A point of correction. DU is NOT a "low level" radioactive waste product left over from nuclear power reactors, as I first stated. It is actually a waste product left over from mineral processing, the enrichment process. Whilst in theory, it is less radioactive than the uranium ore mined at Roxby Downs, it does not mean that is is safe to humans or the environment. It is best kept underground. (I have now corrected this on the posting).
A snippet from http://www.globalsecurity.org/military/systems/munitions/du.htm
"Depleted uranium [DU] results from the enriching of natural uranium for use in nuclear reactors. Natural uranium is a slightly radioactive metal that is present in most rocks and soils as well as in many rivers and sea water. Natural uranium consists primarily of a mixture of two isotopes (forms) of uranium, Uranium-235 (U235) and Uranium-238 (U238), in the proportion of about 0.7 and 99.3 percent, respectively. Nuclear reactors require U235 to produce energy, therefore, the natural uranium has to be enriched to obtain the isotope U235 by removing a large part of the U238. Uranium-238 becomes DU, which is 0.7 times as radioactive as natural uranium. Since DU has a half-life of 4.5 billion years, there is very little decay of those DU materials."
Another interesting page is