Reset timers at correct place in deplete (#2821)

openmc/deplete/coupled_operator.py

@@ -265,6 +265,9 @@ def __init__(self, model, chain_file=None, prev_results=None,
             'fission_yield_opts': fission_yield_opts
         }
 
+        # Records how many times the operator has been called
+        self._n_calls = 0
+
         super().__init__(
             materials=model.materials,
             cross_sections=cross_sections,
@@ -429,6 +432,16 @@ def __call__(self, vec, source_rate):
         # Reset results in OpenMC
         openmc.lib.reset()
 
+        # The timers are reset only if the operator has been called before.
+        # This is because we call this method after loading cross sections, and
+        # no transport has taken place yet. As a result, we only reset the
+        # timers after the first step so as to correctly report the time spent
+        # reading cross sections in the first depletion step, and from there
+        # correctly report all particle tracking rates in multistep depletion
+        # solvers.
+        if self._n_calls > 0:
+            openmc.lib.reset_timers()
+
         self._update_materials_and_nuclides(vec)
 
         # If the source rate is zero, return zero reaction rates without running
@@ -449,6 +462,8 @@ def __call__(self, vec, source_rate):
 
         op_result = OperatorResult(keff, rates)
 
+        self._n_calls += 1
+
         return copy.deepcopy(op_result)
 
     def _update_materials(self):
@@ -508,8 +523,6 @@ def write_bos_data(step):
             "openmc_simulation_n{}.h5".format(step),
             write_source=False)
 
-        openmc.lib.reset_timers()
-
     def finalize(self):
         """Finalize a depletion simulation and release resources."""
         if self.cleanup_when_done: