Refurbishment enters final phase in Unit 2 reactor disassembly
Workers removed the last pressure tube from Darlington’s Unit 2 reactor on March 3, setting the stage for the Darlington Refurbishment project to enter its final phase in disassembling the reactor.
With all 480 pressure tubes removed, the project continues to progress safely, on time and on budget. The final steps drawing the reactor component removal phase to a close are the release of calandria tube inserts and the removal of the calandria tubes themselves. Once this process is complete, the work to rebuild the Unit 2 reactor will begin.
Here’s a quick primer on what’s involved in these final steps:
1. What are calandria tubes and inserts?
Calandria tubes sit inside the reactor’s core, each housing a pressure tube containing nuclear fuel bundles. They are secured at each end on the reactor face by a metal ring known as a calandria tube insert (CTI). There are 960 CTIs per reactor — one at each end of the 480 calandria tubes. The CTI effectively creates a mechanical seal or a leak-tight joint between the calandria tubes and the tube sheets.
2. How are calandria tubes removed?
To form the mechanical seal, the calandria tube deforms into the groove of the CTI. The CTI release series shrinks the CTI to allow it to be removed, which sets the stage for removal of the calandria tube itself.
3. How are inserts released?
CTIs are released from the tube sheet by means of induction heating using the CTI release tooling. During the process, the CTI is shock-heated for 2.2 seconds to reduce the insert diameter by approximately a sixteenth of an inch.
The CTI series is entirely automated, with millwrights and boilermakers completing the work by remote control from the Re-tube Control Centre.
4. How hot is it?
The CTI is shock-heated to approximately 1,100 Celsius for 2.2 seconds at 960 kWs — that’s enough to power a typical home for approximately two weeks.
Refurbishment of Darlington Nuclear, Canada’s largest clean energy project, began in October 2016 when Unit 2, the first of the station’s four reactors to come online in the 1990s, was safely shut down. Since then, it has been defuelled and isolated from the other three units in the operating station, then prepared for reactor component removal, which is underway.
Once complete, new components will be installed, allowing for 30 additional years of non-greenhouse gas emitting power production.
In February, OPG received provincial approval to begin work on the next reactor slated for refurbishment, Unit 3.