Document and test the default Chain fission yields

openmc/deplete/chain.py

@@ -375,9 +375,19 @@ class Chain(object):
             tree.write(str(filename), encoding='utf-8')
 
     def get_thermal_fission_yields(self):
-        """Return dictionary {str: {str: float}}"""
-        # Take lowest energy for back compatability
-        # Should be removed by end of this feature
+        """Return fission yields at lowest incident neutron energy
+
+        Used as the default set of fission yields for :meth:`form_matrix`
+        if ``fission_yields`` are not provided
+
+        Returns
+        -------
+        fission_yields : dict
+            Dictionary of ``{parent : {product : f_yield}}``
+            where ``parent`` and ``product`` are both string
+            names of nuclides with yield data and ``f_yield``
+            is a float for the fission yield.
+        """
         out = {}
         for nuc in self.nuclides:
             if len(nuc.yield_data) == 0:
@@ -393,14 +403,20 @@ class Chain(object):
         ----------
         rates : numpy.ndarray
             2D array indexed by (nuclide, reaction)
-        fission_yields : dictionary of tuple to float, optional
-            Option to use a custom set of fission yields
+        fission_yields : dict, optional
+            Option to use a custom set of fission yields. Expected
+            to be of the form ``{parent : {product : f_yield}}``
+            with string nuclide names for ``parent`` and ``product``,
+            and ``f_yield`` as the respective fission yield
 
         Returns
         -------
         scipy.sparse.csr_matrix
             Sparse matrix representing depletion.
 
+        See Also
+        --------
+        :meth:`get_thermal_fission_yields`
         """
         matrix = defaultdict(float)
         reactions = set()

tests/unit_tests/test_deplete_chain.py

@@ -230,6 +230,7 @@ def test_form_matrix(simple_chain):
     for r, c in product(range(3), range(3)):
         assert new_mat[r, c] == mat[r, c]
 
+
 def test_getitem():
     """ Test nuc_by_ind converter function. """
     chain = Chain()
@@ -338,3 +339,10 @@ def test_capture_branch_failures(simple_chain):
     br = {"C": {"A": 1.0, "B": 1.0}}
     with pytest.raises(ValueError, match="C ratios"):
         simple_chain.set_capture_branches(br)
+
+
+def test_simple_fission_yields(simple_chain):
+    """Check the default fission yields that can be used to form the matrix
+    """
+    fission_yields = simple_chain.get_thermal_fission_yields()
+    assert fission_yields == {"C": {"A": 0.0292737, "B": 0.002566345}}