The picture above is a Carbon "Bucky Ball". So what is so bad about Radioactive Uranium Bucky balls? Well, picture some one throwing very fine, non caking, radioactive "talcum powder" into the air; that in essence is the outcome of this finding.
But it gets worse, imagine that radioactive "talcum powder" behaving and dispersing the exact same way when thrown into the water.
But it gets worse, notice in the picture above that the Buck Ball is actually a cage, now picture plutonium atoms trapped inside that cage.
But it gets worse, now picture how much greater a target these Bucky Balls are for spallation in the upper atmosphere.
What this finding means is that ALL the dispersion models are wrong, and NOT in the good way. It also means that the internal impact and damage from inhaling or consuming these particles is far greater than would other wise be expected. However, don't expect the "it's safe" mantra to change.
If you want to even begin to have an idea how bad this situation is, Google the medical effects of Nano Particles(and remember they are discussing NON-Radioactive nano-particles)