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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 Carrie (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 Carrie (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 Carrie (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 Carrie (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 Carrie (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 Carrie (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 Carrie (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 Carrie (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 Carrie (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 ]

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