documentation

armi/reactor/tests/test_blocks.py

@@ -1632,7 +1632,10 @@ def test_getPitchHomogenousBlock(self):
         # The rectangle outer dimensions is defined by the pitch of the block/assembly.
         # the inner dimensions is defined by whatever thickness is necessary to have
         # the desired area fraction.
-        # The second way is shown in the second half of this test.
+        # The second way is to define all physical material components as unshaped, and
+        # add an additional infinitely thin Void component (no area) that defines pitch.
+        # See second part of HexBlock_TestCase.test_getPitchHomogenousBlock for
+        # demonstration.
         cartBlock = blocks.CartesianBlock("TestCartBlock")
 
         hexComponentArea = areaFractions[0] * rectTotalArea
@@ -1672,34 +1675,6 @@ def test_getPitchHomogenousBlock(self):
         self.assertAlmostEqual(rectTotalArea, cartBlock.getMaxArea())
         self.assertAlmostEqual(sum(c.getArea() for c in cartBlock), rectTotalArea)
 
-        # For this second way, we will simply define the 3 components as unshaped, with
-        # the desired area fractions, and make a 4th component that is an infinitely
-        # thin rectangle with desired pitch. the downside of this method is that now
-        # the block has a fourth component with no volume.
-        cartBlock = blocks.CartesianBlock("TestCartBlock")
-        for aFrac, material in zip(areaFractions, materials):
-            unshapedArgs = {"area": rectTotalArea * aFrac}
-            unshapedArgs.update(compArgs)
-            name = f"unshaped {material}"
-            comp = components.UnshapedComponent(name, material, **unshapedArgs)
-            cartBlock.addComponent(comp)
-
-        # We haven't set a pitch defining component this time so set it now with 0 area.
-        pitchDefiningComponent = components.Rectangle(
-            "pitchComp",
-            "Void",
-            lengthOuter=desiredPitch[0],
-            lengthInner=desiredPitch[0],
-            widthOuter=desiredPitch[1],
-            widthInner=desiredPitch[1],
-            mult=1,
-            **compArgs,
-        )
-        cartBlock.addComponent(pitchDefiningComponent)
-        self.assertEqual(desiredPitch, cartBlock.getPitch())
-        self.assertAlmostEqual(rectTotalArea, cartBlock.getMaxArea())
-        self.assertAlmostEqual(sum(c.getArea() for c in cartBlock), rectTotalArea)
-
 
 class MassConservationTests(unittest.TestCase):
     r"""

armi/tests/refSmallReactor.yaml

@@ -358,14 +358,6 @@ blocks:
         coolant: *component_fuel_coolant
         duct: *component_fuel_duct
         intercoolant: *component_fuel_intercoolant
-    homog fuel:
-        fuel:
-            shape: UnshapedComponent
-            material: UZr
-            Tinput: 25.0
-            Thot: 25.0
-            area: 100.0
-            op: 1.5
 assemblies:
     heights: &standard_heights [25.0, 25.0, 25.0, 25.0, 75.0]
     axial mesh points: &standard_axial_mesh_points [1, 1, 1, 1, 4]

doc/user/inputs/blueprints.rst

@@ -597,11 +597,85 @@ Here is a complete fuel block definition::
                     od: 0.1
 
 
-.. note::
+Making blocks with unshaped components
+--------------------------------------
 
-    Purely homogeneous blocks can most easily be modeled as a series of generic ``Components`` for
-    each material type (*e.g.*, SS316, Sodium) in the block. In such a case, the homogeneous block
-    should contain at least one ``Component`` with the hexagonal outer pitch (``op)`` specified.
+Sometimes you will want to make a homogenous block,  which is a mixture of multiple
+materials, and will not want to define an exact shape for each of the components in
+the block. In this case unshaped components can be used, but ARMI still requires there
+to be at least one component with shape to define the pitch of the block.
+
+In the example below, the block is a rectangular pitch so one of the
+components is defined as a rectangle to indicate this. Its outer dimensions determine
+the pitch of the block. The inner dimensions can be whatever is necessary to
+preserve the area fraction. Note that rectangular blocks have pitch defined by two
+numbers, since they may not be a square. In this case the rectangle component is half
+the area fraction and the other two components are one quarter::
+
+        blocks:
+            fuel:
+                clad:
+                    shape: Rectangle
+                    material: HT9
+                    Tinput: 25.0
+                    Thot: 25.0
+                    lengthOuter: 3.0
+                    lengthInner: 2.4
+                    widthOuter: 2.0
+                    widthInner: 1.25
+                    mult:1.0
+                fuel:
+                    shape: UnshapedComponent
+                    material: UZr
+                    Tinput: 25.0
+                    Thot: 25.0
+                    area = 1.5
+                coolant:
+                    shape: UnshapedComponent
+                    material: Sodium
+                    Tinput: 25.0
+                    Thot: 25.0
+                    area = 1.5
+
+.. warning:: When using this method avoid thermal expansion by setting TInput=THot, or
+   your pitch component dimensions might change, thus changing your pitch.
+
+
+Alternatively, a void (empty) component with zero area can be added for defining the
+pitch, and then all three components can be defined as unshaped. The downside, is there
+are now four components, but only three that have actual area and composition::
+
+        blocks:
+            fuel:
+                clad:
+                    shape: UnshapedComponent
+                    material: HT9
+                    Tinput: 25.0
+                    Thot: 25.0
+                    area: 3.0
+                fuel:
+                    shape: UnshapedComponent
+                    material: UZr
+                    Tinput: 25.0
+                    Thot: 25.0
+                    area = 1.5
+                coolant:
+                    shape: UnshapedComponent
+                    material: Sodium
+                    Tinput: 25.0
+                    Thot: 25.0
+                    area = 1.5
+                PitchDefiningComponent:
+                    shape: Rectangle
+                    material: Void
+                    lengthOuter: 3.0
+                    lengthInner: 3.0
+                    widthOuter: 2.0
+                    widthInner: 2.0
+                    mult:1.0
+
+
+This can similarly be done for hex geometry and and a hexagon with Outer Pitch (`op`).
 
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