The last depleted uranium symposium that occurred was sponsored by the Armed Forces Radiobiology Research Institute. That was three or four years ago. It took place along with the 50th anniversary of the founding of AFRRI. I see these results presented at professional meetings periodically, and they're published in radiobiology research and the Health Physics Society Journal. As to whether there has been a DU conference, the only one that I'm aware of is AFRRI's.
On March 19th, 2013. See this statement in context.