The latest phase of the Darlington nuclear power plant’s refurbishment project began last week with the start of the defueling of Unit 3, according to Ontario Power Generation (OPG). Originally scheduled to begin in May this year, Unit 3’s refurbishment was postponed due to the COVID-19 pandemic.
Located in Clarington, Ontario, Canada, the Darlington plant houses four 878-MWe CANDU pressurized heavy-water reactors, all of which entered commercial operation in the early 1990s. The 10-year refurbishment project—which was 10 years in the planning—commenced in earnest in October 2016, when Unit 2 was taken off line (NN, Dec. 2016, pg. 45). The refurbished Unit 2 was returned to service in early June, and in late July Unit 3 was shut down and disconnected from the grid in preparation for its refurbishment.
Defueling the reactor: The first major work on the project’s critical path, defueling involves the remote-controlled removal of 6,240 fuel bundles from the reactor over the course of three months, according to OPG. The fuel bundles will be placed inside water-filled pools for up to 10 years of safe storage. Once the bundles have been removed, heavy water will be drained from the unit’s reactor systems, the utility said.
OPG also noted that while the fuel handling team has “already experienced success” in its defueling of Unit 2, the process won’t be identical for Unit 3.
What they’re saying: “Continuous learning is the key to success on any project, especially a mega-project like the Darlington refurbishment,” said Subo Sinnathamby, OPG senior vice president of nuclear refurbishment, on September 3. “We have the benefit of having collected more than 4,000 lessons learned during work on Unit 2 and have been applying them to Unit 3 to deliver significantly greater results, including during defueling.”
Steve Gregoris, senior vice president at Darlington Nuclear, said, “Darlington’s fuel handling team has worked very hard to ensure the fuel handling equipment is reliable, and our operations, maintenance, and engineering groups are trained and ready to execute Unit 3’s defuel campaign. We’re ready to build on Unit 2’s success as we work as one team to build Darlington for the future.”
What’s next: Following the completion of Unit 3’s defueling in late fall, workers will begin “islanding,” a process that will physically isolate the reactor from Darlington’s three operating units, OPG said.
The Darlington-1 refurbishment is scheduled to start in the first quarter of 2022 and be completed in the second quarter of 2025, while Darlington-4’s refurbishment is scheduled to begin in the third quarter of 2023, with completion in the fourth quarter of 2026.