"Even as workers race to prevent the radioactive cores of the damaged nuclear reactors in Japan from melting down, concerns are growing that nearby pools holding spent fuel rods could pose an even greater danger.

The pools, which sit on the top level of the reactor buildings and keep spent fuel submerged in water, have lost their cooling systems and the Japanese have been unable to take emergency steps because of the multiplying crises.

By late Tuesday, the water meant to cool spent fuel rods in the No. 4 reactor was boiling, Japan’s nuclear watchdog said. If the water evaporates and the rods run dry, they could overheat and catch fire, potentially spreading radioactive materials in dangerous clouds.  "

William J. Broad and Hiroko Tabuchi report for the New York Times March 15, 2011. [2]