A case for the end of our CANDU era

David Keith is a Canadian physicist, founder of Canada’s Carbon Engineering, co-host of the Energy vs. Climate podcast, and professor of the geophysical sciences at the University of Chicago, where he directs the Climate Systems Engineering Initiative.

In June of this year, Ottawa doubled down on nuclear power, committing to build 10 large reactors of unspecified design. The strategy promises “a modernized, cost-competitive CANDU” by 2030 that can be sold into four new export markets by 2040. I’m thrilled by the government’s renewed commitment to nuclear power.

But recommitting to CANDU – short for Canada Deuterium Uranium – is a strategic misstep that Canada can ill afford in an intensely competitive global economy. Ottawa should follow its bold decision with another: Abandon development of new CANDU reactors.

In the 1950s, Canada had no access to uranium enrichment and no industrial capacity to forge the massive pressure vessels required for modern nuclear reactors. CANDU’s designers found a clever way around that impasse, developing a reactor that replaced the big pressure vessel with many small-diameter high-pressure tubes and that used heavy water, which avoids the need for enriched uranium. The result was a truly independent Canadian reactor design that supplies more than half of Ontario’s electricity.

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But the global nuclear power market has evolved and today, almost all power reactors being built are light-water reactors using pressure vessels and enriched uranium, leaving CANDU well outside the mainstream. The difference matters because CANDU cannot fully benefit from the shared learning and global supply chains developing around light-water pressured reactors.

Worse, the CANDU design carries inherent disadvantages.

The first is maintenance cost. The downside of the pressure-tube design is that reactors have an enormous number of tubes connected through a complicated network of feeder pipes, all of which require inspections and mid-life replacement. It’s inherently harder to maintain a myriad of high-pressure joints than the one large pressure vessel in a standard light-water design.

The second is nuclear proliferation. CANDU’s natural-uranium heavy-water pressure-tube reactor is exactly the right technology for weapons-grade plutonium. India’s bombmakers used plutonium from a Canadian-supplied heavy-water research reactor. Safeguards do suppress the risk, but there’s no escaping the reality that a heavy-water pressure tube design lowers the technical barriers to bomb production that a batch-refueled light-water reactor keeps high. All else equal, the world is safer with fewer such reactors.

The third is safety. If the cooling water in a CANDU boils to steam, the nuclear reaction speeds up, a risk that standard light-water reactor designs don’t have. CANDU does a good job managing this risk, and the fleet has a good safety record, but this is an inherent weakness masked by clever safety engineering. Better to avoid it.

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But in truth, nuclear power in Canada need not be synonymous with CANDU. The only reactor being built in Canada today is a “small” modular reactor (SMR), a scaled-down but otherwise standard pressurized light-water reactor being built at Darlington using a GE Vernova Hitachi design. The constraints that drove the CANDU design choices in the 1950s are gone; the pressure vessel for that new SMR is being made in Canada, and we could now either buy enriched uranium from a global marketplace or make our own.

The good news is building CANDUs created a deep reservoir of skills that are easily transferable. Darlington’s SMR is the only one under construction in the G7, so the project is building Canada a whole set of new skills. And furthermore, Canadian firms Brookfield Renewable Partners and Cameco Corporation now own Westinghouse, whose AP1000 reactor is among the world’s safest modern designs.

On the other hand, what do we get for continuing CANDU? Ottawa lent AtkinsRéalis up to $304-million to revise the CANDU design and offered Romania $3-billion in export financing for two more CANDUs. But the best case is a few sales that we would help finance. There is no credible case for an advanced CANDU design taking a growing share of the global nuclear power market. Every dollar spent keeping CANDU alive distracts from the difficult decisions and investments required to succeed in an increasingly competitive global market.

Canada should maintain its existing CANDU fleet for as long as makes economic sense. But we should start focusing the full energy of Canada’s nuclear industry on the reactors we will build for the next half century.