Maybe someone noted this earlier, but I just realized that the spent fuel cooling ponds in reactors 4,5,6 may not actually be holding "spent fuel" as in depeleted fuel rods. Reactors 4,5,6 were already shut down and emptied for inspections when the quake hit, not for refueling, so to me, that that raises the possibility that those fuel rods were intended to be reloaded into the core and are still hot enough to restart fission (outside the protection of a containment vessel!) in the worst case scenario. Or maybe they are being inspected at a natural refueling point, I don't know.

Does anyone else know what's in 4,5,6?