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Uranium conversion / reprocessing TRU isotopes

  1. Apr 21, 2017 #1
    I am doing a study guide for a nuclear chemistry introductory course FINAL EXAM. A few of the questions have me confused because, although they are asked in a multiple-choice format, the prof. has indicated that multiple choices may be correct for given problems and that you must not only choose the options that are true they must be true and answer the question at hand. Unfortunately, his slides do not provide the amount of detail I believe is needed to answer these questions with 100% confidence.

    6a. Matching: Fill in the bank in column B with the correct choice from column A Column A. Uranium Compounds
    A. Uranium Trioxide (UO3)
    B. Uranium Dioxide (UO2)
    C. Uranium Hexafluoride (UF6)
    D. Uranium Tetrafluoride (UF4)
    E. Uranyl Fluoride (UO2F2)
    F. Triuranium Octoxide (U3O8)
    G. Uranium Peroxide (UO4∙ nH2O)
    Column B. Characteristic/Comment
    1. _____ Produced at conversion plants
    2. _____ Important in uranium purification
    3. _____ Decomposes when heated
    4. _____ Widely used to form pellets
    5. _____ Key compound in uranium conversion
    6 ._____ Hazardous in liquid and gaseous form
    7. _____ Also known as yellowcake

    I HAVE E, C, A, B, D, G, F -> 4 and 7 are obvious but the rest kind of vaguely blend together for some of the choices, given the information I have looked up/ been given. WHICH MOST CORRECTLY ANSWERS THE DESCRIPTION?

    6c. Why is uranium hexafluoride used in gaseous diffusion plants? Note: Because fluorine has only one natural isotope, all the isotopic separative capacity of the diffusion plant is used to enrich the concentration of the lighter uranium isotopes.
    a. It can be used as a gas for processing, as a liquid for feeding and withdrawing, and as a solid for storage.
    b. It increases in volume by more than 30% as it changes from a solid to a liquid.
    c. It is not flammable.
    d. It is not reactive with oxygen, nitrogen, hydrogen, or dry air at room temperature.
    e. It is reactive with water or moisture in the air to form uranyl fluoride (UO2F2) and hydrogen fluoride (hydrofluoric acid).

    question, for a. I have found no UF6 information relating to it being used as a liquid, b. and c. not indicated in notes, d. indicated but with CO2 in the place of hydrogen, e. indicated as being true, but does that really answer the question, like how does the note he added after the question not end up being the answer instead of the options given? I was looking for mass difference but that's not given as a choosable choice.

    6e. Which of the following are TRU isotopes usually found in Spent Nuclear Fuel?
    a. Americium b. Cesium c. Curium d. Neptunium e. Plutonium f. Radium g. Strontium h. Uranium

    a,c,d,e are all TRU isotopes, my question, are they all present in spent nuclear fuel? I have one source that doesn't mention Np in the discussion but gives the half-life in a list of actinides while talking about spent nuclear fuel.
     
  2. jcsd
  3. Apr 21, 2017 #2
    I REALLY APPRECIATE ANY HELP THAT CAN BE GIVEN TO ME HERE - sorry caps lock - I was better at integration of mechanical systems in nuclear engineering haha I thought this introductory nuclear chemistry course would be a good addition toward getting a nuclear engineering graduate certificate with my materials engineering master's but, the lack of detailed specificity in the presentations versus the questions being asked has been a challenge with this course. I greatly appreciate any help that is received!
     
  4. Apr 21, 2017 #3

    Astronuc

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    Staff: Mentor

    Regarding yellow cake, https://www.nrc.gov/reading-rm/basic-ref/glossary/yellowcake.html

    UO2 is typically the final ceramic found in pellets in LWR and CANDU fuel.

    Compare the properties of UF4 and UF6
    https://en.wikipedia.org/wiki/Uranium_tetrafluoride
    https://en.wikipedia.org/wiki/Uranium_hexafluoride

    As for TU isotopes, Np, Pu, Am, Cm are found in spent fuel. Ra is a heavy element but not a TU or actinide. Cs and Sr are fission products, and U is obviously not TU.
    https://dspace.mit.edu/handle/1721.1/41692
     
  5. Apr 22, 2017 #4

    Astronuc

    User Avatar

    Staff: Mentor

    Another article on spent fuel from the EU for moderate burnup fuel (33 GWd/tU). Most utilities will operate fuel to burnups of about 50 to 60 GWd/tU, so that fuel will have greater amounts of Np and TU.
    http://www.radioactivity.eu.com/site/pages/Spent_Fuel_Composition.htm

    Note that Pu isotopes are more prevalent than Np, Cm or Am. Np-237 forms from the neutron capture by U-236, which forms from neutron capture in U-235 that doesn't fission. Np-237 has a long half-life and will be around along time in spent fuel.

    Np-239 will form by neutron capture in U-238 and a beta decay, but Np-239 decays by beta emission relatively quickly to produce Pu-239. The Pu isotopes capture neutrons so there is a build up of Pu-240, Pu-241, Pu-242, Pu-243, each of which undergo beta decay to form isotopes of Am, which undergo beta decay to form Cm isotopes. Several isotopes can also experience alpha decay or fission.
     
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