“While the two previous explosions were hydrogen blasts, caused by a buildup of steam in the reactor unit, this time officials are not sure what the cause was.”
That, plus the fact that radiation is going on, seems to indicate another hydrogen blast.
The containment is still intact. If it were not, you’d expect to see radiation increasing.
Radiation spiked high right after the blast. Not sure if it settled down again or not. They're worried about a possible breach of the supression pool area.
They're still pushing sea water in there, but according to the report I saw, about 1/2 of the fuel rods were exposed above the liquid level.
Note to others - Units 4, 5, and 6 at this facility were off line and in cool shut-down condition at the time of the earthquake so they aren't likely to present significant problems.