My understanding is.

1 - Unlike Cherynobyl, the Japanese plant has a containment shell - Cherynobyl did not.

2 - The US delivered the (core coolant) solution <-- thats what your supposed to use, not sea water. Not sure if they got the pumps working at the plant to get the coolant circulating ? They are still using the sea water as the last ditch effort to cool the rods.

Anyway, they now have the best Brains in the world helping out - fingers crossed.