meltdown is a hollywood term

The fear with Japan's reactor troubles, of course, is the possibility of a nuclear meltdown. But engineers don't even agree on what the term means and prefer to use other ways to describe what happens.

Without water to cool nuclear fuel rods, temperatures above 1,600 degrees Fahrenheit can melt the metal that covers uranium pellets inside the rods, says nuclear consultant Douglas Chin of MPR Associates in Alexandria, Va., an engineering firm. That causes the release of radioactive material inside the rods and the metal to blister and peel away. If the rods grow hot enough, uranium disc pellets, the fuel in the fuel rod, slump into the center of the reactor, where they are cooled by the water still at the bottom of the reactor chamber and pile up in lumps.

http://www.usatoday.com/tech/science/2011-03-15-1Anuke15_VA_N.htm

Just don't call it a meltdown, some engineers say.

"Meltdown is a Hollywood term; nobody really uses it," says radiation safety specialist Bruce Busby of the Fred Hutchison Cancer Research Center in Seattle. "What we are really talking about is core damage ..."

Core damage sounds bad enough, but the distinction does matter.

"Meltdown is what I call the 'Jane Fonda scenario,' " says nuclear consultant Lake Barrett, a former Energy Department and Nuclear Regulatory Commission engineer, referencing the 1979 movie The China Syndrome, in which a melting reactor core breaks through the containment barriers below it.

In such a meltdown, the fuel rods inside a reactor melt together into a mass, hugging the steel floor of a reactor chamber. In this Hollywood depiction, the process goes out of control, the hot fuel eats through the 8-inch steel floor, and goes all the way to China. It reaches the groundwater and spreads radioactivity for hundreds of miles.

In reality, "that's impossible; it didn't even happen at Chernobyl," says Barrett, referring to the 1986 disaster in Soviet Ukraine, the worst nuclear reactor disaster in history.

Busby calls the fuel-rod disintegration more of a "crumbling," where the discs fall apart. Others use different analogies.

"In reality, first (the rods) drip down to the floor of the reactor like a candle melting," Barrett says. "There is still water at the bottom of the reactor. That cools the fuel off."