Water levels in Fukushima reactors?

[FishmanGeertz]

If the reactors have been without water, the core melts very quickly. The Fukashima Daiichi reactors 1-4 lost cooling and water flow shortly after the march earthquake and tsunami and the cores were exposed.

If they were unable to get water flowing back into the reactors for several days, then the reactors have undoubtedly boiled themselves dry and melted down completely within a matter of about 4-5 hours after losing cooling.

I'm not sure if I have my info straight, but how long did the reactors go without any water? I heard it was 2-3 days until they started pumping seawater into them. During the TMI (three mile island) incident, the top of the rods were exposed after only a few hours of cooling loss. This resulted in roughly 90% core damage.

 

[clancy688]

During the TMI (three mile island) incident, the top of the rods were exposed after only a few hours of cooling loss. This resulted in roughly 90% core damage.

TMI2 lost cooling capability immeadiatly after SCRAM. Fukushima had battery driven cooling for at least half a day, so the fuel was safe during this time period.
Because of that, heat energy during the TMI2 accident was probably ten times the amount created in Fukushima when the fuel got uncovered. (Don't take my "ten times" seriously, I'm just guessing - but that's the overall direction)

 

[FishmanGeertz]

TMI2 lost cooling capability immeadiatly after SCRAM. Fukushima had battery driven cooling for at least half a day, so the fuel was safe during this time period.
Because of that, heat energy during the TMI2 accident was probably ten times the amount created in Fukushima when the fuel got uncovered. (Don't take my "ten times" seriously, I'm just guessing - but that's the overall direction)

The reactors lost cooling and water flow immediately after the emergency batteries died. The main question is how long were the reactors without cooling? How much of the core was exposed?