diff --git a/openmc/executor.py b/openmc/executor.py
index de0ca3945..f0ea91370 100644
--- a/openmc/executor.py
+++ b/openmc/executor.py
@@ -8,9 +8,9 @@ from six import string_types
 _summary_indicator = "TIMING STATISTICS"
 
 
-def _run(command, output, cwd):
+def _run(args, output, cwd):
     # Launch a subprocess
-    p = subprocess.Popen(command, shell=True, cwd=cwd, stdout=subprocess.PIPE,
+    p = subprocess.Popen(args, cwd=cwd, stdout=subprocess.PIPE,
                          stderr=subprocess.STDOUT, universal_newlines=True)
 
     storage_flag = False
@@ -51,24 +51,44 @@ def plot_geometry(output=True, openmc_exec='openmc', cwd='.'):
         Path to working directory to run in. Defaults to the current working directory.
 
     """
-    return _run(openmc_exec + ' -p', output, cwd)
+    if output:
+        output = 'full'
+    return _run([openmc_exec, '-p'], output, cwd)
 
 
-def run_volume_calculation(output=True, openmc_exec='openmc', cwd='.'):
+def run_volume_calculation(threads=None, output=True, cwd='.',
+                           openmc_exec='openmc', mpi_args=None):
     """Run stochastic volume calculations in OpenMC
 
     Parameters
     ----------
-    output : bool
+    threads : int, optional
+        Number of OpenMP threads. If OpenMC is compiled with OpenMP threading
+        enabled, the default is implementation-dependent but is usually equal to
+        the number of hardware threads available (or a value set by the
+        :envvar:`OMP_NUM_THREADS` environment variable).
+    output : bool, optional
         Capture OpenMC output from standard out
-    openmc_exec : str
-        Path to OpenMC executable
+    openmc_exec : str, optional
+        Path to OpenMC executable. Defaults to 'openmc'.
+    mpi_args : list of str, optional
+        MPI execute command and any additional MPI arguments to pass,
+        e.g. ['mpiexec', '-n', '8'].
     cwd : str, optional
-        Path to working directory to run in. Defaults to the current working directory.
+        Path to working directory to run in. Defaults to the current working
+        directory.
 
     """
-    return _run(openmc_exec + ' --volume', output, cwd)
+    args = [openmc_exec, '--volume']
 
+    if isinstance(threads, Integral) and threads > 0:
+        args += ['-s', str(threads)]
+    if mpi_args is not None:
+        args = mpi_args + args
+
+    if output:
+        output = 'full'
+    return _run(args, output, cwd)
 
 
 def run(particles=None, threads=None, geometry_debug=False,
@@ -106,27 +126,24 @@ def run(particles=None, threads=None, geometry_debug=False,
 
     """
 
-    post_args = ' '
-    pre_args = ''
+    args = [openmc_exec]
 
     if isinstance(particles, Integral) and particles > 0:
-        post_args += '-n {0} '.format(particles)
+        args += ['-n', str(particles)]
 
     if isinstance(threads, Integral) and threads > 0:
-        post_args += '-s {0} '.format(threads)
+        args += ['-s', str(threads)]
 
     if geometry_debug:
-        post_args += '-g '
+        args.append('-g')
 
     if isinstance(restart_file, string_types):
-        post_args += '-r {0} '.format(restart_file)
+        args += ['-r', restart_file]
 
     if tracks:
-        post_args += '-t'
+        args.append('-t')
 
     if mpi_args is not None:
-        pre_args = ' '.join(mpi_args) + ' '
+        args = mpi_args + args
 
-    command = pre_args + openmc_exec + ' ' + post_args
-
-    return _run(command, output, cwd)
+    return _run(args, output, cwd)
diff --git a/tests/test_particle_restart_eigval/test_particle_restart_eigval.py b/tests/test_particle_restart_eigval/test_particle_restart_eigval.py
index 59f76d93b..1ebbd3ea5 100644
--- a/tests/test_particle_restart_eigval/test_particle_restart_eigval.py
+++ b/tests/test_particle_restart_eigval/test_particle_restart_eigval.py
@@ -7,5 +7,5 @@ from testing_harness import ParticleRestartTestHarness
 
 
 if __name__ == '__main__':
-    harness = ParticleRestartTestHarness('particle_10_1030.*')
+    harness = ParticleRestartTestHarness('particle_10_1030.h5')
     harness.main()