Safe Storage of Nuclear Waste

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baywax
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What's the safest way to dispose of and store nuclear waste? Is there any chance of rocketing it into the sun or is it too heavy?
 

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  • #2
Astronuc
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It costs about >$1000/kg (maybe closer to 10 times that) to lauch material from earth to space, and that is just to orbit. That's more than the cost the energy extracted from the fuel. It's better to bury it on earth.

Handling high level waste requires heavy shielding, and so there is the mass of fuel + mass of shielding to consider.

It would never get to the sun since at some point it would melt/vaporize and then ride the solar wind back out into the solar system.
 
  • #3
chroot
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Launch vehicles explode all the time. You probably don't want a rocket full of nuclear waste blowing up ten miles off the ground, say.

And also, yes, it's very heavy, and there's a lot of it. It'd be incredibly expensive to launch this kind of material into space. In fact, it'd be so expensive that nuclear power would no longer be economical at all.

- Warren
 
  • #4
baywax
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It costs about >$1000/kg (maybe closer to 10 times that) to lauch material from earth to space, and that is just to orbit. That's more than the cost the energy extracted from the fuel. It's better to bury it on earth.

Handling high level waste requires heavy shielding, and so there is the mass of fuel + mass of shielding to consider.

It would never get to the sun since at some point it would melt/vaporize and then ride the solar wind back out into the solar system.
So that would pose a risk of contamination to our planet and others. Plus, we'd all be too broke to do anything about it after paying for the "payload".

What are the alternatives?

Are there any reactive means of neutralizing the waste so that it doesn't pose a problem to future generations. Is there some process whereby the radiation is neutralized?

PS. I see Futuredreamz has a thread about turning waste into electricity. Sorry if this thread somewhat duplicates some of the entries there.
 
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  • #5
Astronuc
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It would be prohibitively expensive to launch waste into space.

At the moment, there are those who support reprocessing of spent fuel in order to recover the unused U, Pu and transuranics, and separate the fission products, which are then vitrified and melted into a synthetic rock (which is geologically stable). The waste in solid form would be buried.

The most radioactive components decay in seconds, minutes, hours, days, weeks, months, . . . . up to years. The more radioactive a substance is, the faster it decays. The fast decaying products become inert quickly and further entrain the long-lived radionuclides. There is some thought that valuble isotopes would be recovered some time later in the future.
 
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Right now it's also more expensive to design and build (and possibly even operate) a reprocessing facility than it is to use uranium ore to make new fuel.
 
  • #7
baywax
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Right now it's also more expensive to design and build (and possibly even operate) a reprocessing facility than it is to use uranium ore to make new fuel.
Yes, I thought the whole process of embedding spent fuel into artificial rock seemed time consuming and expensive.

Another by-product of nuclear power is heated water. When its discharged back into the river, stream or other source from which it is extracted, it upsets the balance of the original temperatures normally found in the source and thus creates an adverse condition for the flora and fauna of that source. Are there steps being taken to cool the discharged water to its original temp. and cease this infringement on the environment of the water ways?

Another question is: is there any contamination to the cooling system that may be discharged back into the water source?
 
  • #8
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Yes, I thought the whole process of embedding spent fuel into artificial rock seemed time consuming and expensive.
Its not very expensive, in sweden the construction and operation of the waste storage (not constructed yet) and all research is funded by a small fee on electricity produced by nuclear power and the fee is insignificant compared to other taxes ect.

Another by-product of nuclear power is heated water. When its discharged back into the river, stream or other source from which it is extracted, it upsets the balance of the original temperatures normally found in the source and thus creates an adverse condition for the flora and fauna of that source. Are there steps being taken to cool the discharged water to its original temp. and cease this infringement on the environment of the water ways?

Another question is: is there any contamination to the cooling system that may be discharged back into the water source?
The heating can be positiv aswell, seals are realy thriving around the water discharge in sweden. If the discharge is straight into the sea the effect is quite small and very local. The temperature difference compared to the rest of the sea is located within a few square km.

You can get around it by using cooling towers or creating a artificial lake where the water can cool before going back into the river if river water is used.

But the waste heat can be used for district heating if the power plant is close to a major city.
 
  • #9
baywax
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Its not very expensive, in sweden the construction and operation of the waste storage (not constructed yet) and all research is funded by a small fee on electricity produced by nuclear power and the fee is insignificant compared to other taxes ect.



The heating can be positiv aswell, seals are realy thriving around the water discharge in sweden. If the discharge is straight into the sea the effect is quite small and very local. The temperature difference compared to the rest of the sea is located within a few square km.

You can get around it by using cooling towers or creating a artificial lake where the water can cool before going back into the river if river water is used.

But the waste heat can be used for district heating if the power plant is close to a major city.
Thank you Azael,

Is there any radiation or other contamination to the waste water (other than heat)?
 
  • #10
vanesch
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Thank you Azael,

Is there any radiation or other contamination to the waste water (other than heat)?
Normally not: the cooling cycle is the 3rd water cycle in a PWR plant. The first water cycle is the one of the reactor vessel (closed circuit, can possibly be contaminated a bit by leakage in fuel rods, which itself is normally not the case). The second cycle is the steam/water Rankine cycle (also closed), normally not in contact with radiactive stuff, it is only in the exceptional case of a failure of the steam generator (the heat exchanger between the first cycle and the second cycle) that some first-cycle water can get into the second cycle.

The condenser of the second cycle is cooled by the third circuit, which is the external cooling water. It gets normally never ever in contact with any radiation or radioactive contamination, as it cools, through a heat exchanger, water which itself is normally not contaminated (and even if it were, by an accident, it is still separated from it in the condenser).

If however, there is a use of cooling towers, there might be the need to add some chlorine to the cooling water (which will be largely, but not entirely recuperated before dumping) in order to avoid legionella bacterial growth. In that case, there will be a small chemical contamination with some chlorine.
 
  • #11
vanesch
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What's the safest way to dispose of and store nuclear waste?
Bury it. That's now more than 25 years that one knows that this is a good solution, and one is still studying all kinds of exotic chemistry and other transport phenomena to find out whether really there's nothing overlooked.

You have to know that most of the activity is over in about 300-400 years (the fission products). One thinks that the human containment will hold it out for a few hundred years (stainless steel vessels and glass). Then it takes about 10 000 years to get rid of the minor actinides, which seem, however, not to get transported easily. Finally, if one were so stupid as to burry the plutonium too, you'd have to wait for about 100 000 years for it to fall back on natural radiation levels of uranium ore. But plutonium too, doesn't get transported easily.

Of course, you cannot bury it just anywhere, you have to study the geology very carefully, because the last thing you want is to put it in streaming ground water which would be too good a transportation vector. Clay layers seem to be very fit for the purpose, as they form a chemical barrier for actinide transport. Also salt depositions seem ok. Granite has an advantage (it is geologically extremely stable), but also a disadvantage (there can be cracks through which groundwater flows).

That said, there is no hurry, because nuclear waste is, on an industrial scale, relatively small volume, so storing it temporarily (even if it is for 50 years or more) is not a big problem - it even makes the underground storage simpler, as the produced heat and radiation will decay seriously over that time. Moreover, especially for "waste" from an open cycle, one might consider keeping it to reprocess later, as it still contains a lot of energetic stuff (95% of it, in fact).
It also gives more time to make one even more sure that the repository is going to be ok.
 
  • #12
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Its very interesting to read about the natural reactors in Oklo that ran 2 billion years ago and the transport of different radionuclides from the reactor area. Even there with extreme conditions and no protection whatsoever all the actinides and the long lived fission products have stayed within a few meters from the reactor zones.
 
  • #13
baywax
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Its very interesting to read about the natural reactors in Oklo that ran 2 billion years ago and the transport of different radionuclides from the reactor area. Even there with extreme conditions and no protection whatsoever all the actinides and the long lived fission products have stayed within a few meters from the reactor zones.
What happened with Chernobyl? How did the radiation from that accident spread? I know there were fires. Was it in the smoke and particles? There were maps showing the spread of the contamination to neighbouring countries. Not sure what happened there, the whole town basically died around that site.
 
  • #14
baywax
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Bury it. That's now more than 25 years that one knows that this is a good solution, and one is still studying all kinds of exotic chemistry and other transport phenomena to find out whether really there's nothing overlooked.

You have to know that most of the activity is over in about 300-400 years (the fission products). One thinks that the human containment will hold it out for a few hundred years (stainless steel vessels and glass). Then it takes about 10 000 years to get rid of the minor actinides, which seem, however, not to get transported easily. Finally, if one were so stupid as to burry the plutonium too, you'd have to wait for about 100 000 years for it to fall back on natural radiation levels of uranium ore. But plutonium too, doesn't get transported easily.

Of course, you cannot bury it just anywhere, you have to study the geology very carefully, because the last thing you want is to put it in streaming ground water which would be too good a transportation vector. Clay layers seem to be very fit for the purpose, as they form a chemical barrier for actinide transport. Also salt depositions seem ok. Granite has an advantage (it is geologically extremely stable), but also a disadvantage (there can be cracks through which groundwater flows).

That said, there is no hurry, because nuclear waste is, on an industrial scale, relatively small volume, so storing it temporarily (even if it is for 50 years or more) is not a big problem - it even makes the underground storage simpler, as the produced heat and radiation will decay seriously over that time. Moreover, especially for "waste" from an open cycle, one might consider keeping it to reprocess later, as it still contains a lot of energetic stuff (95% of it, in fact).
It also gives more time to make one even more sure that the repository is going to be ok.
Hi vanesch, Thank you for your info. Why can't we bury spent plutonium and what do we do with it these days? Is that classified info!?
 
  • #15
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What happened with Chernobyl? How did the radiation from that accident spread? I know there were fires. Was it in the smoke and particles? There were maps showing the spread of the contamination to neighbouring countries. Not sure what happened there, the whole town basically died around that site.
The radionuclides that was spread from Chernobyl was the chemicaly volatile ones. Iodine, cesium ect and gases like Xenon. Se this list http://www.nea.fr/html/rp/chernobyl/c02.html [Broken]
If you look at the half lifes of the isotopes that did escape the reactor most of them decay away in a few days. They are not a problem in a used fuel repository since they decay long before they are placed there.

Not much of the actinides(the group of elements that uranium, plutonium ect belongs to) spread from the reactor.

Hi vanesch, Thank you for your info. Why can't we bury spent plutonium and what do we do with it these days? Is that classified info!?
Plutonium can be safely stored without a problem. But plutonium is very good reactor fuel and its wastefull to burry it.
 
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  • #16
vanesch
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Hi vanesch, Thank you for your info. Why can't we bury spent plutonium and what do we do with it these days? Is that classified info!?
The good way to use plutonium is in fast reactors: it is a very good fuel. For the moment, in certain countries (France, UK,...) one is reprocessing the spend fuel and one extracts the plutonium. In others (Sweden, USA,...) one uses the "open cycle", that is, one considers the spend fuel as waste (which is very wasteful of ressources, but economically for the moment still viable).

Now, plutonium has several problems. It is by far the longest-living nuisible actinide, so in the waste, one counts on 100 000 years for it to take on "background" levels. This is not a problem by itself, but it would be better if this time were limited to 10 000 years of course, which is the case of spend fuel of which the plutonium has been removed but still contains the minor actinides (Np, Am, Cm), simply because the migration models have less uncertainties over 10 000 years than over 100 000 years. So one can put smaller error bars on the predictions of the safety of a repository over 10 000 years than over 100 000 years.
Moreover, plutonium is of course military a sensitive material, although this is over-emphasised: the plutonium from thermal power plants is of such an isotopic composition that it is difficult (although not impossible) to use to make a nuclear weapon.

All these are good reasons on the "waste" side to remove the plutonium. On the "fuel" side, as Azael said, plutonium is a "good fuel", but one has to put a caveat here. It is the perfect fuel for a fast reactor. But in a standard PWR, it is problematic. One can partially reuse it in so-called MOX fuel, but the difficulty is that in a thermal spectrum, the "good" plutonium Pu-239 can fission, but also absorb a neutron to form Pu-240, and so on, which absorps neutrons, which is highly active, and which ends up becoming Pu-241 which decays into Am-241, a nuisance.

So as long as we have a park of just PWR or BWR with thermal spectrum, we have only a limited possibility to re-use the plutonium. The plutonium from used MOX fuel is so good as unusable in a thermal (water) reactor, and will end up producing a lot of minor actinides. The gain in "waste" this way is limited, and the gain in fuel also (about 10-20% economy in fuel).

Genuine plutonium recycling only really makes sense if we have in the park of reactors, also a certain fraction of fast reactors. They can "eat" all the plutonium, and even burn a limited amount of minor actinides.

Otherwise, sooner or later, we will have unusable plutonium (bad isotopic composition) on our hands which we will have to end up considering as waste.
 
  • #18
baywax
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The good way to use plutonium is in fast reactors: it is a very good fuel. For the moment, in certain countries (France, UK,...) one is reprocessing the spend fuel and one extracts the plutonium. In others (Sweden, USA,...) one uses the "open cycle", that is, one considers the spend fuel as waste (which is very wasteful of ressources, but economically for the moment still viable).

Now, plutonium has several problems. It is by far the longest-living nuisible actinide, so in the waste, one counts on 100 000 years for it to take on "background" levels. This is not a problem by itself, but it would be better if this time were limited to 10 000 years of course, which is the case of spend fuel of which the plutonium has been removed but still contains the minor actinides (Np, Am, Cm), simply because the migration models have less uncertainties over 10 000 years than over 100 000 years. So one can put smaller error bars on the predictions of the safety of a repository over 10 000 years than over 100 000 years.
Moreover, plutonium is of course military a sensitive material, although this is over-emphasised: the plutonium from thermal power plants is of such an isotopic composition that it is difficult (although not impossible) to use to make a nuclear weapon.

All these are good reasons on the "waste" side to remove the plutonium. On the "fuel" side, as Azael said, plutonium is a "good fuel", but one has to put a caveat here. It is the perfect fuel for a fast reactor. But in a standard PWR, it is problematic. One can partially reuse it in so-called MOX fuel, but the difficulty is that in a thermal spectrum, the "good" plutonium Pu-239 can fission, but also absorb a neutron to form Pu-240, and so on, which absorps neutrons, which is highly active, and which ends up becoming Pu-241 which decays into Am-241, a nuisance.

So as long as we have a park of just PWR or BWR with thermal spectrum, we have only a limited possibility to re-use the plutonium. The plutonium from used MOX fuel is so good as unusable in a thermal (water) reactor, and will end up producing a lot of minor actinides. The gain in "waste" this way is limited, and the gain in fuel also (about 10-20% economy in fuel).

Genuine plutonium recycling only really makes sense if we have in the park of reactors, also a certain fraction of fast reactors. They can "eat" all the plutonium, and even burn a limited amount of minor actinides.

Otherwise, sooner or later, we will have unusable plutonium (bad isotopic composition) on our hands which we will have to end up considering as waste.
Is there some etiquette to disposing of nuclear waste? I mean, dog owners are faced with the disposal task everyday. I don't know if its done well. But its not on the streets or the grass (in most cases). Its in the landfill decomposing. But, someday, someone is going to build on that land fill.

Someday, there could be a host of other things going on like high water, earthquakes where you least expect them, future excavations. What if records are lost and wiped out, and people in 3490 AD are planning a tunnel through what they think is wilderness and they bore right through this land mine of plutonium? There are a thousand scenarios that come to mind where contamination and severe mutation take place because, today, we couldn't figure out a way to neutralize our nuclear waste.... or perhaps do without nuclear power.

I mean, at one point we only had wind mills and sails for energy. If we bump into a wreck of one of these it doesn't kill or mutate the whole family. Is there a way to ensure, completely, that all nuclear waste can be disposed of in a benign way?
 
  • #19
I just wanted to say to everyone, good questions baywax and great high-information-density answers.
 
  • #20
baywax
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I just wanted to say to everyone, good questions baywax and great high-information-density answers.
Yes Captain... I forgot to thank all the contributors for the extremely in-depth answers we're getting. After the philosophy section, this is a real treat! My gratitude to you guys and here's me hauling back a big (hopefully non-contaminated) beer in your honour, eh!.

edit: speaking of migration levels, after Chernobyl, there was a map showing the spread of the contaminants. It seemed to cover a large area, well into Eastern Germany and even over some of Ireland as I remember. Is this the spread of the irradiated gases Azael mentioned and not to do with the properties of plutonium or uranium?
 
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  • #21
baywax
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I notice in the wicipedia article the mention that "cesium has a relatively short biological halflife (1 to 4 months) while strontium and radium both have very long biological half-lives"

How is the term "biological" being applied here? Does this describe the halflife of cesium when it is present in an organism?

I've worked around linear-accelerators and CT scanners and MRI units etc... I know Barium is used to image areas of anatomy. Is barium part of the radioactive family with a short biological halflife?
 
  • #22
Astronuc
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Barium used for X-ray imaging of the GI tract is not radioactive.
Barium sulphate (BaSO4) is insoluble and used for body imaging (barium meal).
http://www.webelements.com/webelements/elements/text/Ba/phys.html

Density is ~3.5 g/cm3
http://www.webelements.com/webelements/elements/text/Ba/phys.html

Cs is chemically similar to Na and K, so can be taken up and excreted similar. Sr and Ra are chemically similar to Ca, which of course is important in the structure of bones. Sr and Ra tend to accumulate in the bones where they can do damage to the blood system in addition to underming the skeletal structure (as well as cause sarcomas), and could damage the spinal cord if sufficient radioactive Sr or Ra accumulates in the spine/vertebrae.
 
  • #23
vanesch
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Is there some etiquette to disposing of nuclear waste? I mean, dog owners are faced with the disposal task everyday. I don't know if its done well. But its not on the streets or the grass (in most cases). Its in the landfill decomposing. But, someday, someone is going to build on that land fill.
It is DEEP geological disposal: of the order of 200 - 700 meters under the surface of the earth. The current maximum exposure limit during the lifetime of the site in all "reasonable" scenarios is set to 0.3 mSv/year (to give you an idea, the average yearly dose by natural background is 2.4mSv/year). A site is not acceptable if you find a reasonable scenario where there's a higher dose risk than 0.3 mSv/year. However, most scenarios give you rather 10 microsievert (=0.01mSv/year) per year! The "lifetime of the site" is the time it takes for the radiotoxicity to fall back on that of natural uranium ore (which are these famous lifetimes: 300-400 years for fission products, 10 000 years for minor actinides and 100 000 years for plutonium).

Of course, the discussion is "what is a reasonable scenario". Usually one takes that precise records are kept for about 500 years (so no drills etc... during this period). After that, one considers things like a borehole for water and such.
Now, of course, or 1000 years from now we became cavemen, or we're all dead, or we still have nuclear technology which allows us to sample stuff. If we're cavemen, we won't dig holes that deep.

Of course you cannot foresee everything. That's what "reasonable" stands for. People (if they exist) 1000 years from now also have to take up a bit their responsability, like taking samples where they are drilling.

Someday, there could be a host of other things going on like high water, earthquakes where you least expect them, future excavations. What if records are lost and wiped out, and people in 3490 AD are planning a tunnel through what they think is wilderness and they bore right through this land mine of plutonium? There are a thousand scenarios that come to mind where contamination and severe mutation take place because, today, we couldn't figure out a way to neutralize our nuclear waste.... or perhaps do without nuclear power.
These "thousands of scenarios" is exactly what people try to find out, and calculate/estimate the doses that result from it.

I mean, at one point we only had wind mills and sails for energy. If we bump into a wreck of one of these it doesn't kill or mutate the whole family. Is there a way to ensure, completely, that all nuclear waste can be disposed of in a benign way?
You rarely bump into a windmill 500 meters underground, do you ?
 
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  • #24
Little tidbit: http://downlode.org/Etext/wipp/" [Broken] from Sandia National Laboratories analyzing how such a repository of waste should be marked.
 
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  • #25
vanesch
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Although it is *physically* possible to do this, and although there is a big research interest in this at the moment, I seriously question the industrial utility of it.

Indeed, the ultimate goal is to lower the risk of nuclear waste over the long term. Here, the risk is the expected number of death (number of exposed people x probability that they die of their exposure).

The risk for the repository is pretty small ! It is only in pretty unlikely scenarios that we obtain doses that might even become measurable above the background!
Now, these transmutations also involve a lot of manipulations of the waste, transport to the transmutation centre etc... There is always a minor risk in these manipulations that something goes wrong, and that, say, a worker get exposed or something. So it is far from obvious that these transmutations, everything included, REDUCE the overall risk! They might even increase it seriously (while it would still be very low of course).

In other words, we would put the lives of people at a slightly increased risk NOW, just to avoid very very unlikely risks to hypothetical people 1000 years from now.
 

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