I’m doing criticality calculations for a model consisting of a sphere of U-7wt%Mo enriched at 20 at.% surrounded by water (I’m attaching the input file). The resultant keff is 0.52281 when running with OpenMC, and 0.43593 when running with MCNP. Both models use the same cross-section data libraries, number of particles, and number of active and inactive batches. Any suggestions why is there such big difference in the keff? I have tried running for more a critical system by increasing the enrichment, and difference is still large ( ~9%). Increasing the number of particles, and inactive and active batches by a factor of 10 does not make any difference either.
U-7Mo.py (1.38 KB)