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Published on Saturday, March 12, 2011 by CommonDreams.org

Behind the Hydrogen Explosion at the Fukushima Nuclear Plant

by Karl Grossman

The explosion at the Fukushima nuclear power plant is being described as caused by a “hydrogen build-up” The situation harks back to the “hydrogen bubble” that was feared would explode when the Three Mile Island plant in 1979 underwent a partial meltdown.

The hydrogen explosion problem at nuclear power plants involves a story as crazy as can be. As nuts as using nuclear fission to boil water to generate electricity is, the hydrogen problem and its cause cap the lunacy.

Eruption of hydrogen gas as a first reaction in a loss-of-coolant accident has been discussed with great worry in U.S. government and nuclear industry literature for decades.

That is because a highly volatile substance called zirconium was chosen back in the 1940’s and 50’s, when plans were first developed to build nuclear power plants, as the material to be used to make the rods into which radioactive fuel would be loaded.

There are 30,000 to 40,000 rods—composed of twenty tons of zirconium—in an average nuclear power plant. Many other substances were tried, particularly stainless steel, but only zirconium worked well. That’s because zirconium, it was found, allows neutrons from the fuel pellets in the rods to pass freely between the rods and thus a nuclear chain reaction to be sustained.

But there’s a huge problem with zirconium—it is highly volatile and when hot will explode spontaneously upon contact with air, water or steam.

The only other major commercial use of zirconium through the years has been in flashbulbs used in photography. A speck of it, on a flashbulb, ignites to provide a flash of light.

But in a nuclear plant, we’re not talking about specks—but tons and tons of zirconium, put together as a compound called “zircaloy” that clads tens of thousands of fuel rods.

Heat, a great deal of heat, builds up in a very short time with any interruption of coolant flow in a nuclear power plant—the problem at Fukushima after the earthquake that struck Japan.

Zirconium, with the explosive power, pound for pound, of nitroglycerine, will catch fire and explode at a temperature of 2,000 degrees Fahrenheit, well below the 5,000 degree temperature of a meltdown.

Before then, however, zirconium reacts to the heat by drawing oxygen from water and steam and letting off hydrogen, which itself can explode—and is said to have done so at Fukushima.

As a result of such a hydrogen explosion, there is additional heat—bringing the zirconium itself closer and closer to its explosive level.

Whether in addition to being a hydrogen explosion, zirconium also exploded at Fukushima remains to be known.

But what has happened regarding hydrogen at Fukushima, like the “hydrogen bubble” when the Three Mile Island plant in Pennsylvania underwent its near partial meltdown, is no mystery—but precisely what is expected in a loss-of-coolant accident.

It is described in U.S. government and nuclear industry accident studies as a “metal-water” reaction. It’s a reaction, the research has long stated, that can easily trigger a meltdown.

Using tons of a material otherwise used as the speck that explodes in a flashbulb in nuclear power plants —yes, absolutely crazy.

Moreover, in the spent fuel pools usually situated next to nuclear power plants, there are large numbers of additional fuel rods, used ones, disposed of as waste. There must be constant water circulation in the spent fuel pools. In what is labeled a “loss-of-water’ accident in a spent fuel pool, the zirconium cladding of the fuel rods is projected as exploding—sending into the environment the lethal nuclear poisons in a spent fuel pool.

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