Cameco Halts Cigar Lake Mining After Acid Plant Failure at McClean Lake Mill

Cameco (TSX: CCO) has temporarily suspended mining at its Cigar Lake uranium operation in northern Saskatchewan after a sulfuric acid plant failure at Orano's McClean Lake mill forced a halt to processing, tightening near-term supply from one of the sector's most important mines.

Cigar Lake ore can only be processed at the McClean Lake mill, operated by Orano Canada about 70 kilometers northeast of the mine. With the mill offline and ore storage at Cigar Lake limited, Cameco said it stopped mining until enough acid is available for milling to restart.

Cameco and Orano expect the mill to return to operation in about two weeks. Cameco said it does not currently expect the disruption to affect its 2026 production outlook for Cigar Lake, but warned that longer repairs or delays in sourcing sulfuric acid could still hit that forecast.

The interruption stems from a failure in an expansion joint at the McClean Lake sulfuric acid plant. Orano said the incident was managed safely with no serious injuries, and that it is repairing the plant and securing acid from alternative suppliers to support a restart.

A Cameco spokesperson said workers and contractors remain on site and other work is continuing, indicating the suspension is tied to processing logistics rather than a broader shutdown.

Cigar Lake is a major source of global uranium supply and a core Cameco asset, widely regarded as the world's highest-grade uranium mine. Cameco's 2026 production plan for the mine is 17.5 million to 18.0 million pounds of U3O8 on a 100% basis, including 9.5 million to 10.0 million pounds attributable to Cameco. In the first quarter, the operation produced 4.9 million pounds on a 100% basis.

Even within the two-week timeline, the pause removes near-term feed from a market already dealing with tight supply and elevated contracting. Uranium spot prices averaged $73.54 per pound in 2025, while the long-term price reached $86.50 per pound in December, the highest in 14 years, according to Cameco. Utilities placed about 116 million pounds under long-term contracts during 2025.

The episode highlights a structural dependency in the operation: because Cigar Lake relies on a third-party mill and a continuous supply of sulfuric acid, a mechanical issue at a separate facility can quickly interrupt mine output.

Orano told local media that an unplanned outage of this length at McClean Lake is unusual and has not occurred in at least the past decade. The need to source replacement acid comes as sulfuric acid markets have been under pressure globally.

For investors, the immediate question is whether McClean Lake returns on schedule. If it does, the event may remain a short operational disruption. If not, the outage could become more material for Cameco's 2026 volumes and for near-term uranium market sentiment.