Fuel channel assembly installation underway at Darlington's Unit 2

The next step in making Darlington Nuclear Generating Station’s Unit 2 whole again is now underway. Work on fuel channel assembly installation began after the first step in rebuilding the reactor – calandria tube installation – wrapped up last November.

Here’s what you need to know about this critical phase in the Darlington Refurbishment project:

What is the purpose of the fuel channel?

The 480 fuel channels in a Darlington reactor are critical components of the heat transport system. They support the fuel bundles in the reactor, and are located inside the calandria. Pressurized heavy water is pumped into the fuel channels, moving the heat produced to fuel the boiler system, which in turn produces steam to turn the turbines that generate electricity. Fuel channels are surrounded by heavy water, which acts as a moderator.

What does the fuel channel subassembly consist of?

Each fuel channel requires a fuel channel subassembly, consisting of a pressure tube made of zirconium, two stainless steel end fittings, and four annulus spacers, which play a critical role in maintaining the gap between the pressure tube and calandria tube. This ensures there is no contact between the components.

Why is a clean room necessary? What happens in there?

A clean room is necessary from both a climate control and foreign material exclusion perspective as fuel channels are prepared, cleaned, inspected and assembled.

Pressure tube preparation includes putting together the pressure tube and liner, then securing one end-fitting in place using specialized equipment. These tubes are cut to the appropriate length for their designated locations, and they are inspected and tested to ensure they are leak-tight.

Who is involved in the installation?

Trades involved in this work include welders, boilermakers, millwrights and electricians. Each crew has more than 40 workers.

How long does it take?

This work series is scheduled to take approximately 130 days and is set to be completed by mid-March.

What’s next?

Lower feeder installation will follow the fuel channel installation.