High-level radioactive waste

High-level radioactive waste (HLW) in Canada is used (irradiated) nuclear fuel that has been declared as radioactive waste. This type of waste also includes small amounts of radioactive waste from medical isotope production and other applications that generate significant heat via radioactive decay.

Used nuclear fuel produces ionizing radiation. This type of radiation has a strong ability to penetrate matter, so shielding against the radiation is required. Since used nuclear fuel contains significant quantities of radionuclides with long half-lives, it requires long-term management and isolation.

Used nuclear fuel from nuclear power plants, prototype and research reactors

A typical fuel bundle used in a power reactor  measures about 50 cm and weights about 24 kg

A typical fuel bundle used in a power reactor measures about 50 cm and weights about 24 kg

Canada's inventory of used nuclear fuel comes mostly from the operation of nuclear power plants. The remainder of the used nuclear fuel – which accounts for approximately 2% of the total – comes from prototype reactors (used to test full-power reactor designs) and research reactors.

Since the 1960s, Canada's nuclear power reactors have used over 2.5 million fuel bundles. If these bundles were packed end to end, they would fit into a space the size of seven hockey rinks, stacked to the top of the boards.

Used nuclear fuel from the operation of nuclear power plants is kept in onsite interim storage facilities. The storage consists of two phases: wet storage and dry storage.

Wet storage

After being removed from the reactors, used nuclear fuel bundles are stored for 7 to 10 years in storage bays (pools of water), which provide cooling and shielding against radiation.

Used  fuel pool at a Canadian nuclear power plant

Used fuel pool at a Canadian nuclear power plant

The pools for the used nuclear fuel are constructed in-ground and are seismically qualified (which means they are built to meet seismic standards for earthquakes. They are housed in buildings that are separated from the reactor buildings.

The walls and floors of the pools are about two metres thick and made of concrete reinforced with carbon steel.

Robust, heat-resistant and water-tight liners are installed in the pools to prevent water from leaking through possible defects in the concrete.

The pools are inspected regularly, under the supervision of Canadian Nuclear Safety Commission (CNSC) specialists.

Since the March 2011 accident in Fukushima, Japan, all nuclear power plant operators in Canada have acquired additional transportable equipment (such as portable generators and pumps) to ensure pools can be filled with water, regardless of an accident's severity.

Operators have also installed special devices in the fuel pool buildings to remove hydrogen from the air without the need for external power. These devices effectively reduce the risk of an explosion or fire from hydrogen buildup, which may occur during an accident.

Did you know?

Each year, 4,500 to 5,400 fuel bundles per power reactor are added to the pools (based on 80 percent to 95 percent of full-power reactor operation).

Dry storage

After 7 to 10 years in wet storage, the used nuclear fuel can be safely transferred to dry storage.

There are three main types of dry storage units used in Canada: 

  • concrete canisters
  • Modular Air-cooled Storage (MACSTOR) units
  • dry storage containers

Concrete canisters, or silos, were developed in the 1970s by Atomic Energy of Canada Limited (AECL) at Whiteshell Laboratories in Manitoba, to demonstrate that dry storage for used reactor fuel was a feasible alternative to underwater storage.

Silos are now used to store the used fuel from NB Power's Point Lepreau Generating Station, as well as Canadian Nuclear Laboratories' prototype reactors (including those at Chalk River Laboratories, Whiteshell Laboratories, Gentilly-1 and Douglas Point).

Each silo can hold between 325 and 600 bundles, and is built on reinforced concrete foundations.

The MACSTOR units, also developed by AECL, are similar to silos, but much larger. Each MACSTOR unit can store 12,000 bundles of used fuel.

MACSTOR units are currently installed at the Gentilly-2 Nuclear Generating Station.

Dry storage containers were developed by Ontario Power Generation (OPG) and are made of reinforced concrete encased in interior and exterior shells made of carbon steel.

The containers are transportable and are filled with helium (an inert gas), which protects the fuel bundles from potential oxidation.

Each container unit is designed to hold 384 fuel bundles and weighs approximately 60 tonnes when empty and 70 tonnes when loaded.

The dry storage containers are currently used to store the used nuclear fuel from the Pickering, Darlington and Bruce A and B nuclear power plants.

Operating experience and rigorous inspections carried out over the last 35 years have demonstrated that different types of dry storage units used in Canada can all effectively contain radiation.

All transfers of used nuclear fuel from wet storage to dry storage are conducted under surveillance of the International Atomic Energy Agency.

Read Canadian Nuclear Laboratories’ Feasibility Study on the Recycling of Used CANDU Fuel.

Used  fuel pool at a Canadian nuclear power plant

Concrete silos at the Point Lepreau Generating Station

MACSTOR units at the Gentilly-2 Nuclear Generating Station

MACSTOR units at the Gentilly-2 Nuclear Generating Station

OPG dry storage containers

OPG dry storage containers

Used nuclear fuel from research reactors

Research reactors in Canada use highly enriched uranium (HEU) or low-enriched uranium (LEU) as fuel.

CNSC inspector  verifies radiation levels outside a dry storage container

CNSC inspector verifies radiation levels outside a dry storage container


Two of the four SLOWPOKE-2 reactors in Canada use LEU (below 20 percent uranium-235), and two use HEU.

All SLOWPOKE-2 cores are preassembled, last 20 to 30 years, and cannot be modified by the licensee.

Once used, the complete core is removed and is sent to Chalk River Laboratories (for waste management storage) or repatriated to the United States.

McMaster Nuclear Reactor

The McMaster Nuclear Reactor completed its transition from HEU to LEU in 2006-07. Some of the LEU nuclear fuel used in the core originates from France. All remaining inventory of HEU fuel at the reactor was repatriated to the United States.

NRU and ZED-2

The radioactive waste and used nuclear fuel for the NRU and ZED-2 reactors at Chalk River Laboratories is stored onsite.

Other high-level radioactive waste

A small amount of non-nuclear-fuel high-level waste exists in Canada, and all of it is kept at the Chalk River Laboratories (CRL).  

This waste comes from two main sources: the production of medical isotopes and waste generated from early reprocessing experiments conducted from the 1940s to the 1960s.

Production of medical isotopes

Highly enriched uranium targets are used at CRL to produce life-saving medical isotopes. The targets are inserted into the NRU reactor, removed and dissolved to harvest the isotopes. Some of the earlier waste is in liquid form, while more recent waste is being solidified.

Early reprocessing experiments

CRL stores liquid waste which resulted from fuel reprocessing (done between 1949 and 1956). The waste is stored in three tanks. The last transfer of radioactive liquid solutions to any of these storage tanks occurred in 1968, and no liquids have been added since then.

Between 1958 and 1960, AECL conducted some experiments to convert high-level radioactive liquid solutions into a solid (glass). The program generated 50 glass blocks, each weighing about 2 kilograms, which are now safely stored onsite.

Transportation of high-level waste

CNSC inspector  verifies radiation levels outside a dry storage container

Maritime transport of used nuclear fuel in Sweden

The CNSC certifies the design of the packages required for the transport of used nuclear fuel and other high-level radioactive waste.

The design of certified transport packages must demonstrate the ability to retain their contents under accident conditions. 

For instance, Canadian regulations require all certified packages to undergo stringent testing, including the ability to withstand the cumulative effects of a 9-metre drop onto an unyielding surface, a 30-minute thermal test at 800°C, and immersion in 15 metres of water for 1 hour without a breach of containment.

High-level radioactive waste has been transported safely nationally and internationally for over 45 years by road, rail, water and air, without a single radiological incident.

Long-term management of used nuclear fuel

Conceptual design for a deep geological repository housing used nuclear fuel

Conceptual design for a deep geological repository housing used nuclear fuel (source: NWMO)

The Nuclear Waste Management Organization (NWMO) is responsible for the long-term management of Canada's used nuclear fuel from the operation of nuclear power plants.

In May 2010, the NWMO launched its site selection process for a willing and informed community to host a geological repository for the long-term management of Canada's used nuclear fuel.

As Canada's nuclear regulator, the CNSC is responsible for licensing geologic repositories intended to provide long-term management of radioactive waste.

The CNSC signed a service arrangement (PDF) with the NWMO to provide regulatory guidance and support prior to the submission of a licence application.

Independent advisory group

To help CNSC staff prepare for the review of a future licence application by the NWMO for a deep geological repository for Canada’s used nuclear fuel, an independent advisory group (IAG) was established in 2013, composed of Canadian geoscience experts.

The purpose of the IAG is to provide objective, independent advice to CNSC staff on the geoscience aspects of the APM initiative for the long-term management of Canada’s used nuclear fuel through review of NWMO’s geoscientific research program and the CNSC’s internal research program.

In the future, the IAG may be asked to focus on particular topics, with the goal of evaluating areas that are likely to be included in the safety case and/or supporting safety assessments.

About the Nuclear Waste Management Organization

The NWMO was established in 2002 by Ontario Power Generation Inc., Hydro-Québec, New Brunswick Power Corporation and Atomic Energy of Canada Limited, in accordance with the Nuclear Fuel Waste Act, to assume responsibility for the long-term management of Canada's used nuclear fuel.

The NWMO mandate is to implement an Adaptive Phased Management (known as APM) approach to find a solution for the long-term storage of this fuel - a solution that is socially acceptable, technically sound, environmentally responsible, and economically feasible to Canadians.