Uranium tailings management in Canada

In Canada, radioactive waste is defined as any material that contains a radioactive substance, as defined in section 2 of the Nuclear Safety and Control Act, for which no further use is foreseen. There are four general classes of radioactive waste in Canada with uranium mine and mill waste as a particular class.

Uranium mining and milling in Canada dates back to the mid-20th century, with operations in Ontario, Saskatchewan and Northwest Territories. Currently, all operating uranium mines and mills in Canada are located in northern Saskatchewan. Waste rock and uranium tailings exist at operating uranium mine and mill sites in northern Saskatchewan and at closed or decommissioned sites in Saskatchewan, Ontario and the Northwest Territories. In 2019, the total inventory of tailings is 218,308,905 tons (NRC, 2021). This includes about 201 million tons at closed/ decommissioned sites, and about 17.5 million tons from the operating sites.

In situ decommissioning with a disposal end state is an accepted practice for uranium mines and mills waste. Owing to the large volumes of generated tailings and low activity levels, long-term management of tailings in tailings management facilities (TMFs) adjacent to mines and mills is the only practical option for these wastes. At the newer operations in Saskatchewan, tailings are typically managed in (1) in-pit TMFs that feature hydraulic containment during operation, and passive long-term containment following decommissioning, (2) near surface TMFs that includes construction of dams or embankments with engineered surface to provide long-term containment, and (3) purpose-built underground TMF.

The CNSC requires that planning for TMF decommissioning take place throughout the lifecycle of a mine and mill project. The licensee shall perform a safety assessment to identify any radiological or non-radiological hazards to workers, the environment and the public for decommissioning. From a technical perspective, TMF decommissioning typically involves placement of a cover system and implementation of water management plan. Tailings should be consolidated enough before installing a cover system to ensure long-term stability, minimal settlement, and adequate support for the cover system, and most importantly to achieve a lower target permeability than the purpose-built or natural pervious surround to minimize long-term leaching of contaminants. Safety assessment should consider the potential impacts of seismicity, flooding and climate change. The licensee is responsible for implementing and maintaining the post-decommissioning plans and institutional controls unless that responsibility was transferred to a third party with their agreement and the Commission’s approval.

Historically, tailings were placed in natural containment areas, or disposed of as backfill in underground mines, or placed in engineered surface containment areas. Long-term monitoring and maintenance are ongoing at these tailing sites. Remediation efforts have been carried out at certain sites. For example, Project CLEANS (Cleanup of Abandoned Northern Sites) was conducted to assess and reclaim Gunnar mine and mill site and Lorado mill in northern Saskatchewan, which were abandoned with little decommissioning in mid-1960s.

Reference:

• Natural Resources Canada (NRC), 2021. Inventory of Radioactive Waste in Canada 2019.