The reactor design that skips enrichment entirely
Every argument about enrichment concentration has an exception, and it is a design decision made in Canada in the 1950s.
Heavy water absorbs so few neutrons that a reactor moderated with it can sustain a chain reaction on unenriched natural uranium. No enrichment step. No SWU. No dependence on the four organisations that control that stage.
What that does to the supply chain
A pressurised water reactor’s fuel chain runs: mine → mill → conversion → enrichment → fabrication. A CANDU’s runs: mine → mill → conversion → fabrication. It stops one stage earlier, and the stage it skips is the tightest in the industry.
The practical consequence is strategic rather than economic. A CANDU operator cannot be cut off from fuel by an enrichment embargo. India, excluded from the Nuclear Suppliers Group for decades after its 1974 test, built a fleet of heavy water reactors and a domestic fuel complex at Hyderabad precisely because that chain was one it could complete alone.
What it costs
Nothing is free. Heavy water is expensive to produce and a CANDU needs a large inventory of it, both as moderator and coolant. Natural uranium fuel also means lower burnup, so a CANDU gets through more fuel bundles per unit of electricity — the plant refuels continuously, on load, pushing fresh bundles through pressure tubes while running.
That on-load refuelling is itself a consequence of the design: with natural uranium there is not enough reactivity margin to run eighteen months and then shut down for a batch replacement.
Who makes the fuel
Because the product is different, so is the supplier list. CANDU bundles come from Cameco Fuel Manufacturing at Port Hope — the largest such plant in the world — from BWXT in Ontario, from India’s Nuclear Fuel Complex, KEPCO Nuclear Fuel in South Korea, CNNFC at Baotou, and smaller lines in Romania and Argentina.
None of them is on the list of companies that can fuel a PWR. Fabrication is where the fuel chain stops being fungible, and heavy water reactors are the clearest illustration of it.
Every heavy water reactor page on this site carries a “no enrichment required” flag in its fuel panel. Atucha 1 in Argentina is a good example.