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Final work on Unit 2 reactor construction underway

At the end of the second quarter of 2019, the final stages of construction work on OPG’s Darlington Unit 2 Refurbishment Project, involving the installation of lower feeders, were well underway. As a result of slower than expected installation of lower feeders, Unit 2 will now return to service by June 2020 rather than February 2020 as previously anticipated. The refurbishment of Unit 2 remains on budget and the overall budget and schedule for the 10-year refurbishment project also remains on track.

The potential four-month extension to the return to service of Unit 2 is a result of delays related to fabrication and installation of feeder tube components. The fabrication delays had a cascading impact that resulted in upper, middle and lower feeders being installed at the same time, creating logistical and physical challenges with overlapping work. In response, OPG increased project management leadership and oversight, and the project team re-sequenced the work, expanded its training efforts, deployed new tooling to assist workers, and increased the number of trade resources and supervision in the field. The impact of Unit 2 fabrication delays have been fully resolved and will not affect future units.

OPG anticipates that these changes, along with its commitment to completing the work safely and with quality, will allow the overall project to remain on time and on budget. The learnings and actions taken are also being carefully applied to maintain strong cost control, improve schedule performance and reduce risks for all future units.

OPG and its project partners have now completed 85% of the Unit 2 construction work. The installation of fuel channels, upper and middle feeders, and the installation of reactivity safety system mechanisms were recently completed. Thirty-three of 58 major plant systems have also been returned to service. In addition, the project team completed the turbine overhaul, work on steam generators and electrical systems, and all safety improvement projects.

Unit 3 update

Unit 3 is scheduled to commence refurbishment in the first quarter of 2020. The extension of the return to service of Unit 2 will lengthen the overlap of both units but will have no impact on subsequent units. Refurbishment of overlapping units is part of the project plan.

Design and engineering are more than 90% complete and are on track for full completion by the end of 2019. Over 2,800 lessons learned have been captured from Unit 2 refurbishment to date, and are being applied to Unit 3 to reduce risk and improve cost and schedule performance. All long lead material procurement is on track.

This is a pivotal moment for the Darlington Refurbishment Project as major reactor construction work on Unit 2 is being completed and preparation work on Unit 3 is starting.

Environment

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

Safety

  • Five-fold better than Ontario construction industry.

Quality

  • No quality events reported.

Schedule

  • Refurbishment of all four Darlington units remained on schedule
  • Unit 2 expected to return to service by June 2020
  • Unit 3 planned to commence Q1 2020

Cost

  • Refurbishment forecasted to remain on budget for all four Darlington units
  • Lessons learned applied to Unit 3 planning for further efficiencies

Refurbishment timeline

Project Status: ScheduledStart Date: Q3 2021Expected Completion: Q3 2024
Project Status: UnderwayStart Date: October 2016Expected Completion: Q2 2020
Project Status: ScheduledStart Date: Q2 2020Expected Completion: Q3 2023
Project Status: ScheduledStart Date: Q1 2023Expected Completion: 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.