Update _get_start_data to always grab the beginning of timestep time

openmc/deplete/abc.py

@@ -819,9 +819,32 @@ def _get_bos_data_from_restart(self, source_rate, bos_conc):
         return bos_conc, OperatorResult(k, rates)
 
     def _get_start_data(self):
+        """
+        This function fetches the starting state of a depletion simulation
+        in terms of the simulation physical time at which to start and the
+        index at which the depletion simulation should start. When no
+        previous results exist, the time and index are both zero. When 
+        previous results do exist, it returns the time corresponding to
+        beginning the previous results last timestep and the index as 
+        N-1 where N is the number of previous StepResults found in 
+        the previous Results (as expected from 0-based indexing).
+
+        Note that the openmc.deplete.Results.time object is a list of float with
+        [t,t+dt] where t is the beginning of timestep time and t+dt is the end of
+        timestep time. If the previous results correspond to a simulation that
+        finished to completeion, it will contain a results in the form of [t,t],
+        but if a simulation doesn't finish all the given timesteps, it is the t
+        that is the desired start time, not t+dt. Thus, it is always safe to take 
+        time[0].
+
+        Returns
+        _______
+        start_time : float
+        index: int
+        """
         if self.operator.prev_res is None:
             return 0.0, 0
-        return (self.operator.prev_res[-1].time[-1],
+        return (self.operator.prev_res[-1].time[0],
                 len(self.operator.prev_res) - 1)
 
     def integrate(

tests/unit_tests/kill_continue/continue_model.xml

@@ -0,0 +1,34 @@
+<?xml version='1.0' encoding='utf-8'?>
+<model>
+  <materials>
+    <material depletable="true" id="1" name="fuel" volume="3.14159265">
+      <density units="g/cm3" value="10.744"/>
+      <nuclide ao="0.068794" name="U235"/>
+      <nuclide ao="0.27604" name="U238"/>
+      <nuclide ao="0.13793" name="C0"/>
+      <nuclide ao="5.1724" name="O16"/>
+    </material>
+  </materials>
+  <geometry>
+    <cell id="1" material="1" region="-3 1 -2" universe="1"/>
+    <surface boundary="reflective" coeffs="0.0" id="1" type="z-plane"/>
+    <surface boundary="reflective" coeffs="1.0" id="2" type="z-plane"/>
+    <surface boundary="reflective" coeffs="0.0 0.0 1.0" id="3" type="z-cylinder"/>
+  </geometry>
+  <settings>
+    <run_mode>eigenvalue</run_mode>
+    <particles>250</particles>
+    <batches>45</batches>
+    <inactive>15</inactive>
+    <source particle="neutron" strength="1.0" type="independent">
+      <space type="box">
+        <parameters>-0.5 -0.5 0.0 1.0 1.0 1.0</parameters>
+      </space>
+    </source>
+    <output>
+      <summary>false</summary>
+      <tallies>false</tallies>
+    </output>
+    <temperature_default>294</temperature_default>
+  </settings>
+  </model>

tests/unit_tests/test_deplete_continue.py

@@ -4,7 +4,9 @@
 """
 
 import pytest
+import numpy as np
 import openmc.deplete
+from pathlib import Path
 
 from tests import dummy_operator
 
@@ -26,6 +28,70 @@ def test_continue(run_in_tmpdir):
     bundle.solver(operator, [1.0, 2.0, 3.0, 4.0], [1.0, 2.0, 3.0, 4.0],
                   continue_timesteps=True).integrate()
 
+    final_res = openmc.deplete.Results(operator.output_dir / "depletion_results.h5")
+
+    assert np.array_equal(np.diff(final_res.get_times(time_units="s")),[1.0, 2.0, 3.0, 4.0])
+
+
+def test_continue_continue(run_in_tmpdir):
+    """Test to ensure that a continue run can be continued"""
+    # set up the problem
+    bundle = dummy_operator.SCHEMES['predictor']
+    operator = dummy_operator.DummyOperator()
+
+    # initial depletion
+    bundle.solver(operator, [1.0, 2.0], [1.0, 2.0]).integrate()
+
+    # set up continue run
+    prev_res = openmc.deplete.Results(operator.output_dir / "depletion_results.h5")
+    operator = dummy_operator.DummyOperator(prev_res)
+
+    # first continue run
+    bundle.solver(operator, [1.0, 2.0, 3.0, 4.0], [1.0, 2.0, 3.0, 4.0],
+                  continue_timesteps=True).integrate()
+
+    prev_res = openmc.deplete.Results(operator.output_dir / "depletion_results.h5")
+    # second continue run
+    bundle.solver(operator, [1.0, 2.0, 3.0, 4.0, 5.0, 6.0], [1.0, 2.0, 3.0, 4.0, 5.0, 6.0],
+                  continue_timesteps=True).integrate()
+
+    final_res = openmc.deplete.Results(operator.output_dir / "depletion_results.h5")
+
+    assert np.array_equal(np.diff(final_res.get_times(time_units="s")),[1.0, 2.0, 3.0, 4.0, 5.0, 6.0])
+
+def test_killed_and_continue(run_in_tmpdir):
+    """
+    Attempt to continue from a simulation that was killed mid state.
+    The previous state is provided in the form of a few local files:
+
+    continue_model.xml contains the necessary XML information
+    chain_simple.xml contians a simplified version of the CASL chain
+
+    continue_depletion_results.h5 contains the results output by
+    an OpenMC (v0.15.2) depletion simulation that was killed in
+    the middle of the third step
+    """
+    base_path = Path(__file__).parents[0]
+    chain_path = Path(__file__).parents[1]/'chain_simple.xml'
+    model = openmc.Model.from_model_xml(f"{base_path}/kill_continue/continue_model.xml")
+    power = 35000 # W
+
+    time_steps = [1.0,2.0,3.0,4.0] # days
+    prev_results = openmc.deplete.Results(f"{base_path}/kill_continue/continue_depletion_results.h5")
+    operator = openmc.deplete.CoupledOperator(
+        model, prev_results=prev_results, chain_file=chain_path
+    )
+    integrator = openmc.deplete.CECMIntegrator(
+        operator,
+        time_steps,
+        power=power,
+        timestep_units="d",
+        continue_timesteps=True,
+    )
+    integrator.integrate(path=f"{base_path}/kill_continue/continue_depletion_results.h5")
+    final_res = openmc.deplete.Results(f"{base_path}/kill_continue/continue_depletion_results.h5")
+
+    assert np.array_equal(np.diff(final_res.get_times(time_units="d")),[1.0, 2.0, 3.0, 4.0])
 
 def test_mismatched_initial_times(run_in_tmpdir):
     """Test to ensure that a continue run with different initial steps is properly caught"""