Regulatory hold points for facility refurbishments

As structures, systems and components age, they eventually come to a stage where they need to be modernized if safe operations are to be maintained.

In the life of a nuclear power plant, this modernization comes in the form of refurbishment – an enhancement of equipment and systems that can extend a plant’s life by several decades.

Learn more about the establishment, ongoing oversight, and removal of regulatory hold points (RHPs).

Mandatory checkpoints

Reactor operation cannot proceed past any of the 4 RHPs without approval from the Commission. For the Darlington and Bruce facilities, this approval has been delegated to a person authorized by the Commission, specifically the CNSC’s Executive Vice-President and Chief Regulatory Operations Officer.

The 4 RHPs require the operator to seek approval prior to:

loading fuel into the reactor
removing the guaranteed shutdown state and starting the reactor
exceeding 1% full power
exceeding 35% full power

Darlington Nuclear Generating Station

An excellent example of how RHPs help the CNSC maintain rigorous safety standards in Canada is the current refurbishment of the Darlington Nuclear Generating Station in southern Ontario. In December 2015, the Commission renewed the 10-year operating licence for this facility and authorized the licence holder, Ontario Power Generation (OPG), to undertake the refurbishment and life extension of all 4 Darlington reactor units. In 2016, Unit 2 underwent a 3.5-year refurbishment outage, resuming commercial operation in June 2020. Following this, Unit 3 was also refurbished and was returned to service in July 2023. In November 2024, Unit 1 was returned to service following its refurbishment.

Under licence condition 15.4 of the Darlington power reactor operating licence (PROL) (13.00/2045), OPG is required to obtain approval from the Commission (or a person authorized by the Commission) for the removal of each of the pre-established RHPs before proceeding to the next step in return-to-service activities. In support of this refurbishment project, CNSC and OPG staff created unit-specific return-to-service protocols. These protocols establish specific deliverables and schedules, which OPG must meet to fulfill the prerequisites for the removal of RHPs for the return to service of each unit that has undergone a refurbishment.

In accordance with the Darlington licence conditions handbook, OPG will submit special documentation, known as completion assurance documentation, for each RHP. In addition, once sustained operation is at 100% full power, OPG will be required to submit further documentation specifying what activities were completed between the return from 35% to 100% full power.

Figure 1 shows the timeline for the Darlington refurbishment schedule. — Figure 1 - Darlington Nuclear Generating Station refurbishment timeline

Next steps for Darlington

Unit 4, which is the last unit to be refurbished, is now progressing through the return-to-service phase of its refurbishment outage.

Our regulatory oversight is focused on confirming that prerequisites to remove the next of 4 RHPs have been met. Once all prerequisites for all 4 RHPs have been completed and verified by CNSC staff, OPG can return Unit 4 to service.

Upon return to service of Unit 4, all 4 units at the Darlington Nuclear Generating Station will have been refurbished.

For more information about refurbishment activities at Darlington:

Bruce A and B nuclear generating stations

In 2018, the CNSC renewed the 10-year operating licence for the Bruce A and B nuclear generating stations, which authorized the licence holder, Bruce Power, to undertake the refurbishment – referred to as Major Component Replacement (MCR) outages – of 6 of the reactor units, starting with Unit 6 in 2020.

Under licence condition 15.5 of the Bruce PROL (18.02/2028), Bruce Power is required to obtain approval from the Commission for the removal of the pre-established RHPs before proceeding to the next step in return-to-service activities. In support of this refurbishment project, the CNSC approved the deliverables and schedule for the activities needed to meet the prerequisites for releasing the RHPs.

Figure 2 shows the timeline for the Bruce Power refurbishment schedule. — Figure 2 – Bruce A and B Nuclear Generating Station refurbishment timeline

As of September 9, 2023, all RHPs have been removed from Bruce B Unit 6, and the reactor has returned to full power operation. CNSC staff continue to provide oversight of Unit 6 through the normal baseline compliance program.

Next steps for Bruce

Bruce Power has begun the MCR outage for Unit 3. Fuel has been removed from the reactor, systems have been placed in a lay-up state, and bulkheads have been installed to separate the reactor from the containment system. Work is underway to remove the major components, which will be followed by inspections and then the installation of new components. Unit 3 will follow the same process for return to service once all work has been completed.

The Bruce A Unit 4 MCR outage is expected to start in early 2025.

For more information about the Bruce A and B nuclear generating station refurbishment, read:

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Date modified:: 2026-01-21

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