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Why Uranium?

  1. Jun 7, 2010 #1
    Hi there, first time poster. I'm trying to settle a dispute which is kind of stupid...

    Now I realize this question might seem dumb but I was wondering why exactly we use Uranium (Uranium-235 to be more exact) in Nuclear power plants?

    From what I understand, in very basic terms, nuclear energy is what gets released when we break apart nuclei of atoms. Obviously other elements have their own nuclei. Wouldn't we get nuclear energy if we, say, break apart the nuclei of Iron or Lead or Silver or pretty much every other element?

    If not, what makes the nucleus of Uranium "breakable" but not the other elements? Or is it that other elements CAN be used to release nuclear energy but using Uranium is far more practical for some reason?

    Thanks in advance.
  2. jcsd
  3. Jun 7, 2010 #2
    Uranium is used because it is the most practical. It has a long half life which means that there is an abundance of it distributed across the earth. It also has a much higher release of energy per nucleon, making it more advantageous to use. In specific uranium-235 is used more commonly because it has a greater neutron absorption rate of thermal neutrons compared to other elements, such as uranium-238. (Since its the neutrons that are fired into the atoms to make them more unstable and split). And finally, no uranium isnt in specific that special it just has a better cost effectivness +other pros comapred to any other element. All the elements above Iron can and will undergo fission in the right environment.
  4. Jun 7, 2010 #3


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  5. Jun 7, 2010 #4
    Elements tend to try to obtain a stable state. Iron appears (for some reason) to be the most stable state, the more protons an element has in its nucleus above the number in Iron the less stable it is. It is therefore more "willing" to give up its protons/electrons, i.e. it uses less energy to break them apart.

    I'm no scientist, but that's basically what the TV documentary told me a few days ago ;)
  6. Jun 7, 2010 #5


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    There's a famous "binding energy curve" which shows that putting nucleae together releases energy for light nucleae, up to iron. Above iron, breaking apart heavy nucleae releases energy. As another poster said, iron is the "most stable" and hence the "less energetic".

    The first kind of process is what's called nuclear fusion, it is what powers the stars, the sun (a star), thermonuclear weapons,... and what people try to do with fusion reactors, but that's not yet fully up and running. It is not a spontaneous process, and that's what makes it hard: you have to "convince" light nucleae to undergo fusion.

    Splitting nucleae is what's called nuclear fission. USUALLY, you can fission nucleae by hitting it with accelerated particles (say, protons). But that's not a very energy-efficient way of doing so.
    However, A VERY SMALL NUMBER of nucleae split SPONTANEOUSLY when they absorb a slow neutron, and an even smaller number splits with the emission of neutrons itself. In fact, of all stuff occuring in nature, only ONE nucleus does so: uranium-235.
    Some artificially produced nucleae do so too, like plutonium, but they are not found in nature on earth.

    So a "spontaneous chain reaction" is only possible with uranium, if you limit yourself to naturally occuring materials. That's what's done in a nuclear reactor.

    So of all energy-providing nuclear reactions (and there are many of them), only one specific reaction can happen spontaneously with "natural" materials, without having the need of very high pressures, temperatures, accelerators and so on, but by just "putting stuff together", and that's fission with uranium.
  7. Jun 7, 2010 #6
    Wouldn't have been Atom (Jim Al'kahili) would it?
  8. Jun 7, 2010 #7
    Ah yes, it was, I watched it on replay :)
  9. Jun 7, 2010 #8
    All clear now.

    Thanks everyone for answering and vanesch in particular. You explained that so very well. Much appreciated.
  10. Jun 7, 2010 #9
    I thought nuclear weapons worked by firing a neutron into Uranium in order to split the nuclae and cause a chain reaction, so that's fission isn't it?
  11. Jun 7, 2010 #10
    That is the process behind simple nuclear weapons. Thermonuclear weapons use fission to start a fusion reaction in hydrogen.
  12. Jun 7, 2010 #11
    His documentaries are great

    Thermonuclear weapons use an initial fission reaction to initiate a fusion reaction, this is done by using the fission reaction to compress the material used for fusion to let atoms fuse together. I hope that makes sense. And i hope I'm right as well.

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