There are NO shells (whatever that word means) or warheads made of DU. All DU munitions are solid slugs or one size or another. They do shed small particles when they hit something (such as a tank), and these particles may be a health hazard when/if ingested. Rather than "ducking questions", the effects of DU have been the subject of several long-term studies by the US Department of Veterans Affairs - a summary of these studies is here.