"Fully depleted" uranium is Lead (Pb) so depleted uranium is not really depleted, hence it is in a state of ongoing radioactive decay, hence it is a "nuclear weapon"

It is used mainly because it is denser than lead - makes for a heavier projectile, means more energy on target, means more likely to punch through steel armouring. When it does punch through it is partly atomised into a dust/vapour and that is radio active dust, breathe that in and your cancer chances are increased.

Side note: I have a pet theory that lung cancer rates were driven by airborne nuclear testing programmes. When they ended cancer rates began to fall, so at that point smoking (which is blamed for these cancers) had to be curtailed to account for the fall in rates. Hence there was a lot of smoking bans introduced. Government can then claim their bans have saved lives, when the truth is their airborne testing programmes caused death.