Adding block for positive side of spheres and adding a nested spheres…

… test

src/openmc_cad_adapter/surfaces.py

@@ -283,6 +283,11 @@ def to_cubit_surface_inner(self, ent_type, node, extents, inner_world=None, hex=
         cad_cmds.append( f"sphere radius {self.r}")
         ids = emit_get_last_id(ent_type, cad_cmds)
         move(ids, self.x0, self.y0, self.z0, cad_cmds)
+        if node.side != '-':
+            cad_cmds.append( f"brick x {extents[0]} y {extents[1]} z {extents[2]}" )
+            wid = emit_get_last_id( ent_type , cad_cmds)
+            cad_cmds.append(f"subtract body {{ {ids} }} from body {{ {wid} }}")
+            ids = wid
         return ids, cad_cmds
 
     @classmethod

test/gold/nested_spheres.jou

@@ -0,0 +1,28 @@
+set echo off
+set info off
+set warning off
+graphics pause
+set journal off
+set default autosize off
+#CELL 4
+sphere radius 30.0
+#{ id1 = Id("body") }
+body { id1 } name "Cell_4"
+group "mat:void" add body { id1 } 
+#CELL 3
+sphere radius 20.0
+#{ id2 = Id("body") }
+body { id2 } name "Cell_3"
+group "mat:void" add body { id2 } 
+#CELL 2
+sphere radius 10.0
+#{ id3 = Id("body") }
+body { id3 } name "Cell_2"
+group "mat:void" add body { id3 } 
+graphics flush
+set default autosize on
+zoom reset
+set echo on
+set info on
+set warning on
+set journal on

test/test_local.py

@@ -34,6 +34,20 @@ def test_planes(request, run_in_tmpdir):
     diff_gold_file('plane.jou')
 
 
+def test_nested_spheres(request, run_in_tmpdir):
+    inner_sphere = openmc.Sphere(r=10.0)
+    middle_sphere = openmc.Sphere(r=20.0)
+    outer_sphere = openmc.Sphere(r=30.0)
+
+    inner_cell = openmc.Cell(region=-inner_sphere)
+    middle_cell = openmc.Cell(region=-middle_sphere)
+    outer_cell = openmc.Cell(region=-outer_sphere)
+
+    g = openmc.Geometry([outer_cell, middle_cell, inner_cell])
+    to_cubit_journal(g, world=(500, 500, 500), filename='nested_spheres.jou')
+    diff_gold_file('nested_spheres.jou')
+
+
 # Test the XCylinder and YCylinder classes, the ZCylinder surface is tested
 # extensively in the OpenMC example tests
 @reset_openmc_ids