openmc.examples.sphere_with_shielded_pocket

openmc.examples.sphere_with_shielded_pocket() → Model

Create a continuous energy deep-shielding model with a far detector pocket.

A concrete sphere is centered at the origin. A 2 MeV isotropic neutron source sits in a small air cavity just inside the sphere surface on the -x side, and a small steel pocket is embedded flush with the surface on the +x axis, so roughly a meter of concrete separates the source from the pocket while only a few centimeters of concrete back the cavity. The sphere is enclosed in a vacuum-bounded box, with a void gap in between, so that solvers that sample uniformly over a rectangular domain (e.g., random ray) can be applied directly. The geometry is designed for testing weight window and variance reduction workflows:

• The probability that an analog source neutron reaches the steel pocket is ~4e-5 (the product of the concrete attenuation and the pocket’s small solid angle), so an analog simulation with a few hundred histories essentially never tallies the steel, while even crude global weight windows allow particles to reach it reliably.

• Because the cavity sits near the surface, deep shielding (and thus a wide weight window dynamic range) exists only within the small solid angle subtended by the pocket, which keeps weight window splitting cheap and convergent and the whole model fast enough for regression testing.

Returns:

model – A deep-shielding model with a steel pocket behind a thick concrete shield

Return type:

openmc.Model