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Thread: Spent fuel rods.

  1. #1
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    Spent fuel rods.

    i was wondering if calcium or carbon blocked the radiation from spent fuel rods. because the radiation is kinda like xray.. i think. and bone obsorbs.. or blocks the xrays?

    another babble topic i guess..
    but if we could find a way to use the radioactive waste, instead of trying to bury it. we could sold the problem of radioactive waste. and in doing so we will have found an application for the radioactive waste.

    why must we hide it away underwater in containers. why not try to harness it?

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    I'll leave the details to someone who properly understands Nuclear Physics but here's my knowledge:

    Calcium etc. will absorb radiation to a degree basically radiation absorbtion goes up with atomic mass (I know this isn't entirely true since you can get secondary types of radiation from the energy transfer causing the shielding to emit radiation but I don't understand the process well enough to say when it occurs) hence why lead and concrete are often used for reactor shielding: they're cheap and dense Calcium is a lighter metal than lead and consequently you'd need more of it to shield the same amount (plus elemental calcium is rather reactive: not ideal when you want to be absolutely sure you won't have a breach in the protection)

    As for harnessing nuclear waste again, not really my field but in a sense research has gone into this with stuff like Breeder reactors where the "waste" of the fuel rods can also be used as nuclear fuel. That said only a small amount of nuclear waste is spent fuel rods: low grade waste includes things like protective suits and gloves which have been contaminated: this sort of stuff doesn't really lend itself to use in a reactor, it's too radioactive to be safe but not really radioactive enough to get useful energy out of it.

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    Not knowing all that much about it, I think that spent fuel is used in two applications. One is in the irradiation of food, to get rid of bacteria. The other is in coating bullets (so-called depleted uranium shells).
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    Quote Originally Posted by Jens View Post
    Not knowing all that much about it, I think that spent fuel is used in two applications. One is in the irradiation of food, to get rid of bacteria. The other is in coating bullets (so-called depleted uranium shells).
    Depleted uranium is a byproduct of the enrichment process. It's isotope 238. It's not spent fuel, otherwise it wouldn't be uranium anymore, but a lighter element. Uranium 235 is fuel.

    Cobalt 60 is what is used for food etc. irradiation. It is intentionally created, it's not radioactive waste.
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    Quote Originally Posted by Jens View Post
    Not knowing all that much about it, I think that spent fuel is used in two applications. One is in the irradiation of food, to get rid of bacteria. The other is in coating bullets (so-called depleted uranium shells).
    I don't know much about food irradiation, but depleted uranium is definitely not made from spent fuel. Natural uranium consists of three isotopes, U238 (about 99.27%), U235 (about 0.7%) and a wee trace of U234. The isotope that's fissile, which is what you want for making a humongous KABOOM!, is U235. Uranium which has been processed by separating the isotopes to produce a mixture with a higher U235 concentration than the natural product is called "enriched". Weapons production requires "highly enriched" uranium (over 80% U235 IIRC; what is left over from this process (the U238 and U234) is called "depleted uranium". Because of its physical properties (very high density and pyrophoricity) it has been used to make projectiles designed to penetrate armor. DU has also been used in balancing counterweights for the control surfaces of the Boeing 747 (again IIRC).

    BTW, the fuel used for power-producing fission reactors is usually slightly (about 2.5%) enriched. It turns out that it's just possible to produce a self-sustaining chain fission reaction with natural uranium, but this requires that all your materials be very highly purified and that you get the geometry of the reactor structure just right. CP-1, the world's first working fission pile and, I think, the original plutonium production reactors at Hanford, used natural uranium as fuel, but for the purpose of generating power commercially it's less of a PITA to enrich the fuel a little bit to make sure that your reactor will start up and go.

    Anyway, DU is not derived from spent fuel.

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    Is there a perk to enriching The other two isotopes?

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    U-238 and U-234? Sure. Uranium which contains effectively zero U-235 is substantially less radioactive than most uranium, hence its use for things like counterweights and bullets.

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    I used to cruise in a Yacht that had a Uranium weight at the bottom of it's Keel Fin.
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    Can u de-enrich U-235 spent fuel rods? Like.. we could enrich them.. then when its all used up put it back in its original form.... maybe.

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    Quote Originally Posted by Chunky View Post
    i was wondering if calcium or carbon blocked the radiation from spent fuel rods. because the radiation is kinda like xray.. i think. and bone obsorbs.. or blocks the xrays?
    I should think that bone absorbs more X-rays than the surrounding tissue but that it is only a relative thing, that is, that bone only attenuates the radiation. A radiologist knows the the factors involved, and so can make a prediction of how long the exposure must be at a specific rates to optimize the contrast between the tissues under investigation on the sensitive material used. The processing after exposure can also affect the contrast to some extent.

    Quote Originally Posted by Chunky View Post
    another babble topic i guess..
    but if we could find a way to use the radioactive waste, instead of trying to bury it. we could sold the problem of radioactive waste. and in doing so we will have found an application for the radioactive waste.

    why must we hide it away underwater in containers. why not try to harness it?
    As I understand it, it is possible to process spent fuel to get materials that can be used for further energy production, such processing could increase the energy output of a unit of nuclear fuel by several tens of times, and reducing the amount of highly radioactive waste, though the extra steps means a much larger investment. But as these reprocessing plants could potentially supply materials for nuclear weapons and there have been several accidents at such plants in the past, there is quite a bit of resistance to them.

    I suppose that at some time in the future, it will be necessary to use such plants if we want to continue using nuclear power, and there may be lamentation over the usable fuel that was thrown away by us.

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    Quote Originally Posted by Infinity Watcher View Post
    I'll leave the details to someone who properly understands Nuclear Physics but here's my knowledge:

    Calcium etc. will absorb radiation to a degree basically radiation absorbtion goes up with atomic mass (I know this isn't entirely true since you can get secondary types of radiation from the energy transfer causing the shielding to emit radiation but I don't understand the process well enough to say when it occurs) hence why lead and concrete are often used for reactor shielding: they're cheap and dense Calcium is a lighter metal than lead and consequently you'd need more of it to shield the same amount (plus elemental calcium is rather reactive: not ideal when you want to be absolutely sure you won't have a breach in the protection)

    As for harnessing nuclear waste again, not really my field but in a sense research has gone into this with stuff like Breeder reactors where the "waste" of the fuel rods can also be used as nuclear fuel. That said only a small amount of nuclear waste is spent fuel rods: low grade waste includes things like protective suits and gloves which have been contaminated: this sort of stuff doesn't really lend itself to use in a reactor, it's too radioactive to be safe but not really radioactive enough to get useful energy out of it.
    i didnt mean to quote it all..but anyways, the part about gloves and aprons and masks and such that are now radioactive. what would happen if we burned them? would the ashes be radioactive? and if not, then, did the flames have some type of curing process? is if so... would a lead barrier be replaced with a wall of flame??

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    Quote Originally Posted by Chunky View Post
    Can u de-enrich U-235 spent fuel rods? Like.. we could enrich them.. then when its all used up put it back in its original form.... maybe.
    Sort of. Spent fuel rods can be processed to extract the produced plutonium and remaining uranium (which may or may not need to be enriched), but spent fuel rod reprocessing is, iirc, primarily a chemical process, so there won't be any isotopic enrichment. You could mix in the U238 from the enrichment tailings into the spent rods, but what would it gain?

    U238 is useful stuff, but probably not useful enough to actually be produced, instead of being a byproduct.
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    Quote Originally Posted by Infinity Watcher View Post
    Breeder reactors where the "waste" of the fuel rods can also be used as nuclear fuel. That said only a small amount of nuclear waste is spent fuel rods: low grade waste includes things like protective suits and gloves which have been contaminated: this sort of stuff doesn't really lend itself to use in a reactor, it's too radioactive to be safe but not really radioactive enough to get useful energy out of it.
    Different type of radiation, too. First, there's alpha, then beta, then neutron, and EM (x-ray and gamma).

    Alpha are helium-4 nucleii -- two protons and two neutrons. They're highly destructive to human cells, but only penetrate an inch or two of air, most clothing, even paper, stops them cold. The danger is when the substances which emit them, like radon, polonium, and radium, come into contact with human tissues, either by direct contact with skin, or far worse, by inhalation or ingestion. This is why people working with radioactive materials wear radiation exposure suits. A thin layer of shielding and an air filter is all that's needed to stop them, except for radon, which is a gas and must be displaced by good air from a known source.

    Beta radiation is either highly energetic electrons or positrons. The electrons (B-) aren't much of a problem, but the positrons (B+) give off gamma radiation when they annihilate with an electron.

    Neutrons are the only type of radiation that can make something else radioactive. They do so by colliding and combining with the nuclei of various elements, rendering them into unstable isotopes. It's this process which turns fertile material like U-233 and thorium-232 into fissile material which is then used as nuclear fuel.

    X-rays and Gamma rays are just EM waves of different energies, with gamma rays being the more energetic. They're by-products of radioactive decay.

    Breeders are are very attractive as a fuel source, because with current uranium reserves and using techniques to extract uranium from sea-water, there's enough energy to sustain human civilization for several billion years. Our sun will red giant before we run out of fuel. The downsides are that all nuclear energy produces nuclear waste, as well as fuel which can be enriched into weapons-grade.

    Quote Originally Posted by Jens View Post
    Not knowing all that much about it, I think that spent fuel is used in two applications. One is in the irradiation of food, to get rid of bacteria. The other is in coating bullets (so-called depleted uranium shells).
    DU isn't a coating. The entire bullets are made of DU, often alloyed with small amounts of another metal for stabilization of physical properties. DU, by the way, has a lower concentration (about one-third) of U-235 than naturally-occurring uranium. DU itself is fairly harmless, with a body half-life of 15 days. Meanwhile, the most favored alternatives containing tungsten are many times more carcinogenic than DU. DU get's an undeserved bad rap due to its "uranium" content and the associated "nuclear" stigma.

    Quote Originally Posted by ktesibios View Post
    I don't know much about food irradiation, but depleted uranium is definitely not made from spent fuel.
    Are you sure about this? While most DU comes from the initial processing of natural uranium, but nuclear reprocessing also produces U-238. The two sources of DU result in different isotope ratios, however, including U-236 and trace amounts of transuranics. Source. Regardless of its source, it's still DU.

    Quote Originally Posted by Chunky View Post
    i didnt mean to quote it all..but anyways, the part about gloves and aprons and masks and such that are now radioactive. what would happen if we burned them? would the ashes be radioactive?
    Yes. Burning is a chemical process (oxidation). It does nothing to change the nuclear properties of the elements involved. If they're radioactive before burning, they're radioactive afterwards.

    Quote Originally Posted by swampyankee View Post
    U238 is useful stuff, but probably not useful enough to actually be produced, instead of being a byproduct.
    It's been explored for use in dense and shielded concrete storage containers for spent nuclear fuel. Source. But mainly, though, you're right - we produce more of it than we can used. There are over a million tons of it sitting around in stockpiles the countries which use process and use uranium as a nuclear fuel.

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    Quote Originally Posted by DoggerDan View Post
    Yes. Burning is a chemical process (oxidation). It does nothing to change the nuclear properties of the elements involved. If they're radioactive before burning, they're radioactive afterwards.
    Which incidentally is one of the reasons why coal fires power plants are the cause for more radioactive pollution that nuclear plants.
    Radioactive elements in the coal are still there in the ash and there's no control over what happens to them because the ash is not from a nuclear plant and therefore managed under completely different rules.
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    Quote Originally Posted by HenrikOlsen View Post
    Which incidentally is one of the reasons why coal fires power plants are the cause for more radioactive pollution that nuclear plants.
    Radioactive elements in the coal are still there in the ash and there's no control over what happens to them because the ash is not from a nuclear plant and therefore managed under completely different rules.
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