>> NOT putting the fuel tanks UNDERGROUND!<<
(As in US and most other places, I presume: this would seem to be a real Brain-Fart within an otherwise punctilious/conservative design approach elsewhere.)

Tsunami is a Japanese word! and earthquakes are their daily bugaboo. Above-ground tanks supplying their
BACKUP
(only ONE! == another error) for the absolutely necessary mondo core-cooling pumps is, in hindsight:
absolutely an inexcusable Duhh-grade oversight. Pity..

For those being queried about 'reactors', One more Time -- save your breath:
here's a video by a avuncular Brit physicist, reviewing the BASICS, including the role of Boron in the control rods and various other simple concepts of the sort,
always mangled by Murican-HS-edjakated talking heads, who majored in bizness.

http://www.youtube.c...tch?v=-bcrLiATLq0

As to the 'mood' of Japanese boffins du jour; I seriously doubt that they are in panic-mode -- rather they are fully aware of what Might.. occur if even a few hasty/stupid actions were to be taken, next.
Clearly the infusion of sea water has forever decommissioned each reactor where used: all SS parts shall have been corroded and filled with micro-cracks via Cl and other ions at v. high temps
-- beyond any hope of salvage. Fortunately these reactors were already scheduled for denouement after 40 years of decent service.

Concur that any Cs, I-131 etc. came from some spot in core where the Zr cladding had disintegrated
(probable source point for voluminous H generation for the explosions)
-- but How Many grams/kilos really did melt??
More disturbing is the inability to raise the sea-water level to cover fully the entire core == SOON.

WHY?? It is almost unthinkable that there exists already a sizable hole at bottom of containment vessel, and surely they have opened other valves
so that the incoming sea-water is not merely compressing any gases within -- that's the Q I want to see an answer to. Should be forthcoming within hours, I'd think.

Luck to Nippon..