to maintaining a safe workplace.

Delaying the start of the unit 3 refurbishment by four months after the successful return-to-service of unit 2 was a carefully thought-out decision to ensure we had the appropriate measures to protect both the operational and project staff in this unprecedented environment. The time taken to put these measures in placed ensured there were no COVID-19 outbreaks on the project or schedule impact during execution.

New SMRs are planned to be built at Darlington. Congratulations. With the refurbishment project extending the operation of the existing Darlington units well beyond the potential start-up of the SMR, are there any benefits or challenges with constructing and operating a new reactor at an existing operating plant site?

OPG’s track record in successfully operating nuclear generating stations and executing mega projects has paved the way for building new SMRs at the Darlington site.  OPG has partnered with GE Hitachi, SNC Lavalin and Aecon to complete planning, design, and construction of four BWRX-300 SMRs on land adjacent to the existing Darlington station. Working with these three companies, OPG is leveraging decades of nuclear energy and large project experience, including lessons learned from the Darlington refurbishment project and OPG’s operating experience, to build and operate SMRs.