Shape of bounds of cylindrical weight window mesh?

[kingyue]

For example, if len(mesh.r_grid) is 3 and len(mesh.z_grid) is 2

Shape of openmc.WeightWindows.lower_ww_bounds should be

[[0,0,0],[0,0,0]]

or

[[0,0],[0,0],[0,0]]

?

[kingyue]

related issue: Weight window bounds ordering · Issue #2123 · openmc-dev/openmc (github.com)