Oh, I don't know. Lacking implosive compression the consequence would have been, not the sort of blast you seem to have in mind, but rather a "demon core"-style radiation accident. That said, it'd still be enthusiastically messy albeit in a more limited fashion, and there'd still be no reason for anyone to assemble the material that way - not least for what grisly example became of the last guy who took so little care.

Still, as you note, it's remarkable to think of the density of the material - a soccer ball's worth that masses about as much as me.