hydrogen rupture?
Could be. I would have expected a larger explosion if the containment and vessel went at the same time. Could even just be the outer building (not the containment) from an accumulation of hydrogen. That large black mass that rises up and falls down in the center of the explosion is a concern though. It is possible that the vessel is intact and the containment blew but that probably means that there is no longer the ability to cool the core and it is now or soon will be in full meltdown.