Darlington Nuclear's Unit 2 rebuild officially underway

The rebuilding of Darlington’s Unit 2 reactor is officially underway, as staff begin installing new calandria tubes.

Calandria tubes (CTs) provide access through the calandria for the fuel channel assemblies. As well, they insulate the hot fuel channel from the relatively cool moderator, protecting the calandria from the internal pressure of the moderator. Part of the fuel assembly, replacement of these 480 calandria tubes, signals the start of physically rebuilding the reactor with new components

Work to refurbish the reactor began in October 2016. First, the reactor was defuelled, and then isolated from the station’s other three operating units. This was followed by the disassembly phase which involved taking it apart, component by component.

​“We’ve spent the last several weeks inspecting the remaining components, including the calandria vessel, and cleaning and conditioning all other areas of the reactor, to allow us to start CT installation,” said Dietmar Reiner, Senior Vice President, Nuclear Projects. “We are ready to rebuild.”

The Canadian-designed CTs are manufactured in Ontario by Cameco. They are prepared in a clean room environment at the Darlington Energy Complex to guard against foreign material, then transported to the U2 airlock before being taken in to the vault. There, they will be installed by a team made up of boilermakers and millwrights, with support from Engineering, Quality Control and Radiation Protection.

This work is scheduled to take about four months, and wrap up in the fall. This leads into installation of the remainder of the fuel channel components, including end fittings, annulus spacers and pressure tubes.

“It’s no easy task, but the right team is in place to complete the work safely, with quality, on time and on budget,” said Mike Allen, Senior Vice President, Refurbishment.

“It will require precise control with every task, every torque and every weld,” he said. “Safety and quality workmanship will allow us to complete refurbishment of Unit 2, allowing it to continue providing clean reliable power for Ontarians for the next 30 years.”

Learn more about calandria tube installation.