Rabbit Lake Uranium Mill Complex

Located 800 kilometers northwest of Saskatoon, Rabbit Lake was a very challenging project to execute in extreme environmental conditions.

This difficult task took place above the 58th parallel in Northern Saskatchewan, where Fluor was responsible for the construction of a grass-roots uranium-processing facility.

Because of the region's extreme weather conditions, all facilities for the 1,500-tons-per-day uranium mill and concentrator were to be located within one large, well-heated building.

The scope of work included a 28,000-square meter main complex that housed the process units, acid plant, power plant, laboratory, offices, workshop, and warehouses.

The approximate 400 kilometers of highway were only open for a few weeks in the winter when the lakes and boggy ground were frozen. The schedule for the project had to reflect this very serious constraint on availability of access for construction materials and equipment.

The key to mastery of logistics for the remote project was centered on construction of a 156-mile ice highway that used the extreme winter climate to the project's advantage.

In spite of the challenges and only short periods of summer construction, the project was completed on schedule in April 1975.

Client's Challenge

In 1968, an affiliate of Gulf Oil Corporation acquired the rights to explore for minerals on 3.5 million acres in the Wollaston Lake Ford Belt located in the province's northeastern border. Using sophisticated technology, Gulf confirmed the existence of uranium deposits averaging five pounds of uranium oxide per ton of ore.

Originally, the plant was equipped with a semi-autogenous mill rated for 1,650-tons-per-day capacity. Screening followed with the oversized rock going back to the mill, and select rock being pumped into the cyclone separators. Acid leaching with counter-current decantation was followed by solvent extraction. The uranium solution is then treated with ammonia, which gives ammonium diuranate precipitate. This is dried in a multi-hearth dryer to produce U3O8, which is finally packed into steel drums for transportation.

As the ore grade declined, it became necessary to treat 2,000 tons per day rather than the designed 1,500. To achieve this increased tonnage, Fluor subsequently installed a ball mill following the cascade mill. The ball mill operates in a closed circuit with the hydrocyclones.

The diesel generator plant consisted of three 2,500-kilowatt units. Waste heat from the plant was channeled to heat the offices and workshop areas for energy conservation. At such a remote location, it was advantageous to minimize the labor force, and a high degree of automation was installed in the plant.

Fluor's Solution

Procurement, expediting, and logistics played a critical role in this restricted site location. The schedule for the project had to reflect this very serious constraint on availability of access for construction materials and equipment.

Mobilization started immediately after the November 1971 contract award to meet the first ice haul period. In the summer of 1972, all construction facilities had to be readied and foundation work was started on the main building. Engineering had to progress rapidly to meet construction and structural steel drawings so that building materials could be sent up during the next season's ice haul period. Advanced planning required that different materials were delivered during each ice haul.

Fuel was always the major priority. The project entailed 235 truckloads in the first ice haul, 477 truckloads in the second ice haul, then 374 truckloads over a Canadian Government installed semi-permanent road.

In addition to supply deliveries, some winter concrete work was required. The concrete set required special attention to be heated and the work area thermally maintained at 25 degrees centigrade for over a week.

Delivering significant cost savings to the Client, Fluor housed only three of the six counter-current decantation thickeners in the building. Heat balances revealed that it was adequate to house half the thickeners outside.

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Conclusion

Due to the remote location and extreme weather conditions, the Rabbit Lake uranium mill complex was a challenging construction project.

Advanced procurement, logistics, expediting, and planning were critical areas to support the brief winter ice haul routes.

At full production in 1978, the Rabbit Lake mill produced over 4 million tons of uranium oxide. The uranium oxide, or yellow cake, would be processed for sale to nuclear power plants, primarily in Europe.