I don't think it was 500 tons or even close. (Just trying to stop mis-information from spreading)
I'm a friendly so don't shoot!
Well, that's what it says here:
http://www.signonsandiego.com/uniontrib/20040522/news_1n22uranium.html
"Of the uranium, 500 tons is naturally occurring ore or yellowcake, a slightly processed concentrate that cannot be directly used in a bomb. Some 1.8 tons is classified as low-enriched uranium..."