Read in material temperatures from xml subelement

Closes #1280 by reading the temperature from an xml
subelement as it is written, not an attribute.

Added loading of temperature and volume material attributes
from xml in unit test

openmc/material.py

@@ -931,8 +931,11 @@ class Material(IDManagerMixin):
         mat_id = int(elem.get('id'))
         mat = cls(mat_id)
         mat.name = elem.get('name')
-        if 'temperature' in elem.attrib:
-            mat.temperature = float(elem.get('temperature'))
+
+        temp_node = elem.find("temperature")
+        if temp_node is not None:
+            mat.temperature = float(temp_node.text)
+
         if 'volume' in elem.attrib:
             mat.volume = float(elem.get('volume'))
         mat.depletable = bool(elem.get('depletable'))

tests/unit_tests/test_material.py

@@ -189,6 +189,8 @@ def test_from_xml(run_in_tmpdir):
     m1.add_nuclide('H1', 1.0)
     m1.add_nuclide('O16', 2.0)
     m1.add_s_alpha_beta('c_H_in_H2O')
+    m1.temperature = 300
+    m1.volume = 100
     m1.set_density('g/cm3', 0.9)
     m1.isotropic = ['H1']
     m2 = openmc.Material(2, 'zirc')
@@ -209,6 +211,8 @@ def test_from_xml(run_in_tmpdir):
     assert m1.name == 'water'
     assert m1.nuclides == [('H1', 1.0, 'ao'), ('O16', 2.0, 'ao')]
     assert m1.isotropic == ['H1']
+    assert m1.temperature == 300
+    assert m1.volume == 100
     m2 = mats[1]
     assert m2.nuclides == [('Zr90', 1.0, 'wo')]
     assert m2.density == 10.0