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CANDU stands for "CANada Deuterium Uranium".

It's a Canadian-designed power reactor of PHWR type (Pressurized Heavy Water Reactor) that uses heavy water (deuterium oxide) for moderator and coolant, and natural uranium for fuel.

Use of natural uranium as a fuel

• CANDU is the most efficient of all reactors in using uranium: it uses about 15% less uranium than a pressurized water reactor for each megawatt of electricity produced
• Use of natural uranium widens the source of supply and makes fuel fabrication easier. Most countries can manufacture the relatively inexpensive fuel
• There is no need for uranium enrichment facility
• Fuel reprocessing is not needed, so costs, facilities and waste disposal associated with reprocessing are avoided
• CANDU reactors can be fuelled with a number of other low-fissile content fuels, including spent fuel from light water reactors. This reduces dependency on uranium in the event of future supply shortages and price increases

Use of heavy water as a moderator

• Heavy water (deuterium oxide) is highly efficient because of its low neutron absorption and affords the highest neutron economy of all commercial reactor systems. As a result chain reaction in the reactor is possible with natural uranium fuel
• Heavy water used in CANDU reactors is readily available. It can be produced locally, using proven technology. Heavy water lasts beyond the life of the plant and can be re-used

CANDU reactor core design

• Reactor core comprising small diameter fuel channels rather that one large pressure vessel
• Allows on-power refueling - extremely high capability factors are possible
• The moveable fuel bundles in the pressure tubes allow maximum burn-up of all the fuel in the reactor core
• Extends life expectancy of the reactor because major core components like fuel channels are accessible for repairs when needed

CANDU 6

CANDU 6 is our 700 MWe class nuclear power reactor. The first CANDU 6 plants went into service in the early 1980s as leading-edge technology, and the design has continuously evolved since to maintain superior technology and performance.

It was licensed in the early 1980s in Canada, Argentina and the Republic of Korea. In 1996, Cernavoda Unit 1 was licensed in Romania, and Wolsong Unit 2 was licensed in Korea. Wolsong Units 3 and 4 were licensed in Korea in 1997 and 1999 respectively. Qinshan Units 1 and 2 were licensed in China in 2002 and 2003 respectively. In 2007, Cernavoda Unit 2 was licensed in Romania. These units came into service ahead of schedule and on budget. There are 11 CANDU 6 units in operation.

Enhanced CANDU 6

• natural uranium fuelling
• a design based on our highly successful CANDU 6 reactors
• superior safety performance and economics
• very high localization
• suitability for small and medium electric grids

The EC6 is a 700 MWe class heavy-water moderated and heavy-water cooled pressure tube reactor. Heavy water is a natural form of water used as a moderator to slow down the fission chain reaction neutrons in the reactor. It is one of the most efficient moderators and enables the CANDU design to use natural uranium as fuel, which is unique to CANDU reactors. The use of natural uranium increases a country’s energy independence as fuel can be manufactured locally, and reprocessing and associated issues can be avoided.

Heavy water coolant passes through the reactor core and removes the heat generated by the fission chain reactions. This heated reactor coolant heats light (ordinary) water and converts it to steam, which drives a turbine-generator to produce electricity.

The EC6 reactor is the evolution of the proven CANDU 6 design. It is based on the Qinshan Phase III CANDU 6 plant in China, designed to meet industry and public expectations of nuclear power generation that is safe, reliable and environmentally friendly.

It has been enhanced by using the experience and feedback that AECL gained in the development, design, construction and operation of 11 CANDU 6 units operating in five countries. CANDU 6 reactors are performing well on four continents with over 150 reactor-years of excellent and safe operation.

While retaining the basic features of the CANDU 6 design, the EC6 reactor incorporates innovative features and state-of-the-art technologies that enhance safety, operation and performance.

The latest CADDS tools and innovative integrated systems linking material management, documentation, safety analysis and project execution databases are used to ensure that accurate and complete configuration management can be readily maintained by the plant owner.

The EC6 reactor has projected an average annual operational performance factor of 94% and 92% lifetime including mid-life retubing. The performance factor is the ratio of available capacity to the theoretically possible capacity, and this characterizes the reliability of the plant. In recent years, the global CANDU 6 fleet achieved an average lifetime performance factor of 89%, which ranked the fleet in the world’s top reactor performance echelons. In the last decade, three of the CANDU units in South Korea ranked in the top 10 list for world reactors.

The EC6 reactor design benefits from the proven principles and characteristics of the CANDU 6 design and decades of operation.

Proven CANDU strengths include:

• Two independent safety shutdown systems
• Refuelling during on-power operation
• Passive water tank located in the containment
• Modular, horizontal fuel channel core
• Separate low-temperature, low-pressure moderator that provides inherently passive heat sinks by permitting heat to be removed from the reactor core under abnormal conditions
• Reactor vault that is filled with cool light water that surrounds the reactor core and provides an additional passive heat sink for mitigation of severe accidents
• Reactor building access for maintenance activities during on-power operation