SCI 270: On Nuclear Technology Practice Problems  
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9. Nuclear Fission and Nuclear Reactors

  1. Give the nuclear reactions for the syntheses of neptunium and plutonium used in the fast breeder reactor for their productions.

    Nuclear reaction:
    ____238U + n ® 239U + g ® Np + b ® Pu + b ____
    Half lives:
    239Np ___ 2.35 d _____ 239Pu __ 244e4 y __


  2. Consult a handbook or a nuclear data source and give the range of known (or synthesized) plutonium isotopes. Which one has the longest half life and what is its decay mode?

    _____________ Varies __________
    Range of mass numbers
    of Pu isotopes: From _228__ to _ 247 _
    Isotope with the
    longest half life _244, 8.2e7 y __
    (modes): __alpha, beta, EC, SF,____



  3. Assume the thermal-neutron induced fission of 235U (mass = 235.0439) gives two fragments of mass 140 and 93, and the some neutrons. After having consulted the properties of nuclides of mass numbers 140 and 93, we know that 140Ce (mass = 139.90539) and 93Nb (mass = 92.90638) are stable nuclides. Write the nuclear reaction equation for this fission process. Estimate the total energy (including energies of beta-decay of the fission products) in this fission process.

    reaction:__ 235U + n ® 140Ce + 93Nb + 3 n ___
    released: _ Q = __ 200.08 ___ MeV/fission
    released: _ Q = __ 1.93e13 __ J/mole


  4. How much natural uranium must be processed in order to produce 1.0 kg of 235U, if only 50% of this isotope is extracted from natural uranium? What methods are used to separate 235U from natural uranium?

    of 235U __0.72 %__;   238U __99.3 % ___
    Amount of natural
    uranium required: _ 285.7 kg _
    Methods used for extracting 235U:

    1. Gas diffusion of UF6 based on mass difference. _

    2. __ Centrifuging of UF6 gas_____

    3. __ Electromagnetic method to separate UF6+ ions ___

    4. ___Thermal diffusion __

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