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Neutron flux in coolant and fuel pin in PWR

  1. Nov 7, 2016 #1
    In PWR, fast neutron produced from fission in fuel has been moderated into thermal neutron by the a series of collisiion with coolant,i.e. H2O. So the multi-group neutron flux in coolant and fuel pin has much diffenrce, e.g. the relative higher fast neutron in fuel pin and relative higher thermal neutron in coolant as to the uniform.
    Are there specific data about comparision of multi-group neutron flux in coolant and fuel pin in PWR, if it don't need to use MCNP to simulate it ? Thank you very much.
  2. jcsd
  3. Nov 10, 2016 #2


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    I'm not sure about the question, but one would ordinarily use a lattice code, e.g., CASMO or WIMS, in conjunction with a core simulator, e.g., SIMULATE or PANTHER, respectively, to calculate the neutron flux and fission density. Using MCNP is also an option.

    WIMS Physical models :
    explicit water gap;
    grids homogenisation;
    WIMS Numerical models :
    condensed to 6 groups for pin by pin calculation;
    2D XY diffusion theory (GOG);
    DMOD option (local transport theory correction for neighbouring rods of perturbing cells such as guide tubes or Gd burnable absorber rods)


    In general, one would use a small number of groups, e.g., 2 or 4, which are collapsed from a larger number of groups. The WIMS paper mentions 69 groups, but newer versions (WIMS 9 or 10) use more groups. The group neutron spectrum is usually not reported since that would be a tremendous volume of data over time/burnup for even 1/8 or 1/4 of an assembly. Usually, there is a numerically processed mean or smeared value.

    Meshing the lattice is also important, and finer meshes are more often used now, because we have access to faster processors and greater memory capacity.
  4. Nov 11, 2016 #3


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    Normally, one does not look at the neutron energy spectrum in the coolant or fuel, unless one is digging into the details of a calculation, e.g., looking at specific cross-sections, or effects of specific nuclides/isotopes. The codes process the multigroup data and collapse into two, three or four groups, depending on the code system, and the flux is smeared over the fuel, cladding and coolant.
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