The Blind River refinery produces uranium trioxide which feeds into the hexafluoride conversion plant.
Cameco said the "appropriate conditions" were currently in place to resume normal operations.
"The provinces and communities where we operate are certainly not out of the woods when it comes to this global pandemic, and we must remain vigilant in how we manage our activities during these challenging times," said CEO Tim Gitzel. "However, we are confident that we can maintain the required roster of qualified operators to run the UF6 plant going forward, enabling us to carefully bring the plant and the UO3 refinery back into production."
During the shutdown of the two sites Cameco's other Ontario operations, including uranium dioxide production at the Port Hope conversion facility and fuel bundle production at Cameco Fuel Manufacturing, continued.
However, there is no change in the status of the world's highest-grade uranium mine, Cigar Lake in Saskatchewan, where operations remain on care and maintenance indefinitely.
Cameco has suspended its annual production guidance for the time being, saying it would not provide guidance until it had "sufficient basis to do so".
Cameco shares (TSX: CCO) have gained more than 88% to $14.99 since hitting a 12-month low of C$7.69 on March 18.