I was making some flux distribution plots over my reactor when I noticed an artifact with the control drums. I am using openmc.Plane surfaces to cut the 120-degree B4C surface of the control drum out of the cylinder, but it appears that these surfaces are somehow affecting the neutron flux distribution. I noticed this in flux map 1, which is the distribution for the exact core geometry shown in the first image. If you look closely there is a shadow ‘X’ in the control drums where the planes are, which I assumed was some kind of flux shadow cast by the B4C. I rotated the drums to halfway (control surfaces facing away from each other in each pair) and extracted the rods a bit to change the flux shape and got the third image, flux map 2. On the second flux map the ‘X’ inscribed in the control drums is even more apparent and could not be caused by the B4C. This isn’t causing any problems I don’t think, but I thought it was weird that it should appear exactly where the two planes used to slice the drum regions intersect. For reference the flux maps are 4 meters by 4 meters and each pixel represents 0.25 cm2 of area in the core. It is a 2D mesh tally and there is nothing above or below the geometry shown that would cause this.
Core Geometry:
Flux Map 1 (Drums in):
Flux Map 2 (Drums rotated to half):
