A bomb would have to be exploded underground to take out the melted core material.
Unfortunately, from my point of view, that would send the lethal radiation into the atmosphere rather than the sea.
While I’m not advocating above ground nuclear testing, it was done for several decades by several countries. I don’t doubt that there were negative repercussions upon the health of both humans and animals. However, it was not exactly apocalyptic.
So, how can the failed Fukushima reactor leaking even reach the level of the former testing, as far as being some sort of “great danger?” It’s not good, granted, not good at all, but this reaction comes across as scare-mongering and more than a little hysterical.