Fix OpenCG compatibility module to work with simple cells

openmc/opencg_compatible.py

@@ -9,6 +9,8 @@ except ImportError:
     raise ImportError(msg)
 
 import openmc
+from openmc.region import Intersection
+from openmc.surface import Halfspace
 
 
 # A dictionary of all OpenMC Materials created
@@ -480,12 +482,24 @@ def get_opencg_cell(openmc_cell):
     if openmc_cell._translation is not None:
         opencg_cell.setTranslation(openmc_cell._translation)
 
-    surfaces = openmc_cell._surfaces
-
-    for surface_id in surfaces:
-        surface = surfaces[surface_id][0]
-        halfspace = surfaces[surface_id][1]
+    # Add surfaces to OpenCG cell from OpenMC cell region. Right now this only
+    # works if the region is a single half-space or an intersection of
+    # half-spaces, i.e., no complex cells.
+    region = openmc_cell.region
+    if isinstance(region, Halfspace):
+        surface = region.surface
+        halfspace = -1 if region.side == '-' else 1
         opencg_cell.addSurface(get_opencg_surface(surface), halfspace)
+    elif isinstance(region, Intersection):
+        for node in region.nodes:
+            if not isinstance(node, Halfspace):
+                raise NotImplementedError("Complex cells not yet supported "
+                                          "in OpenCG.")
+            surface = node.surface
+            halfspace = -1 if node.side == '-' else 1
+            opencg_cell.addSurface(get_opencg_surface(surface), halfspace)
+    else:
+        raise NotImplementedError("Complex cells not yet supported in OpenCG.")
 
     # Add the OpenMC Cell to the global collection of all OpenMC Cells
     OPENMC_CELLS[cell_id] = openmc_cell