Even with so much being neuetralized? But yes, I understand that is the concern now..that it can be contained..unfortunately nobody will know until it happens.
And given the Japanese architectural engineering prowess on display from all the video abounding showing how little structual damage occured despite the intense shaking of a very violent earthquake, them pressure containment vessels could withstand a direct hit of a small nuke right now and retain pressure integrity AFAIC.
There's no way any meltage of the core occured. There is undoubtedly deformation of the fuel and moderator rod assembly, i.e., warpage due to unmitigated intense heat of the nuclear pile while it was uncovered for a short time (as the coolant bled off).
Even so, the nuclear pile was never totally uncooled. Even IF the entire nuclear pile was only in contact with steam, the steam was still exchanging heat from the nuclear pile into the secondary torus water reervoir; all that's part of the calculated cooling design specs (albeit not optimal but within putative tolerances ostensibly to avoid outright core meltdown).
In fact, even in the Sci-Fi event the reactor core did melt in entirety, the secondary containment vessel is designed and constructed such that the molten slag of the entire nuclear core would be confined entirely within the secondary torus water reservoir (resting upon a graphite floor a meter thick acting as moderator). It might take a decade for that to cool, but there'd be no catastrophe.
There's no way for un-enriched fuel to go critical, and the graphite - along with the incorporated molten moderating rod material - would dampen over time whatever residual reaction was still occuring.