Posted on 03/15/2011 5:19:24 PM PDT by TigerLikesRooster
While I agree with you in principle, there is still an element of official decorum and propriety that should be paid attention to. Even figurehead monarchs understand the importance of projecting the right tone at the right time. I personally think that an advanced version of ‘Turbo Tax’ could probably be used to run the Presidency more effectively than what we have seen lately. That said, the President does have a responsibility to project a proper respectful image.
http://bravenewclimate.com/2011/03/15/fukushima-15-march-summary/
This source is more credible than any other I’ve seen, so far.
There is one and only one way for Hydrogen to be produced in large enough quantities to produce an explosion. Namely, H is produced as a result of a chemical reaction with the zirconium in the Zircaloy cladding of the fuel rods. And this chemical reaction takes place when the fuel rods reach a temperature of 1200 C (2200 F). Hence the presence of H means the rod temp has reached at least 1200 C. For at least the top parts of the fuel rods.
And this means that the water is boiling away (or leaking) faster than it can be replaced. Because no parts of the fuel rods would reach that temperature if they were completely surrounded by water.
The reaction is similar, but not identical, to these from highschool chemistry.
Na (metal) + H2O -—> NaOH + H
Mg (metal) + HCl -—> MgCl + H [leaving out the 2’s]
With zirconium, it is
Zr + H20 -—> ZrO + H [Zr + 2H20 -—> ZrO2 + 2H2]
That is, Zr metal is converted to Zr-oxide, releasing hydrogen in the process. This does not occur at low temperatures. However, once started the reaction is exothermic, that is, it releases heat. Hence, it tends to get hotter, thus boiling away more water, and speeding up the release of more hydrogen. If nothing happens to get things cool, the process feeds on itself in a runaway fashion.
The problem is made worse by what is known as the “two phase problem.” That is, at the surface of the Zircaloy there is a mixture of liquid water, water vapor (steam), and hydrogen gas. The gases carry heat away poorly, and in effect they provide an insulating layer that hinders the liquid from effective cooling. And zirconium oxide is a much poorer conductor of heat than the metal, so the growing amount of ZrO2 further hinders heat transfer from the fuel rods. Hence, as time goes on, things get hotter.
The rods are about 3 meters long (10 ft), and the water bath normally covers them completely. In this loss of cooling scenario, they are not uncovered all at once. The water level slowly drops, exposing the upper parts of the rods, and the above applies basically to the circa 10-cm region around the water level; above is hot, below is cool. But at this level, all is turbulent. And as the water level drops, this region keeps revealing new sections of the rods to the H-producing reaction. (The region above the turbulent interface is filled with very hot steam and previously released hydrogen, keeping the ZrO reaction going.)
Worser problems: The Zircalloy tubes (filled with uranium oxide pellets or some mix with plutonium) do not like this situation at all. They are much hotter than they can stand, they experience huge localized hot spots, a thermal gradient, the Zircaloy becomes soft, and the cladding is rapidly being converted to zirconium oxide (there are some other chemical reactions, too). They then begin to swell, bend, balloon, buckle, get wart-like bubbles, and eventually develop holes. (The rods always have a fairly high internal pressure owing to the Xenon generated by the radioactive decay). The swelling and buckling may reduce the space between the rods, which then impairs the water circulation, leading to more super-hot spots. At an advanced stage, this becomes a runaway process with a total meltdown unstoppable and inevitable. The whole Pacific Ocean could not stop it.
The holes are what cause isotopes of cesium, xenon, iodine and other unsavory nucleotides to get released.
So far, it seems that only a few upper centimeters of the fuel rods have undergone this process, and only maybe a two or three rods have developed holes (out of perhaps 50 rods—not sure of the total number). The concern is, if they have not been able to pump enough water in to prevent this level of Zr-hydrogen reaction, why won’t it get worse? The plant operators know everything—and more—than I have described, but they have not been able to get enough water into the reactor vessels.
The hydrogen problem, again, is that the water level is falling faster than they can pump it in (pump out hot water, replace with cool water). Water, water everywhere but not enough to cool.
If the cooling system had failed and temeperatures were high enough to melt down some parts of the fuel rods, then they may have been high enough to dissociate the Hydrogen and Oxygen in the water first used to cool the fuel rods.
Without an ignition source, you'd get a buildup of an explosive (and in a stoichometrically ideal ratio) mixture, given a little time.
I'll gladly defer to someone more knowledgeable.
I was wondering why they’re not using gaseous nitrogen to neutralize the hydrogen gas buildups, I suppose they have enough to worry about, but I’d think it would be easy enough and safe and provide a good fire suppressant.
In my post, I said the entire problem was “thermal”, that is, at high temperatures chemical reactions occur. Are you disagreeing?
This notion about dissociation of water into H2 and O2 needs an ocean of better understanding. Start with, it is wrong.**
You must understand that in a reactor volume the water, H2O, is not isolated; every molecule can interact with the fuel rods, that is, the zirconium atoms in the zirconium alloy called Zircaloy. This is a surface chemistry effect, and there the Zr atoms react with water to create ZrO2 and H. The hydrogen forms bubbles, which rise to the top and collect there.
Indeed, we want every water molecule to hit the surface, get hot, and move away, carrying heat away. That is what heat transfer means.
But you can’t stop the little devils from having a relationship, namely oxygen atoms in water preferring to marry zirconium atoms coventently.
There is no “dissociation” other than a chemical reaction that results in two new compounds, one of which is hydrogen gas, from the H2O. There are also interactions with hot H2O molecules with the containment vessel surface.
**It is true that at a high enough temperature, which depends on the pressure, that water molecules of H2O break down into H2 and O2 molecules. Roughly, this is about 1400 C. But you can look up all the enthalpy, free energy, bond energy factors as you wish.
Consider that you have a flask of hot water vapor—steam—at this high temperature where the “dissociation” occurs. You cannot separate the oxygen molecules from the hydrogen molecules. As soon as the flask cools, they recombine to make just water vapor. NO EXPLOSION—because the thermal energy originally needed to dissociate the water molecule is returned to the kinetic energy (translational and rotational) of the molecules in a hot gas.
So, in such a closed system you have caused dissociation-—but it has no effect. The original water returns to water.
The point is that the water in a reactor is not isolated-—the water molecules react with the surfaces they encounter. The reaction kinetics depend on the temperature. I described a tiny bit of what happens at the Zircaloy surface. Do you disagree?
The water molecules also interact with the containment walls—”stainless steel”, that is, a mixture of iron, cobalt, chromium, nickel, et al. with a pinch of vanadium and manganese.
It is not thermal dissociation of water-—it is chemical reactions. It is chemical reactions that carry away the oxygen atoms in water and leave hydrogen to bubble.
It is this hydrogen, when it mixes with air-—80% nitrogen, 20% oxygen—that leads to fires and sometimes explosions.
Do you disagree?
You obviously skipped high school chemistry.
“gaseous nitrogen to neutralize the hydrogen gas”
LOL. Sorry, you must have missed school wholly.
See: Proverbs: 26:4 & 5; 27:22
Admittedly, I haven't looked up the combustion temperature of magnesium, but I have witnessed firsthand the somewhat pyrotechnic results of the efforts of a probie to put it out with water.
The situations are, as you have explained, different.
Thank you for clearing that up.
OK, you pass the sniff test :)
“WHERE THE HELL IS OBAMA????”
THERE IS NOTHING WRONG, REMEMBER? THERE IS ABSOLUTELY ZERO DANGER, EVERYTHING IS FINE, AND EVERYTHING IS UNDER CONTROL.
AMAZES ME THAT SO MANY INSIST THERE IS NO DANGER AND EVERYTHING IS UNDER CONTROL, AND THEN INSIST THE U.S. RUSH TO THE RESCUE.
“President on duty”
There has been no President on duty in America for over two years!
Perhaps the “ONE” will kill affirmative action for all time
sure was an expensive test.
That’s a pretty thorough explanation of the reaction chemistry. Thanks.
One of the more serious problems (there are several), as I now understand it, is that not every fuel rod undergoing this ZrOx process is inside the core; that is, inside the primary containment vessel.
There is a Spent Nuclear Fuel storage pool that is near the top of the reactor, but outside the Secondary Containment. At Unit #4, which had the fire, the fuel stored in the pool is relatively “fresh” out of the core, so the water level in this pool is critical to keeping it cool, but the water is boiling off faster than it can be replenished, and the pool design does not include the multiple water supply redundancies that are found on the core, itself; there’s just about no way to get a high enough flow of water to that pool without someone physically going out onto the refueling platform with a fire hose and lashing it to the pool railing.
Whoever does that will die.
Ref. “Figure 20” on this page:
http://bravenewclimate.com/2011/03/13/fukushima-simple-explanation/
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