OpenMC Guide
StatePoint Files in OpenMC
Understanding StatePoint Files
OpenMC stores all simulation results in StatePoint files (*.h5 format).
What's Inside
- Tally results
- Statistical uncertainties
- K-effective (for criticality)
- Simulation settings
Common Uses
- Get tally data
- Check convergence
- Plot results
- Export to other formats
Basic Usage
Basic result extraction:
Opening Results
python
# Load the results
sp = openmc.StatePoint('statepoint.100.h5')
# Basic information
print(f"k-effective = {sp.keff.nominal_value:.5f} ± {sp.keff.std_dev:.5f}")
# Get a specific tally
tally = sp.get_tally(name='flux')
mean = tally.mean
rel_err = tally.std_dev / tally.meanTutorial snippet — no separate file in examples repo
Tip: Always check the relative error of your results. Values above 0.1 (10%) indicate poor statistics and may need more particles.
Working with Data
Tally data can be converted to pandas DataFrames for analysis:
Data Analysis
python
# Convert tally to DataFrame
df = tally.get_pandas_dataframe()
# Filter results
flux = df[df['score'] == 'flux']
u235 = df[df['nuclide'] == 'U235']
# Basic statistics
print(f"Average flux: {flux['mean'].mean()}")
print(f"Max flux: {flux['mean'].max()}")Tutorial snippet — no separate file in examples repo
Simple Plot
python
import matplotlib.pyplot as plt
# Plot flux by tally bin
flux = df[df['score'] == 'flux']
plt.figure()
plt.plot(flux['mean'].values, 'o-')
plt.xlabel('Tally Bin')
plt.ylabel('Flux')
plt.grid(True)
plt.savefig('flux.png')Tutorial snippet — no separate file in examples repo
K-eff Plot
python
# Plot k-effective convergence
keff_by_gen = sp.k_generation
batches = range(1, len(keff_by_gen) + 1)
plt.figure()
plt.plot(batches, keff_by_gen, 'o-')
plt.xlabel('Batch')
plt.ylabel('k-effective')
plt.grid(True)
plt.savefig('keff.png')Tutorial snippet — no separate file in examples repo
Best Practices
Analysis Tips
- Always check uncertainties
- Plot results to spot issues
- Save raw data for later
- Document your analysis
- Use pandas for complex analysis