CANDU technology

CANDU advantages

CANDU stands for CANada Deuterium Uranium, because it was invented in Canada, uses deuterium oxide (also known as heavy water) as a moderator, and uranium as a fuel.

CANDU fuel bundle

CANDU fuel bundle. Source: Nuclear Waste Management Organization.

CANDU reactors are unique in that they use natural, unenriched uranium as a fuel; with some modification, they can also use enriched uranium, mixed fuels, and even thorium. Thus, CANDU reactors are ideally suited for using material from decommissioned nuclear weapons as fuel, helping to reduce global arsenals.

CANDU reactors can be refueled while operating at full power, while most other designs must be shut down for refueling. Moreover, because natural uranium does not require enrichment, fuel costs for CANDU reactors are very low.

CANDU reactors are exceptionally safe. The safety systems are independent from the rest of the plant, and each key safety component has three backups. Not only does this redundancy increase the overall safety of the system, but it also makes it possible to test the safety system while the reactor is operating under full power.

CANDU reactor schematic

Source: Candu.

CANDU reactors in Canada

There are currently 19 CANDU reactors in operation in Canada: 8 at Bruce Power, 6 in Pickering, 4 in Darlington, and one in Point Lepreau.

CANDU reactors in operation in Canada
Reactor Net capacity (MWe) Start year
Bruce A: Unit 1 750 1977
Bruce A: Unit 2 750 1977
Bruce A: Unit 3 750 1978
Bruce A: Unit 4 750 1979
Bruce B: Unit 1 817 1985
Bruce B: Unit 2 817 1984
Bruce B: Unit 3 817 1986
Bruce B: Unit 4 817 1987
Darlington: Unit 1 881 1992
Darlington: Unit 2 881 1990
Darlington: Unit 3 881 1993
Darlington: Unit 4 881 1993
Pickering A: Unit 1 515 1971
Pickering A: Unit 4 515 1973
Pickering B: Unit 1 516 1983
Pickering B: Unit 2 516 1984
Pickering B: Unit 3 516 1985
Pickering B: Unit 4 516 1986
Point Lepreau 680 1983


Bruce Power

There are eight CANDU reactors at the Bruce Power site on the shores of Lake Huron in Tiverton, Ontario, making it one of the largest nuclear power facilities in the world.

Unit 1 was taken offline in 1997 and Unit 2 in 1995. In 2006, life-extension projects started on these two reactors. Both returned to the grid in 2012 with plans to deliver safe and reliable power to Ontarian households for the next 25 to 30 years.

Bruce Power nuclear power plant

Bruce Power nuclear power plant.


The Darlington nuclear generating station is Canada’s second-largest nuclear facility by total energy output. Its four CANDU reactors are owned and operated by Ontario Power Generation (OPG). Capable of producing up to 31 million MWh annually, the Darlington station can power up to 2.5 million households.

In February, 2010, OPG announced plans to proceed with the detailed planning phase for the mid-life refurbishment of the Darlington station.

Darlington nuclear power plant

Darlington nuclear power plant.


The Pickering nuclear generating station is Ontario’s smallest commercial nuclear facility. Its four CANDU reactors – the smallest in Canada – are owned and operated by Ontario Power Generation (OPG). Despite their smaller size, the CANDU units at the Pickering station can power up to 2.5 million households.

Pickering nuclear power plant

Pickering nuclear power plant.

Point Lepreau

Point Lepreau was the first CANDU 6 reactor to be licensed for operation, the first to achieve criticality and first to begin commercial operation. It is owned and operated by New Brunswick Power (NB Power) and supplies approximately 30% of the province’s electricity.


The Gentilly-2 CANDU 6 reactor is owned and operated by Hydro-Québec. Its construction began in 1974, it went into service in 1983, and was safely shut down in 2012.

CANDU reactors around the world

Canada has exported CANDU reactors to Argentina, China, India, Pakistan, Romania, and South Korea. There are 31 CANDU reactors in operation globally, not including 16 reactors in India that are based on the CANDU design, but are not technically CANDUs.

CANDU reactors in operation around the world
Country Type of reactor Units Net capacity (MWe)
Argentina CANDU 1 600
Canada CANDU 19 13,513
China CANDU 2 1,280
India CANDU & CANDU-derived 2 + 16 277 + 3,480
Pakistan CANDU 1 125
Romania CANDU 2 1,305
South Korea CANDU 4 2,579