From 7fcc20472690c49cf2b0508b099dc440b6249dc4 Mon Sep 17 00:00:00 2001
From: Paul Romano <paul.k.romano@gmail.com>
Date: Mon, 23 May 2022 14:43:34 -0500
Subject: [PATCH] Implement Material.get_nuclide_atoms method

---
 openmc/material.py                | 19 +++++++++++++++++++
 tests/unit_tests/test_material.py | 10 ++++++++++
 2 files changed, 29 insertions(+)

diff --git a/openmc/material.py b/openmc/material.py
index 073dab7121..ea42d64b16 100644
--- a/openmc/material.py
+++ b/openmc/material.py
@@ -858,6 +858,25 @@ class Material(IDManagerMixin):
 
         return nuclides
 
+    def get_nuclide_atoms(self):
+        """Return number of atoms of each nuclide in the material
+
+        .. versionadded:: 0.13.1
+
+        Returns
+        -------
+        dict
+            Dictionary whose keys are nuclide names and values are number of
+            atoms present in the material.
+
+        """
+        if self.volume is None:
+            raise ValueError("Volume must be set in order to determine atoms.")
+        atoms = {}
+        for nuclide, atom_per_bcm in self.get_nuclide_atom_densities().items():
+            atoms[nuclide] = 1.0e24 * atom_per_bcm * self.volume
+        return atoms
+
     def get_mass_density(self, nuclide=None):
         """Return mass density of one or all nuclides
 
diff --git a/tests/unit_tests/test_material.py b/tests/unit_tests/test_material.py
index 374b5a3d8a..fd0e4f6247 100644
--- a/tests/unit_tests/test_material.py
+++ b/tests/unit_tests/test_material.py
@@ -294,6 +294,16 @@ def test_get_nuclide_atom_densities(uo2):
         assert density > 0
 
 
+def test_get_nuclide_atoms():
+    mat = openmc.Material()
+    mat.add_nuclide('Li6', 1.0)
+    mat.set_density('atom/cm3', 3.26e20)
+    mat.volume = 100.0
+
+    atoms = mat.get_nuclide_atoms()
+    assert atoms['Li6'] == pytest.approx(mat.density * mat.volume)
+
+
 def test_mass():
     m = openmc.Material()
     m.add_nuclide('Zr90', 1.0, 'wo')