Update documentation describing HexLattice orientation (#3709)

Author: paulromano

docs/source/io_formats/geometry.rst

@@ -316,9 +316,10 @@ the following attributes or sub-elements:
     *Default*: None
 
   :orientation:
-    The orientation of the hexagonal lattice. The string "x" indicates that two
-    sides of the lattice are parallel to the x-axis, whereas the string "y"
-    indicates that two sides are parallel to the y-axis.
+    The orientation of the hexagonal lattice. The string "x" indicates that each
+    lattice element has two faces that are perpendicular to the x-axis, whereas
+    the string "y" indicates that each lattice element has two faces that are
+    perpendicular to the y-axis.
 
     *Default*: "y"
 

docs/source/usersguide/geometry.rst

@@ -415,11 +415,11 @@ to help figure out how to place universes::
 
 
 Note that by default, hexagonal lattices are positioned such that each lattice
-element has two faces that are parallel to the :math:`y` axis. As one example,
-to create a three-ring lattice centered at the origin with a pitch of 10 cm
-where all the lattice elements centered along the :math:`y` axis are filled with
-universe ``u`` and the remainder are filled with universe ``q``, the following
-code would work::
+element has two faces that are perpendicular to the :math:`y` axis. As one
+example, to create a three-ring lattice centered at the origin with a pitch of
+10 cm where all the lattice elements centered along the :math:`y` axis are
+filled with universe ``u`` and the remainder are filled with universe ``q``, the
+following code would work::
 
   hexlat = openmc.HexLattice()
   hexlat.center = (0, 0)

openmc/lattice.py

@@ -1083,8 +1083,11 @@ class HexLattice(Lattice):
         from the outermost ring), and i is the index with a ring starting from
         the top and proceeding clockwise.
     orientation : {'x', 'y'}
-        str by default 'y' orientation of main lattice diagonal another option
-        - 'x'
+        The orientation of the lattice. The 'x' orientation means that each
+        lattice element has two faces that are perpendicular to the x-axis,
+        while the 'y' orientation means that each lattice element has two faces
+        that are perpendicular to the y-axis. By default, the orientation is
+        'y'.
     num_rings : int
         Number of radial ring positions in the xy-plane
     num_axial : int