Saturday, March 12, 2011

Hydrogen, Zirconium, Flashbulbs -- and Nuclear Craziness

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.

6 comments:

cloudsforest said...

Hi Karl, thank you for the very good explanation. I have a question: if the explosion was due to the metal-water reaction, then it should be inside the reactor vessel, how the vessel can stay undemaged as the Japanese authority announced? Or the hydrogen gas was vent to somewhere in the plant? thank you.

Gene Dyer said...

Maybe it was not fuel inside the reactor. Maybe spent fuel in a storage area lost its cooling - which would explain why the explosion was in the outside building and not inside of the containment building.
Gene

Mark said...

The zirconium had to have a high temp to react to the water, thus it was inside. The spent fuel rod pool I assume was at atmospheric pressures and probably vented.

Zirconium, think magnesium. It's great for light weight airplanes, but yes, it burns and was also used as getters in vacuum tubes, flash photography, and underwater flares. It requires great heat to get to that stage of burning. Even iron reacts with water to form rust and releases hydrogen, but the hydrogen dissipates harmlessly.

Also, hydrogen causes an effect on metal piping called "hydrogen embrittlement" that causes ALL metals to become brittle and break. So let's say there is some rust or reaction to the water or steam and hydrogen is released. the remaining metal is then exposed to hydrogen. Hydrogen at elevated temperatures and pressures will form metal hydrides (MH or MH2). Metal hydrides are not especially strong and then cause weakness. Also, since hydrogen is a small molecule, it is able to permeate the metal, following imperfections in the metal, causing embrittlement along the metal's imperfection, making the imperfection worse. Catastrophic failure. Regular steam boilers blow up all the time and hydrogen embrittlement is partial cause.

Sara said...

Karl, I heard you on democracynow this morning. They still have not linked to the study you cited from the NRC. Could you post a link to it? Also to the document you quoted from 1985 that stated the likelihood of a meltdown at one of our reactors? Thanks!

rod said...

Many of the claims made in this article seem to have serious flaws and appear to show a lack of scientific knowledge. I would be more inclined to believe an article that had citations for the "facts" it purports.

rod said...

Let's talk about the volatility of zirconium. Many metals in powder form exhibit explosive characteristics. Aluminum is one example, but try lighting an aluminum rod. Even flour can explode under certain conditions, but, I have yet to encounter an exploding loaf of bread. Zirconium alloys are not the same as a flashbulb. Until Karl injects some scientific rigor into his arguments, I will consider him the journalistic equivilent of Chicken Little.