If the water boils, it could evaporate, exposing the rods. The fuel rods are encased in safety containers meant to prevent them from resuming nuclear reactions, nuclear officials said, downplaying the risk of that happening.
But they acknowledged that there could have been damage to the containers. They also confirmed that the walls of the storage pool building were damaged.
Though Kan and other officials urged calm, Tuesday's developments fueled a growing panic in Japan and around the world amid widespread uncertainty over what would happen next. In the worst case scenario, one or more of the reactor cores would completely melt down, a disaster that could spew large amounts of radioactivity into the atmosphere.
"I worry a lot about fallout," said Yuta Tadano, a 20-year-old pump technician at the Fukushima plant, who said he was in the complex when quake hit.
"If we could see it we could escape, but we can't," he said, cradling his 4-month-old baby, Shoma, at an evacuation center.
The radiation fears added to the catastrophe that has been unfolding in Japan, where at least 10,000 people are believed to have been killed and millions of people have spent four nights with little food, water or heating in near-freezing temperatures as they dealt with the loss of homes and loved ones. Up to 450,000 people are in temporary shelters.
I've thought about what I would take if I had an hour to get out of my house with the possibility of never coming back. It is a sobering reflection on the pain the people of Japan must be suffering.
With all the wasted energy and foolishness on curtailing the use of lightbulbs, the environmentalists have done next to nothing about the use of nuclear material for energy.
Chasing the splinters and ignoring the logs.