The Foundation of Canada's Nuclear Fleet

Canada’s nuclear energy program is built on a uniquely homegrown technology: the CANDU reactor. CANDU stands for CANada Deuterium Uranium, a pressurized heavy-water reactor designed to use natural uranium fuel without requiring enrichment. This fundamental choice has shaped the country’s energy landscape for over six decades, delivering a steady stream of carbon-free power to millions of homes and businesses. Today, as the nation pursues a legally binding target of net-zero emissions by 2050, CANDU reactors have evolved from a mid-century engineering achievement into one of the most effective tools for deep, rapid decarbonization.

The importance of nuclear power in Canada’s climate strategy is difficult to overstate. In 2022, nuclear reactors provided about 15 percent of the country’s total electricity, but more critically, they accounted for nearly 60 percent of Ontario’s generation mix – a province that has already eliminated coal-fired power. Across the rest of the country, provinces like New Brunswick also depend on CANDU units for a significant share of their clean energy; Point Lepreau, for example, supplies roughly one-third of New Brunswick’s electricity from a single 660 MW CANDU 6 unit. While wind and solar expansion accelerates, the reliable baseload from CANDU reactors ensures grid stability and allows natural gas plants to be phased down rather than kept online as backup.

Unlike pressurized water reactors built elsewhere, CANDU technology employs a horizontal fuel channel design and heavy water as both moderator and coolant. This yields a neutron economy so efficient that unenriched uranium can sustain a chain reaction. The practical benefit for climate policy is substantial: Canada avoids both the emissions of fossil generation and the energy-intensive enrichment processes that supply conventional light-water reactors. Moreover, the ability to refuel on-power means CANDU units have exceptionally high capacity factors – often above 90 percent – enabling them to reliably supply the grid day and night through all seasons. In 2023, Bruce Power’s eight units achieved an average capacity factor of 92.5 percent, making them some of the most productive reactors in the world.

Low-Carbon Electricity and Public Health Co-Benefits

The climate advantage of a CANDU reactor begins with its near-zero operational emissions. After accounting for the full lifecycle – construction, mining, fuel fabrication, and decommissioning – nuclear power produces roughly 12 grams of CO₂ equivalent per kilowatt-hour. That figure is comparable to wind and substantially lower than solar photovoltaic systems, and it is one to two orders of magnitude below natural gas combined-cycle plants. For a country where heating demand drives winter electricity peaks, replacing fossil baseload with nuclear has an outsized impact on national emissions inventories. The Intergovernmental Panel on Climate Change (IPCC) consistently ranks nuclear among the lowest-carbon energy sources in its lifecycle assessments.

The phase-out of coal in Ontario, completed in 2014, offers a powerful real-world demonstration. The Bruce Power and Darlington nuclear stations, along with the Pickering plant, filled the void left by shuttered coal units. Ontario’s electricity sector greenhouse gas emissions plummeted from around 40 megatonnes in 2000 to less than 4 megatonnes by 2018. That rapid decline – one of the single largest greenhouse gas reductions in North America – was made possible by CANDU reactors operating at full capacity while renewable portfolios were still scaling up. The health co-benefits have been equally striking: a study by the Canadian Nuclear Association estimated that eliminating coal and using nuclear power avoided thousands of premature deaths and hundreds of thousands of asthma episodes, particularly in urban areas downwind of old coal plants.

In Saskatchewan and Alberta, both provinces with current coal and natural gas dependence, policymakers are now evaluating the potential of small modular reactors (SMRs) derived from CANDU expertise. These designs envision a future where nuclear plants, large and small, provide non-emitting, dispatchable heat and power for district heating systems and industrial processes such as bitumen extraction and potash mining – hard-to-abate sectors that are vital to the Canadian economy but challenging to decarbonize with renewables alone. A 2024 analysis from the University of Alberta estimated that replacing natural gas boilers in the oil sands with CANDU-based SMR heat could reduce the sector’s emissions by up to 12 megatonnes per year by 2040.

Heavy Water and the On-Power Refueling Advantage

The heavy-water moderator in a CANDU reactor does more than allow natural uranium fuel; it creates operational flexibility that directly supports climate goals. Because the moderator and coolant are separate, the reactor can be refueled while running at full power. Two robotic fueling machines, one at each end of a fuel channel, insert fresh fuel bundles while spent ones are pushed out the opposite side. There is no need for lengthy shutdowns every 18 to 24 months, as required by typical light-water reactors. This continuous process leads to the remarkable capacity factors observed at Bruce Power and Darlington, where units frequently operate for more than 90 percent of the year.

From a climate perspective, every hour a CANDU unit runs displaces fossil generation that would otherwise be called upon. When wind speeds drop or solar output fades, nuclear plants remain steady. The combination of CANDU baseload with expanding wind and solar capacity is not a rivalry but a strategic partnership: nuclear handles the base of the demand curve, while renewables reduce the need for natural gas in the intermediate and peak bands. As carbon pricing rises under the federal backstop framework, the economic case for keeping CANDU units running becomes even stronger. According to the International Energy Agency, extending the life of existing nuclear plants is one of the most cost-effective measures for climate mitigation, often cheaper than building new renewables with storage when accounting for system integration costs.

Life Extension and Refurbishment: Maximizing the Existing Fleet

Canada is not starting from scratch. The country has a fleet of 19 operating CANDU reactors at four sites – Bruce A and B, Darlington, Pickering, and Point Lepreau – representing a combined capacity of about 13.6 gigawatts. Keeping these units in service through mid-life refurbishment is a central pillar of the national climate strategy. The Darlington Refurbishment Project, undertaken by Ontario Power Generation, is a benchmark for complex nuclear overhauls. By replacing pressure tubes, calandria tubes, and steam generators, the plant’s four units are being renewed for another 30 years or more of operation.

That project, now nearing completion with a strong safety and budget record, has proven that CANDU reactors can be modernized at predictable costs. The refurbishment of Bruce Power’s six units began in 2020 and is projected to extend operations into the 2060s. Together, these initiatives secure approximately 6,300 megawatts of zero-carbon baseload capacity for decades – capacity that would otherwise need to be replaced by new natural gas plants or massive overbuilds of renewables with storage. The economics are compelling: the levelized cost of refurbished nuclear electricity in Ontario is estimated to be in the range of 5 to 8 cents per kilowatt-hour, competitive with new gas and far lower than new nuclear builds.

The climate payoff is enormous. Combined, the Darlington and Bruce refurbishments are expected to avert more than 200 million tonnes of CO₂ emissions over the extended lifetimes, assuming they displace a mix of gas and coal. That is roughly equivalent to taking every car in Canada off the road for six years. The Canadian Nuclear Safety Commission maintains rigorous oversight, ensuring that aging management programs and modern seismic safety margins meet or exceed current standards. The result is a fleet that gets safer and cleaner as it ages. Meanwhile, the Pickering station is slated for a phased shutdown beginning in 2025, but policy discussions around a potential life extension are ongoing given its continued value for grid stability and emissions reduction.

Fuel Cycle Innovations and Waste Management

A common question in climate discussions is the fate of used nuclear fuel. Canada’s approach is anchored in a long-term plan under the Nuclear Waste Management Organization (NWMO), which is advancing a deep geological repository in a willing host community. After decades of research, the project has narrowed its focus to two siting areas in Ontario – the Ignace area and the Wabigoon Lake Ojibway Nation area. The repository will isolate used fuel bundles more than 500 meters underground in stable crystalline rock, ensuring no harmful release to the environment over geological timescales. Community engagement has been a cornerstone, with the NWMO emphasizing free, prior, and informed consent as the foundation of its site selection process.

Meanwhile, CANDU reactors offer unique fuel cycle advantages that could reduce waste and extract more energy. Because the design is neutron-efficient, it can run on a mix of fuels including recovered uranium from reprocessed light-water reactor fuel, thorium, and potentially even spent fuel directly. Research at Canadian Nuclear Laboratories has demonstrated the feasibility of advanced fuel cycles like DUPIC (Direct Use of spent PWR fuel In CANDU), which would effectively double the energy extracted from nuclear fuel while shrinking waste volumes. Another promising avenue is the use of recycled uranium from reprocessed CANDU spent fuel itself, creating a closed loop that reduces the need for new mining. While such cycles are not commercially deployed today, they provide a pathway to an even more sustainable nuclear fuel cycle as pressure on resources intensifies.

The ability to burn natural uranium also reduces reliance on enrichment facilities, a geopolitical consideration that aligns with Canada’s clean energy ambitions. As nations work to secure low-carbon supply chains, Canada’s domestic uranium mining and fuel fabrication industries – centered in Saskatchewan and Ontario – benefit from short, transparent logistics that lower lifecycle carbon footprints. For a country aiming to lead in environmental, social, and governance (ESG) standards, the CANDU fuel cycle is a strategic asset. Furthermore, the heavy-water production at plants like the Bruce Heavy Water Plant historically required significant energy input, but modern efficiency improvements and the use of excess nuclear heat have minimized that footprint.

Small Modular Reactors and the Next Generation of CANDU

While extending the current fleet is the immediate priority, the long-term climate roadmap increasingly features advanced CANDU designs and small modular reactors. The government’s SMR Action Plan, released in 2020, identifies CANDU technology as a foundation for next-generation projects. The Canadian-designed CANDU SMR concept, sometimes called the EC6 or the Advanced CANDU Reactor (ACR)-1000, incorporates passive safety systems, simplified construction, and the flexibility to use various fuels. These units, with capacities ranging from 300 to 700 megawatts, could be deployed in provinces currently without nuclear infrastructure, such as Saskatchewan or Alberta, providing high-temperature heat for industrial processes.

An even more transformative idea is the potential marriage of CANDU designs with molten salt or helium-cooled reactors that operate at higher temperatures. At such temperatures, nuclear heat can drive thermochemical processes to produce clean hydrogen, synthetic fuels, and feedstocks for the chemical industry. For Canada, home to vast oil sands operations and heavy industry, the ability to supply clean hydrogen from nuclear power could be the missing piece in a net-zero puzzle. A study by Natural Resources Canada suggests that nuclear-produced hydrogen could cut petroleum refining emissions by up to 15 megatonnes per year by 2050, while also creating a new export commodity. The Alberta government has already allocated funds to study nuclear hydrogen integration at existing industrial clusters near Edmonton and Fort McMurray.

The first projects are already moving forward. In Saskatchewan, the utility SaskPower is evaluating a CANDU-based SMR for potential deployment in the mid-2030s, with support from Ontario Power Generation’s SMR development team. The lessons learned from decades of CANDU operation – including robust supply chains, domestic fuel manufacturing, and deep regulatory experience – are being poured into these new designs. This institutional knowledge dramatically lowers the risk profile compared to starting from scratch. Internationally, countries like Romania, Poland, and Argentina have signed agreements to explore CANDU technology, leveraging Canadian expertise to phase out coal. Romania’s two operating CANDU units at Cernavodă are already among the cleanest electricity sources in Eastern Europe, and the country is planning to build two additional CANDU units with Canadian support.

Economic and Workforce Dimensions

Climate action is often framed as a trade-off between environmental integrity and economic prosperity. Canada’s CANDU fleet challenges that narrative. The nuclear sector supports approximately 76,000 direct and indirect jobs across the country, from uranium mining in northern Saskatchewan to engineering and manufacturing in Ontario. The Bruce Power Life-Extension Program alone sustains about 22,000 jobs annually and injects billions of dollars into the provincial economy. As the world moves toward low-carbon supply chains, Canadian industries powered by CANDU electricity have a competitive advantage in carbon-conscious markets.

Moreover, the refurbishment projects are creating a new generation of skilled trades and engineers, many from Indigenous communities and other traditionally underrepresented groups. The Nuclear Waste Management Organization’s siting process, built on the principle of free, prior, and informed consent, has fostered partnerships with First Nations that go far beyond procurement quotas. For example, the Saugeen Ojibway Nation has negotiated deep collaborative agreements with Bruce Power and Ontario Power Generation, ensuring that the energy transition respects Indigenous rights and creates shared value. These social dimensions are an essential piece of any credible climate strategy.

The export potential is also significant. Countries looking to phase out coal, such as Poland, Romania, and Argentina, have signed agreements with Canadian firms to explore CANDU technology. By exporting clean, reliable nuclear technology, Canada can help other nations bend their own emissions curves while strengthening domestic supply chains. The World Nuclear Association notes that CANDU reactors are particularly attractive for countries that seek energy independence without establishing enrichment facilities. Recent developments include a memorandum of understanding between Canadian nuclear vendors and Polish utility PGE for deploying CANDU-based SMRs as part of Poland's coal transition plan.

Policy and Public Support: Anchoring Nuclear in Canada’s Climate Plan

The federal government’s climate architecture – anchored by the Canadian Net-Zero Emissions Accountability Act – recognizes nuclear energy as a key pillar. The 2023 federal budget included substantial tax incentives for clean energy technologies, including nuclear. The Clean Electricity Regulations, now being finalized, will effectively require all electricity generation to be net-zero by 2035. While the regulations include some flexibility for existing natural gas plants, the clear intent is to maximize non-emitting baseload, and no technology currently matches CANDU’s combination of low emissions, reliability, and domestic content.

Public opinion, once a potential barrier, has shifted steadily. A 2023 poll by the Canadian Nuclear Association found that 57 percent of Canadians support nuclear power as part of the climate solution, up from 44 percent five years earlier. In Ontario, where the benefits are most visible, support exceeds 70 percent. This growing social license is grounded in operational excellence: CANDU stations have maintained an exemplary safety record, with no serious accidents in the technology’s history. Open communication about refurbishments, waste management, and emergency preparedness has built trust over decades. Provincial energy boards have noted that public engagement events for SMR proposals in Saskatchewan and Ontario have drawn constructive participation rather than opposition.

Provinces retain authority over electricity generation, and the diverging policies illustrate the stakes. Ontario’s Phase II of the Darlington refurbishment and the pursuit of SMRs at the Darlington site show a province betting heavily on nuclear for climate and economic growth. In contrast, provinces without nuclear – such as Alberta and Saskatchewan – currently rely on fossil fuels for the bulk of their power. As federal carbon pricing escalates to $170 per tonne by 2030, the cost of that reliance will become increasingly painful, making CANDU and SMR solutions more attractive. A recent analysis by the Pembina Institute, while traditionally favoring renewables, acknowledged that nuclear could play a role in Alberta’s grid if SMR costs continue to decline.

Climate Resilience and Grid Reliability

Beyond emissions reduction, CANDU reactors contribute to climate resilience by providing stable power during extreme weather events. During the 2021 heat dome in British Columbia and the 2023 wildfires across the Northwest Territories, hydroelectric output faltered due to drought and evacuation risks, while CANDU plants in unaffected regions continued to operate at full capacity. In Ontario, the Bruce Power and Darlington stations maintained output during the January 2024 ice storm that knocked out transmission lines and wind turbines, helping to stabilize the grid. As climate change increases the frequency of such events, the dispatchable, weather-independent nature of nuclear generation becomes a critical asset for energy security. The Canadian Climate Institute has highlighted the need for "firm, low-carbon capacity" as part of a resilient electricity system, a role that CANDU reactors fulfill uniquely well.

How CANDU Technology Fits into the Broader Decarbonization Mosaic

Climate solutions are not either/or propositions; they require a portfolio. CANDU reactors complement hydroelectricity, wind, solar, and emerging storage technologies in a resilient grid. Quebec’s massive hydro dams already provide clean electricity, but even that province is exploring nuclear as a way to meet winter peak demand without building new dams. British Columbia, with its rich hydro resource, is also evaluating SMRs for remote communities and industrial heat. The common thread is that CANDU-derived technology provides a dense, always-on power source that can anchor a decarbonized grid.

The University of Saskatchewan’s Global Institute for Water Security recently modeled a net-zero grid for the Prairies that combined wind, solar, and a CANDU SMR. The results, published in 2022, showed that adding a single 300-megawatt SMR reduced the required battery storage by over 40 percent and cut total system costs by 15 percent compared to a renewables-only scenario. This kind of analysis is reshaping conversations in provincial energy ministries, where the reliability and affordability of nuclear are now seen as complementary, not contradictory, to rapid renewable deployment.

Finally, the deep decarbonization of heat remains a frontier where CANDU products can excel. District energy systems in cities like Toronto and Saskatoon are evaluating low-temperature nuclear heat from SMRs to replace natural gas boilers. Ontario Tech University’s Clean Energy Research Laboratory has demonstrated the feasibility of coupling a small CANDU-6 reactor to a desalination plant and hydrogen electrolyzer, showing how one nuclear unit can simultaneously supply electricity, fresh water, and zero-emission fuel. For a country with a long coastline and a growing clean fuel industry, such cogeneration could be the engine of a sustainable economy. The federal government’s upcoming hydrogen strategy update is expected to include nuclear hydrogen as a priority technology, recognizing the synergies between CANDU heat and electrolysis.

The Path Ahead: Maintaining Momentum

Canada’s climate targets are among the most ambitious in the world: a 40-45 percent reduction in emissions below 2005 levels by 2030 and net-zero by 2050. CANDU reactors, by extending the life of existing units and laying the foundation for a new generation of advanced designs, offer a proven and practical route to achieving those targets. The alternative – retiring nuclear plants and replacing them with natural gas – would lock in emissions for decades and make the math of climate action almost impossible.

Regulators, industry, and Indigenous communities are now working together on a roadmap for an SMR fleet that could begin deployment in the 2030s. The first regulatory reviews are underway, and the CNSC’s pre-licensing design review process for CANDU-based SMRs has provided early confidence. With sustained investment and political will, Canada could see its second nuclear era – one defined not just by clean electricity, but by a system that integrates nuclear heat, hydrogen, and industrial decarbonization in a seamless, circular economy.

The CANDU reactor, born of Canadian ingenuity in the mid-20th century, has become a 21st-century climate solution. Its capacity to deliver massive, reliable, carbon-free energy while creating jobs and fostering energy sovereignty makes it an irreplaceable asset. As the world’s climate window narrows, the quiet hum of heavy-water pipes and steam turbines in stations like Darlington and Bruce will remain one of Canada’s strongest signals of commitment to a livable planet.

For more detailed information on nuclear energy in Canada, visit the Canadian Nuclear Association, and for the latest on SMR developments, see Canada's SMR Action Plan.