Nuclear meltdown likely happening at Japanese reactor

A meltdown may be under way at one of Fukushima Daiichi's nuclear power reactors in northern Japan, an official with Japan's Nuclear and Industrial Safety Agency told CNN Sunday.

"There is a possibility, we see the possibility of a meltdown," said Toshihiro Bannai, director of the agency's international affairs office, in a telephone interview from the agency's headquarters in Tokyo. "At this point, we have still not confirmed that there is an actual meltdown, but there is a possibility."

Though he said engineers have been unable to get close enough to the core to know what's going on, he based his conclusion on the fact that they measured radioactive cesium and radioactive iodine in the air Saturday night.

"What we have seen is only the slight indication from a monitoring post of cesium and iodine," he said. Since then, he said, plant officials have injected sea water and boron into the plant in an effort to cool its nuclear fuel.

The reported presence of Cesium 127 was disturbing, experts agreed, because it was evidence that the core had overheated, if only for a portion of time. The radioactive debris is produced when the core is exposed above the coolant water level and overheats. One of the other potential by-products of such overheating is hydrogen. Hydrogen is believed to be the cause of the blast at Fukushima.

How bad might it get? Bergeron says, "if the core does melt, then it will slump to the bottom of the reactor vessel, melt through to into the containment floor" which will lead to that safety measure to fail. "It's likely to spread like a molten pool to the edge of the steel shell and melt through." You could have containment failure in less than a day." Then the core would exposed to the external environment. In that worst-case scenario, the only thing that can be done is to entomb the melted core in sand and cement, much as was done in Chernobyl. Said Bergeron, "A lot of first responders will die."