Yellowcake is an initial concentration of uranium, on the way to making it suitable for fuel.
Cameco will integrate the material "into their commercial processing stream at its refinery in Port Hope" (Ontario). Lyle Krahn, Cameco spokesman.
Cameco said the deal was made earlier this year- "at that point U. S. led crews began removing the yellowcake from the Saddam-era containers, some leaking or weakened by corrosion, and reloading the material into about 3500 secure barrels. In April, truck convoys started moving the yellowcake from Tuwaitha to Badhdad's international airport.
"Then, for two weeks in May, it was ferried on 37 flights to Diego Garcia.... On June 3, an American ship left the island for Montreal."

I fail to see any mystery. To me- echoing bearded bruce- it seems to be normal procedure.

The material was not waste- just an early stage concentration, leading to industrial use. Operators of Canada's uranium mines, closed at present, have called for the mines' re-opening, and resumption of production of yellowcake.
The United States produces much of the material, from several mines, as do other countries with reserves of uranium.

The Toronto Globe and Mail, article by Brian Murphy, Associated Press, July 5, 2008.