Not so. I used to work out there and I live within 20 minutes of the place. One of the characteristics of uranium is that it is pyrophoric, if refined enough like to weapons grade purity, it is prone to catch on fire. Fissionable uranium is handled in small quantities, because large quantities can reach critical mass and do BAD stuff. Plus they are handled in containment areas specifically designed to reduce exposures if a fire breaks out.

Not to worry, it was contained and according to local sources is already out. There will be an investigation as always, and countermeasures will be put in place to reduce the chance of this happening again.

Y-12 is the weapons facility and they handle LOTS of weapons-grade fissionable materials, so let the experts do what they do.