It just changes its state by heating from a solid into a gas. The nuclear material is then mixed with a liquid silicon material and then cools into a plasma-like crystaline structure mixed in with the glass (technically, a plasma).
I'm not sure what you mean by "gassification 'is at' the molecular or atomic 'level' depending on the species".
Thanks for the refresher on basic chemistry. A pure isotope, like U235, remains atomic in its gaseous state, while a compound like Uranium Hexafluoride will remain molecular if gassified.
Species also refers to animals. The only radioactive animal I'm familiar with is this guy:
![](http://tonova.typepad.com/photos/uncategorized/godzilla.jpg)