Set DAGMC cell instances on surface crossing (#3052)

src/particle.cpp

@@ -557,9 +557,14 @@ void Particle::cross_surface(const Surface& surf)
     sqrtkT_last() = sqrtkT();
     // set new cell value
     lowest_coord().cell = i_cell;
+    auto& cell = model::cells[i_cell];
+
     cell_instance() = 0;
-    material() = model::cells[i_cell]->material_[0];
-    sqrtkT() = model::cells[i_cell]->sqrtkT_[0];
+    if (cell->distribcell_index_ >= 0)
+      cell_instance() = cell_instance_at_level(*this, n_coord() - 1);
+
+    material() = cell->material(cell_instance());
+    sqrtkT() = cell->sqrtkT(cell_instance());
     return;
   }
 #endif

tests/regression_tests/dagmc/universes/inputs_true.dat

@@ -47,9 +47,18 @@
     <run_mode>eigenvalue</run_mode>
     <particles>100</particles>
     <batches>10</batches>
-    <inactive>2</inactive>
+    <inactive>5</inactive>
     <output>
       <summary>false</summary>
     </output>
   </settings>
-  </model>
+  <tallies>
+    <filter id="1" type="cellinstance">
+      <bins>4 0 4 1 4 2 4 3 4 4</bins>
+    </filter>
+    <tally id="1" name="cell instance tally">
+      <filters>1</filters>
+      <scores>scatter</scores>
+    </tally>
+  </tallies>
+</model>

tests/regression_tests/dagmc/universes/results_true.dat

@@ -1,2 +1,13 @@
 k-combined:
-9.156561E-01 4.398617E-02
+9.887663E-01 1.510336E-02
+tally 1:
+4.340758E+00
+4.265459E+00
+4.712319E+00
+4.654778E+00
+4.151897E+00
+3.588090E+00
+2.965925E+00
+1.852746E+00
+0.000000E+00
+0.000000E+00

tests/regression_tests/dagmc/universes/test.py

@@ -72,13 +72,20 @@ def __init__(self, *args, **kwargs):
 
         self._model.geometry = openmc.Geometry([bounding_cell])
 
+        # add a cell instance tally
+        tally = openmc.Tally(name='cell instance tally')
+        # using scattering
+        cell_instance_filter = openmc.CellInstanceFilter(((4, 0), (4, 1), (4, 2), (4, 3), (4, 4)))
+        tally.filters = [cell_instance_filter]
+        tally.scores = ['scatter']
+        self._model.tallies = [tally]
+
         # settings
         self._model.settings.particles = 100
         self._model.settings.batches = 10
-        self._model.settings.inactive = 2
+        self._model.settings.inactive = 5
         self._model.settings.output = {'summary' : False}
 
-
 def test_univ():
     harness = DAGMCUniverseTest('statepoint.10.h5', model=openmc.Model())
     harness.main()