During those searches the inspectors found radiation traces in rooms left by the previous presence of weapons-grade uranium, with an enrichment of 40% to 60%.
I remember the IAEA found enriched uranium but it was traced to imported components. That is not to say this was the only enriched uranium and that the B-52 story is false.
The following link which is pdf says ‘much’ so the B-52 story could be true. Manna from heaven.
The centrifuge connection' D Albright, C Hinderstein - Bulletin of Atomic Scientists, March/April, 2004 - bulletinarchive.org ... Much of the highly enriched uranium that the IAEA found in Iran by taking environmen- tal samples may be consistent with material produced in Pakistan. ...