In CANDU® reactors, nuclear fuel consists of uranium dioxide processed into ceramic pellets, which are then sealed in tubes. Several of these tubes are welded together to form ‘fuel bundles.’ The heat generated by the ‘fissioning’ or splitting of the uranium atoms is used to turn water into steam, which runs the turbines that create electricity.
Just what is nuclear waste?
The process of generating electricity from uranium results in the by-products known as nuclear waste. In a nuclear plant, there are three types of nuclear waste: Used fuel, intermediate level waste, and low level waste. Different management techniques are used for the handling and storage of each type of waste.
When a fuel bundle no longer contains enough fissionable uranium to heat water efficiently, it is replaced by a new fuel bundle. The used fuel contains more than 99 per cent of the radioactive by-products of nuclear reactors.
The used fuel bundle, which is still emitting heat and radioactivity, is removed from the reactor by remote control and discharged into a water-filled ‘bay.’ It looks like a swimming pool but is built of reinforced concrete, lined to prevent leaks, and designed to withstand earthquakes.
The water in the bay cools and shields the bundles as the heat and radioactivity gradually declines. Thousands of used fuel bundles are stored in each bay for ten years or more.
Dry storage containers
After the used fuel bundles become ‘cool’ enough, they are transferred to CNSC-licensed dry storage containers made of concrete and steel. Then the containers are welded closed, and the International Atomic Energy (IAEA) affixes sophisticated seals to the containers to verify that Canada is in compliance with the International Non-proliferation Treaty.
When loaded these containers weigh about 70 tonnes and have a design life of 50 years. Studies indicate that, with ongoing maintenance and inspection, they can be safely used for a much longer time.
Long-term management of used fuel
The Nuclear Waste Management Organization, which consists of representatives of Canada’s nuclear utilities, was mandated in 2002 by the Canadian Government’s Nuclear Fuel Waste Act to submit a proposal for the long-term management of used nuclear fuel.
To understand what Canadians believe is important in managing used fuel over the long term, the NWMO conducted a study in which more than 18,000 people participated. Their opinions, as well as input from more than 500 specialists and 2500 Aboriginal people, helped shape the NWMO proposal, which was submitted to the Minister of Natural Resources in November 2005 and approved by the government in June 2007.
In 2010, the NWMO began the process to identify an informed and willing host for Canada’s own repository, and opened it to all interested communities. Communities in Saskatchewan and Ontario have expressed an interest in learning more about the project. It is these communities and surrounding areas the NWMO is now working with to find a potential site.
The plan, called Adaptive Phased Management, is for the ultimate isolation and containment of used fuel from Canadian nuclear facilities in a central repository deep underground. The used fuel would be contained by engineered barriers and the surrounding geology. It would also be constantly monitored and would remain retrievable indefinitely, if necessary.
Importantly, Adaptive Phased Management is flexible. Throughout the plan’s implementation Canadians will be engaged in a voluntary, transparent process, invited to make their views known at key decision points, and have genuine opportunities to influence progress and outcomes.
Intermediate level waste
This consists mostly of used reactor components, as well as the resins and filters used to keep reactor water systems clean. These items, which cannot be handled without shielding, are loaded into specially reinforced and shielded transportation packages licensed by the CNSC for shipment to the Western Waste Management Facility (WWMF). There, the waste is stored in steel-lined in-ground storage structures.
Low level waste
This category consists of minimally radioactive materials such as mop heads, rags, paper towels, floor sweepings and protective clothing used in the nuclear stations during routine operation and maintenance. These items, which do not require shielding, are packed in plastic bags and shipped to the WWMF in CNSC-licensed steel containers for processing and storage. When possible, these materials are then compacted or incinerated to reduce their volume, so that the concrete warehouses used to store them can be designed with smaller environmental footprints.