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Registered Member #2431
Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639
Chris Russell wrote ...
Patrick wrote ... I dont know that anyone can be sure that bulk fission has been stopped, and the cesium is a potential sign that fuel rods are damaged/destroyed. If the fuel melts/breaks away from the control rods, then they can pile up at the bottom of the reactor assume different geometry and begin heating again.
I was specifically responding to your concerns about void coefficients; that implies that the core was still fissioning after the shutdown. That's not the case. The control rod insertion essentially stopped the fission, dropping the reactor's thermal output by 90%. The residual heat in the reactor is the result of many radioactive byproducts that cool off much more gradually. If the core has undergone a meltdown, fission may have resumed, but that's got little to do with whether the reactor was shut down in the first place.
Oh, I see this is a fair point.
Chris Russell wrote ...
Let's keep it civil, folks. I'd hate to have to lock an important thread like this one because tempers couldn't be kept in check.
As the starter of this thread, my intent was to give everyone a thread to discuss, scientific, technical, medical and humanitarian/historic matters related to these current events and limited to only these topics. I would like this to remain civil, and not out-emoting rival members.
EDIT: Where are the fuel pools? Of all the pics of pools Ive seen here in the US, they seem to be away from the actual containment vessel. In a seperate location. Or am I wrong? Also where are the fuel pools at the Fukihisma facility? Surely no idiot would put them next to/above the reactor itself !?!
Registered Member #89
Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145
Patrick wrote ...
EDIT: Where are the fuel pools? Of all the pics of pools Ive seen here in the US, they seem to be away from the actual containment vessel. In a seperate location. Or am I wrong? Also where are the fuel pools at the Fukihisma facility? Surely no idiot would put them next to/above the reactor itself !?!
They are very next to the reactor, they actually share a wall with the outer containment. Spent fuel rods are apparently way too dangerous and uneconomical to transport anywhere until they have lost most of their activity, afaik. And not only they are next to the reactor, but they are in a rather plain concrete pool that is exposed to surroundings and workers, with just like 2-3 meters of water in between. Since spent fuel is no longer emmitting neutrons the water covering it won't become radioactive (nor absorb any radioactive substances if rods are properly sealed) and I guess this was considered safe enough practice so far.
Registered Member #2431
Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639
Patrick wrote ...
Surely no idiot would put them next to/above the reactor itself !?!
Nevermind...
Marko wrote ...
Spent fuel rods are apparently way too dangerous and uneconomical to transport anywhere until they have lost most of their activity...
Even too difficult to transport a hundred meters ?
Marko wrote ...
And not only they are next to the reactor, but they are in a rather plain concrete pool that is exposed to surroundings and workers, with just like 2-3 meters of water in between. Since spent fuel is no longer emmitting neutrons the water covering it won't become radioactive (nor absorb any radioactive substances if rods are properly sealed) and I guess this was considered safe enough practice so far.
... not Russel! Registered Member #1
Joined: Thu Jan 26 2006, 12:18AM
Location: Tempe, Arizona
Posts: 1052
Marko wrote ...
Patrick wrote ...
EDIT: Where are the fuel pools? Of all the pics of pools Ive seen here in the US, they seem to be away from the actual containment vessel. In a seperate location. Or am I wrong? Also where are the fuel pools at the Fukihisma facility? Surely no idiot would put them next to/above the reactor itself !?!
They are very next to the reactor, they actually share a wall with the outer containment. Spent fuel rods are apparently way too dangerous and uneconomical to transport anywhere until they have lost most of their activity, afaik. And not only they are next to the reactor, but they are in a rather plain concrete pool that is exposed to surroundings and workers, with just like 2-3 meters of water in between. Since spent fuel is no longer emmitting neutrons the water covering it won't become radioactive (nor absorb any radioactive substances if rods are properly sealed) and I guess this was considered safe enough practice so far.
It's important to note that as originally designed, the fuel pools could have run dry without causing permanent harm or releasing significant amounts of radiation into the environment. The intent in putting the fuel pools near the reactor was probably to limit the amount of handling required to get the spent fuel assemblies from the reactor to the pool. Now that they're capable of self-heating to the point of combustion, it certainly seems like a very poor idea to put the fuel pool near the reactor, or to have the fuel pool's cooling dependent on the reactor's.
Edit:
> Even to difficult to transport a hundred meters ?
My understanding is that if you were to go to a fuel pool, get a long pole, grab one of the freshly-added fuel assemblies, and pull it up to the surface, everyone in the vicinity would have received a lethal dose of radiation before the top of the assembly even broke the surface of the water. That doesn't sound like anything you'd ever want to transport anywhere unless you absolutely had to. If I remember correctly, even the "cooled" fuel assemblies had to be moved in a specialized container that could survive a worst-case train derailing.
Registered Member #2431
Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639
Chris Russell wrote ...
I just don't understand why one would intentionally short-circuit a very important safety mechanism. It's truly mind-boggling to consider that the collective chain of thought must have gone something like: "Okay, now we can safely store fuel from the reactor for several years. We don't have long term storage facilities built yet, but there's no sense building them 20 years before we even need them. Now let's build some reactors!" *cut to 20 years later* "Wow, nobody wants a long term storage facility anywhere near them. We could build storage facilities anyway, and we really should, but that would be politically unpopular. Oh well, let's just densely pack the fuel. What are the odds that a fuel pool will ever lose cooling? Besides, someone else will solve this problem in the future." *cut to 20 more years later* "Well crap, the fuel pool is on fire."
Edit: to be fair, the original builders probably expected that a significant portion of the spent fuel would be reprocessed after chilling in the pool, rather than sent to long-term storage facilities.
I believe this was well said...and in the above qoute from Chris, shows there line of thinking.
I would also sort of let the original builders of the hook. The original builders arnt responsible for the idiocy of the politicans years after the fact. Even so... more thought should have been put in to this cooling schem.
Registered Member #2431
Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639
Oops! This is a double post. Sorry, I thought I was responding to Chris russell's ninja edit. My bad.
Chris Russell wrote ...
My understanding is that if you were to go to a fuel pool, get a long pole, grab one of the freshly-added fuel assemblies, and pull it up to the surface, everyone in the vicinity would have received a lethal dose of radiation before the top of the assembly even broke the surface of the water.
Yes I have always been told the same, immeadiate fatal exposure.
Chris Russell wrote ...
That doesn't sound like anything you'd ever want to transport anywhere unless you absolutely had to.
Yes, but seeing as how you and others have just informed me that the fuel pool is way more dangerous then the reactor intself ( if on fire, no containment), maybe it should be protected just like the reactor....perhaps this dangerous task (moving fuel rods) must now be done?
Instead of dumping them in a glorified olympic swimming pool and saying --Adios, metals I never want to see again.
EDIT: They are removed when expended and super-dooper hot anyway. So how is that transport safely done?
Registered Member #2099
Joined: Wed Apr 29 2009, 12:22AM
Location: Los Altos, California
Posts: 1716
The plan: The used fuel storage pools can't lose their water due to a pump or pipe failure -- they are solid reinforced concrete with no drains on the side or bottom. Normally there's at least 5 meters of water above the top of the fuel rods, and it's exchanged rapidly enough to keep the temperature not over 40 degrees C. [i] If the circulation fails, the decay heat may eventually cause the water to boil. But it should take a couple of weeks to boil off the top 5 meters of water, and that should be long enough to find a way to refill the pool. (megacuries of fission product decay activity is not that many thermal kilowatts)
Maybe at the #4 unit, the earthquake or tsunami or a hydrogen explosion caused a leak in the concrete. But now there are reports saying the #4 pool is NOT dry, and radiation levels are falling. Interesting technical blog here: with this detail about the fuel cooling pools: (updated March 16)
Registered Member #2431
Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639
Klugesmith, I was under the belief that most water has boiled off (from decay of dense storage)...or that hydrogen explosions cracked walls/pipes (not being able to add water), to the point were significant water loss has occured?
this PDF is most recent, says pools' are low. ]fuel_rods.pdf[/file]
I predict changes in many nations' handling and storage practices given what we've all seen. Particularly active processes which were presumed to be near failure proof.
I suggest a return to the non-dense packing of fuel rods, such that water loss cannot cause high-heat metallic fires.
I also predict that we will learn in the months and years from now, both contagious failure, and sequential failure modes conspired to cause overall failures too ridiculous to have considered plausible in the 1960-70's.
Registered Member #3414
Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245
Patrick wrote ...
.EDIT: They are removed when expended and super-dooper hot anyway. So how is that transport safely done?
Remotely operated cranes presumably. This would also explain why the pool is so close to the reactor. I posted a cutaway view in an earlier post which shows the crane.
A few years ago I installed the remote handling system at the target station of a particle accelerator, very complicated bits of equipment. This is a photo of the 'hand' on the end of one of the 'arms'. Photo taken under sodium lighting (and flash), which is used because they last 20 years or so.
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Nuclear events taking place in Japan.
