Canada has never pursued nuclear weapons, but it now possesses one of the world's easiest technical pathways to build them, according to nuclear security experts. The country's unique reactor design, abundant uranium supplies, and emerging small modular reactor (SMR) technology are converging to create what researchers call a "threshold nuclear arms power" situation, where the only barrier is political will, not technical capability.

Why Does Canada's Reactor Design Make Weapons Production Easier?

Canada's CANDU heavy water reactors, which power stations like the Pickering facility near Toronto, operate fundamentally differently from the light water reactors used in most of the world's 440-odd nuclear plants. While CANDU reactors use natural, unenriched uranium containing only about 0.7 percent of the U-235 isotope needed for weapons, they excel at producing plutonium-239, the isotope used in nuclear bombs.

The critical difference lies in how these reactors refuel. Light water reactors require enriched uranium, seal their cores, and run for 18 to 24 months before refueling. This makes it relatively easy for international inspectors to track fuel going in and spent fuel coming out. CANDU reactors, by contrast, use "online refueling," meaning operators can continuously swap fuel rods while the reactor is running.

"All uranium-fuelled reactors produce plutonium. The issue with the CANDU is that it has online refuelling. You're refuelling continuously, which makes it harder for the IAEA," explained Ed Lyman, director of nuclear safety for the Union of Concerned Scientists in Washington, D.C.

Ed Lyman, Director of Nuclear Safety, Union of Concerned Scientists

This design feature makes it significantly harder for the International Atomic Energy Agency (IAEA) to detect if a country is diverting fissile material for weapons purposes. India leveraged this exact advantage in 1974, using a Canadian heavy water reactor to produce the plutonium for its first nuclear weapon, the "Smiling Buddha" test.

What New Technology Is Changing Canada's Nuclear Equation?

Canada is now branching into small modular reactors, a next-generation nuclear technology designed to be cheaper, safer, and more flexible than traditional large reactors. However, some SMR designs require enriched uranium, which introduces a new proliferation concern.

Specifically, Canada is considering reactors that use high-assay low-enriched uranium (HALEU), uranium enriched to levels as high as 20 percent. While international standards classify anything below 20 percent as "low-enriched uranium" with lower oversight, nuclear experts argue this threshold is misleading.

"Anything below 20 percent is considered low-enriched uranium and has a much lower level of oversight. The IAEA considers it indirect-use material you can't directly use in a bomb. But there's evidence, both historical and technical, that that's not true, and that the actual cutoff for weapon-usable uranium is below 20 percent. Could be 15 percent, could be 10 percent," noted Ed Lyman.

Ed Lyman, Director of Nuclear Safety, Union of Concerned Scientists

One proposed Canadian SMR, the ARC 100 reactor planned for New Brunswick, would become the only commercial fast-breeder reactor in the world outside Russia. While ARC Canada argues its design mitigates proliferation risks through a 20-year sealed fuel cycle, the broader concern remains: if Canada develops a fleet of SMRs using HALEU and builds domestic enrichment plants to support them, the country would gain what experts call a "threshold capability for bombs."

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How Could Canada Develop Domestic Uranium Enrichment?

Canada currently imports enriched uranium from France and the U.S., despite being the world's second-largest uranium producer. This arrangement means Canada often buys back its own mined uranium after other countries have added value through enrichment. However, geopolitical instability is forcing policymakers to reconsider this dependency.

Canada's official nuclear energy strategy acknowledges that "geopolitical volatility has exposed fragility in nuclear fuel supply chains at every stage," including mining, milling, refining, conversion, enrichment, and fabrication. The strategy notes that "the longer-term question of whether Canada should develop domestic enrichment capability remains under assessment."

According to nuclear weapons expert Steve Fetter of the University of Maryland, who served as head of national security and international affairs in the White House Office of Science and Technology Policy, the technical barriers to Canadian weapons development are minimal.

"The only thing that inhibits Canada is the will to do it, the political decision to do it," said Steve Fetter, nuclear weapons expert at the University of Maryland.

Steve Fetter, Nuclear Weapons Expert, University of Maryland

Fetter noted that Canada's path mirrors that of the United Kingdom after World War II. When the U.S. froze out both countries from nuclear cooperation following the Manhattan Project, the U.K. chose to develop its own indigenous nuclear program and eventually became a nuclear weapons power. Canada made a different political choice.

Key Factors That Make Canada a Threshold Nuclear Power

• Abundant Domestic Uranium: As the world's second-largest uranium producer, Canada controls its own fuel supply and has never needed to enrich uranium domestically, reducing international scrutiny of enrichment activities.
• CANDU Reactor Design: The online refueling capability makes it extremely difficult for international inspectors to detect diversion of weapons-grade plutonium, unlike light water reactors used globally.
• Plutonium Production Efficiency: Heavy water reactors produce plutonium-239 that is easier to weaponize than plutonium from light water reactors, a fact demonstrated by India's 1974 nuclear test.
• Tritium Abundance: CANDU reactors produce tritium in abundance, a critical component of modern two-stage thermonuclear weapons that Canada has in significant quantities.
• SMR Enrichment Plans: Proposed small modular reactors using HALEU would require Canada to develop domestic enrichment capabilities, further shortening the technical path to weapons-grade material.

What Do Experts Say About Canada's Nuclear Future?

Former IAEA director and Nobel Peace Prize laureate Mohamed ElBaradei stated that "any country which has a complete fuel cycle is a latent nuclear weapons country, in the sense that it is not far from making a nuclear weapon." Canada is moving closer to completing that full cycle.

Scientists consulted by CBC News indicated that Canada would likely have little economic incentive to build its own enrichment facilities in the near term. However, the strategic calculus could shift if geopolitical tensions worsen or if the government prioritizes energy independence over cost considerations. The fact that Canada's nuclear energy strategy explicitly lists enrichment capability as "under assessment" suggests the conversation is no longer theoretical.

The convergence of CANDU reactor technology, SMR development, and enrichment discussions means that Canada's technical threshold for nuclear weapons capability will likely shrink in the coming years, regardless of whether the country ever chooses to cross it. For now, policy and politics remain the only barriers between Canada and a weapons program, but those barriers are becoming increasingly fragile as technology advances.