Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Safe Storage of Nuclear Waste

  1. Feb 25, 2008 #1

    baywax

    User Avatar
    Gold Member

    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?
     
  2. jcsd
  3. Feb 25, 2008 #2

    Astronuc

    User Avatar

    Staff: Mentor

    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.
     
  4. Feb 25, 2008 #3

    chroot

    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    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
     
  5. Feb 25, 2008 #4

    baywax

    User Avatar
    Gold Member

    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.
     
    Last edited: Feb 25, 2008
  6. Feb 25, 2008 #5

    Astronuc

    User Avatar

    Staff: Mentor

    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.
     
  7. Feb 27, 2008 #6
    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.
     
  8. Feb 27, 2008 #7

    baywax

    User Avatar
    Gold Member

    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?
     
  9. Feb 27, 2008 #8
    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.
     
  10. Feb 27, 2008 #9

    baywax

    User Avatar
    Gold Member

    Thank you Azael,

    Is there any radiation or other contamination to the waste water (other than heat)?
     
  11. Feb 28, 2008 #10

    vanesch

    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    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.
     
  12. Feb 28, 2008 #11

    vanesch

    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    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.
     
  13. Feb 28, 2008 #12
    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.
     
  14. Feb 28, 2008 #13

    baywax

    User Avatar
    Gold Member

    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.
     
  15. Feb 28, 2008 #14

    baywax

    User Avatar
    Gold Member

    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!?
     
  16. Feb 28, 2008 #15
    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
    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.

    Plutonium can be safely stored without a problem. But plutonium is very good reactor fuel and its wastefull to burry it.
     
  17. Feb 29, 2008 #16

    vanesch

    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    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. Feb 29, 2008 #17
  19. Feb 29, 2008 #18

    baywax

    User Avatar
    Gold Member

    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?
     
  20. Feb 29, 2008 #19
    I just wanted to say to everyone, good questions baywax and great high-information-density answers.
     
  21. Feb 29, 2008 #20

    baywax

    User Avatar
    Gold Member

    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?
     
    Last edited: Feb 29, 2008
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?



Similar Discussions: Safe Storage of Nuclear Waste
  1. Nuclear waste (Replies: 15)

  2. Nuclear waste. (Replies: 8)

  3. Nuclear waste waste (Replies: 20)

Loading...