CANDU

CANDU
Name	CANDU reactor
Type	Pressurized Heavy Water Reactor
Developer	Atomic Energy of Canada Limited
First critic	1962
Status	Operational and Decommissioned units
Fuel	Natural uranium, thorium (experimental), mixed oxide
Moderator	Heavy water (deuterium oxide)
Coolant	Heavy water
Electric output	500–1200 MWe (typical range)

CANDU The CANDU design is a class of pressurized heavy-water nuclear reactors developed in Canada that use heavy water as both moderator and primary coolant and can operate on natural uranium fuel. The design evolved through collaboration among Atomic Energy of Canada Limited, provincial utilities like Ontario Hydro, engineering firms such as AECL, and research institutions including Chalk River Laboratories and Canadian Nuclear Laboratories. CANDU plants have been built and operated in countries including Canada, India, Korea, Argentina, Romania, and China, and have influenced international reactor export projects and nuclear policy debates involving bodies like the International Atomic Energy Agency and the Nuclear Energy Agency.

Introduction

The CANDU family originated from mid-20th century projects linked to Chalk River Laboratories, postwar programs such as the Canadian Nuclear Program, and key figures affiliated with AECL and provincial utilities. Early prototypes and demonstration units were built at sites like Douglas Point, Pickering Nuclear Generating Station, and Bruce Nuclear Generating Station. CANDU designs emphasize heavy-water moderation, pressure-tube architecture, and on-power refueling, distinguishing them from light-water reactor types developed by companies like Westinghouse and General Electric. Deployments and transfers involved international agreements with governments such as India and Argentina, and were influenced by export controls and non-proliferation regimes administered by organizations like the Nuclear Suppliers Group.

Design and Technical Features

CANDU reactors use separate pressure tubes within a calandria that contains heavy water moderator, a concept developed through engineering contributions from AECL and tested at facilities including Chalk River Laboratories. The pressure-tube design contrasts with the large pressure vessel approach of Pressurized Water Reactor designs used in United States and French plants financed by firms such as Framatome. Key components include on-power refueling machines, horizontal fuel channels, steam generators connected to turbines made by manufacturers like GE and Siemens, and heavy water systems supplied by companies such as Eureka Chemical Company and serviced under contracts with utilities like Ontario Power Generation. Design features facilitate the use of natural uranium fuel and experimental fuels like thorium-based assemblies tested in cooperation with national laboratories such as Atomic Energy of Canada Limited and research groups at McMaster University.

Fuel Cycle and Refueling

CANDU reactors are notable for using natural uranium fuel, enabling initial deployment without indigenous uranium enrichment capacity—a factor in international agreements involving India, Pakistan, and export controls shaped by the Nuclear Non-Proliferation Treaty and the Nuclear Suppliers Group. The on-power refueling system allows individual fuel channels to be refueled by remote machines developed by AECL collaborators, minimizing downtime and enabling flexible fuel management strategies. Variants have tested alternative fuel cycles including recovered uranium from reprocessing programs, mixed oxide fuel involving suppliers like BNFL and Canadian Nuclear Laboratories, and thorium fuel cycles explored with institutions such as McMaster University and research partners in China and India.

Safety Systems and Performance

Safety systems in CANDU plants include multiple, redundant shutdown systems, heavy water moderator heat removal, containment structures built to seismic standards informed by work at organizations like the United States Geological Survey and regulatory frameworks from bodies such as the Canadian Nuclear Safety Commission and the United States Nuclear Regulatory Commission. Historical operations at Pickering, Bruce, and Darlington stations illustrate reliability metrics used by utilities like Ontario Hydro and Ontario Power Generation, while incidents worldwide prompted regulatory reviews by agencies including the International Atomic Energy Agency and safety upgrades influenced by studies at institutions such as Canadian Nuclear Laboratories. Performance improvements have addressed issues like corrosion, pressure-tube integrity, and outage reduction using inspection technologies from suppliers including AECL partners and nuclear engineering programs at University of Toronto and McMaster University.

Operational History and Global Deployment

CANDU reactors have seen varied operational histories across provinces and countries: large multi-unit stations at Bruce Nuclear Generating Station and Darlington Nuclear Generating Station in Ontario, single-unit deployments at Embalse in Argentina and multi-unit fleets in Korea (e.g., Wolsong Nuclear Power Plant), as well as early units at Douglas Point. Agreements with countries like Romania (e.g., Cernavodă Nuclear Power Plant) and export discussions with nations such as China and Pakistan reflect diplomatic and commercial dimensions involving ministries and utilities including Ontario Hydro, Nuclearelectrica, and national energy ministries. Operational records include prolonged service lives, refurbishments managed by contractors like AECL and national utilities, and international collaboration on life-extension programs supported by organizations including the IAEA and research universities worldwide.

Variants and Modernizations

Several CANDU variants have been developed: the original CANDU designs, the larger CANDU 6, the multi-unit CANDU-PHW series, and modernized versions such as the Enhanced CANDU 6 and Advanced CANDU Reactor concepts developed by AECL and successor corporations. Upgrades and refurbishments include digital control system replacements, new steam generator installations, pressure-tube replacement programs, and heavy-water management improvements performed in cooperation with firms like SNC-Lavalin, Ontario Power Generation, and international partners. Variant projects have explored integration with combined-cycle plants, small modular reactor concepts, and fuel innovations tested collaboratively with research centers such as Chalk River Laboratories and academic partners.

Economic and Environmental Considerations

Economic evaluations of CANDU projects involve capital cost comparisons with reactor types from firms like Westinghouse, Framatome, and GE-Hitachi, operational cost factors managed by utilities including Ontario Power Generation and life-cycle analyses discussed at conferences hosted by organizations such as the World Nuclear Association and OECD Nuclear Energy Agency. Environmental aspects include greenhouse gas displacement relative to fossil fuel plants in regions served by entities like Hydro-Québec and environmental assessments subject to regulators like the Canadian Environmental Assessment Agency. Fuel-use flexibility, including potential thorium cycles and recycled fuel options, factors into long-term waste-management strategies coordinated with national agencies such as Canadian Nuclear Laboratories and international frameworks administered by the International Atomic Energy Agency.

Category:Nuclear reactors