Tokyo Electric Power Co. said Thursday that the water level in the No. 1 reactor's pressure vessel at the Fukushima No. 1 power plant is much lower than thought and that some of the fuel rods have melted and sunk to its bottom.

But Tepco also said the temperature in the pressure vessel has been kept at around 100 to 120 degrees, which is cool enough to keep the reactor safe, for now.

The low water level, however, indicates that the pressure vessel could have holes or cracks through which radioactive water is leaking.