Darlington nuclear station is undergoing refurbishment (Credit: OPG)Canada’s Darlington Refurbishment Project has completed a significant milestone with the successful separation of the unit 3 reactor and its systems from the three remaining operating units at Darlington Nuclear Generating Station.

Ontario Power Generation said workers had installed the last bulkhead section to complete a physical protective barrier on 6 January, 10 days ahead of the originally planned 44-day schedule, adding that “more significantly, it was done safely”.

Installation of the bulkhead involved welding together 16 steel panels each weighing more than 5000kg. It is part of ”islanding” (or physically isolating) Darlington 3 to create a safe and defined work area for refurbishment and protect workers and the plant.

More than 4000 lessons learned were captured from the refurbishment of Darlington 2, which had returned to service in June 2020. Welding techniques and weld quality were identified as areas for improvement, leading to enhanced training and assessment programmes. The bulkheads were sequenced to streamline work flow and gain efficiencies.

To certify islanding is complete, a series of positive and negative pressure tests, called a Containment Pressure Test (CPT), were conducted to verify an airtight seal around the bulkhead. A successful CPT on 14 January marked the end of the islanding activities and the start of the next segment of work, the Removal series, which will see the reactor taken apart. The removal series is scheduled to last 311 days, OPG said.

“We’ve isolated the refurbishment unit from the day-to-day operations of Darlington Nuclear,” said Subo Sinnathamby, Senior vice president, nuclear refurbishment.

“This means the other operating units at the power plant will continue producing electricity for the province while we simultaneously remove critical components on unit 3. I’m most proud that we achieved this milestone safely and ahead of schedule and on budget.”  OPG completed defueling of Darlington 3 in November 2020, also ahead of the targeted completion date.

The Darlington Refurbishment Project will enable the four Candu reactor units to operate until 2055, and will take 10 years to complete. The refurbishment of Darlington 3 began in September, after a four-month postponement due to the COVID-19 pandemic. Refurbishment of Darlington 1 is scheduled to begin in 2022 and Darlington 4 in 2023. The project is scheduled for completion by 2026.

Photo: Darlington site (Credit: OPG)