“Orano’s McClean Lake mill has encountered operational challenges with its sulphuric acid plant that caused it to shut down in order to repair the issue. Orano is currently working to bring the acid plant back online and is assessing options to obtain acid supply from an alternative source while it waits for replacement parts to complete the repair. With limited ore storage capacity at Cigar Lake, we have temporarily suspended mining activities until sufficient acid is available to allow milling to resume at McClean Lake,” the company said.
Cameco said that at present, the mill is expected to return to operation in around two weeks, and the disruption is not expect to impact its 2026 production outlook for Cigar Lake. “However, there is a risk that the repairs to the acid plant take longer than planned and that mining at Cigar Lake is unable to resume on the expected schedule,” the company notes – adding that additional delays could affect its 2026 production outlook.
Cigar Lake is the world’s highest grade uranium mine, with an average ore grade of 16.33% U3O8. Cameco developed an innovative jet-boring technique specifically for the project, freezing the ground and using a high-pressure water jet to mine out cavities in the frozen ore. The mixture of ore and water is then pumped to underground grinding and processing circuits. Thickened ore slurry is pumped to the surface and transported in tanker trucks 70 kilometres to the McClean Lake mill – operated by Orano – where it is processed into uranium concentrate.
The McClean Lake mill was originally built to process uranium from the McClean Lake mine, with a grade of 2.4% U3O8, but was subsequently upgraded to process high-grade uranium: according to its 77.5%-owner, and operator, Orano, it is the only facility in the world capable of processing high-grade uranium ore without dilution, and can process ore grades more than 100 times the world’s average grade.
Sulphuric acid is a key reagent used in the leaching, counter-current decantation, solvent extraction and yellowcake precipitation processes at the mill. The mill has its own acid plant, but globally, supplies of sulphuric acid have been impacted by the conflict in the Middle East and the closure of the Strait of Hormuz. According to the American Chemical Society’s Chemical & Engineering News, about half of the seaborne trade in sulphur normally passes through the Strait of Hormuz. Since the start of war in Iran, sulphur shipments have almost completely stopped. And China – the world’s largest exporter of sulphuric acid – has restricted exports since the beginning of May.
Cigar Lake produced 4.9 million pounds U3O8 (1885 tU) in the first quarter of 2026 (of which Cameco’s share was 2.7 million pounds), with total production for 2026 expected to be between 17.5 and 18.0 million pounds in 2026.
