Fix for pandas version 3 (#3743)

Author: GuySten

openmc/data/photon.py

@@ -203,7 +203,9 @@ def transitions(self, transitions):
         for subshell, df in transitions.items():
             cv.check_value('subshell', subshell, _SUBSHELLS)
             cv.check_type('transitions', df, pd.DataFrame)
-        self._transitions = transitions
+        self._transitions = {
+            subshell: df.convert_dtypes() for subshell, df in transitions.items()
+        }
 
     @classmethod
     def from_ace(cls, ace):

openmc/tallies.py

@@ -1982,7 +1982,7 @@ def get_pandas_dataframe(self, filters=True, nuclides=True, scores=True,
 
         # Expand the columns into Pandas MultiIndices for readability
         if pd.__version__ >= '0.16':
-            columns = copy.deepcopy(df.columns.values)
+            columns = copy.deepcopy(list(df.columns.values))
 
             # Convert all elements in columns list to tuples
             for i, column in enumerate(columns):