The used fuel container is one of the principal engineered barriers in a multiple-barrier deep geological repository. The important features of the design are corrosion resistance, mechanical strength, geometry, capacity and compatibility with surrounding sealing materials.

Our current conceptual design is for a used fuel container with lateral placement in the repository. This particular container has a length of 2.5 metres. The container holds 48 used CANDU fuel bundles (four layers of 12 bundles) in a steel basket within a standard carbon steel pipe which is protected by a copper-coated, corrosion-resistant outer layer.

The repository storage containers are part of a series of engineered and natural barriers that will work together to contain and isolate used nuclear fuel in the deep geological repository. They are made of thick, solid steel and welded shut. The steel provides the mechanical strength to withstand the pressures of the overlying rock and future glaciations. The outermost layer of the container consists of corrosion-resistant copper coating.

The containers will undergo non-destructive examination using ultrasonic (high-frequency sound waves that can characterize thickness and internal structure) as well as surface testing to ensure there are no flaws in the weld or copper coating, confirming there are no leaks.

There are strict requirements to ensure that radiation does not leak from the underground repository and that people and the environment are protected. The project cannot proceed without meeting these strict requirements.

 

Canada's plan for the long-term management of used nuclear fuel involves containing and isolating the used fuel in a deep geological repository. A multiple-barrier system of engineered and natural barriers will ensure the ongoing safety of the public and workers over the long term. These barriers include:

• The nuclear fuel pellet;
• The fuel element and fuel bundle;
• The used nuclear fuel container;
• Bentonite clay; and
• The geosphere — the host rock for the repository.

Each of these barriers provides a layer of protection so that if the performance of one degrades or is compromised, other barriers will still contain and isolate the used nuclear fuel.

The regulatory review of the repository will require a number of safety assessments which look at a wide range of scenarios to ensure people and the environment are protected. "Disruptive scenarios" are conducted to test a range of hypothetical circumstances such as the impact of container failure at 10,000 or 60,000 years, or the failure of the seals within the repository shafts.

 

The safety case for the project must demonstrate with confidence that it will meet or surpass the stringent requirements of the regulatory authorities.

No. The repository design and safety case are developed to ensure that temperatures generated will not influence the ability of the multiple-barrier system or the surrounding rock to contain and isolate the used nuclear fuel.

Specific requirements include a repository layout and container spacing that prevent temperatures from going above 100 degrees Celsius on the container surface. The containers of used nuclear fuel would reach their highest temperatures less than 100 years after being placed in the repository. Temperatures would then gradually decrease to levels near those existing before repository construction.

The design of the repository would ensure that this heat does not lead to faulting or create release pathways for radiation through the surrounding rock. Monitoring will ensure that the facility is performing safely as designed.

Yes. There is enough bentonite clay available to meet the needs of Canada's plan, as well as other used fuel repositories being planned around the world.

 

Bentonite clay is one of the barriers within the deep geological repository that will isolate used fuel from people and the environment in the long term. It is a natural material that swells when exposed to water, making it an excellent sealing material. It is also very stable, as seen in natural formations formed millions to hundreds of millions of years ago.

 

Bentonite clay is available in many countries around the world. It is estimated that Canada's deep geological repository would consume one to two per cent of the annual capacity in North America. Worldwide, deep geological repositories that are planned or expected will only consume about five to six per cent of the global bentonite supply.