Explosion damage might not be compromising...

There are official statements floating about that indicate that the damage seen very clearly now in photos and in the videos concerning the explosion at Fukushima Daiichi No. 1 may NOT have damaged the actual secondary containment itself, but rather may simply have 'removed' the top portion of the reactor building that serves essentially as a weather enclosure over the refueling floor, protecting equipment mounted there. This is NOT considered a barrier as far as reactor safety is concerned.

However, it is impossible to prove this without inspection closely and completely and since that is highly unlikely to happen the safe assumption would be that it is indeed compromised until proven otherwise.