WASHINGTON — The chief of the U.S. Nuclear Regulatory Commission said today all the water is gone from one of the spent fuel pools at Japan's most troubled nuclear plant.

This means there's nothing to stop the fuel rods from getting hotter and ultimately melting down.

The outer shell of the rods also could ignite with enough force to propel the radioactive fuel inside over a wide area.

Gregory Jaczko did not say today how the information was obtained, but the NRC and U.S. Department of Energy both have experts on site at the Fukushima Dai-ichi complex of six reactors.

He says officials believe radiation levels are extremely high, and that could affect workers' ability to stop temperatures from escalating.

By The Associated Press