Ok, Uncle Cecil, why are spent fuel rods underwater, anyhow?
I WAG to increase absorption of (remaining) neutron emissions?
- Jinx
That’s part of the reason. It’s also to soak up heat. Splitting atoms produces energy, which often shows up as heat. Without the water, the fuel rods would literally melt from their own heat, making them much more difficult to handle.
As I understand it, the secondary fission products which produce this heat are very radioactive, which is the same thing as saying they have a short half-life. After several weeks those fission products have themselves broken down and it’s safe to pull them out of the water without fear of them melting. At that point, they can be reprocessed (though the US doesn’t do that.)
In Russia, they eventually embed the waste in ceramic “logs.” The ceramic is not water-soluble, so the waste is less likely to end up in the water supply.
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If you were radioactive, would you glow? (30-Apr-1999)
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Not quite right … the spent fuel rods will not be emitting any significant number of neutrons. Neutrons are emitted in quantity only when fission is actively happening. When the fuel rods are removed, fission stops.
It is the other forms of harmful radiation - alpha, beta, and gamma. Water will shield against alpha and beta. Gamma radiation will penitrate, so the whole thing still needs to be incased in concrete.
FYI - although you didn’t ask I’ll still bring it up. The radiation from spent fuel cannot make other things radioactive. Only neutron radiation (from active nuclear reactions) can make surrounding material radioactive. That said, if some of the radioactive fission by-products dissolve in water, then the water becomes dangerous … but not because the water molocules themselves are radioactive.
Actually, the heat has very little to do with it. The main reason spent fuel rods will remain under water for the remainder of their existence is more closely in line with your comment on the US not recycling them. Recycling is not only even more dangerous than original processing, but is also much more expensive. Therefore, why waste money trying to recycle the rods, when you can just purchase new ones for less.
The storage of the spent fuel rods, however, is a major pain in the butt!!! By keeping the rods under water the radioactive release is confined to the pool of water. Also, the water is not your ordinary water, it is a very special de-ionized water with some special minerals added to help slow down the reaction process.
Granted, after some portion of time has elapsed, the rods will not melt if pulled out of the water, but the person doing the pulling most certainly will.
sford:
How is the water dangerous if it’s not radioactive?
It is dangerous if it has radioactive materials dissolved in it. The water molocules themselves are not radioactive, but the materials dissolved in the water are. Drink a glassful and you’ll get sick. (True, it’s not the water itself that is dangerous in that case … don’t quibble.)
In the States, the uranium is maintained in a ceramic pellet, that does not dissolve in water very easily. The ceramics used in the pellets also help control the fission process, thus adding an extra layer of protection from meltdown.
I am fully aware of the fact that it can still meltdown, however, the use of the ceramic pellets, the de-ionized, de-mineralized water, and multiple other safety devices help prevent the meltdown from occurring.
Really? I thought that was after reprocessing, which the US only does in military and research settings. I didn’t think the fresh fuel rods kept the uranium in ceramic form.
At any rate, I don’t think the fuel rod is 100% ceramic. I believe that it has a metal casing, which is almost certainly rendered radioactive from neutron radiation during the fission process. I believe that the water used for spent rod storage does not dissolve significant quantities of radioactive materials, but is the same true for the primary coolant in a reactor? I seem to remember that it has to be continuously filtered, and that some dangerous isotopes are removed in the process.
But my knowledge here is shakey at best.
The uranium used in all US Nuclear power reactors is in the form of small ceramic pellets. There is actually more ceramic than uranium. This not only helps control the fission process, but unlike plutonium, the fuel in fuel rods is unusable in “nuclear warheads” without some very expensive and very space and time consuming processing.
One should remember the difference between radiation and radioactive. Radiation is simply the neutron flying away from its parent radioactive material. You can be exposed to radiation without ever becoming radioactive. However, even ceramic may break down a little bit under extreme duress. A little bit of radioactive particles in the water is of little concern and can be filtered out. The coolant can become radioactive and is always filtered. But by the time the rods are dumped into the storage water, the main concern are to contain the radiation. Sellafield in Britain and La Hague in France are re-processing facilities that work wonders, especially in the financial departments. The high cost of re-processing, combined with the high amount of extra radioactive waste make it’s worth questionable. However, in such a limited space such as Britain and Europe, I can understand. A different process has been discussed to create larger ceramic squares out of the used ceramic pellets. That would probably be one of the best bets to helping reduce the waste products.
Sorry I can not answer the question about the canisters, I left the Nuclear industry a few years ago and do not recall their exact molecular make-up. I will try to find my thesis on Safer Nuclear Power for you, though.
Again, though, you can actually go swimming in the upper layers of the cooling pool without ill-effect. Further, we place divers in the water all the time to maintain checks. It is only when you get within striking range of the radiation or if you start drinking the de-ionised water that you may have some problems.
(Sorry about being late with this…)
Actually, nuclear radiation is any sub-atomic particle or photon escaping the nucleus. Neutron radiation is usually only released in significant quantities during fission or certain fusion reactions. A “normal” radioactive material (e.g. spent fuel rods) gives off alpha (protons), beta (electrons), or gamma (photons) radiation.
Exposure to alpha, beta, and gamma radiation does not make other materials radioactive. Thus, even though spent fuel rods are highly radioactive, they don’t make the surrounding water radioactive. But exposure to neutron radiation can and does make other materials radioactive. The primary coolant water in a reactor is bathed in neutrons, which will form deuterium (sp?) and tritium (which is radioactive) out of the hydrogen atoms. I’m not sure what it does to the oxygen atoms, but I assume it changes their isotope as well, rendering them potentially radioactive.
Neutron radiation can also damage crystalline structures, which translates to making metal less strong and more brittle.
On the rocks, please…
(edited to fix vB code - use [ and ] instead of the HTML < and > )
[Edited by Arnold Winkelried on 11-20-2001 at 04:57 PM]
Yeeks! Talk about a newbie. (I know … “Preview reply is your friend.”)
One last quickie…before this thread is closed.
Almost everything in this world is essentially radioactive and gives off one form of radiation or another. In fact, the average American will be subjected to the similar amounts of radiation that a normal radiological worker will during their lifetimes (about 300millrems per year). This radiation will come from the ground beneath them, the buildings around them, the Sunshine from above, and the food from within. Some people can show very high radiation levels during a standard body scan if they just happened to consume something as innocuous as a banana the morning of their body scan.
However, alpha radiation only travels a few inches and can not penetrate the skin. Beta radiation can travel a few feet and can not penetrate skin, but can penetrate the eyeballs and some other soft tissues. Gamma radiation is only a bit more serious, but it is the neutron radiation that we all love and adore. But it takes a fairly good amount of this to do any lasting damage. The body can regenerate the damaged cells, and will not cause the victim to pass genetic disorders to his or her offspring, unless:
- The sperm or egg was directly affected and somehow survived, which is unlikely.
- The fetus was affected directly, most probable and common cause of radiation related birth defects)
However, by lengthening the time of exposure (chronic), you can actually offset the damage. The same amount of radiation in an acute dose will have far worse effects than in a chronic case. But living in a high radiation area for a long time is not suggested. Radiation poisoning can be quite painful, or so I hear, anyway.
Cheers,
For Some Quick Clarification:
I should have said:
“Almost all natural things emit radiation during the decaying process.”
Many man-made things also emit radiation as part of their normal operation, as well.
My most humble apologies.
Just to clarify, this does not mean that if you should chance to find yourself in the core of an operating reactor, you should stick around for a while. A longer exposure time is only helpful if it’s the same amount of total radiation, spread out more.
Thanks Chronos,
that was a good point. Yes, I meant same size dosages chronic versus acute.
First Post!
Anyway, I’ve worked on some projects at a few nuclear plants, and I’ve gotten a few “walk-downs” (i.e. tours) of the facilities. On one occasion, we walked right past a fuel pool, and I asked the engineer leading me about the danger of the water and what would happen if I fell in. He explained that the water near the top of the pool is fine, but if you swam down towards the fuel, you’d be in trouble. People have fallen in, but nothing serious ever happened to them.
Just thought I’d pass that info along.
LAST ONE IN IS A ROTTEN EGG!!!
(first one in had better have some good insurance)
While I was still working in the industry, we had several people fall in to the pool. It actually happens somehwat regularly as newbies have an incredible urge to stare at the spent fuel. They then stare too much and in they go. However, none of them ever suffered from their fall, unless they swallowed some of the water. And it was the Boron (remember boric acid?) that upset their tummies. As the pool is fairly deep, it is similar to staring down from a highrise, some people just have this wierd urge to jump.
Most people who get close enough to jump in to the pool will have pretty good insurance already, though, and the company will surely put them through all sorts of tests.
That said, I never tried going for a swim and was actually scared most of the time that I would fall in, so I avoided the pools alltogether.
I did some research involving oilfield produced water (geological formation water that gets sucked up with the oil)a while back. It turns out that some of it is radioactive, depending on the source. (OK, lets not quibble - It is probably stuff dissolved in the water that is radioactive. There is a LOT of stuff dissolved in formation water. Salinities are typically about 100 part per thousand, then there’s the metals, etc.) In fact, Louisiana had quite a disposal problem with a lot of pipes that they had used to transport the stuff. I’m told the pipes became radioactive during years of transporting the produced water. But if I read you right, that’s impossible (unless there was significant fission going on in the pipes-which besides being nearly impossible would have created more problems than radioactive pipes). Perhaps there was just enough radioactive material imbedded in the pipes that they became hazardous?? Or is there something that I’m not following here?
Also, while working on an environmental project at Los Alamos, I apparently got a dose from something, according to my radiation badge. It wasn’t enough to be concerned about according to the Los Alamos people, who apparently routinely get that kind of dose. But if I remember right, it was about 10 times more radiation than any of the 6 techs that worked for me there, according to the badge results. I didn’t go anywhere the techs didn’t go, and nearly all of our work was either out-of-doors or in the mobile lab that we brought with us. So, my question is, are the badge results normally that widely variable at the lower end of the range, or maybe just inaccurate? If a similar number of people were to wear badges around home and office in some normal place, would that kind of result be surprising or not? We did not go to the places at Los Alamos that apparently still exist where you can pick up pieces of uranium on the ground. We were more interested in the environmental effects of low concentrations of high explosives, and we were avoiding sites with radiation problems.
Fishhead