MSNBC - headlines the term meltdown, but dig a little deeper, and the term isn’t clearly defined.

A “meltdown” is not a technical term. Rather, it is an informal way of referring to a very serious collapse of a power plant’s systems and its ability to manage temperatures.

Yaroslov Shtrombakh, a Russian nuclear expert, said a Chernobyl-style meltdown was unlikely.

“It’s not a fast reaction like at Chernobyl,” he said. “I think that everything will be contained within the grounds, and there will be no big catastrophe.”

In 1986, the Chernobyl nuclear reactor exploded and caught fire, sending a cloud of radiation over much of Europe. That reactor — unlike the Fukushima one — was not housed in a sealed container, so there was no way to contain the radiation once the reactor exploded.

Edwin Lyman, a senior scientist with the Union of Concerned Scientists, which opposes nuclear energy, told msnbc.com Friday that TEPCO was facing a potential catastrophe.

“What’s critical is, are they able to restore cooling and prevent fuel damage? If the fuel starts to get damaged, eventually it will melt through the reactor vessel and drop to the floor of the containment building,” raising the odds that highly radioactive materials could be released into the environment, he said.
msnbc.com

But Steve Kerekes, spokesman for the U.S.-based Nuclear Energy Institute, said that while the situation was serious, a meltdown remains unlikely and, even if it occurred would not necessarily pose a threat to public health and safety.