CERT

Center for Exascale Radiation Transport

Texas A&M Engineering Experiment Station

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Gallery

  • correct_soln_32k_angles
    Fast (neutron) flux - 32K angles
  • ray_effects_8k_angles_0
    Fast flux at early time - 8K angles - Noticeable ray effects
  • ray_effects_8k_angles_1
    Fast flux at middle time - 8K angles - Noticeable ray effects
  • ray_effects_8k_angles_2
    Fast flux at late time - 8K angles - Noticeable ray effects
  • ray_effects_168_angles
    Fast flux at early time - 168 angles - Ray effects dominate solution
  • slow_neutrons_168_angles
    Slow flux at late time - 168 angles - Strong inherited ray effects

 

Neutron Density Plots

We use PDT, a parallel deterministic transport code developed at Texas A&M University, to simulate neutrons in a graphite block. We plot contours of the computed neutron densities (n/cm2-s) at select points in time using VisIt. The pictures show a block of graphite cut out to show the center. There is a source of fast neutrons in the center-left of the block.

While real neutrons can travel at any speed less than the speed of light and in any direction, simulated neutrons are forced to travel in a finite number of discrete directions and at averaged speeds. This discretization is required to map the continuous transport equation onto a form efficiently solvable by computers. The angular and energy discretizations introduce numerical error.

We are interested in a class of error known as “ray effects” that occur because neutrons only travel in discrete directions (or rays). This leads to the spikiness of the contours plotted above, which should be spherical shells. The fast neutrons show prominent ray effects, even when a large number (over 8000) of angles are used. As these neutrons collide with simulated carbon nuclei in the block, they slow down. The slow neutrons inherit ray effects from their fast progenitors.

Center for Exascale Radiation Transport

Center for Large Scale Scientific Simulations

Nuclear Engineering - Texas A&M University

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