Address comments by @pshriwise

docs/source/usersguide/geometry.rst

@@ -188,8 +188,8 @@ the :class:`openmc.Cell` class::
 
 In this example, an instance of :class:`openmc.Material` is assigned to the
 :attr:`Cell.fill` attribute. One can also fill a cell with a :ref:`universe
-<usersguide_universes>` or :ref:`lattice <usersguide_lattices>`. If you provide
-no fill to a cell, it will be filled with void on export to XML.
+<usersguide_universes>` or :ref:`lattice <usersguide_lattices>`. If no fill 
+is provided to a cell, it will be filled with void by default.
 
 The classes :class:`Halfspace`, :class:`Intersection`, :class:`Union`, and
 :class:`Complement` and all instances of :class:`openmc.Region` and can be

openmc/cell.py

@@ -89,9 +89,9 @@ class Cell(IDManagerMixin):
         :meth:`Cell.add_volume_information` method. For 'distribmat' cells
         it is the total volume of all instances.
     atoms : collections.OrderedDict
-        Mapping of nuclides to the total number of atoms for each nuclide present
-        in the cell, or in all of its instances for a 'distribmat' fill. For example,
-        {'U235': 1.0e22, 'U238': 5.0e22, ...}.
+        Mapping of nuclides to the total number of atoms for each nuclide
+        present in the cell, or in all of its instances for a 'distribmat'
+        fill. For example, {'U235': 1.0e22, 'U238': 5.0e22, ...}.
 
     """
 
@@ -140,10 +140,7 @@ class Cell(IDManagerMixin):
             string += '\t{0: <15}=\t{1}\n'.format('Temperature',
                                                   self.temperature)
         string += '{: <16}=\t{}\n'.format('\tTranslation', self.translation)
-
-        # Print volume only when it is set to avoid breaking regression
-        if self._volume is not None:
-            string += '{: <16}=\t{}\n'.format('\tVolume', self.volume)
+        string += '{: <16}=\t{}\n'.format('\tVolume', self.volume)
 
         return string
 
@@ -364,13 +361,7 @@ class Cell(IDManagerMixin):
     def volume(self, volume):
         if volume is not None:
             cv.check_type('cell volume', volume, (Real, UFloat))
-
-            # Note that ufloat(0.0, 0.1) >= 0.0 is False
-            # We need special treatment for UFloat input
-            val = volume
-            if isinstance(val, UFloat):
-                val = volume.nominal_value
-            cv.check_greater_than('cell volume', val, 0.0)
+            cv.check_greater_than('cell volume', volume, 0.0, equality=True)
 
         self._volume = volume
 

tests/regression_tests/distribmat/results_true.dat

@@ -7,3 +7,4 @@ Cell
 	Region         =	-9
 	Rotation       =	None
 	Translation    =	None
+	Volume         =	None

tests/regression_tests/multipole/results_true.dat

@@ -39,3 +39,4 @@ Cell
 	Rotation       =	None
 	Temperature    =	[500. 700.   0. 800.]
 	Translation    =	None
+	Volume         =	None

tests/unit_tests/test_cell.py

@@ -130,13 +130,13 @@ def test_volume_setting():
     c.volume = 3
     c.volume = u.ufloat(3, 0.7)
 
-    # Test errors for -ve and 0 volume
-    with pytest.raises(ValueError):
-        c.volume = 0.0
+    # Allow volume to be set to 0.0
+    c.volume = 0.0
+    c.volume = u.ufloat(0.0, 0.1)
+
+    # Test errors for -ve volume
     with pytest.raises(ValueError):
         c.volume = -1.0
-    with pytest.raises(ValueError):
-        c.volume = u.ufloat(0.0, 0.1)
     with pytest.raises(ValueError):
         c.volume = u.ufloat(-0.05, 0.1)