[justa-hairyape]

The first structure on the left is now gone?

That is right. Only steel beam structure left. The explosion could have blown the walls away from the internal vessel, but it was a very large explosion. They have to assume containment breached.

[dragnet2]

We saw the shock waves come off that reactor.

Unreal...

[J Aguilar]

As a summary:

Fukushima 1 reactor #1 external building concrete cover is gone. #1 is an old 460 MW boiling water reactor (BWR).

The state of the primary containment (see link on BWR) remains unknown.