[rottndog]

I am not sure why when the control rods go in hydraulically that the plant cannot be shut down. I realize it is still hot but would expect that within a few hours that the plant could be totally shut down.

When the 'poles are in the holes', the reactor plant is shut down. However, it continues to produce heat at a slowly decreasing rate--fission reactions are still happening, but not enough to sustain criticality. Since the reactor plant is very heavily insulated, it retains all of that heat, minus minimal ambient losses, plus what is still being produced. A shutdown reactor requires cooling until the amount of heat produced no longer exceeds the ambient heat losses of the system. Depending on the size and design of the reactor plant (and many other variables), this can take days, weeks, or even months.

[Frantzie]

I would have hoped once the poles were in the holes that at least it would avert meltdown but I understand the fission is still happening.

I am afraid at least one is going to meltdown over there. The poor Japanese and it will not be good for the Pacific Ocean.