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I don't think this has been posted, but, to add to contributions from Gaianne this morning, also from nb41 and from Alvarez, there's a comment from Oil Drum contributor donshan cited by Euan Mearns in his latest article:

The Oil Drum | Fukushima Dai-ichi status and potential outcomes

Like aluminum, zirconium and is alloys (Zircaloy-2) oxidize instantly in air. A thin film of ZrO2 is so impervious to oxygen diffusion that the reaction stops. Even in 300 C (572F) water or steam at over 1000 psi, the oxidation rate is extremely slow and corrosion properties of Zircaloy fuel cladding are outstanding and safe, AS LONG as they are not overheated and cooling water flow is maintained. In fact it is standard practice to autoclave fuel rods in hot-pressured water or steam to precoat these rods with the optimum coating of ZrO2.

But these fuel rods must NEVER be overheated. That is why multiple redundant cooling systems are required. All these backup-cooling systems failed in Japan. Even after reactor shutdown, if the fuel rods are uncovered cladding temperatures can rapidly rise to 800C , or higher, due to fission product decay heat. As in any chemical reaction the rate accelerates rapidly with temperature, but in the case of zirconium, the protective character of a thin ZrO2 film is destroyed by this high temperature and catastrophic oxidation occurs. However this catastrophic oxidation occurs below the melting point, so I object to the media using the common term "meltdown" which is misleading.

This loss of the last battery powered cooling, led to the fuel rods becoming uncovered in a manner similar that also occurred in the Three Mile Island accident (although due to different reasons). When overheated in steam the oxidation reaction above accelerates exponentially. As the zirconium oxidizes the coating thickens, cracks and turns white from internal fractures that increase the diffusion rate of steam to the metal. . It then has the look and mechanical properties of eggshells. Hydrogen from this process is released, but also is absorbed by the underlying metal cladding which causes embrittlement and metal fracture. Soon cracks form in the cladding releasing the trapped fission products inside. This is not "melting', but rather catastrophic disintegration of the cladding structural integrity and containment of fission products. If the process continues the cladding can fracture away exposing the fuel pellets which in the worst-case scenario can drop out and collect on the bottom of the reactor vessel. It is the worse case scenario that I believe is causing the Japanese to inject boric acid. Boron is a neutron absorber and will prevent any possibility of a pile of fuel pellets on the bottom of the vessel from going critical and restarting the chain reaction.

by afew (afew(a in a circle)eurotrib_dot_com) on Thu Mar 17th, 2011 at 11:54:57 AM EST
[ Parent ]
Everyone is talking about zirconium. I recently found this

What's Behind the Two Fukushima Explosions? Does Zirconium Explode at 2,000 Degrees? | techyum ::

So...what's really behind the two Fukushima explosions? Were they hydrogen, or something else? You tell me, Dr. Fabulous. But here's what I know, and here's how an anti-nuclear activist just pissed me off by setting off my bullshit detector.

CommonDreams.org has a piece by Karl Grossman, journalism professor, anti-nuke activist and author of the 1980 book Cover Up: What You Are Not Supposed to Know About Nuclear Power, that is getting a lot of play in the wake of a second hydrogen explosion at the Fukushima I plant. It appears to have been written before the second explosion.

In this article, Grossman makes some claims about the element zirconium, used in the fuel cladding around the nuclear fuel, that set off my bullshit detector for no good reason. I don't, or didn't, know squat about zirconium or zircaloy. But his arguments sounded strange.

Behind the Hydrogen Explosion at the Fukushima Nuclear Plant | Common Dreams

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.



So, in what may be my last act of "advising", I'll advise you to cut the jargon. -- My old PhD advisor, to me, 26/2/11
by Migeru (migeru at eurotrib dot com) on Thu Mar 17th, 2011 at 12:00:15 PM EST
[ Parent ]
There are 30,000 to 40,000 rods--composed of twenty tons of zirconium--in an average nuclear power plant.  (??)

From previous discussions and diagrams it appeared that a single reactor vessel had four assemblies of about 25 rods each. Treating all six reactors at Fukushima as "one plant" that gives 600 rods in the reactors at any one time. There may be a fraction of that number of new rods on site for replenishment at any given time. Even if these rods were changed every year for 40 years and were still on site that would only be 24,000 rods -- for six reactors.

However, those calculations are for the BWR designs by GE. Have any reactors been built that use substantially more rods per reactor, say 200 rods at any given time? If so, that should produce higher neutron flux densities and I don't know how that might impact the metallurgy, etc.

"It is not necessary to have hope in order to persevere."

by ARGeezer (ARGeezer a in a circle eurotrib daught com) on Thu Mar 17th, 2011 at 12:57:57 PM EST
[ Parent ]
Nuclear fuel - Wikipedia, the free encyclopedia
In boiling water reactors (BWR), the fuel is similar to PWR fuel except that the bundles are "canned"; that is, there is a thin tube surrounding each bundle. This is primarily done to prevent local density variations from affecting neutronics and thermal hydraulics of the reactor core. In modern BWR fuel bundles, there are either 91, 92, or 96 fuel rods per assembly depending on the manufacturer. A range between 368 assemblies for the smallest and 800 assemblies for the largest U.S. BWR forms the reactor core. Each BWR fuel rod is back filled with helium to a pressure of about three atmospheres (300 kPa).
So at a minimum there are 91 x 368 fuel rods per core, or no less than 33,500 rods per core.

For PWRs, the figures are similar so the 368 assemblies is not a typo of the kind that 4 assemblies of 92 adds up to 368 bundles.

There are about 179-264 fuel rods per fuel bundle and about 121 to 193 fuel bundles are loaded into a reactor core. Generally, the fuel bundles consist of fuel rods bundled 14x14 to 17x17.
That's at least 21,500 rods in a PWR.

So, in what may be my last act of "advising", I'll advise you to cut the jargon. -- My old PhD advisor, to me, 26/2/11
by Migeru (migeru at eurotrib dot com) on Thu Mar 17th, 2011 at 01:05:57 PM EST
[ Parent ]
Perhaps this is terminology? Cut-away diagrams of a BWR showed four assemblies with each assembly consisting of what appeared to be 25 rods. Could there be a confusion between rods and pellets? Likewise, Arvid described 96 rods as comprising an assembly for a reactor. It is either terminology or I am misunderstanding something.

"It is not necessary to have hope in order to persevere."
by ARGeezer (ARGeezer a in a circle eurotrib daught com) on Thu Mar 17th, 2011 at 01:12:10 PM EST
[ Parent ]
Danger of Spent Fuel Outweighs Reactor Threat - NYTimes.com
Figures provided by Tokyo Electric Power on Thursday show that most of the dangerous uranium at the power plant is actually in the spent fuel rods, not the reactor cores themselves. The electric utility said that a total of 11,195 spent fuel rod assemblies were stored at the site.

That is in addition to 400 to 600 fuel rod assemblies that had been in active service in each of the three troubled reactors. In other words, the vast majority of the fuel assemblies at the troubled reactors are in the storage pools, not the reactors.



"People only accept change when they are faced with necessity, and only recognize necessity when a crisis is upon them." - Jean Monnet
by Melanchthon on Thu Mar 17th, 2011 at 02:06:48 PM EST
[ Parent ]
Get your news early on European Tribune.

So, in what may be my last act of "advising", I'll advise you to cut the jargon. -- My old PhD advisor, to me, 26/2/11
by Migeru (migeru at eurotrib dot com) on Thu Mar 17th, 2011 at 02:24:28 PM EST
[ Parent ]
11,195 spent fuel rods is a lot more believable than 40,000.

"It is not necessary to have hope in order to persevere."
by ARGeezer (ARGeezer a in a circle eurotrib daught com) on Thu Mar 17th, 2011 at 02:47:22 PM EST
[ Parent ]
11,195 spent fuel rod assemblies

Danger of Spent Fuel Outweighs Reactor Threat - NYTimes.com

At Daiichi, each assembly has either 64 large fuel rods or 81 slightly smaller fuel rods, depending on the vendor who supplied it.


"People only accept change when they are faced with necessity, and only recognize necessity when a crisis is upon them." - Jean Monnet
by Melanchthon on Thu Mar 17th, 2011 at 02:51:05 PM EST
[ Parent ]
"Fuel rod" seems to commonly be used for "fuel rod assembly". Am I correct that each assembly consists of the zirconium tube and the cylindrical pellets?

"It is not necessary to have hope in order to persevere."
by ARGeezer (ARGeezer a in a circle eurotrib daught com) on Thu Mar 17th, 2011 at 04:39:49 PM EST
[ Parent ]
Plus the presurized helium inside and what ever attachments there are on the tube to allow it to fit into one of the four assemblies. Or are you saying that the core of a reactor consists of more than four assemblies, each containing ~25 tubes filled with pellets. I really don't know how schematic the diagrams are.

"It is not necessary to have hope in order to persevere."
by ARGeezer (ARGeezer a in a circle eurotrib daught com) on Thu Mar 17th, 2011 at 04:43:07 PM EST
[ Parent ]
The reactor core contains hundreds of assemblies, each of them containing about a hundred tubes, arranged in four bundles. Assemblies can be individually moved. About 1/5 of the fuel is replaced each year.

So, in what may be my last act of "advising", I'll advise you to cut the jargon. -- My old PhD advisor, to me, 26/2/11
by Migeru (migeru at eurotrib dot com) on Thu Mar 17th, 2011 at 04:50:38 PM EST
[ Parent ]
No, an assembly consists of 100-odd zirconium rods or canisters containing the fuel pellets.
The assembly is designed to be grabbed by a crane.

So, in what may be my last act of "advising", I'll advise you to cut the jargon. -- My old PhD advisor, to me, 26/2/11
by Migeru (migeru at eurotrib dot com) on Thu Mar 17th, 2011 at 04:44:22 PM EST
[ Parent ]
Wikipedia: Size of BWRs
A modern BWR fuel assembly comprises 74 to 100 fuel rods, and there are up to approximately 800 assemblies in a reactor core, holding up to approximately 140 tons[vague] of uranium. The number of fuel assemblies in a specific reactor is based on considerations of desired reactor power output, reactor core size and reactor power density.
That's 50 thousand to 80 thousand fuel rods, which means each rod is 2 to 3 tons of uranium. The density of uranium dioxide is about 11 tons per cubic metre.

So, in what may be my last act of "advising", I'll advise you to cut the jargon. -- My old PhD advisor, to me, 26/2/11
by Migeru (migeru at eurotrib dot com) on Thu Mar 17th, 2011 at 03:44:09 PM EST
[ Parent ]
That is confusing, especially in conjunction with the diagrams we have seen. I think we need to implement Migeru's new sig line on this issue. A diagram showing, in turn, a fuel rod, an assembly and a complete core would be helpful.

"It is not necessary to have hope in order to persevere."
by ARGeezer (ARGeezer a in a circle eurotrib daught com) on Thu Mar 17th, 2011 at 04:55:08 PM EST
[ Parent ]
As fas as I can tell:

This is a diagram of a single fuel assembly consisting of 96 rods in 4 bundles of 24 with the corner rod of a 5x5 array missing. The cut in the middle is not really there, it's to show certain internal structures of the arrangement.

The fuel rods are 4m+ long and very thin.

There are hundreds or these hundred-rod assemblies in each reactor core. As you can see the assembly has a hole at the top through which a crane's hook could grab the assembly in order to lift it out of place or lower it down into place.

So, in what may be my last act of "advising", I'll advise you to cut the jargon. -- My old PhD advisor, to me, 26/2/11

by Migeru (migeru at eurotrib dot com) on Thu Mar 17th, 2011 at 05:15:27 PM EST
[ Parent ]
Apparently here they call "rod" what I have been calling an "assembly". In that case the "rod" would actually contain of a hundred cylindrical canisters.

So, in what may be my last act of "advising", I'll advise you to cut the jargon. -- My old PhD advisor, to me, 26/2/11
by Migeru (migeru at eurotrib dot com) on Thu Mar 17th, 2011 at 05:25:35 PM EST
[ Parent ]
Try here. They talk of "pins", "assemblies" and "core".

So, in what may be my last act of "advising", I'll advise you to cut the jargon. -- My old PhD advisor, to me, 26/2/11
by Migeru (migeru at eurotrib dot com) on Thu Mar 17th, 2011 at 05:28:30 PM EST
[ Parent ]
You can see the square assemblages here

Nuclear Wasteland - IEEE Spectrum

BLUE GLOW OF SUCCESS: Fuel assemblies cool in a water pond at the French nuclear complex at La Hague. The blue light is generated by Cherenkov radiation, which arises from a particle's traveling through a medium faster than the speed of light in that medium


Any idiot can face a crisis - it's day to day living that wears you out.
by ceebs (ceebs (at) eurotrib (dot) com) on Thu Mar 17th, 2011 at 05:43:09 PM EST
[ Parent ]
Thanks. I clearly had mistaken an assembly of rods for the core.

"It is not necessary to have hope in order to persevere."
by ARGeezer (ARGeezer a in a circle eurotrib daught com) on Thu Mar 17th, 2011 at 05:48:53 PM EST
[ Parent ]
That Euan Mearns article also has apparently good information on the water drops, too.
by afew (afew(a in a circle)eurotrib_dot_com) on Thu Mar 17th, 2011 at 12:01:18 PM EST
[ Parent ]
Maybe in the comments - the body just refers to Reuters: Japan dumps water on overheating reactor
Japanese military helicopters and fire trucks poured water on an overheating nuclear facility on Thursday and the plant operator said electricity to part of the crippled complex could be restored in a desperate bid to avert catastrophe.

Washington and other foreign capitals expressed growing alarm about radiation leaking from the earthquake-shattered plant, 240 km (150 miles) north of Tokyo. The United States said it was sending aircraft to help Americans leave Japan.

...

Workers were trying to connect a 1-km (0.6-mile) long power cable from the main grid to restart water pumps to cool reactor No. 2, which does not house spent fuel rods considered the biggest risk of spewing radioactivity into the atmosphere.



So, in what may be my last act of "advising", I'll advise you to cut the jargon. -- My old PhD advisor, to me, 26/2/11
by Migeru (migeru at eurotrib dot com) on Thu Mar 17th, 2011 at 12:16:06 PM EST
[ Parent ]
The Oil Drum | Fukushima Dai-ichi status and potential outcomes

I have been watching the NHK feed and grimly laughing at the helicopter operation. Here is some info:

Capacity of spent fuel pools: 1200-1500 tons water 15 meters deep
Needed to cover rods: 15 meters, 400-500 tons water

For reactor 3, they think there might be enough water that they only need < 100 tons, perhaps less

One helicopter can drop 7.5 tons/load. BUt it can't hover, due to the radiation level. If I heard right, those on board are limited to 100 mSieverts/hour (check the time units). They had measured 250/hr at 30 meters and 87/hr at 90 meters. They dumped from 90 meters. See image. Looks more like crop dusting. There was one drop which looked a little better, but at the speed they are going, hitting the building with much is not likely.

By email from Joules Burn to Euan Means.

by afew (afew(a in a circle)eurotrib_dot_com) on Thu Mar 17th, 2011 at 12:24:38 PM EST
[ Parent ]
afew:
Needed to cover rods: 15 meters, 400-500 tons water
I thought that was 15 feet, not metres. Anyway, I estimated 650 tonnes of water upthread, but with the expected evaporation you'd probably need more water than for a cold pool.

So, in what may be my last act of "advising", I'll advise you to cut the jargon. -- My old PhD advisor, to me, 26/2/11
by Migeru (migeru at eurotrib dot com) on Thu Mar 17th, 2011 at 12:28:46 PM EST
[ Parent ]
Yeah, units are the bugbear. But I found the observation of the likelihood of putting very much water in from a moving helicopter at 90 metres up sounded accurate (though may be just truthy).

Fighting forest fires with planes and choppers is not an exact science, at the best of times. But at least they can get in lower than 90m.

by afew (afew(a in a circle)eurotrib_dot_com) on Thu Mar 17th, 2011 at 12:40:32 PM EST
[ Parent ]
I think the more important observation is that even with a perfect hit you'd be adding 7.5 tonnes of water which would raise the water level by only 15 cm when the fuel assemblies are over 4m tall.

So dropping water from helicopters is just useless.

So, in what may be my last act of "advising", I'll advise you to cut the jargon. -- My old PhD advisor, to me, 26/2/11

by Migeru (migeru at eurotrib dot com) on Thu Mar 17th, 2011 at 12:49:25 PM EST
[ Parent ]
I'd written it off as theatre.

I'm not sure for whose benefit.

And don't they have fireboats?

The range and flow of a fireboat must be an order of magnitude or two higher than a truck, surely?

by ThatBritGuy (thatbritguy (at) googlemail.com) on Thu Mar 17th, 2011 at 12:54:25 PM EST
[ Parent ]
That's a damn reckless form of Kabuki.

So, in what may be my last act of "advising", I'll advise you to cut the jargon. -- My old PhD advisor, to me, 26/2/11
by Migeru (migeru at eurotrib dot com) on Thu Mar 17th, 2011 at 12:55:25 PM EST
[ Parent ]
Politicians and Corporate Management seem to have convinced themselves pretending to do something about a situation is the same as doing something.

She believed in nothing; only her skepticism kept her from being an atheist. -- Jean-Paul Sartre
by ATinNM on Thu Mar 17th, 2011 at 01:38:16 PM EST
[ Parent ]
Of course they do

(h/t DoDo)

So, in what may be my last act of "advising", I'll advise you to cut the jargon. -- My old PhD advisor, to me, 26/2/11

by Migeru (migeru at eurotrib dot com) on Thu Mar 17th, 2011 at 12:57:22 PM EST
[ Parent ]
Addledum: I found the location of the above photo. I estimate the length of the longest water spray at about 130-140 m.

*Lunatic*, n.
One whose delusions are out of fashion.
by DoDo on Sat Mar 19th, 2011 at 03:37:52 AM EST
[ Parent ]
This may not be obvious from tele photos, but if you check on Google maps, any point a ship can stop at is at least 200 m away even from the center of No. 4 (to the south where the cooling water exits), and the more suitable location is 350-400 m away (east of the reservoir).

*Lunatic*, n.
One whose delusions are out of fashion.
by DoDo on Thu Mar 17th, 2011 at 01:28:38 PM EST
[ Parent ]
And 250 m even if you get a ship on the reservoir.

*Lunatic*, n.
One whose delusions are out of fashion.
by DoDo on Thu Mar 17th, 2011 at 01:33:21 PM EST
[ Parent ]
and it might be that theres no access to number 4 from the seaward side. That looks to be where the walls are still standing.

Any idiot can face a crisis - it's day to day living that wears you out.
by ceebs (ceebs (at) eurotrib (dot) com) on Thu Mar 17th, 2011 at 01:41:50 PM EST
[ Parent ]

I numbered the reactors.

No way firefighting ships can get near enough.

by afew (afew(a in a circle)eurotrib_dot_com) on Thu Mar 17th, 2011 at 01:36:52 PM EST
[ Parent ]
You can't provide some protection from storm surges and tsunamis and remain accessible to waterships.

So, in what may be my last act of "advising", I'll advise you to cut the jargon. -- My old PhD advisor, to me, 26/2/11
by Migeru (migeru at eurotrib dot com) on Thu Mar 17th, 2011 at 01:38:58 PM EST
[ Parent ]
Assuming the breakwater is a temporary obstacle that could be removed, and there's no spent fuel in that pool - if that even makes a difference at this point - I make that a distance of around 200m. Which doesn't sound totally impractical.

There's also the advantage of at least some cover from the turbine buildings.

by ThatBritGuy (thatbritguy (at) googlemail.com) on Thu Mar 17th, 2011 at 01:48:21 PM EST
[ Parent ]
250 m. Plus you need to calculate with more due to the height. I looked around and found no fireboat range above 400 feet.

*Lunatic*, n.
One whose delusions are out of fashion.
by DoDo on Thu Mar 17th, 2011 at 02:11:19 PM EST
[ Parent ]
Nevertheless, Kyodo News reports Operation to pour water at Fukushima nuke plant said effective
An unprecedented attempt to douse an apparently overheating spent fuel pool with tons of coolant water at a stricken nuclear plant in Fukushima bore some fruit Thursday, but the emission of smoke newly confirmed at another pool suggests the difficulties that lie in the way of resolving the crisis triggered by the March 11 quake and tsunami.

Up to 64 tons of water were aimed by helicopters and fire trucks of the Self-Defense Forces as well as a water cannon truck of the Metropolitan Police Department into the pool at the No. 3 unit of Tokyo Electric Power Co.'s Fukushima Daiichi plant.

The utility said vapor rising from the partially destroyed No. 3 reactor building suggests the operation went some way toward cooling down the pool that could otherwise emit highly contaminated radioactive materials.



So, in what may be my last act of "advising", I'll advise you to cut the jargon. -- My old PhD advisor, to me, 26/2/11
by Migeru (migeru at eurotrib dot com) on Thu Mar 17th, 2011 at 12:53:57 PM EST
[ Parent ]
Aren't most of the fuel rods in the pools spent fuel? So the risk of criticality is much lower?
by ThatBritGuy (thatbritguy (at) googlemail.com) on Thu Mar 17th, 2011 at 12:13:25 PM EST
[ Parent ]
The Oil Drum | Fukushima Dai-ichi status and potential outcomes
We have had much debate about whether or not it is possible for the fission chain reaction to re-start in a pile of reactor rubble. The consensus is that this is unlikely though possible.
by afew (afew(a in a circle)eurotrib_dot_com) on Thu Mar 17th, 2011 at 12:26:10 PM EST
[ Parent ]
Not just criticality, but there should be a difference in the rate of self-heating.

*Lunatic*, n.
One whose delusions are out of fashion.
by DoDo on Thu Mar 17th, 2011 at 12:43:55 PM EST
[ Parent ]
I think spent fuel might heat up faster given that a lot of the fission products are a lot more radioactive than fissile Uranium-235.

So, in what may be my last act of "advising", I'll advise you to cut the jargon. -- My old PhD advisor, to me, 26/2/11
by Migeru (migeru at eurotrib dot com) on Thu Mar 17th, 2011 at 12:46:22 PM EST
[ Parent ]
Got any idea of the non-linear affect?

My intuition, and it's only that, is the players in this are thinking they are in Landscape A when the thing has undergone a Thom Catastrophe.

but I know diddly about the science and engineering involved.

She believed in nothing; only her skepticism kept her from being an atheist. -- Jean-Paul Sartre

by ATinNM on Thu Mar 17th, 2011 at 01:41:42 PM EST
[ Parent ]
ATinNM:
the players in this are thinking they are in Landscape A when the thing has undergone a Thom Catastrophe
I'm wondering about the Prime Minister's physics background. I wonder who's actually in charge - presumably some TEPCO engineers since the management has been out of its depth since Saturday's explosion - and what ability the government has to provide them with resources.

So, in what may be my last act of "advising", I'll advise you to cut the jargon. -- My old PhD advisor, to me, 26/2/11
by Migeru (migeru at eurotrib dot com) on Thu Mar 17th, 2011 at 02:23:18 PM EST
[ Parent ]
It's clear everybody is operating outside existing emergency protocols.  They are making decisions on the fly with unknown follow-on affects and effects.  

Example: pumping sea water through pumps and lines not designed for sea water.  Did they screen the sea water?  If not, what else have they introduced to the system?  Clams?  Miscellaneous fish parts?

(And etc. & etc.)

She believed in nothing; only her skepticism kept her from being an atheist. -- Jean-Paul Sartre

by ATinNM on Thu Mar 17th, 2011 at 02:59:04 PM EST
[ Parent ]

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