NEI: Explosion may have damaged a portion of the reactor’s primary containment structure

[TNLib]

Keep in mind this is the NEI (pro-nuke source). But it's looking like the damage has been done to the primary containment structure.

This is official as it gets with some lite pro-nuke spin but the technical updates are a good source for keeping up to date with what is happening at the plant.

http://www.nei.org/newsandevents/information-on-the-japanese-earthquake-and-reactors-in-that-region/">Link