Bruce unit 4 is the third of six units at the Ontario site to undergo Major Component Replacement (MCR), a process which involves removing and replacing the key components of a CANDU pressurised heavy water reactor. This is a multi-year, multi-billion dollar undertaking – but adds 30-35 years to the reactor’s operating life.
Calandria tubes are key components of a CANDU reactor. Made of a zirconium alloy known as Zircaloy, the calandria tube is the outer part of the fuel channel and houses the pressure tube, in which the fuel is placed.
A six-axis robotic tooling system was used in an automated series which inserts a calandria tube insert into each calandria tube and rolls the joint to a precise target diameter, creating a leak-tight seal between the two components. The tooling operates from both faces of the reactor and uses microscopic measurements throughout the process to deliver consistent and repeatable results. It was made in Canada with design, testing, training and function led by Bruce Power, Shoreline Power Group, ATS Automation and Calian Engineering.
The work was completed 25 days ahead of the same milestone in Unit 3 – which was the first time the robotic system had been used on a reactor face – thanks to the application of lessons learned and further refinements to the process. Work on Unit 4 now moves on to fuel channel installation.
“Once again, Ontario’s nuclear sector is demonstrating its world leadership and proven track record of delivering large-scale refurbishments on budget and ahead of schedule,” said Stephen Lecce, Minister of Energy and Mines. “With electricity demand projected to rise by up to 90 per cent by 2050, Ontario continues to set the benchmark for the world as we build new nuclear for the next generation, creating 150,000 new jobs.”
Bruce 4 began its Major Component Replacement outage in February 2025 and marks the half-way point in Bruce Power’s Life-Extension Program, which will see units 3-8 renewed and returned to service by 2033. The CAD13 billion (USD9 billion) refurbishment is one of the largest infrastructure projects in Canada. Unit 6 completed its Major Component Replacement in 2024, and unit 3 completed its Major Component Replacement earlier this year, seven months ahead of schedule in June. Unit 5’s Major Component Replacement is set to begin in November, with units 7 and 8 to follow. Bruce units 1 and 2 have already been refurbished.
