Recall that, post Gulf War, Iraq was under a weapons inspection regime. The IAEA knew where the 500 T of yellowcake were stored and had placed their seal on each container. It couldn't be tampered with without the knowledge and approval of the IAEA.
A fresh supply of smuggled yellowcake would, however, be available for exploitation in any way that the Hussein regime deemed fit.
That's a solid point, at least until they kicked out the inspectors.