Yes CANDU!

Let's celebrate Canada Day with 5 great reasons to love the CANDU reactor

If I were to ask you to name a nuclear powerhouse country, Canada probably wouldn’t be the first to come to mind. But that’s exactly what the land of Maple was as World War II drew to a close. When the Nazis menaced Britain, a decision was made to transfer the British nuclear program, which by that point contained the cream of the crop of continental scientists as well, to Canada in 1942. At the Chalk River Laboratory, a unique lineage of heavy water (deuterium oxide) reactors came into being. They were used to study the production of plutonium from uranium. After the war, Canada desired to turn this technology to a peaceful purpose. In 1962, the world’s first CANDU reactor — standing for CANadian Deuterium Uranium — was born.

The name could not have been more appropriate as the CANDU reactor was born from a can-do attitude. Unlike its southern neighbor, Canada in the 50s was not particularly industrially advanced. It certainly did not have the ability to produce the heavy-forged reactor vessel that most reactors used. And while uranium was plentiful in Canadian mines, they didn’t have the capability to enrich uranium. Fortuitously, the experimental reactors developed at Chalk River used many pressure tubes rather than a single reactor vessel, and the heavy water moderator allowed the fission chain reaction to be sustained while using natural uranium.

“Are there still CANDUs? I mean, I learned about them in school, but I haven’t heard anything about them since. Are they still running?” That’s what my Canadian friend said to me after I told him I was working on an article on the CANDU. Yes, yes indeed there are. In fact, they are the reason why the Ontario grid is so low in carbon intensity, and the refurbishment of the Bruce and Darlington plants will see them providing rock-solid baseload into the 2060s. I couldn’t help but be a little sad though, that a Canadian would speak so lightly of what is undoubtedly one of his country’s greatest engineering achievements.

CANDUs are more than a cool story. It is a unique technology that still has so much to give to the world. Less than 50 of the world’s current 440 reactors are of the CANDU type. Here are ten reasons why in the future, we can do with more CANDU.

1. It can eat just about any fuel

Heavy water is simply H20 where one of the hydrogen atoms contain an extra neutron. This means, if yet another neutron smashes into it, that neutron is less likely to be absorbed and more likely to hang around to split another atom. This excellent “neutron economy” is why the CANDU can eat unenriched uranium.

But that’s not all. What we currently call “high-level nuclear waste” is actually just “unused CANDU fuel”. Building CANDUs close to regular light water reactors can be synergystic, allowing the same fuel to be burnt again, once in the light water reactor, and again in the CANDU. “It will burn everything but the kitchen sink, and it will even burn the kitchen sink if it’s been glazed with thorium.”

2. Outstanding uptime with online refueling

Unlike lightwater reactors which can go for month before requiring fresh fuel, CANDU reactors are fed continuously with fuel rod bundles going in one end and out of the other without the reactor itself ever going offline. In fact, Darlington NPP’s Unit 1 achieved more than 962 days of continuous operation, a world record. Needless to say, this is a highly desirable characteristic for grid stability, even if it is a bother to keep this “hungry baby” fed on the daily.

3. Four layers of safety features, passive as well as active

The unique geometry of the CANDU, with the horizontal fuel channels, is in itself a passive safety feature. In the case of a runaway reaction, the temperature of the pressure tubes will spike, causing the tubes to sag in the middle. Since natural uranium is not such a rich fuel, as soon as the geometry is distubed, the fission chain reaction will automatically cease.

Now, this is not the only safety feature by far. The CANDU reactor is equipped with control rods held in place by electromagnets. In the absence of a power signal, the rods drop, stopping the reaction. This is another passive safety feature, meaning the system “fails to safety” and no active measure is needed to trigger implementation.

The CANDU system also have two active safety systems: a supply of light water is on hand to flush away the heavy water, stopping the reaction and cooling the system. There is also a pressurized pump that can inject Gadolinium “neutron poison” into the system, which again will stop the chain reaction.

4. Modular, without being small (necessarily)

Small Modular Reactors (SMRs) are all the rage these days. In fact, Canada itself is increasingly eyeing non-CANDU SMRs such as GE Hitachi’s BWRX-300 for new-builds. No shade on the BWRX-300, it’s fantastic with that Japanese ABWR championship DNA. I’m a huge fan of them for everywhere else. But why is Canada not championing their own CANDU technology, with a 96 percent indigenous supply chain?

The reason why SMRs are so hot is that the idea that we can speed up the nuclear buildouts by standardizing components and factory producing them. But due to its pressure tube lattace structure, a large part of the CANDU is already modular, even though it doesn’t have to be small. Even in regular SMRs, not every part of the plant can be modularized, with 60 percent “modular” being considered pretty good.

And if a small plant is genuinely desired because the need for electricity is not that massive, well that’s where the CANDU SMR comes in. Same CANDU technology you know and love, smol size. Why not, Saskatchewan?

5. The perfect starter reactor for developing countries

Since the 50s when the CANDU technology was developed in part because Canada couldn’t do heavy forging, the numbers of countries that actually can actually went down. Hard to imagine, but even the US just…kinda forgot. In fact, there are only 4 countries left with the heavy forging capabilities to make a nuclear reactor vessel: France, Japan, China and Russia. They might be joined by South Korea and Czechia soon, but the list is not long. If we are to have the nuclear renaissance we need, one can easily see heavy forging capacity becoming a bottleneck.

Luckily, since CANDU was built so Canada can have an indigenous nuclear industry in the 1950s, as long as your country is at least as industrially advanced as Canada in the 1950s, you can build CANDUs. This combined with the ability to take unenriched uranium as fuel can point to the way forward for many developing countries who have ambitions to be energy independent.

(But wait…wasn’t selling CANDU technology to India how the Indians got their bomb? Time to quickly set the record straight. Canada actually gave India a research reactor called CIRUS, “the ideal facility to develop a plutonium device” which they made the Indians promise not to use for weapons but…*surprise Pikachu face* that’s exactly what happened.)

Not bad, eh? But wait there’s more!

The CANDU reactor could in the future prove to be an intriguing platform for advanced nuclear. I don’t quite understand it enough to write about it yet, but I’ve been told that very interesting things happen in our ‘hungry baby’ when we start feeding it spicey fuel such as Thorium. It’s that lovely neutron economy which makes the CANDU such an intriguing platform to investigate advanced fuel cycles. What happens when you feed it LWR spent fuel mixed with a little natural uranium? What happens if you just straight up feed it lightly-enriched uranium?

It’s also got a unique ability to produce medical isotopes, which I think can be an article in and of itself. Basically, short-lived isotopes such as Lutecium-177 cannot be made in conventional nuclear reactors because they are sealed up for months at a time. This is why they are usually made in research reactors, which unfortunatly are shutting down more they are being opened. By sending special fuel bundles with target material thorugh the CANDU, you can “cook” them just right to create massive amounts of medical isotopes and just collect on the other end.

THE ELEMENTAL TAKE

It’s a crime that the Canadians, perhaps with their national propensity towards modesty, have not been shouting from the rooftops about their CANDU technology. It’s proven, stable tech that has stood the test of time, yet still has a lot of avenues of unexplored upsides.

It’s not too late. The last CANDU reactor to be commissioned appears to be China’s Qinshan phase 3, completed in 2003. But there’s still dormant projects in Romania and Argentina that can be restarted. Most importantly, with the refurbishment of the Bruce and Darlington units, why isn’t Canada trying to replicate its own successful ‘Ontario model’ throughout the nation? (Incredibly, almost all the CANDUs in Canada are in the state of Ontario with the exception of one in New Brunswick.) Canada can return to its historical place as a frontrunner in nuclear while truly making meaningful strides towards its ambitious decarbonization targets.