You need quite a lot of pure uranium for it to be dangerous/harmful. They were handling pure chunks of the stuff in Los Alamos without too many ill effects (discounting the one where Slotin dropped a hemisphere and created a prompt critical mass, that is bad). Just a low concentration of uranium in water isn't really all that dangerous unless swallowed. And then it's mostly because Uranium is more poisonous than lead, it's biological half time (how fast the body removes it again) isn't long enough to give you a fatal dose either.
The actinides and fission products really ARE the main concern in a nuclear accident, not the uranium (long term you want to get rid of it, mostly because of the poisonous nature of it). Look at what they've been dealing with in Fukushima, you'll find it's the Strontium that is the main concern right now outside the reactor.
Edit to add:
Uranics are harmful if you STAY in the environment and don't go to a place that isn't contaminated. Obviously then the body can't get rid of the stuff because it keeps getting replenished.Uranium however isn't the acute danger that other radioactive elements present.
Biting the hand that feeds IT
