Canada’s nuclear waste needs a forever home. Scientists may be close to finding one

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Canada’s Candu nuclear reactors have been running for more than half a century. Ontario, home to all but one of the active reactors, gets about 60 per cent of its electrical power from nuclear, which has the benefit of producing next to no greenhouse gases.

To help meet climate targets while fulfilling the province’s electricity needs, the provincial government has announced plans to spend billions refurbishing an aging nuclear plant at Pickering, east of Toronto. It is part of a worldwide trend. After stagnating for years over worries about cost and safety that followed accidents in Chornobyl and Fukushima, nuclear power is getting a fresh look.

But what do we do about the radioactive waste? That problem troubles many Canadians. Canada’s nuclear authorities believe that they have the answer: They will isolate the used reactor fuel in a “deep geological repository,” or DGR. In other words, they will bury the stuff, entombing it so far below the Earth’s surface that no one will ever need to worry about it.

By the end of this year, Canada’s Nuclear Waste Management Organization (NWMO) plans to choose a community that will play host to that unusual tomb. Ignace, in Northwestern Ontario, has already put up its hand, announcing on July 10 that it was officially willing. A second municipality, South Bruce in Southern Ontario, will hold a referendum on Oct. 28.

Wherever it goes, creating the DGR will be a massive undertaking, costing an estimated $26-billion and taking years of preparation and construction. Earlier this year, the agency invited The Globe to a testing facility in Oakville outside of Toronto to explain how it would work.

How burying nuclear waste would work

Canada’s nuclear-waste inventory is comprised mostly of spent Candu fuel bundles – more than 3.3 million of them. Each is the size of a fire log and is an assembly of sealed tubes that contain ceramic uranium pellets, the reactor’s fuel. While in service, fuel bundles are housed within a six-metre-long tube, a pressure tube, of which there are hundreds in each Candu reactor. Highly radioactive upon removal, the bundles must be stored in pools of water for a decade before being moved to dry storage containers. From there, the hope is to send them to a deep geological repository for permanent disposal.

CANDU reactor vessels,

also known as calandrias, contain several hundred fuel channels

Fuel channels house pressure tubes

Pressure tube

Pressure tubes contain bundles of fuel rods and heavy water coolant

Fuel rods, made from zirconium alloy, are packed with uranium pellets

Uranium pellet

How the Candu bundles

would be stored

The container prevents any water near the container from reaching the fuel and radionuclides. It is engineered to remain intact and keep the used nuclear fuel completely isolated until the fuel’s radioactivity has decreased to the level of natural uranium.

Corrosion-resistant copper coating

Fuel basket

12 carbon steel channels hold 48 fuel bundles

Head

Steel container core

FRONT VIEW

(head off)

60 cm

SIDE VIEW

250 cm

60 cm

Canada’s deep geological repository (DGR)

Constructed more than 500 metres below ground, the repository would consist of a network of placement rooms to store the used nuclear fuel. It would be excavated within a sedimentary or crystalline rock formation that meets the safety and technical requirements of the project. The used fuel containers would be placed inside bentonite clay buffer boxes before being transferred to the placement rooms, where all remaining space around the boxes would be filled with granular bentonite clay. The clay’s low permeability properties help protect the soil and groundwater below the waste.

~500 m

Excavated rock formation

1

Bentonite clay spacer blocks

2

3

Granular bantonite backfill

1

2

3

4

5

Bentonite clay buffer box

4

Used fuel container

5

MURAT YÜKSELIR / THE GLOBE AND MAIL, SOURCE:

CANADIAN NUCLEAR SAFETY COMMISSION;

NUCLEAR WASTE MANAGEMENT ORGANIZATION

How burying nuclear waste would work

Canada’s nuclear-waste inventory is comprised mostly of spent Candu fuel bundles – more than 3.3 million of them. Each is the size of a fire log and is an assembly of sealed tubes that contain ceramic uranium pellets, the reactor’s fuel. While in service, fuel bundles are housed within a six-metre-long tube, a pressure tube, of which there are hundreds in each Candu reactor. Highly radioactive upon removal, the bundles must be stored in pools of water for a decade before being moved to dry storage containers. From there, the hope is to send them to a deep geological repository for permanent disposal.

CANDU reactor vessels, also known as calandrias, contain several hundred fuel channels

Fuel channels house pressure tubes

Pressure tube

Pressure tubes contain bundles of fuel rods and heavy water coolant

Fuel rods, made from zirconium alloy, are packed with uranium pellets

Uranium pellet

How the Candu bundles

would be stored

The Nuclear Waste Management Organization is proposing a nuclear fuel container that would prevent any water from reaching the fuel and radionuclides. It is engineered to remain intact and keep the the used nuclear fuel completely isolated until the fuel's radioactivity has decreased to the level of natural uranium.

Corrosion-resistant copper coating

Fuel basket

12 carbon steel channels hold 48 fuel bundles

Head

Steel container core

FRONT VIEW

(head off)

60 cm

SIDE VIEW

250 cm

60 cm

Canada’s deep geological repository (DGR)

Constructed more than 500 metres below ground, the repository would consist of a network of placement rooms to store the used nuclear fuel. It would be excavated within a sedimentary or crystalline rock formation that meets the safety and technical requirements of the project. The used fuel containers would be placed inside bentonite clay buffer boxes before being transferred to the placement rooms, where all remaining space around the boxes would be filled with granular bentonite clay. The clay’s low permeability properties help protect the soil and groundwater below the waste.

~500 m

Excavated rock formation

1

Bentonite clay spacer blocks

2

3

Granular bantonite backfill

1

2

3

4

5

Bentonite clay buffer box

4

Used fuel container

5

MURAT YÜKSELIR / THE GLOBE AND MAIL, SOURCE:

CANADIAN NUCLEAR SAFETY COMMISSION;

NUCLEAR WASTE MANAGEMENT ORGANIZATION

How burying nuclear waste would work

Canada’s nuclear-waste inventory is comprised mostly of spent Candu fuel bundles – more than 3.3 million of them. Each is the size of a fire log and is an assembly of sealed tubes that contain ceramic uranium pellets, the reactor’s fuel. While in service, fuel bundles are housed within a six-metre-long tube, a pressure tube, of which there are hundreds in each Candu reactor. Highly radioactive upon removal, the bundles must be stored in pools of water for a decade before being moved to dry storage containers. From there, the hope is to send them to a deep geological repository for permanent disposal.

CANDU reactor vessels, also known as calandrias, contain several hundred fuel channels

Pressure tubes contain bundles of fuel rods and heavy water coolant

Fuel rods, made from zirconium alloy, are packed with uranium pellets

Fuel channels house pressure tubes

Pressure tube

Uranium pellet

How the Candu bundles would be stored

The Nuclear Waste Management Organization is proposing a nuclear fuel container that would prevent any water from reaching the fuel and radionuclides. It is engineered to remain intact and keep the the used nuclear fuel completely isolated until the fuel's radioactivity has decreased to the level of natural uranium.

Corrosion-resistant copper coating

Fuel basket

12 carbon steel channels hold 48 fuel bundles

Head

Steel container core

SIDE VIEW

FRONT VIEW

(head off)

250 cm

60 cm

Canada’s deep geological repository (DGR)

Constructed more than 500 metres below ground, the repository would consist of a network of placement rooms to store the used nuclear fuel. It would be excavated within a sedimentary or crystalline rock formation that meets the safety and technical requirements of the project. The used fuel containers would be placed inside bentonite clay buffer boxes before being transferred to the placement rooms, where all remaining space around the boxes would be filled with granular bentonite clay. The clay’s low permeability properties help protect the soil and groundwater below the waste.

Bentonite clay buffer box

4

1

Used fuel container

5

2

4

5

~500 m

3

Excavated rock formation

1

Bentonite clay spacer blocks

2

3

Granular bantonite backfill

Note: diagrams are not to scale.

MURAT YÜKSELIR / THE GLOBE AND MAIL, SOURCE: CANADIAN NUCLEAR SAFETY COMMISSION;

NUCLEAR WASTE MANAGEMENT ORGANIZATION

A science-fiction point of view

Candu reactors produce energy by putting pellets of uranium in metal tubes of zirconium alloy. The tremendous heat generated by the process of nuclear fission turns water into steam, which is then used to drive electrical turbines.

About the size of an ear plug, the pellets have the same generating power as 400 kilograms of coal. The energy from 10 pellets would power an average Canadian home for a year. While inside the reactor, the pellets rest in log-sized containers called bundles. After the fuel is used up, which takes 12 to 20 months, the bundles are removed from the core, still hot and highly radioactive.

The problem is not that they pose any immediate threat to public health. When the bundles come out of the reactor, they go into big holding bays that look like swimming pools. Water is such a good buffer for radioactivity that, according to the experts, you can walk around the pool without suffering any ill effects.

After seven to 10 years as it cools and becomes less radioactive, the fuel goes into big, 79-tonne casks that confine the remaining radioactivity within walls of concrete and steel. The casks are good for decades.

The problem is not that the reactors produce an impossible amount of waste, either. Decades of nuclear-power generation in Canada has yielded 3.3 million fuel bundles. Stacked like firewood, they would fill nine hockey rinks up to the top of the boards.

The problem is that the fuel remains a potential hazard for a long, long – very long – time. Though it loses most of its radioactivity in the first 10 years, bringing it down to one-thousandth of its value when it was removed from the reactor, the remaining radiation lingers on for hundreds, thousands, even hundreds of thousands of years. Only after about a million years does its radioactivity return to a level equal to that of the uranium ore from which it was created.

So, when designing a solution, the agency had to think in science-fiction terms about what might happen in the distant future.

What if society were to break down after a world war or devastating pandemic, leaving the remaining humans incapable of overseeing a sophisticated waste-storage system? What if another ice sheet like the one that once covered central Canada were to crush whatever storage system had been devised?

Those are the questions that furrow the brows of the 250 men and women who work at the NWMO, a non-profit created in 2002 and overseen by Canada’s nuclear electricity producers.

To answer them, they had to solve two puzzles: where to bury the waste and how to make sure it stays buried.

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Puzzle one: where to bury the waste

The first problem was relatively simple. Just find a deep, stable rock formation in which to sink a shaft. Canada, in its vastness, is blessed with a wealth of them.

Near Ignace lies the Revell batholith, an immense, 2.7-billion-year-old mass of igneous rock formed when magma rose into the Earth’s crust, cooling before it reached the surface. At the place where the shaft would go, it is about 40 kilometres long, 15 kilometres wide and three kilometres deep.

Under South Bruce lies the Cobourg Formation. It was formed around 400 million years ago, the result of sediment deposited at the bottom of an equatorial sea. Over the eons, as the globe’s tectonic plates shifted and continents drifted, it migrated to what is now Canada and the United States. It takes its name from the city of Cobourg on the shores of Lake Ontario, where it comes to the surface.

Specialists would bore down about 700 metres to reach it, creating a shaft deeper than the CN Tower is tall.

The tough, dense limestone at that depth has few natural faults. It is low in water and, like the Revell batholith, highly impermeable, which means less risk of waste one day leaking into our lakes, streams or groundwater. Earthquakes in both areas are rare and mild.

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Puzzle two: creating a nuclear-waste coffin

The second problem is a little more complicated. Once they have built their underground tomb, authorities must ensure the waste stays intact essentially forever. That means devising what amounts to a nuclear-waste coffin.

Drawing on the experience of other countries, the NWMO has settled on nestling the used nuclear-fuel bundles in torpedo-shaped canisters with a copper coating. Over the past couple of decades, it has been working on designing the ideal canister with the ideal coating.

The model it has come up with is two and half metres long. Engineers figure it is strong enough to survive even if the site were covered by an ice sheet three kilometres deep. That, combined with all the rock and dirt underneath, would subject it to the same weight it would endure if it was placed 4.5 kilometres underwater.

To make sure, they have subjected the canisters to extreme pressure in a “crush-test” lab. One of the crushed canisters is on display in the agency’s Oakville facility. It looks as if it has been stepped on by a giant, yet bears no splits or cracks. The steel chosen for the task is highly ductile, meaning it will bend but not break.

The copper coating is to prevent corrosion. First giving the canister an electroplating bath and then applying more copper by spray nozzle, engineers would create a cladding three millimetres thick. Copper is such a heroic enemy of corrosion that they calculate it would take a million years just to reduce its thickness by one-tenth. Once the spent fuel was placed inside the canister, a dome-like cap would be welded onto one end to seal it.

The final step in a burial is to seal the tomb. For this purpose, engineers plan to use bentonite, a naturally occurring clay used to seal dams, fill up oil-drilling boreholes and even to make cosmetic face masks for skin care. Dense and heavy, it is ideal for keeping things out. In the 1970s, an excavation in Italy’s Umbria region uncovered an ancient forest that had been covered with bentonite. The huge tree trunks were so well-preserved the wood could have been used for making chairs and tables.

Those copper-covered canisters would be nestled in bentonite “buffer boxes.” The boxes would then be stacked like coffins in the DGR burial chamber. The boxes are designed to keep out not just any water that might get into the DGR chamber but the microbes that produce corrosive sulfides. The clay would act as an ally of the canisters’ copper coating.

Bentonite has another key property: It swells. The swelling would fill up any fissures or gaps and make the chamber even more waterproof.

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Opponents to the plan

Despite all the agency’s carefully laid plans, many are not convinced. Some local critics say the whole idea of building a deep geological repository is a mistake. A South Bruce group that is against hosting the DGR calls it “a centuries-long science experiment.” No one, says the website for Protect Our Waterways, “has ever designed, built, and operated a DGR for high-level nuclear waste, anywhere in the world.”

One of the concerns of critics is that, because the DGR has been designed for Candu waste, authorities haven’t done enough to prepare for the novel wastes that might come from new reactor types, such as the small modular reactors Ontario is developing. The agency responds that it is working with potential host communities on ways to manage any new types of waste.

The opposition doesn’t end there. The Green Party of Ontario wants the province to back off on nuclear power altogether. Rather than build more reactors and “add to our huge pile of dangerous nuclear waste,” it says on its party website, the government should bring more solar and wind power on stream.

There are doubts among Indigenous groups, too. First Nations around both South Bruce and Ignace have been talking with the NWMO, but are not saying whether they will sign on this year.

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DGR plans around the world

The agency, however, says that a broad scientific consensus has emerged that DGR is the best way to deal with waste. Among the countries that are working on it are France, South Korea, Japan, Britain and the United States.

In Finland, authorities have already dug 50 kilometres of tunnels in two-billion-year-old rock. The DGR facility on Olkiluoto Island is the first in the world. Waste containers will come down by elevator to be stored in vertical bore holes.

Sweden has approved plans to build a DGR of its own. To be located near the nuclear plant at Forsmark, 150 kilometres north of Stockholm, it will have space for 6,000 copper canisters of waste when it opens in the 2080s.

To further reassure the public, the agency notes that even if it succeeds in choosing a willing community this year, at least 10 years will pass before it starts digging, leaving time for environmental assessments and other preparatory steps. It might be another 10 or more years before any waste actually makes the descent into its tomb.

That would bring us to sometime in the 2040s. For 40 or so years after that, big trucks carrying specially designed waste containers would trundle from the reactor sites to the DGR facility, where the fuel canisters would be lowered into their final resting place. When the nuclear tomb is full, it would be filled with crushed rock and more clay.

Finally, the shaft leading down to it would be filled, sealing off the tomb for what amounts to eternity.

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