Skip to Content

Unit 2 New Fuel Load Underway

The refurbishment of Darlington’s Unit 2 reactor remains on budget, and the projected costs and 10-year schedule for the refurbishment of all four units remain on track. Safety performance is strong with over 19.8 million hours worked on the project since October 2016, with one Lost Time Accident occurring in the second quarter of 2019.

At the end of the third quarter, the project team neared completion of construction work on Unit 2. Ninety per cent of the critical work for Unit 2 has been finished. By late October, we successfully completed the installation of all 960 feeder tubes and now a total of 40 of 58 major plant systems have been declared available for service.

The team is now preparing for another milestone on the project: loading fuel into the reactor core.

OPG worked with BWXT Nuclear Energy Canada over a five-year span to develop a detailed plan for loading each of the 6,240 new fuel bundles into the core in the correct location and sequence. This work series involves the insertion of shield plugs, closure plugs and fuelling the core with fuel bundles.

Unit 2 is scheduled to return to service by Q2 2020.

Unit 3

By the end of the third quarter, the project team completed 94% of the engineering design for Unit 3 refurbishment, and planning and readiness activities remained on track.

OPG continues to refine our four-unit refurbishment schedule based on operating experience and our detailed review of more than 3,000 lessons learned from Unit 2 refurbishment. In response to the recently revised schedule for Unit 2 refurbishment, we will now commence Unit 3 refurbishment in the second quarter of 2020, instead of the first quarter of 2020. This decision was made to enable the project team to dedicate their focus to successfully returning Unit 2 to service ahead of the start of work on Unit 3, as initially planned. It also allows the team to bring preparatory work forward, ahead of Unit 3 breaker open, when the reactor will be taken offline.

Subsequent Units: 1 and 4

The project team continues to work on plans and preparations for the refurbishment of Units 1 and 4, based on operating experience and lessons learned from Unit 2 refurbishment.

Overall, the Darlington Refurbishment Project remains on budget and on schedule for completion in 2026.

Environment

  • No reportable spills or infractions and emissions.
  • Emissions were well below regulatory limits.

Safety

  • 19.8 million hours have been worked on the project, with only one Lost Time Accident.
  • Ten-fold better safety performance than Ontario construction industry.

Quality

  • Lower feeder weld failure rates higher than expected during early feeder installation.
  • Significant improvement as work series progressed.

Schedule

  • Refurbishment of all four Darlington units remained on schedule.
  • Unit 2 expected to return to service by Q2 2020.
  • Unit 3 planned to commence Q2 2020.

Cost

  • Refurbishment forecasted to remain on budget for all four Darlington units.
  • Lessons learned from Unit 2 are being applied to planning for Unit 3 and subsequent units to achieve further efficiencies.

Refurbishment timeline

Project Status: ScheduledStart Date: Q4 2021Expected Completion: Q4 2024
Project Status: UnderwayStart Date: October 2016Expected Completion: Q2 2020
Project Status: ScheduledStart Date: Q2 2020Expected Completion: Q3 2023
Project Status: ScheduledStart Date: Q2 2023Expected Completion: Q2 2026
Shut down
First segment
Breaker open
Shutting down the reactor and disconnecting it from Ontario's power grid.
Refurbishment timeline
Breaker open
Shutting down the reactor and disconnecting it from Ontario's power grid.

Following years of detailed planning, approvals and preparations, the Darlington Refurbishment Project team carries out the first major step in project execution: Shutting down the reactor and disconnecting it from the power grid. This is done through a process also known as ‘breaker open,” which involves cooling the reactor and stopping nuclear fission in accordance with Canadian Nuclear Safety Commission regulations and operational procedures.

Workers at a GE plant in Poland prepare a massive generator stator for shipment to Darlington Nuclear.
Workers at a GE plant in Poland prepare a massive generator stator for shipment to Darlington Nuclear.
Defuelling
Removing fuel and heavy water from the reactor.
Refurbishment timeline
Defuelling
Removing fuel and heavy water from the reactor.

Now that the reactor has been safely shut down and the reactor disconnected, workers use remote-controlled tooling to remove 6,240 fuel bundles from the unit and place them in water-filled fuel bays for up to ten years of safe storage. Once the fuel has been removed, workers drain heavy water from the reactor and the heat transport system, then store, clean and purify it before pumping it back in, after unit reassembly.

Islanding
Safely separating the shutdown reactor from the operating plant.
Refurbishment timeline
Islanding
Safely separating the shutdown reactor from the operating plant.

With the fuel and heavy water removed, the unit undergoing refurbishment must be separated from the operating plant. This is done through a process known as Islanding, whereby workers disconnect equipment and put physical barriers in place.

Islanding allows the unit to be refurbished safely and efficiently while limiting impact on the operating units and rest of the station.

Containment pressure testing
Confirming the safe separation of the shutdown unit from the operating plant.
Refurbishment timeline
Containment pressure testing
Confirming the safe separation of the shutdown unit from the operating plant.

Workers perform a containment pressure test at this stage to confirm that the disconnected unit has been safely and completely isolated from the rest of the operating plant.

This process involves raising the pressure in the unit to ensure that any contamination is contained.

Disassembly
Feeder removal
Removing all 960 feeder tubes from the reactor.
Refurbishment timeline
Feeder removal
Removing all 960 feeder tubes from the reactor.

After opening the airlocks to allow for the free movement of materials and equipment, workers remove 960 feeder tubes from the reactor.

Feeder tubes carry heated heavy water to boilers and return the water back to the reactor for reheating.

Removal of the feeders is the first step in the disassembly of
the unit, and sets the stage for replacement of parts.

Fuel channel removal
Removing all 480 fuel channels from the reactor.
Refurbishment timeline
Fuel channel removal
Removing all 480 fuel channels from the reactor.

Fuel channels are made of several components: a pressure tube, two stainless steel end-fittings and annulus spacers, which separate the pressure tube from the calandria tubes, preventing them from touching.

Once all end fittings have been taken out, workers remove all 480 pressure tubes through a process that involves these of engineered tooling mounted on a massive Re-tube Tooling Platform, inside the vault.

Calandria tube removal
Removing all 480 calandria tubes from the reactor.
Refurbishment timeline
Calandria tube removal
Removing all 480 calandria tubes from the reactor.

A calandria tube is a long cylindrical tube made of zirconium that surrounds the pressure tube and forms a leak tight seal of the calandria vessel – the heart of the reactor.

A Darlington CANDU reactor contains 480 calandria tubes, which are removed using specialized tooling, which workers operate remotely and transport in protective flasks to OPG’s Re-tube Waste Processing Building for storage preparation.

Reassembly
Calandria tube installation
Inspecting and cleaning the calandria vessel then installing all 480 calandria tubes inside the reactor.
Refurbishment timeline
Calandria tube installation
Inspecting and cleaning the calandria vessel then installing all 480 calandria tubes inside the reactor.

With all the reactor components removed, workers carefully clean and inspect the calandria vessel to ensure materials show no degradation.

Once this process is complete, workers install 480 new calandria tubes inside the reactor.

Workers complete much of this work manually and directly on the face of the reactor, with direction provided by operators in our Re-tube Control Centre.

After installation, inspection and testing, workers reattach the bellows assemblies, which allow for any movement of pressure tubes and calandria tubes, caused by temperature changes.

Fuel channel installation
Assembling 480 fuel channels in clean rooms then installing them inside the reactor.
Refurbishment timeline
Fuel channel installation
Assembling 480 fuel channels in clean rooms then installing them inside the reactor.

Fuel channels are made of several sub-components: a pressure tube, two stainless steel end-fittings and annulus spacers.

The reactor’s 480 fuel channels are critical parts of the heat transport system, which hold the reactor’s fuel bundles.

At this stage, workers pre-assemble the fuel channels in a climate- and foreign material-controlled clean room then prepare them for delivery to the vault for installation.

Feeder installation
Installing all 960 feeder tubes prior to filling the moderator system.
Refurbishment timeline
Feeder installation
Installing all 960 feeder tubes prior to filling the moderator system.

Each of the reactor’s 960 feeder tubes is unique in shape, size and length, and these new components are delivered in three sections: upper, middle and lower. Because of their unique composition, installing them inside the reactor is a process similar to putting together a puzzle.

Starting with upper section, workers install feeder tubes, making their way down to the lower section, where the feeder tubes are attached to end fittings.

Once this work is complete and regulatory approval received, the project team fills the moderator with clean heavy water and prepares to load the reactor with new fuel.

Power up
Fuel load
Loading 6,240 fuel bundles into the reactor’s fuel channels.
Refurbishment timeline
Fuel load
Loading 6,240 fuel bundles into the reactor’s fuel channels.

At this stage, workers refill the moderator with heavy water, load each of the 6,240 fuel bundles into the fuel channels, then fill and pressurize the heat transport system.

A fuel bundle contains natural uranium in the form of ceramic pellets.

Containment restored
Confirming the containment of the unit has been restored then removing tooling and physical barriers.
Refurbishment timeline
Containment restored
Confirming the containment of the unit has been restored then removing tooling and physical barriers.

Unit containment is restored once we’ve removed all tooling, including the Re-Tube Tooling Platform, needed to perform refurbishment; the airlocks have been closed; the physical barriers removed from inside the vault; and the 59 key systems have been returned to service.

Operators in the Re-Tube Control Centre can then begin the process of achieving first criticality, which means sustaining the chain reaction of splitting atoms and releasing heat.

Breaker close
Reconnecting the reactor to Ontario’s power grid following rounds of inspections and approvals.
Refurbishment timeline
Breaker close
Reconnecting the reactor to Ontario’s power grid following rounds of inspections and approvals.

Throughout refurbishment, the Canadian Nuclear Safety Commission carries out inspections and grants approvals for the project to progress from one milestone to the next. At this stage, the CNSC continues this oversight, confirming the newly refurbished unit can be operated safely and granting approval for the reactor to be gradually brought back to full power and reconnected to Ontario’s power grid.

Shut down
Before disassembling a CANDU® reactor, workers must disconnect it from the power grid. But shutting down the unit is not just a matter of pulling a plug. Workers must remove fuel and heavy water, and isolate the unit from the rest of the station.
Breaker open
Shutting down the reactor and disconnecting it from Ontario's power grid.
Refurbishment timeline
Breaker open
Shutting down the reactor and disconnecting it from Ontario's power grid.

Following years of detailed planning, approvals and preparations, the Darlington Refurbishment Project team carries out the first major step in project execution: Shutting down the reactor and disconnecting it from the power grid. This is done through a process also known as ‘breaker open,” which involves cooling the reactor and stopping nuclear fission in accordance with Canadian Nuclear Safety Commission regulations and operational procedures.

Defuelling
Removing fuel and heavy water from the reactor.
Refurbishment timeline
Defuelling
Removing fuel and heavy water from the reactor.

Now that the reactor has been safely shut down and the reactor disconnected, workers use remote-controlled tooling to remove 6,240 fuel bundles from the unit and place them in water-filled fuel bays for up to ten years of safe storage. Once the fuel has been removed, workers drain heavy water from the reactor and the heat transport system, then store, clean and purify it before pumping it back in, after unit reassembly.

Islanding
Safely separating the shutdown reactor from the operating plant.
Refurbishment timeline
Islanding
Safely separating the shutdown reactor from the operating plant.

With the fuel and heavy water removed, the unit undergoing refurbishment must be separated from the operating plant. This is done through a process known as Islanding, whereby workers disconnect equipment and put physical barriers in place.

Islanding allows the unit to be refurbished safely and efficiently while limiting impact on the operating units and rest of the station.

Containment pressure testing
Confirming the safe separation of the shutdown unit from the operating plant.
Refurbishment timeline
Containment pressure testing
Confirming the safe separation of the shutdown unit from the operating plant.

Workers perform a containment pressure test at this stage to confirm that the disconnected unit has been safely and completely isolated from the rest of the operating plant.

This process involves raising the pressure in the unit to ensure that any contamination is contained.

Disassembly
Taking a reactor apart is a complex job that includes removing, storing or replacing thousands of critical components. With our project partners, skilled tradespeople and nuclear professionals, we’re safely disassembling our reactors one at a time.
First segment
Feeder removal
Removing all 960 feeder tubes from the reactor.
Refurbishment timeline
Feeder removal
Removing all 960 feeder tubes from the reactor.

After opening the airlocks to allow for the free movement of materials and equipment, workers remove 960 feeder tubes from the reactor.

Feeder tubes carry heated heavy water to boilers and return the water back to the reactor for reheating.

Removal of the feeders is the first step in the disassembly of
the unit, and sets the stage for replacement of parts.

Fuel channel removal
Removing all 480 fuel channels from the reactor.
Refurbishment timeline
Fuel channel removal
Removing all 480 fuel channels from the reactor.

Fuel channels are made of several components: a pressure tube, two stainless steel end-fittings and annulus spacers, which separate the pressure tube from the calandria tubes, preventing them from touching.

Once all end fittings have been taken out, workers remove all 480 pressure tubes through a process that involves these of engineered tooling mounted on a massive Re-tube Tooling Platform, inside the vault.

First segment
Calandria tube removal
Removing all 480 calandria tubes from the reactor.
Refurbishment timeline
Calandria tube removal
Removing all 480 calandria tubes from the reactor.

A calandria tube is a long cylindrical tube made of zirconium that surrounds the pressure tube and forms a leak tight seal of the calandria vessel – the heart of the reactor.

A Darlington CANDU reactor contains 480 calandria tubes, which are removed using specialized tooling, which workers operate remotely and transport in protective flasks to OPG’s Re-tube Waste Processing Building for storage preparation.

Reassembly
Putting the reactor back together requires quality, precision workmanship on every task. Rebuilding involves inspecting, cleaning and installing thousands of components to ensure the unit’s safe and efficient operation for at least another 30 years.
First segment
Calandria tube installation
Inspecting and cleaning the calandria vessel then installing all 480 calandria tubes inside the reactor.
Refurbishment timeline
Calandria tube installation
Inspecting and cleaning the calandria vessel then installing all 480 calandria tubes inside the reactor.

With all the reactor components removed, workers carefully clean and inspect the calandria vessel to ensure materials show no degradation.

Once this process is complete, workers install 480 new calandria tubes inside the reactor.

Workers complete much of this work manually and directly on the face of the reactor, with direction provided by operators in our Re-tube Control Centre.

After installation, inspection and testing, workers reattach the bellows assemblies, which allow for any movement of pressure tubes and calandria tubes, caused by temperature changes.

First segment
Fuel channel installation
Assembling 480 fuel channels in clean rooms then installing them inside the reactor.
Refurbishment timeline
Fuel channel installation
Assembling 480 fuel channels in clean rooms then installing them inside the reactor.

Fuel channels are made of several sub-components: a pressure tube, two stainless steel end-fittings and annulus spacers.

The reactor’s 480 fuel channels are critical parts of the heat transport system, which hold the reactor’s fuel bundles.

At this stage, workers pre-assemble the fuel channels in a climate- and foreign material-controlled clean room then prepare them for delivery to the vault for installation.

First segment
Feeder installation
Installing all 960 feeder tubes prior to filling the moderator system.
Refurbishment timeline
Feeder installation
Installing all 960 feeder tubes prior to filling the moderator system.

Each of the reactor’s 960 feeder tubes is unique in shape, size and length, and these new components are delivered in three sections: upper, middle and lower. Because of their unique composition, installing them inside the reactor is a process similar to putting together a puzzle.

Starting with upper section, workers install feeder tubes, making their way down to the lower section, where the feeder tubes are attached to end fittings.

Once this work is complete and regulatory approval received, the project team fills the moderator with clean heavy water and prepares to load the reactor with new fuel.

Power up
Restarting a reactor is a process that involves a number of step-by-step approvals to confirm the quality of work and to ensure that equipment, systems, operating procedures and trained staff are ready to proceed with the start-up process.
Fuel load
Loading 6,240 fuel bundles into the reactor’s fuel channels.
Refurbishment timeline
Fuel load
Loading 6,240 fuel bundles into the reactor’s fuel channels.

At this stage, workers refill the moderator with heavy water, load each of the 6,240 fuel bundles into the fuel channels, then fill and pressurize the heat transport system.

A fuel bundle contains natural uranium in the form of ceramic pellets.

Containment restored
Confirming the containment of the unit has been restored then removing tooling and physical barriers.
Refurbishment timeline
Containment restored
Confirming the containment of the unit has been restored then removing tooling and physical barriers.

Unit containment is restored once we’ve removed all tooling, including the Re-Tube Tooling Platform, needed to perform refurbishment; the airlocks have been closed; the physical barriers removed from inside the vault; and the 59 key systems have been returned to service.

Operators in the Re-Tube Control Centre can then begin the process of achieving first criticality, which means sustaining the chain reaction of splitting atoms and releasing heat.

Breaker close
Reconnecting the reactor to Ontario’s power grid following rounds of inspections and approvals.
Refurbishment timeline
Breaker close
Reconnecting the reactor to Ontario’s power grid following rounds of inspections and approvals.

Throughout refurbishment, the Canadian Nuclear Safety Commission carries out inspections and grants approvals for the project to progress from one milestone to the next. At this stage, the CNSC continues this oversight, confirming the newly refurbished unit can be operated safely and granting approval for the reactor to be gradually brought back to full power and reconnected to Ontario’s power grid.

Shut down
Breaker open
Shutting down the reactor and disconnecting it from Ontario's power grid.
Refurbishment timeline
Breaker open
Shutting down the reactor and disconnecting it from Ontario's power grid.

Following years of detailed planning, approvals and preparations, the Darlington Refurbishment Project team carries out the first major step in project execution: Shutting down the reactor and disconnecting it from the power grid. This is done through a process also known as ‘breaker open,” which involves cooling the reactor and stopping nuclear fission in accordance with Canadian Nuclear Safety Commission regulations and operational procedures.

Defuelling
Removing fuel and heavy water from the reactor.
Refurbishment timeline
Defuelling
Removing fuel and heavy water from the reactor.

Now that the reactor has been safely shut down and the reactor disconnected, workers use remote-controlled tooling to remove 6,240 fuel bundles from the unit and place them in water-filled fuel bays for up to ten years of safe storage. Once the fuel has been removed, workers drain heavy water from the reactor and the heat transport system, then store, clean and purify it before pumping it back in, after unit reassembly.

Islanding
Safely separating the shutdown reactor from the operating plant.
Refurbishment timeline
Islanding
Safely separating the shutdown reactor from the operating plant.

With the fuel and heavy water removed, the unit undergoing refurbishment must be separated from the operating plant. This is done through a process known as Islanding, whereby workers disconnect equipment and put physical barriers in place.

Islanding allows the unit to be refurbished safely and efficiently while limiting impact on the operating units and rest of the station.

Containment pressure testing
Confirming the safe separation of the shutdown unit from the operating plant.
Refurbishment timeline
Containment pressure testing
Confirming the safe separation of the shutdown unit from the operating plant.

Workers perform a containment pressure test at this stage to confirm that the disconnected unit has been safely and completely isolated from the rest of the operating plant.

This process involves raising the pressure in the unit to ensure that any contamination is contained.

Disassembly
Feeder removal
Removing all 960 feeder tubes from the reactor.
Refurbishment timeline
Feeder removal
Removing all 960 feeder tubes from the reactor.

After opening the airlocks to allow for the free movement of materials and equipment, workers remove 960 feeder tubes from the reactor.

Feeder tubes carry heated heavy water to boilers and return the water back to the reactor for reheating.

Removal of the feeders is the first step in the disassembly of
the unit, and sets the stage for replacement of parts.

Fuel channel removal
Removing all 480 fuel channels from the reactor.
Refurbishment timeline
Fuel channel removal
Removing all 480 fuel channels from the reactor.

Fuel channels are made of several components: a pressure tube, two stainless steel end-fittings and annulus spacers, which separate the pressure tube from the calandria tubes, preventing them from touching.

Once all end fittings have been taken out, workers remove all 480 pressure tubes through a process that involves these of engineered tooling mounted on a massive Re-tube Tooling Platform, inside the vault.

Calandria tube removal
Removing all 480 calandria tubes from the reactor.
Refurbishment timeline
Calandria tube removal
Removing all 480 calandria tubes from the reactor.

A calandria tube is a long cylindrical tube made of zirconium that surrounds the pressure tube and forms a leak tight seal of the calandria vessel – the heart of the reactor.

A Darlington CANDU reactor contains 480 calandria tubes, which are removed using specialized tooling, which workers operate remotely and transport in protective flasks to OPG’s Re-tube Waste Processing Building for storage preparation.

Reassembly
Calandria tube installation
Inspecting and cleaning the calandria vessel then installing all 480 calandria tubes inside the reactor.
Refurbishment timeline
Calandria tube installation
Inspecting and cleaning the calandria vessel then installing all 480 calandria tubes inside the reactor.

With all the reactor components removed, workers carefully clean and inspect the calandria vessel to ensure materials show no degradation.

Once this process is complete, workers install 480 new calandria tubes inside the reactor.

Workers complete much of this work manually and directly on the face of the reactor, with direction provided by operators in our Re-tube Control Centre.

After installation, inspection and testing, workers reattach the bellows assemblies, which allow for any movement of pressure tubes and calandria tubes, caused by temperature changes.

Fuel channel installation
Assembling 480 fuel channels in clean rooms then installing them inside the reactor.
Refurbishment timeline
Fuel channel installation
Assembling 480 fuel channels in clean rooms then installing them inside the reactor.

Fuel channels are made of several sub-components: a pressure tube, two stainless steel end-fittings and annulus spacers.

The reactor’s 480 fuel channels are critical parts of the heat transport system, which hold the reactor’s fuel bundles.

At this stage, workers pre-assemble the fuel channels in a climate- and foreign material-controlled clean room then prepare them for delivery to the vault for installation.

Feeder installation
Installing all 960 feeder tubes prior to filling the moderator system.
Refurbishment timeline
Feeder installation
Installing all 960 feeder tubes prior to filling the moderator system.

Each of the reactor’s 960 feeder tubes is unique in shape, size and length, and these new components are delivered in three sections: upper, middle and lower. Because of their unique composition, installing them inside the reactor is a process similar to putting together a puzzle.

Starting with upper section, workers install feeder tubes, making their way down to the lower section, where the feeder tubes are attached to end fittings.

Once this work is complete and regulatory approval received, the project team fills the moderator with clean heavy water and prepares to load the reactor with new fuel.

Power Up
Fuel load
Loading 6,240 fuel bundles into the reactor’s fuel channels.
Refurbishment timeline
Fuel load
Loading 6,240 fuel bundles into the reactor’s fuel channels.

At this stage, workers refill the moderator with heavy water, load each of the 6,240 fuel bundles into the fuel channels, then fill and pressurize the heat transport system.

A fuel bundle contains natural uranium in the form of ceramic pellets.

Containment restored
Confirming the containment of the unit has been restored then removing tooling and physical barriers.
Refurbishment timeline
Containment restored
Confirming the containment of the unit has been restored then removing tooling and physical barriers.

Unit containment is restored once we’ve removed all tooling, including the Re-Tube Tooling Platform, needed to perform refurbishment; the airlocks have been closed; the physical barriers removed from inside the vault; and the 59 key systems have been returned to service.

Operators in the Re-Tube Control Centre can then begin the process of achieving first criticality, which means sustaining the chain reaction of splitting atoms and releasing heat.

Breaker close
Reconnecting the reactor to Ontario’s power grid following rounds of inspections and approvals.
Refurbishment timeline
Breaker close
Reconnecting the reactor to Ontario’s power grid following rounds of inspections and approvals.

Throughout refurbishment, the Canadian Nuclear Safety Commission carries out inspections and grants approvals for the project to progress from one milestone to the next. At this stage, the CNSC continues this oversight, confirming the newly refurbished unit can be operated safely and granting approval for the reactor to be gradually brought back to full power and reconnected to Ontario’s power grid.

Shut down
Breaker open
Shutting down the reactor and disconnecting it from Ontario's power grid.
Refurbishment timeline
Breaker open
Shutting down the reactor and disconnecting it from Ontario's power grid.

Following years of detailed planning, approvals and preparations, the Darlington Refurbishment Project team carries out the first major step in project execution: Shutting down the reactor and disconnecting it from the power grid. This is done through a process also known as ‘breaker open,” which involves cooling the reactor and stopping nuclear fission in accordance with Canadian Nuclear Safety Commission regulations and operational procedures.

Defuelling
Removing fuel and heavy water from the reactor.
Refurbishment timeline
Defuelling
Removing fuel and heavy water from the reactor.

Now that the reactor has been safely shut down and the reactor disconnected, workers use remote-controlled tooling to remove 6,240 fuel bundles from the unit and place them in water-filled fuel bays for up to ten years of safe storage. Once the fuel has been removed, workers drain heavy water from the reactor and the heat transport system, then store, clean and purify it before pumping it back in, after unit reassembly.

Islanding
Safely separating the shutdown reactor from the operating plant.
Refurbishment timeline
Islanding
Safely separating the shutdown reactor from the operating plant.

With the fuel and heavy water removed, the unit undergoing refurbishment must be separated from the operating plant. This is done through a process known as Islanding, whereby workers disconnect equipment and put physical barriers in place.

Islanding allows the unit to be refurbished safely and efficiently while limiting impact on the operating units and rest of the station.

Containment pressure testing
Confirming the safe separation of the shutdown unit from the operating plant.
Refurbishment timeline
Containment pressure testing
Confirming the safe separation of the shutdown unit from the operating plant.

Workers perform a containment pressure test at this stage to confirm that the disconnected unit has been safely and completely isolated from the rest of the operating plant.

This process involves raising the pressure in the unit to ensure that any contamination is contained.

Disassembly
Feeder removal
Removing all 960 feeder tubes from the reactor.
Refurbishment timeline
Feeder removal
Removing all 960 feeder tubes from the reactor.

After opening the airlocks to allow for the free movement of materials and equipment, workers remove 960 feeder tubes from the reactor.

Feeder tubes carry heated heavy water to boilers and return the water back to the reactor for reheating.

Removal of the feeders is the first step in the disassembly of
the unit, and sets the stage for replacement of parts.

Fuel channel removal
Removing all 480 fuel channels from the reactor.
Refurbishment timeline
Fuel channel removal
Removing all 480 fuel channels from the reactor.

Fuel channels are made of several components: a pressure tube, two stainless steel end-fittings and annulus spacers, which separate the pressure tube from the calandria tubes, preventing them from touching.

Once all end fittings have been taken out, workers remove all 480 pressure tubes through a process that involves these of engineered tooling mounted on a massive Re-tube Tooling Platform, inside the vault.

Calandria tube removal
Removing all 480 calandria tubes from the reactor.
Refurbishment timeline
Calandria tube removal
Removing all 480 calandria tubes from the reactor.

A calandria tube is a long cylindrical tube made of zirconium that surrounds the pressure tube and forms a leak tight seal of the calandria vessel – the heart of the reactor.

A Darlington CANDU reactor contains 480 calandria tubes, which are removed using specialized tooling, which workers operate remotely and transport in protective flasks to OPG’s Re-tube Waste Processing Building for storage preparation.

Reassembly
Calandria tube installation
Inspecting and cleaning the calandria vessel then installing all 480 calandria tubes inside the reactor.
Refurbishment timeline
Calandria tube installation
Inspecting and cleaning the calandria vessel then installing all 480 calandria tubes inside the reactor.

With all the reactor components removed, workers carefully clean and inspect the calandria vessel to ensure materials show no degradation.

Once this process is complete, workers install 480 new calandria tubes inside the reactor.

Workers complete much of this work manually and directly on the face of the reactor, with direction provided by operators in our Re-tube Control Centre.

After installation, inspection and testing, workers reattach the bellows assemblies, which allow for any movement of pressure tubes and calandria tubes, caused by temperature changes.

Fuel channel installation
Assembling 480 fuel channels in clean rooms then installing them inside the reactor.
Refurbishment timeline
Fuel channel installation
Assembling 480 fuel channels in clean rooms then installing them inside the reactor.

Fuel channels are made of several sub-components: a pressure tube, two stainless steel end-fittings and annulus spacers.

The reactor’s 480 fuel channels are critical parts of the heat transport system, which hold the reactor’s fuel bundles.

At this stage, workers pre-assemble the fuel channels in a climate- and foreign material-controlled clean room then prepare them for delivery to the vault for installation.

Feeder installation
Installing all 960 feeder tubes prior to filling the moderator system.
Refurbishment timeline
Feeder installation
Installing all 960 feeder tubes prior to filling the moderator system.

Each of the reactor’s 960 feeder tubes is unique in shape, size and length, and these new components are delivered in three sections: upper, middle and lower. Because of their unique composition, installing them inside the reactor is a process similar to putting together a puzzle.

Starting with upper section, workers install feeder tubes, making their way down to the lower section, where the feeder tubes are attached to end fittings.

Once this work is complete and regulatory approval received, the project team fills the moderator with clean heavy water and prepares to load the reactor with new fuel.

Power Up
Fuel load
Loading 6,240 fuel bundles into the reactor’s fuel channels.
Refurbishment timeline
Fuel load
Loading 6,240 fuel bundles into the reactor’s fuel channels.

At this stage, workers refill the moderator with heavy water, load each of the 6,240 fuel bundles into the fuel channels, then fill and pressurize the heat transport system.

A fuel bundle contains natural uranium in the form of ceramic pellets.

Containment restored
Confirming the containment of the unit has been restored then removing tooling and physical barriers.
Refurbishment timeline
Containment restored
Confirming the containment of the unit has been restored then removing tooling and physical barriers.

Unit containment is restored once we’ve removed all tooling, including the Re-Tube Tooling Platform, needed to perform refurbishment; the airlocks have been closed; the physical barriers removed from inside the vault; and the 59 key systems have been returned to service.

Operators in the Re-Tube Control Centre can then begin the process of achieving first criticality, which means sustaining the chain reaction of splitting atoms and releasing heat.

Breaker close
Reconnecting the reactor to Ontario’s power grid following rounds of inspections and approvals.
Refurbishment timeline
Breaker close
Reconnecting the reactor to Ontario’s power grid following rounds of inspections and approvals.

Throughout refurbishment, the Canadian Nuclear Safety Commission carries out inspections and grants approvals for the project to progress from one milestone to the next. At this stage, the CNSC continues this oversight, confirming the newly refurbished unit can be operated safely and granting approval for the reactor to be gradually brought back to full power and reconnected to Ontario’s power grid.