Number density bug fix

armi/reactor/blueprints/blockBlueprint.py

@@ -119,12 +119,12 @@ def construct(
             if cs["inputHeightsConsideredHot"]:
                 if "group" in c.name:
                     for component in c:
-                        component.applyHotHeightDensityReduction()
+                        component.adjustNDensForHotHeight()
                         componentBlueprint.insertDepletableNuclideKeys(
                             component, blueprint
                         )
                 else:
-                    c.applyHotHeightDensityReduction()
+                    c.adjustNDensForHotHeight()
                     componentBlueprint.insertDepletableNuclideKeys(c, blueprint)
             components[c.name] = c
             if spatialGrid:

armi/reactor/components/component.py

@@ -232,7 +232,7 @@ def __init__(
         self.temperatureInC = Thot
         self.material = None
         self.setProperties(material)
-        self.applyMaterialMassFracsToNumberDensities()  # not necessary when duplicating...
+        self.setNDensFromMassFracsAtTempInC()  # not necessary when duplicating...
         self.setType(name)
         self.p.mergeWith = mergeWith
         self.p.customIsotopicsName = isotopics
@@ -327,42 +327,44 @@ def setProperties(self, properties):
         self.material.parent = self
         self.clearLinkedCache()
 
-    def applyMaterialMassFracsToNumberDensities(self):
+    def setNDensFromMassFracsAtTempInC(self):
         """
-        Set initial (cold) number densities of this component based Material composition.
+        Set number densities for the component based on material mass fractions using hot temperatures.
+
+        Notes
+        -----
+        - the density returned accounts for the radial expansion of the component
+          due to the difference in self.inputTemperatureInC and self.temperatureInC
+        - axial expansion effects are not included here.
+
+        See Also
+        --------
+        self.adjustNDensForHotHeight
         """
-        density = self.material.getProperty("density", Tc=self.inputTemperatureInC)
+        density = self.material.getProperty("density", Tc=self.temperatureInC)
 
         self.p.numberDensities = densityTools.getNDensFromMasses(
             density, self.material.p.massFrac
         )
 
-    def applyHotHeightDensityReduction(self):
+    def adjustNDensForHotHeight(self):
         """
-        Set initial (hot) number densities of this component based Material composition.
+        Adjust number densities to account for prescribed hot block heights (axial expansion).
 
         Notes
         -----
-        We apply the hot-height density reduction here to account for pre-expanded
-        block heights in blueprints.
-        Future temperature changes can be handled by multiplications of 1/(1+dLL)**2
-        instead of 1/(1+dLL)**3 since we have pre-expanded in the axial direction.
-        """
-        denistyIfNotPreExpandedAxially = self.material.getProperty(
-            "density", self.temperatureInK
-        )
+        - We apply this hot height density reduction to account for pre-expanded
+          block heights in blueprints.
+        - This is called when inputHeightsConsideredHot: True.
 
-        # axial expansion factor must be applied because ARMI expects hot heights
-        # to be entered on assemblies in the blueprints  so that it doesn't have to
-        # handle the problem of fuel axially expanding at a different rate than clad.
+        See Also
+        --------
+        self.setNDensFromMassFracsAtTempInC
+        """
         axialExpansionFactor = 1.0 + self.material.linearExpansionFactor(
             self.temperatureInC, self.inputTemperatureInC
         )
-
-        self.p.numberDensities = densityTools.getNDensFromMasses(
-            denistyIfNotPreExpandedAxially / axialExpansionFactor,
-            self.material.p.massFrac,
-        )
+        self.changeNDensByFactor(1.0 / axialExpansionFactor)
 
     def getProperties(self):
         """Return the active Material object defining thermo-mechanical properties."""

armi/reactor/converters/tests/test_blockConverter.py

@@ -55,7 +55,7 @@ def _perturbTemps(self, block, cName, tCold, tHot):
         "Give the component different ref and hot temperatures than in test_Blocks."
         c = block.getComponent(Flags.fromString(cName))
         c.refTemp, c.refHot = tCold, tHot
-        c.applyHotHeightDensityReduction()
+        c.adjustNDensForHotHeight()
         c.setTemperature(tHot)
         return block
 

armi/reactor/tests/test_blocks.py

@@ -2259,7 +2259,7 @@ def test_coldMass(self):
         and hot height.
         """
         fuel = self.b.getComponent(Flags.FUEL)
-        fuel.applyHotHeightDensityReduction()
+        fuel.adjustNDensForHotHeight()
         # set ref (input/cold) temperature.
         Thot = fuel.temperatureInC
         Tcold = fuel.inputTemperatureInC

armi/reactor/tests/test_components.py

@@ -215,7 +215,7 @@ def test_getComponentArea(self):
         )
 
         # show that area expansion is consistent with the density change in the material
-        self.component.applyHotHeightDensityReduction()
+        self.component.adjustNDensForHotHeight()
         hotDensity = self.component.density()
         hotArea = self.component.getArea()
         thermalExpansionFactor = self.component.getThermalExpansionFactor(
@@ -231,7 +231,7 @@ def test_getComponentArea(self):
                 area=math.pi,
             )
         )
-        coldComponent.applyHotHeightDensityReduction()
+        coldComponent.adjustNDensForHotHeight()
         coldDensity = coldComponent.density()
         coldArea = coldComponent.getArea()
 
@@ -493,6 +493,15 @@ def test_changeNumberDensities(self):
         self.component.changeNDensByFactor(3.0)
         self.assertEqual(self.component.getNumberDensity("NA23"), 3.0)
 
+    def test_MassConserved(self):
+        """Demonstrate that mass is conserved at different temperatures."""
+        circle1 = Circle("circle", "HT9", 20, 300, 1.0)
+        circle2 = Circle("circle", "HT9", 20, 600, 1.0)
+        self.assertAlmostEqual(
+            circle1.p.numberDensities["FE"] * circle1.getArea(),
+            circle2.p.numberDensities["FE"] * circle2.getArea(),
+        )
+
 
 class TestTriangle(TestShapedComponent):
     componentCls = Triangle

doc/release/0.2.rst

@@ -37,6 +37,7 @@ Bug fixes
 #. Remove ``copy.deepcopy`` from ``armi/reactor/converters/uniformMesh.py``
 #. Clarify docstring for ``armi/reactor/components/complexShapes.py::Helix``
 #. Bug fix in ``armi/reactor/components/complexShapes.py::Helix::getCircleInnerDiameter``
+#. Bug fix and clarity improvements for how number densities are initialized for components.
 #. TBD