A New Approach for Designing, Safe Operation and Decommissioning of High Grade Uranium Mill Facilities

Abstract

COGEMA Resources Inc.'s operation at McClean Lake will consist of milling and processing ores from the richest uranium deposits in the world. These deposits, located in the Athabasca basin of northern Saskatchewan, Canada, include those of Cigar Lake, McClean Lake and Midwest Projects. All the ores from these deposits will be processed at the McClean Lake JEB mill. The ore grades vary up to 30% uranium, and in some cases pure massive pitchblende is encountered. The McClean Lake JEB mill, is designed with an initial capacity of 6 million lb. U3O8annually. Following approval of the Cigar Lake Project by both governments, the capacity of the mill will be expanded to 24 million lb. U3O8.Although the initial grade of ores to be processed at the JEB Mill (2% uranium to 4.75%uranium) are much less than those expected from Cigar Lake (up to 30% uranium), they are still high enough to warrant special radiation protection measures. The philosophical tenet for the mill design includes health, safety and environment protection for the short and long term. Thus, the design ensures a maintenance free solution after decommissioning to protect future generations and the land. To this end, the ore receiving facility for Cigar Lake and Midwest ores will be remotely operated to protect employees from gamma radiation. The leaching area of the mill is based on a two-floor concept with an elevated concrete slab of about 40 cm separating the upper and lower floors. The vessels also have concrete cells around them and access is strictly restricted to protect personnel. A dual ventilation system has been established in the mill with specific pressure gradients. With the single pass ventilation, a positive pressure will be maintained in the clean areas(control rooms) and a negative pressure will be kept in the potentially contaminated areas, from where the air will be exhausted to the atmosphere. Due to the presence of radiation and other industrial hazards, the mill has been zoned according to different processes to reduce the risk of exposures and fire. Once the Cigar Lake and Midwest ores are leached in their dedicated leaching circuits, the ore streams will be blended with the McClean Lake ores to control the slurry grades below10% uranium, a more manageable level. Upon processing of the ores to make the product yellowcake, the wastes will be managed. The tailings management scheme at McClean Lake has been designed principally to ensure maximum containment of contaminants in the long term by channeling clean ground water around the clay-like consolidated tailings, via the path of least resistance. When processing of Cigar Lake and Midwest ores commence, a paste tailings preparation step will be added to the mill to reformat the tailings into a paste like consistency. These paste tailings will be deposited sub-aqueously in the mined out JEB pit, at the McClean Lake facility. The paste tailings will be deposited underwater from a floating barge. The paste tailings system ensures long term containment of contaminants and allows for a quicker decommissioning. The advantage of the sub-aqueous system for tailings management ensures that personnel are shielded from gamma radiation. Also, there are no airborne dust emissions and radon emanation is significantly reduced due to the water cover. The water cover also eliminates the exposure of the tailings to atmospheric oxygen and the potential for acidic drainage. Financial assurance for decommissioning the McClean Lake facility is available to secure funds for the future. These funds have been posted under the auspices of both federal and provincial governments. It ensures that there will be no burden on the future generations and the environment is safe and well protected.