There are 20 tailings management sites that have resulted from the opera­tion of uranium mines in Canada: 14 in Ontario, four in Saskatchewan and two in the Northwest Territories. Decommissioning of uranium mines and mills is governed by the Uranium Mine and Mills Regulations under the NSCA. The Cluff Lake Project is described here as an example of the type of activities that are undertaken for safe decommissioning.

Cluff Lake project

The Cluff Lake Project, which is owned and operated by AREVA, was completed at the end of 2002, when ore reserves were depleted. More than 28 million tonnes of U3O8 was produced over the 22-year life of the project.

Site facilities included the mill and tailings management area (TMA), four open-pit and two underground mines, the camp for workers and site infra­structure. Cluff Lake was the first of the northern Saskatchewan uranium mines to be decommissioned. The decommissioning licence was received from the CNSC in July 2004. The objective is to return the site as closely as practical to its original state in a manner that both protects the environ­ment and allows traditional uses such as fishing, trapping and hunting to be carried out safely.

Decommissioning the mill involved two phases, which were completed in 2004 and 2005. The mill demolition work was broadly similar to demolition of other comparable size industrial facilities, with special measures needed to protect workers from residual contamination and industrial hazards, and to prevent the spread of contaminants into the environment. Waste materi­als were disposed of in one of the open pits at the site, together with much larger volumes of waste rock.

Decommissioning of the TMA was initiated by covering the tailings with till[32] in stages to promote consolidation. The local till material developed from an adjacent borrow area was used for covering the tailings materials. When consolidation was complete, the TMA cover was contoured to provide positive drainage, using locally available till with a minimum cover thickness of 1 m, and then re-vegetated. Extensive characterization of the tailings and the site ’s geology and hydrogeology has been performed to acquire reliable data on which to base the assessment of long-term perform­ance. One of the objectives of the follow-up monitoring program is to verify the key assumptions used in the long-term performance assessment.

Two open pits have been used for the disposal of waste rock, with one of these two pits also used to accept industrial waste during operations and decommissioning. This waste included the mill demolition waste.