Meltdown
BBC:
BBC News - Setbacks at Japan nuclear plant: A reactor at Japan's crippled nuclear plant has been more badly damaged than originally thought, operator Tepco has said. Water is leaking from the pressure vessel surrounding reactor 1 - probably because of damage caused by exposed fuel rods melting, a spokesman said.... Work to restore cooling systems had been most advanced at reactor 1, the smallest and oldest at the site. But a spokesman for the power giant said when a faulty gauge had been repaired, it showed water levels in the pressure vessel 5m (16ft) below the level needed to cover fuel rods.
"All the fuel is unprotected at this point and the water levels are below that," said Junichi Matsumoto. "However temperatures in the reactor pressure vessel have cooled to 100 to 120 degrees so we have come to the conclusion that the fuel mass... is actually not at the proper levels but somewhat below that or even possibly at the bottom of the vessel." He said there was likely to be a large leak in the pressure vessel, possibly caused by the fallen fuel. "As for a meltdown, it is certain that it has crumbled and the fuel is located at the bottom (of the vessel)," he added. The water is said to be leaking into the containment vessel and from there into the reactor building.
Experts said the announcement from Tepco did not mean that the situation at the plant had worsened because it was likely that the fuel had dropped to the bottom of the core soon after the 11 March earthquake...
