Hello,
I am using OpenMC to generate multi-group cross sections for a reactor model, with 8-group and 18-group energy structures. I am encountering an issue that appears only when running simulations with a very large number of particles (on the order of billions).
At high particle counts, the inverse neutron velocity becomes equal to zero for some specific regions, but only in the highest energy group. For lower numbers of particles, this issue appears in fewer regions, and when using a relatively small number of particles, the inverse velocity is always non-zero in all regions and energy groups.
Has anyone encountered a similar issue before, or does anyone have insight into what could cause this behavior?
Thank you in advance.