Log in

No account? Create an account
Quizzing the Anonymous
Ignoramus et ignorabimus
15th-Mar-2011 03:11 am
Here is what I think is going on in these Japanese reactors.

These are pressurized light water reactors (PLWR) meaning that they operate under near-critical conditions: if water phase separates into steam and liquid, the heat transfer becomes inefficient and the fuel rods overheat. When the pumps lost power and failed, the engineers let the seawater into the reactor vessel; at this point the core was already partially exposed and melted.

If there is no pressure, steam bubbles are formed near hot surfaces, reducing the heat transfer, so cooling is very inefficient. Overheated zirc casings and fission products (which include platiunum group catalysts) begin to react with water producing hydrogen. The excess steam and this hydrogen need be purged, hence the release of radioactive vapor containing iodine and xenon and high probability of explosion in the enclosure (into which the steam is vented). Because the explosion destroyed most of the control equipment mounted at the top of the reactor (relief valves, etc.) nearly all they can do is adding more (hopefully, fresh) water and (I hope) relieve the excess pressure (it is possible that it is constantly venting, i.e., they lost this last control, too). In the Three Mile Island accident the controls were not damaged.

Steam bubbles + inefficient cooling + release of pressure due to a stuck valve for less than two hours (!) is what led to core melting in the Three Mile Island accident in 1979. If the high pressure cannot be restored, pumping hot water would be impossible even if the pumps are operational, because it will turn into steam in the pump heads and destroy the pumps (that happened, too, in 1979, and they needed to shut down the pumps after losing pressure). If the core overheats, the zirc cracks and the oxide pellets drop to the bottom of the vessel and melt, forming the "corium". The contact with static, low pressure water does not cool this lava too well (because the coolant is isolated by steam) and the danger of melting through the bottom of the containment vessel is quite real. All controls have been destroyed and rebuilding these controls means human sacrifice, as the radiation is very strong. They can only add more water and let the steam out. There is enough heat from the decaying radionuclides to keep it boiling for months if not years.

I do not think the evacuated people will return anytime soon, and they should be happy to be alive and well. This will continue over many months. The art of PLWR operation is that cooling should never be interrupted; there are layers of engineering controls and backup systems preventing this from happening. When the unthinkable happens, little can be done. I am amazed by the "optimistic spin" given to these events in the media. So far, it went from bad to worse. The dimension of the problem is not sinking in.
15th-Mar-2011 08:50 am (UTC)
А кто автор?
15th-Mar-2011 09:14 am (UTC)
The "optimistic spin" seems to be a desperate attemt to prevent panic, which can only worsen the situation.
I agree that there is no way to avoid human sucrifice. Unfortunately, we still cannot use robots for this.
And they must ask for a help right from the beginning.
15th-Mar-2011 05:04 pm (UTC)
There are times when panic is entirely appropriate reaction, and it is one of such times.
15th-Mar-2011 01:14 pm (UTC)
Персонал покинул зону реактора по сообщениям радио. Это конец?
15th-Mar-2011 04:55 pm (UTC)
At best, it means that so much volatile radionuclides have been released that they cannot stay. At worst, the steel container is about to be melted through. They know (they have thermocouple readings) but they would not not tell. We will know pretty soon. I'm afraid that's it.
15th-Mar-2011 04:54 pm (UTC)
Um. I am pretty sure the Fukushima reactors are BOILING water reactors (BWRs), not pressurized water reactors (PWRs).

15th-Mar-2011 05:04 pm (UTC)
Technically, yes, but it still needs 8 Mpa to keep boiling in check (it is about 1/2 critical pressure, so this does not make difference). Right now it is venting and the distinction does not matter. Once the cooling was lost, the temperature increased and they needed to relieve the pressure, which result in the loss of density of water; eventually, so much was lost that they needed to start injecting water. Because they had no power to do that I guess they completely depressurized and poured water in. It had been several days, but we are still not being told what happened and what exactly did they do. This is not a good sign.
15th-Mar-2011 05:14 pm (UTC)
From what I've read, that's pretty much what's happening.
But what will happen if the core melts through the bottom?
And, of course, why did they build so many stations in tsunami-prone areas? This wasn't even the largest tsunami possible. Why not on the western coast, or at least 20 m higher?
15th-Mar-2011 06:30 pm (UTC)
This will mean uncontrolled venting i.e. the amount of nuclear emission much larger than on common venting just to release extra pressure. IAEA says that now every reactor is in a cold shutdown but seawater cooolig still continues. If it's true new emissions are unlikely.
15th-Mar-2011 06:49 pm (UTC)
I remember that on a Tree Mile Island a venting valve remained open after pressure release due to mechanical failure thus making impossible to gain a pressure of coolant inside a vessel to prevent boiling.

Now inner vessels seems to be intact so after the excess pressure release I suppose the pressure in a vessel is still above the atmospheric and eventually every reactor came to the state of cold shutdown isn't it?
15th-Mar-2011 08:07 pm (UTC)
спасибо за рассказ
16th-Mar-2011 12:07 am (UTC)
For what it is worth...
15th-Mar-2011 08:30 pm (UTC)
They also have a problem cooling spent fuel rods in a cooling pond. Those probably have much less protection around them than the reactor.

If zirconium is responsible for hydrogen production, at some point (pretty quickly?) it should all be oxidized and it will be just molten cores exposed. I mean, there isn't anything there that could explode besides zirconium, right?
16th-Mar-2011 12:05 am (UTC)
Overheated zircalloy gets covered by the oxides and oxides hydrates slowing down the reaction, but the layers crack and the reaction goes further, it is not that fast. Apart form that you have half of the periodic system there. There is another matter: they injected seawater which has chloride in it. Now this chloride is being turned into hydrochloric acid by radiation and it will react with the metals, too. Frankly, I cannot imagine what kind of chemistry is going on there. No one studied what chloride solutions can do in such thermal and radiation regimes. As they add more seawater that gets evaporated, they are getting more briny solutions. The whole thing is the total mess...
30th-Mar-2011 01:34 pm (UTC)
Кое-что неясно:

> If there is no pressure, steam bubbles are formed near hot surfaces, reducing the heat transfer, so cooling is very inefficient

но heat transfer кроме того пропорционален разности температур. Хоть steam bubbles reduce the heat transfer, но при достаточно высокой температуре контейнеров с топливом, если заливать туда всё время новую воду, их нагревание вероятно прекратится. Произойдет ли это до 1200С (как я понял, это критическая температура коррозии и горения циркония) ? Если да, то вроде не так всё безнадежно ?

Также интересно, что бы произошло если б они загерметизировали внутренний контур и поливали бы его водой снаружи ? Тогда бы steam bubbles там не было. Хватило ли бы давления чтоб разорвать conatinment vessel ?

> If the core overheats, the zirc cracks and the oxide pellets drop to the bottom of the vessel and melt, forming the "corium"
> low pressure water does not cool this lava too well (because the coolant is isolated by steam) and the danger of melting through the bottom of the containment vessel is quite real

Но ведь в TI этого не произошло (и в Фукушиме повидимому тоже).

30th-Mar-2011 05:04 pm (UTC)
Of course, eventually corium cools down, one way or the other. If the heat transfer is too slow or non-existent, smaller chunks of the material melt together forming larger blobs that cool even slower and so develop higher core and surface temperature. Once the temperature is higher than the certain threshold, chemical reactions with steam at the surface will produce H2, resulting in possible explosions (when the gas contacts air) and hydrogen embrittlment of the pressure vessel. These larger blobs can also sink to the bottom and start melting through the lower part of the steel vessel. This particular type of LW reactor has most of its controls at the bottom (e.g., the control rods), so there are many weak spots, and pools of molten corium at the bottom can melt and ouse through before water cools these pools. This did not happen at the TMI but (i) the bottom of the vessel was considerably weakened and (ii) that reactor had the controls at the top, so this bottom was solid, uninterrupted steel. The evidence is mounting (contrary to the first optimistic reports) that the corium did escape from the pressure vessel at Unit 2 reactor. Our experts say this openly:

If this is true, the lava is on the flooded concrete floor. If it is a glob, it forms crust of insulating oxide on the outside(further slowing down its cooling) and where it touches the floor it start reacting with the CaCO3 and water in the concrete. This reaction produces CO and H2, which are combustible, explosive gases. The danger is not that it will burn through 20+ feet of concrete (though it it is a large glob it can), but that sufficient amount of such gases will accumulate so that there is a pressure explosion, weakening the structure and releasing the nukes. There is another problem, which is long term. The nukes in the corium undergo alpha-decay that knock on the atoms. It is like Wigner effect in crystals. There is always a possibility for catastrophic release of this energy by sudden cracking (normally, it is released by chipping off microparticles). Then the oxide crust is locally destroyed, water rushes into the hot core, and there is a sudden explosion as it is turned into the mixture of H2 and steam. Such explosive erosion still goes on inside Chernobyl's Sarcophagus as the rainwater seeps inside. It is small scale, but it goes on and on. This is one of the reasons why the debri was immediately covered with sand, clay, lead and B4C rather than doused with water.

There are no good options here, it is a race against time. The question is whether water can cool this stuff faster than it compromise the structures and reacts. As the situation always verges on gas explosion, it is pure luck; the danger does not recede on the time scale of days. On the other hand, draining this water can make things only worse, resulting in the resumption of melting before new (chemically robust) coolant/blanketing material (lead and tin were suggested) is introduced. You are damned if you pump the water out and you damned if you don't. I am afraid they can do very little there but sit and pray that there is no catastrophic explosion. They cannot really do anything to control it at this point. Doing anything drastic comes with its own grave risks that are commensurate with doing nothing.
(Deleted comment)
3rd-Apr-2011 03:08 am (UTC)
No, I do not.
3rd-Apr-2011 08:43 am (UTC)
Shkrobius said that people in Japan should consider taking iodine.

Most of Japan has negligible radiation. Most of the people "in Japan" should not even consider taking iodine.

Shkrobius was irresponsible to give such a blanked recommendation. Iodine pills can create health problems.

3rd-Apr-2011 04:46 pm (UTC)
Do not be a fool.Taking iodine is a profilactics measure. If there is a sudden, massive emission of radioactive iodine, the body needs be saturated with nonradioactive one. The danger of inaction is much greater than the harm of this preventive action. Everything can create health problems, including ordinary table salt.

Incidentally, it is a "blanket" rather than "blanked" recommendation. I do not want to see you in my journal again.
3rd-Apr-2011 08:21 pm (UTC)
So, a personal insult, a quibble on a typo, and a general description of what iodine is for. No substantive answer to my assertion that most of Japan has not been exposed to any significant radiation.

Are you actually recommending that people who have not been exposed to radiation should take pills before any radiation release, just in case? I haven't seen any responsible source recommend that. How many weeks of pills do you want them to take? What is your reference?

What if your advice kills someone with a seafood allergy, who doesn't realize that the pills are unsafe for them?

By the way, it's "prophylactic" not "profilactics."
3rd-Apr-2011 10:32 pm (UTC)
You assertion is neither here nor there, because you do not understand what the problem is, that's the trouble.

That the current levels are relatively low does not mean that the threat of the sudden release of airborne iodine has been eliminated; it has not been. If such an accident happens, it would be too late to take the pills; the body must be saturated with iodine before the exposure. This is the standard precaution in radiological emergencies; I am not inventing anything new here. The risk of taking iodide pills is immeasurably lower than the risks of the exposure to iodine in such catastrophic release. I do not care whether the Japanese authorities suggest doing this; it needs be done. If I'd be in Japan, I would do it, and my radiochemist colleague in Japan (he is in Kanazawa, across the island) is taking the pills. Better be safe than sorry. It is prudent to do it until the danger is eliminated.

Now, about the seafood allergies. The current wisdom is that iodide cannot cause such allergic reactions; the rare cases of suspected iodine allergies of these types are caused by iodinated metabolites in the seafood rather than the I-. What radiologists call "iodine allergy" (where the scare comes from) is a reaction to contrast agents(e.g., 2,4,5-triiodobenzoic acid) rather than the iodide proper. Susceptibility to seafood allergy does not increase the risk of allergic reaction to such constrast agents more than any other allergy. Here is a link for you where you can read about it
You connect the issues that are completely disconnected.

Now, the Japanese authorities & what they recommend. The Japanese authorities presently assert that their initial decision to limit the distribution of iodide pills was a grave error

Finally, did not I tell you that you were not welcome here? If you do not like being insulted, do not introduce yourself to strangers by throwing ridiculous accusations. I am strongly tempted to ban you for good.
This page was loaded Jul 23rd 2019, 5:29 pm GMT.