Merge pull request #2142 from shimwell/adding_specific_activity

added specific_activity to openmc.Material

openmc/material.py

@@ -91,10 +91,6 @@ class Material(IDManagerMixin):
     fissionable_mass : float
         Mass of fissionable nuclides in the material in [g]. Requires that the
         :attr:`volume` attribute is set.
-    activity : float
-        Activity of the material in [Bq]. Requires that the :attr:`volume`
-        attribute is set.
-
     """
 
     next_id = 1
@@ -150,11 +146,6 @@ class Material(IDManagerMixin):
 
         return string
 
-    @property
-    def activity(self):
-        """Returns the total activity of the material in Becquerels."""
-        return sum(self.get_nuclide_activity().values())
-
     @property
     def name(self):
         return self._name
@@ -908,22 +899,46 @@ class Material(IDManagerMixin):
 
         return nuclides
 
-    def get_nuclide_activity(self):
-        """Return activity in [Bq] for each nuclide in the material
+    def get_activity(self, units: str = 'Bq/cm3', by_nuclide: bool = False):
+        """Returns the activity of the material or for each nuclide in the
+        material in units of [Bq], [Bq/g] or [Bq/cm3].
 
         .. versionadded:: 0.13.1
 
+        Parameters
+        ----------
+        units : {'Bq', 'Bq/g', 'Bq/cm3'}
+            Specifies the type of activity to return, options include total
+            activity [Bq], specific [Bq/g] or volumetric activity [Bq/cm3].
+            Default is volumetric activity [Bq/cm3].
+        by_nuclide : bool
+            Specifies if the activity should be returned for the material as a
+            whole or per nuclide. Default is False.
+
         Returns
         -------
-        dict
-            Dictionary whose keys are nuclide names and values are activity in
-            [Bq].
+        Union[dict, float]
+            If by_nuclide is True then a dictionary whose keys are nuclide 
+            names and values are activity is returned. Otherwise the activity
+            of the material is returned as a float.
         """
+
+        cv.check_value('units', units, {'Bq', 'Bq/g', 'Bq/cm3'})
+        cv.check_type('by_nuclide', by_nuclide, bool)
+
+        if units == 'Bq':
+            multiplier = self.volume
+        elif units == 'Bq/cm3':
+            multiplier = 1
+        elif units == 'Bq/g':
+            multiplier = 1.0 / self.get_mass_density()
+
         activity = {}
-        for nuclide, atoms in self.get_nuclide_atoms().items():
+        for nuclide, atoms_per_bcm in self.get_nuclide_atom_densities().items():
             inv_seconds = openmc.data.decay_constant(nuclide)
-            activity[nuclide] = inv_seconds * atoms
-        return activity
+            activity[nuclide] = inv_seconds * 1e24 * atoms_per_bcm * multiplier
+
+        return activity if by_nuclide else sum(activity.values())
 
     def get_nuclide_atoms(self):
         """Return number of atoms of each nuclide in the material

tests/unit_tests/test_material.py

@@ -471,28 +471,46 @@ def test_mix_materials():
     assert m5.density == pytest.approx(dens5)
 
 
-def test_activity_of_stable():
-    """Creates a material with stable isotopes to checks the activity is 0"""
+def test_get_activity():
+    """Tests the activity of stable, metastable and active materials"""
+
+    # Creates a material with stable isotopes to check the activity is 0
     m1 = openmc.Material()
-    m1.add_element("Fe", 1)
-    m1.set_density('g/cm3', 1)
+    m1.add_element("Fe", 0.7)
+    m1.add_element("Li", 0.3)
+    m1.set_density('g/cm3', 1.5)
+    # activity in Bq/cc and Bq/g should not require volume setting
+    assert m1.get_activity(units='Bq/cm3') == 0
+    assert m1.get_activity(units='Bq/g') == 0
     m1.volume = 1
-    assert m1.activity == 0
+    assert m1.get_activity(units='Bq') == 0
 
+    # Checks that 1g of tritium has the correct activity scaling
+    m2 = openmc.Material()
+    m2.add_nuclide("H3", 1)
+    m2.set_density('g/cm3', 1)
+    m2.volume = 1
+    assert pytest.approx(m2.get_activity(units='Bq')) == 3.559778e14
+    m2.set_density('g/cm3', 2)
+    assert pytest.approx(m2.get_activity(units='Bq')) == 3.559778e14*2
+    m2.volume = 3
+    assert pytest.approx(m2.get_activity(units='Bq')) == 3.559778e14*2*3
 
-def test_activity_of_tritium():
-    """Checks that 1g of tritium has the correct activity"""
-    m1 = openmc.Material()
-    m1.add_nuclide("H3", 1)
-    m1.set_density('g/cm3', 1)
-    m1.volume = 1
-    assert pytest.approx(m1.activity) == 3.559778e14
+    # Checks that 1 mol of a metastable nuclides has the correct activity
+    m3 = openmc.Material()
+    m3.add_nuclide("Tc99_m1", 1)
+    m3.set_density('g/cm3', 1)
+    m3.volume = 98.9
+    assert pytest.approx(m3.get_activity(units='Bq'), rel=0.001) == 1.93e19
 
-
-def test_activity_of_metastable():
-    """Checks that 1 mol of a Tc99_m1 nuclides has the correct activity"""
-    m1 = openmc.Material()
-    m1.add_nuclide("Tc99_m1", 1)
-    m1.set_density('g/cm3', 1)
-    m1.volume = 98.9
-    assert pytest.approx(m1.activity, rel=0.001) == 1.93e19
+    # Checks that specific and volumetric activity of tritium are correct
+    m4 = openmc.Material()
+    m4.add_nuclide("H3", 1)
+    m4.set_density('g/cm3', 1.5)
+    assert pytest.approx(m4.get_activity(units='Bq/g')) == 355978108155965.94  # [Bq/g]
+    assert pytest.approx(m4.get_activity(units='Bq/g', by_nuclide=True)["H3"]) == 355978108155965.94  # [Bq/g]
+    assert pytest.approx(m4.get_activity(units='Bq/cm3')) == 355978108155965.94*3/2 # [Bq/cc]
+    assert pytest.approx(m4.get_activity(units='Bq/cm3', by_nuclide=True)["H3"]) == 355978108155965.94*3/2 # [Bq/cc]
+    # volume is required to calculate total activity
+    m4.volume = 10.
+    assert pytest.approx(m4.get_activity(units='Bq')) == 355978108155965.94*3/2*10 # [Bq]