There were large amounts of yellowcake (unenriched uranium oxides) stored at a nuclear facility in Tuwaitha, containing materials left over from Iraq's old, pre-Gulf War nuclear program. It had been tallied by U.N. nuclear inspectors, and was no big secret. The facility was compromised before our forces arrived, and various materials scattered around. Fortunately, most was accounted for. Yellowcake is not that dangerous as such, but it's possible that during the security breach, or maybe even prior to the war, scrap from this area could have gotten out and ended up in scrap piles.

One hopes that they are investigating this in detail, however.