Ignoring negative volume components in mass-weighted averaging

armi/physics/neutronics/crossSectionGroupManager.py

@@ -451,13 +451,15 @@ def _getAverageComponentTemperature(self, compIndex):
         weights = np.array([self.getWeight(b) / b.getHeight() for b in blocks])
         weights /= weights.sum()  # normalize by total weight
         components = [sorted(b.getComponents())[compIndex] for b in blocks]
-        weightedAvgComponentMass = sum(w * c.getMass() for w, c in zip(weights, components))
+        weightedMass = [w * c.getMass() for w, c in zip(weights, components)]
+        weightedAvgComponentMass = sum(m for m in weightedMass if m > 0.0)
         if weightedAvgComponentMass == 0.0:
             # if there is no component mass (e.g., gap), do a regular average
             return np.mean(np.array([c.temperatureInC for c in components]))
         else:
             return (
-                weights.dot(np.array([c.temperatureInC * c.getMass() for c in components])) / weightedAvgComponentMass
+                sum([c.temperatureInC * mass if mass > 0.0 else 0.0 for c, mass in zip(components, weightedMass)])
+                / weightedAvgComponentMass
             )
 
     def _performAverageByComponent(self):
@@ -844,7 +846,10 @@ def _getAverageComponentNucs(self, components, bWeights):
         densities = np.zeros(len(allNucNames))
         totalWeight = 0.0
         for c, bWeight in zip(components, bWeights):
-            weight = bWeight * c.getArea()
+            compArea = c.getArea()
+            if compArea <= 0.0:
+                continue
+            weight = bWeight * compArea
             totalWeight += weight
             densities += weight * np.array(c.getNuclideNumberDensities(allNucNames))
         if totalWeight > 0.0:

armi/physics/neutronics/tests/test_crossSectionManager.py

@@ -27,6 +27,7 @@
 
 from armi import settings
 from armi.context import PLATFORM, Platform
+from armi.materials.water import Water
 from armi.physics.neutronics import crossSectionGroupManager
 from armi.physics.neutronics.const import CONF_CROSS_SECTION
 from armi.physics.neutronics.crossSectionGroupManager import (
@@ -585,6 +586,47 @@ def test_ComponentAverageDuctHet1DCylinder(self):
                         f"{nuc} temperature should be different from {compTemp} for component {c}",
                     )
 
+    def test_compAverageNegativeVolume(self):
+        """Test creation of a representative block when negative-volume components are present.
+
+        .. test:: Create representative blocks using a volume-weighted averaging.
+            :id: T_ARMI_XSGM_CREATE_REPR_BLOCKS2
+            :tests: R_ARMI_XSGM_CREATE_REPR_BLOCKS
+        """
+        xsgm = self.o.getInterface("xsGroups")
+        xsgm.interactBOL()
+
+        annularFuel = self.r.core.getAssemblies(Flags.FUEL | Flags.ANNULAR, includeBolAssems=True)[0]
+        # set temperatures of each gap component before performing average
+        # give the gaps some mass (material is arbitrary)
+        for i, b in enumerate(annularFuel.getBlocks(Flags.FUEL)):
+            gaps = b.getComponents(Flags.GAP)
+            for c in gaps:
+                c.temperatureInC = 500.0 + 100.0 * i
+                c.material = Water()
+                c.setNumberDensities({"H": 0.5, "O": 0.25})
+            # make some of the negative-volume gaps have positive volume by adjusting liner temperature
+            liner = b.getComponent(Flags.LINER | Flags.OUTER)
+            liner.setTemperature(500.0 + 100.0 * i)
+
+        xsgm.createRepresentativeBlocks()
+        xsgm.updateNuclideTemperatures()
+
+        reprBlock = xsgm.representativeBlocks["UA"]
+        for c in reprBlock.getComponents(Flags.GAP):
+            if c.getName() == "gap3":
+                # gap3 temp is 700 C because the 500 C and 600 C components have negative volume
+                self.assertAlmostEqual(c.temperatureInC, 700.0)
+            elif c.getName() == "gap4":
+                # gap4 temp is between 500 C and 600 C because the 700C component has negative volume
+                self.assertLess(c.temperatureInC, 600.0)
+                self.assertGreater(c.temperatureInC, 500.0)
+            else:
+                # other gap components all have positive volume
+                self.assertAlmostEqual(c.temperatureInC, 600.0)
+        outerLiner = reprBlock.getComponent(Flags.LINER | Flags.OUTER)
+        self.assertAlmostEqual(outerLiner.temperatureInC, 600.0)
+
     def test_checkComponentConsistency(self):
         xsgm = self.o.getInterface("xsGroups")
         xsgm.interactBOL()