OpenMC Guide

❮ TalliesStatePoint Files ❯

Running Simulations in OpenMC

Running Your First Simulation

Now that we've created our geometry, materials, and settings, let's run our simulation. The simplest way is using OpenMC's Model class:

Basic Run

python
# Create model from components we made earlier
model = openmc.Model(
    geometry=geometry,     # From geometry creation
    materials=materials,   # From materials definition
    settings=settings,     # From settings setup
    tallies=tallies       # From tallies setup
)

# Run the simulation
model.run()

Tip: Always start with a small number of particles (e.g., 1000) to test your model before running long simulations. This helps catch errors quickly.

Common Run Options

You can customize how your simulation runs based on your needs:

Debug Mode

python
# Run with geometry debugging
model.run(output=True)  # Show output
model.run(geometry_debug=True)  # Check geometry

Parallel Run

python
# Run with 4 processors
model.run(mpi_args=['mpiexec', '-n', '4'])

# Set thread count
model.run(openmc_exec_kwargs={
    'threads': 2
})

Understanding Output

OpenMC creates several output files during and after simulation:

Key Files

  • statepoint.*.h5: Results
  • tallies.out: Tally data
  • summary.h5: Model info
  • particles.h5: Particle tracks

Common Issues

  • Geometry errors
  • Lost particles
  • Memory limits
  • Convergence issues

Reading Results

python
# Load results (from previous section)
sp = openmc.StatePoint('statepoint.100.h5')

# Get k-effective (for criticality runs)
keff = sp.keff
print(f'k-effective = {keff.nominal_value:.5f} ± {keff.std_dev:.5f}')

# Get tally results
tally = sp.get_tally(name='flux')
mean = tally.mean
rel_err = tally.std_dev / tally.mean

Best Practices

Running Tips

  • Start with few particles to test setup
  • Use geometry debug mode to check for errors
  • Monitor memory usage for large models
  • Save statepoints periodically for long runs
  • Use parallel processing for speed when needed

Additional Resources

Related Topics

❮ TalliesStatePoint Files ❯