thank you very much for your help...I thought the problem was more complicated than that :). My problem with the hexagonal lattice is that I have to limit it to a 7x7 lattice and try to put it in a "circular" cluster surface. Maybe, it would be easier to adjust the dimensions in the cluster...
I have been encountering "zero lattice element hit" when I try to run it in MCNP5. The input file is provided below. The square lattice runs fine, but the hexagonal does not. Hope someone can help me here. Thank you.