Can we define a hexagonal mesh for tallying over hexagonal assemblies?
There is no equivalent of a “hexagonal mesh” tally the same way there is a rectangular mesh tally. However, there is a new feature in the next release of OpenMC called “distribcell” filters which should allow you to obtain tallies over hexagonal lattices easily. It works the same way as a cell filter, but it will return separate tallies for each instance of the cell that appears throughout the geometry.
Best,
Paul