openmc

name: openmc description: > Use when writing OpenMC Python code for neutron/photon transport simulations, geometry construction (CSG surfaces, cells, universes, lattices), material definition (nuclides, elements, enrichment, density), settings configuration (eigenvalue, fixed-source, batches, particles, source distributions), or when debugging OpenMC Python errors. Covers fission reactor design and research neutronics workflows. when_to_use: > Activate for: k-eigenvalue criticality, k-effective, keff, criticality search, Material class, set_density, add_nuclide, add_element, enrichment, boron, ZCylinder, ZPlane, RectLattice, HexLattice, Universe, Cell, fill, region, halfspace, CSG, Settings, batches, inactive, particles, IndependentSource, Box source, eigenvalue, fixed source, export_to_xml, geometry.xml, materials.xml, settings.xml. Tally, scores, filters, EnergyFilter, MeshFilter, tally normalization, statepoint, StatePoint, keff, sp.keff, get_tally, mesh tally, get_reshaped_data, Model.run, model.xml, from_model_xml, gotchas, WeightWindows. CoupledOperator, burnup, depletion, mgxs, openmc.lib, TemporarySession. R2S, R2SManager, rigorous 2-step, shutdown dose, activation dose, decay photon source, get_activation_materials, continuous reprocessing, continuous feed, MSR reprocessing, molten salt reactor depletion, TransferRates, ExternalSourceRates, add_transfer_rate, add_external_source_rate, integrator selection, CECMIntegrator, CF4Integrator, EPCRK4Integrator, LEQIIntegrator, SICELIIntegrator, SILEQIIntegrator, continue_timesteps, cram48, cram16, MicroXS HDF5, write_microxs_hdf5, read_microxs_hdf5, depletion Chain, Chain.reduce, decay_modes, DecayTuple, ReactionTuple, StepResult, OperatorResult, ReactionRates, AtomNumber. complete example, end-to-end, full simulation script, workflow, getting started, how does OpenMC work, overview, patterns, parallel. plot, geometry plot, plot_geometry, voxel plot, visualization, slice plot, color_by, colors, plots.xml, threads, MPI, OpenMP, variance reduction, survival biasing, weight window generation. photon_transport, keff_trigger, surf_source_read, ufs_mesh, max_history_splits, cutoff. cylindrical mesh, spherical mesh, rectilinear mesh, unstructured mesh, CylindricalMesh, SphericalMesh, RectilinearMesh, UnstructuredMesh, from_domain, from_rect_lattice, build_cells, material_volumes, get_homogenized_materials, write_data_to_vtk, MeshMaterialVolumes, MOAB, libMesh, VTK, mesh construction. LegendreFilter, SpatialLegendreFilter, SphericalHarmonicsFilter, ZernikeFilter, ZernikeRadialFilter, expansion filter, Legendre moments, spherical harmonics, Zernike polynomial, angular moments, scattering moments, PolarFilter, AzimuthalFilter, DelayedGroupFilter, UniverseFilter, CellInstanceFilter, CellFromFilter, MaterialFromFilter, CellBornFilter, MeshBornFilter, MeshSurfaceFilter, CollisionFilter, TimeFilter, WeightFilter, MuSurfaceFilter, ParentNuclideFilter, filter reference, full filter list. file source, FileSource, compiled source, CompiledSource, custom source, mesh source, MeshSource, source strength, set_total_strength, normalize_source_strengths, source constraints, fissionable rejection, fissionable only, surface source, surf_source, surf_source_write, surf_source_read, source restart, SourceParticle, write_source_file, read_source_file, source bank, ParticleList, Normal distribution, Legendre distribution, Mixture distribution, Muir distribution, muir, PowerLaw distribution, delta_function, combine_distributions, PointCloud, spherical_uniform, distribution base, Univariate, Spatial base, UnitSphere base, openmc.stats, Watt distribution, Maxwell distribution, Uniform distribution, Box distribution, Point distribution, CartesianIndependent, SphericalIndependent, MeshSpatial, Isotropic, PolarAzimuthal, Monodirectional, energy distribution, spatial distribution, angular distribution, source distribution reference. stochastic volume calculation, VolumeCalculation, volume_calculations, material volume, volume result, volume uncertainty, ufloat volume, volume estimate, run_mode volume, particle track, Track, Tracks, ParticleTrack, tracks.h5, track plotting, track visualization, particle_restart, restart particle, require_statepoint_data. atomic_mass, atomic_weight, half_life, decay_constant, decay_photon_energy, decay_energy, dose_coefficients, gnds_name, zam, isotopes, water_density, nuclear data units, eV vs MeV, half-life seconds, dose conversion, ICRP, water density temperature, data-functions. IncidentNeutron, IncidentPhoton, Decay, ThermalScattering, query cross section, from_hdf5, reaction MT, MT=18 fission, MT=102, reaction cross section, photon cross section, thermal scattering, S(alpha,beta) query. get_activity, get_decay_heat, decay heat, waste classification, waste_disposal_rating, NCrystal, from_ncrystal, ncrystal_cfg, Macroscopic, material Mixture, mix_materials, Nuclide class, Element class, activation material. CMFD, CMFDRun, CMFDMesh, cmfd acceleration, coarse mesh, k_cmfd, cmfd fission source, CMFD feedback, cmfd_on, cmfd_balance. DAGMC, DAGMCUniverse, DAGMCCell, CAD geometry, h5m, DAGMC file, UWUW, material override, sync_dagmc_universes, dagmc_universe_cell_ids, imprint mesh, graveyard. random ray, random-ray, multigroup solver, energy_mode multi-group, MGXSLibrary, XSdata, MG data file, mgxs.h5, convert_to_random_ray, convert_to_multigroup, distance_active, distance_inactive, ray_source. composite surface, RightCircularCylinder, RCC, HexagonalPrism, Polygon, ConicalFrustum, frustum, CylinderSector, IsogonalOctagon, OrthogonalBox, RectangularParallelepiped, Vessel, CruciformPrism, ConeOneSided, XConeOneSided, YConeOneSided, ZConeOneSided, one-sided cone, TRISO, pack_spheres, create_triso_lattice, TRISO packing, borated_water, pin, subdivide, cylinder_from_points, model builder. ZTorus, XTorus, YTorus, torus, Quadric, ZCone, XCone, YCone, double cone, get_rotation_matrix, get_all_cells, get_all_materials, determine_paths, num_instances, cell paths, cell atoms, remove_redundant_surfaces, geometry introspection. rotate_cells, translate_cells, update_densities, update_cell_temperatures, update_material_volumes, differentiate_mats, differentiate_depletable_mats, in-place mutation, parametric sweep, material perturbation, IFP, kinetics parameters, generation time, beta effective, beta_eff, delayed neutron fraction, add_kinetics_parameters_tallies, get_kinetics_parameters, KineticsParameters, ifp-time-numerator, ifp-beta-numerator, ifp-denominator. TallyDerivative, sensitivity, perturbation theory, first-order derivative, nuclide_density derivative, temperature derivative, density derivative, tally arithmetic, hybrid_product, summation, average, diagonalize_filter, CrossScore, AggregateScore, AggregateNuclide, CrossNuclide, tally algebra, Summary, summary.h5, standalone summary, geometry reconstruction. RayTracePlot, WireframeRayTracePlot, SolidRayTracePlot, 3D plot, ray tracing, camera_position, look_at, horizontal_field_of_view, Phong shading, wireframe, volume rendering, orthographic, perspective projection. lib.find_cell, lib.find_material, lib.sample_external_source, source_bank, lib.calculate_volumes, lib.Mesh, lib filter classes, lib non-parity, find cell at point, find material at point, geometry query. license: MIT metadata: openmc-version: v0.15.3

OpenMC Knowledge Base

Coverage: Materials · CSG Geometry · Composite Geometry · Lattice Geometry · Settings · Settings Advanced · Tallies · Statepoint · Model API · Model Mutation · Kinetics · Sensitivity · Gotchas · Depletion · MGXS · Nuclear Data · Data Functions · openmc.lib · Patterns · Overview · Parallel · Plots · Mesh · Filters · Sources · Volume & Tracks · CMFD · DAGMC · Random Ray

Not yet covered (Phase 6): README, community docs, public release

Task Routing

Entry Points

Broad / orientation / "how does OpenMC work" / "getting started" / unclear scope: Read docs/overview.md

Complete example / end-to-end script / "full simulation" / "copy-paste runnable" / workflow: Read docs/patterns.md

Load the docs relevant to the task at hand. For narrow questions, load one file (e.g., only tallies.md for a filter question). For cross-cutting tasks, load the files that span the question (e.g., tallies.md + statepoint.md for construction-through-readback). Never load all docs indiscriminately — choose based on what the task actually requires.

Cluster A — Build a Model

Materials / nuclides / enrichment / density / get_activity / get_decay_heat / decay heat / waste classification / waste_disposal_rating / NCrystal / from_ncrystal / ncrystal_cfg / Macroscopic / material Mixture / mix_materials / Nuclide class / Element class / activation material: Read docs/materials.md

CSG geometry — surfaces, cells, regions, universes / torus / ZTorus / XTorus / YTorus / Quadric / ZCone / XCone / YCone / double cone / get_rotation_matrix / get_all_cells / get_all_materials / get_all_surfaces / get_all_universes / determine_paths / num_instances / cell paths / cell atoms / remove_redundant_surfaces / geometry introspection: Read docs/geometry-csg.md

Composite surfaces / convenience builders / TRISO — RightCircularCylinder / RCC / HexagonalPrism / Polygon / ConicalFrustum / frustum / CylinderSector / IsogonalOctagon / OrthogonalBox / RectangularParallelepiped / Vessel / CruciformPrism / ConeOneSided / XConeOneSided / YConeOneSided / ZConeOneSided / one-sided cone / TRISO / pack_spheres / create_triso_lattice / borated_water / pin / subdivide / cylinder_from_points / model builder: Read docs/geometry-composite.md

Simulation settings — batches, particles, source, run mode, physics mode, photon transport, electron treatment, resonance scattering, ptables, convergence trigger, keff trigger, IndependentSource: Read docs/settings.md (For the full distribution reference — Watt, Maxwell, Uniform, Box, Point, CartesianIndependent, SphericalIndependent, MeshSpatial, Isotropic, PolarAzimuthal, Monodirectional, Normal, Legendre, Mixture, Muir/muir, PowerLaw, delta_function, combine_distributions, PointCloud, spherical_uniform — see Cluster J below: docs/sources.md)

Advanced settings — particle limits, surface source, weight windows file, UFS, statepoint schedule, verbosity, seed, trace, volume calculations, event-based parallelism: Read docs/settings-advanced.md

Building a complete model (geometry + materials + settings together): Read docs/geometry-csg.md + docs/materials.md + docs/settings.md

Cluster B — Lattice Geometry

Lattice geometry — RectLattice, HexLattice, nested universes, assembly geometry: Read docs/geometry-lattices.md

Lattice geometry + CSG (pin universe construction + lattice fill): Read docs/geometry-lattices.md + docs/geometry-csg.md

TRISO particles + lattice (pack_spheres → create_triso_lattice → RectLattice) / TRISO packing workflow / pebble bed: Read docs/geometry-composite.md + docs/geometry-lattices.md

Cluster C — Tallies and Results

Tallies / tally construction / filters / scores / normalization / EnergyFilter / MeshFilter / common filters at a glance: Read docs/tallies.md

Full filter reference / complete filter list / filter reference / all filter types / expansion filter / Legendre / spherical harmonics / Zernike / collision filter / time filter / cell instance / CellBorn / MeshBorn / MeshSurface / delayed group / parent nuclide / polar filter / azimuthal filter: Read docs/filters.md

Weight windows / variance reduction / WeightWindows / WeightWindowsList: Read docs/tallies.md (see §Weight Windows subsection)

Statepoint post-processing / keff / tally results / mesh tally readback: Read docs/statepoint.md

Tally + statepoint together (construction through readback): Read docs/tallies.md + docs/statepoint.md

TallyDerivative / sensitivity / perturbation theory / first-order derivative / nuclide_density derivative / temperature derivative / density derivative / tally arithmetic / hybrid_product / summation / average / diagonalize_filter / CrossScore / AggregateScore / AggregateNuclide / CrossNuclide / tally algebra / wwinp_to_wws / hdf5_to_wws / WeightWindowsList.from_wwinp / collision-track readers / read_collision_track_file / read_collision_track_hdf5: Read docs/tallies.md

Summary / summary.h5 / standalone summary / geometry reconstruction / openmc.Summary / StatePoint.link_with_summary / Summary.add_volume_information: Read docs/statepoint.md

Sensitivity + readback together (TallyDerivative construction through derivative result): Read docs/tallies.md + docs/statepoint.md

Cluster D — Depletion and Nuclear Data

Depletion / burnup / CoupledOperator / IndependentOperator / material volume / depletion chain / R2S / R2SManager / shutdown dose / activation / decay photon source / continuous reprocessing / continuous feed / TransferRates / ExternalSourceRates / add_transfer_rate / integrator selection / CE/CM / CF4 / EPCRK4 / LEQI / SICELIIntegrator / cram48 / MicroXS HDF5 / write_microxs_hdf5 / read_microxs_hdf5 / Chain API / chain.nuclides / Chain.reduce / decay_modes / DecayTuple / ReactionTuple / StepResult / OperatorResult / ReactionRates / AtomNumber: Read docs/depletion.md

Nuclear data / cross_sections.xml / OPENMC_CROSS_SECTIONS / DataLibrary / IncidentNeutron / IncidentPhoton / Decay / ThermalScattering / query cross section / from_hdf5 / reaction MT / MT=18 fission / MT=102 / reaction cross section / photon cross section / thermal scattering / S(alpha,beta) query / chain generation: Read docs/nuclear-data.md

Nuclear data scalar functions / units / atomic_mass / atomic_weight / half_life / decay_constant / decay_photon_energy / decay_energy / dose_coefficients / gnds_name / zam / isotopes / water_density / eV vs MeV / half-life seconds / amu / ICRP / dose conversion / water density temperature: Read docs/data-functions.md

Depletion + nuclear data together (chain loading, operator setup): Read docs/depletion.md + docs/nuclear-data.md

Cluster E — Advanced / In-Memory

Multigroup cross sections / mgxs.Library / EnergyGroups / MGXS types: Read docs/mgxs.md (For MG data-file authoring — MGXSLibrary / XSdata / export_to_hdf5 / from_hdf5 / random-ray XS files — see Cluster M below: docs/random-ray.md)

openmc.lib / in-memory simulation / TemporarySession / lib.run / live Material / batch control / lib.find_cell / lib.find_material / lib.sample_external_source / source_bank / lib.calculate_volumes / lib.Mesh / lib.RegularMesh / lib.Filter / lib filter classes / lib non-parity / find cell at point / find material at point / geometry query / lib vs top-level / non-interchangeable: Read docs/openmc-lib.md

Cluster F — Debugging / Gotchas

Diagnosing silent zero tallies / wrong normalization / unexpected behavior ("why is my tally wrong"): Read docs/gotchas.md

Cluster G — Model API

Model API / Model.run() / export_to_xml / from_model_xml / keff_search / criticality search: Read docs/model.md

Cluster H — Visualization and Parallel Execution

Geometry visualization / plots / plot_geometry / openmc.Plot / voxel / slice plot / color_by / RayTracePlot / WireframeRayTracePlot / SolidRayTracePlot / 3D plot / ray tracing / camera_position / look_at / horizontal_field_of_view / Phong shading / wireframe / volume rendering / orthographic / perspective projection / ProjectionPlot: Read docs/plots.md

Parallel execution / MPI / threading / threads= / OpenMP / variance reduction / survival biasing / weight window generation / WeightWindowGenerator: Read docs/parallel.md (see also docs/tallies.md §Weight Windows for WeightWindows/WeightWindowsList)

Cluster I — Mesh & Filters

Cylindrical mesh / spherical mesh / rectilinear mesh / unstructured mesh / non-regular mesh / custom mesh / MOAB / libMesh / from_domain / from_rect_lattice / build_cells / material_volumes / get_homogenized_materials / write_data_to_vtk / VTK / MeshMaterialVolumes / mesh construction helpers: Read docs/mesh.md

Legendre filter / SpatialLegendre / spherical harmonics filter / Zernike filter / ZernikeRadial / expansion filter / functional expansion / scattering moments / angular flux moments / PolarFilter / AzimuthalFilter / DelayedGroupFilter / UniverseFilter / CellInstanceFilter / CellFromFilter / MaterialFromFilter / CellBornFilter / MeshBornFilter / MeshSurfaceFilter / CollisionFilter / TimeFilter / WeightFilter / MuSurfaceFilter / ParentNuclideFilter / full filter list / filter reference: Read docs/filters.md

Cluster J — Sources & Distributions / Volume & Tracks

Source class family / file source / compiled source / mesh source / custom source / surface source / source bank / source constraints / fissionable rejection / source restart / write_source_file / read_source_file / SourceParticle / ParticleList: Read docs/sources.md

Full distribution reference / all distribution classes / Watt / Maxwell / Uniform / Box / Point / CartesianIndependent / SphericalIndependent / MeshSpatial / Isotropic / PolarAzimuthal / Monodirectional / Normal / Legendre / Mixture / Muir / muir / PowerLaw / delta_function / combine_distributions / PointCloud / spherical_uniform / Univariate / Spatial / UnitSphere base hierarchy / openmc.stats: Read docs/sources.md

Stochastic volume calculation / VolumeCalculation / volume_calculations / material volume / volume uncertainty / ufloat volume / run_mode volume / particle track / Track / Tracks / ParticleTrack / tracks.h5 / track plotting / track visualization / particle_restart / restart particle / require_statepoint_data: Read docs/volume-tracks.md

Source + surface-source restart workflow (surf_source_write + surf_source_read round-trip): Read docs/sources.md + docs/settings-advanced.md (settings-advanced.md owns the dict schemas; sources.md owns the workflow)

Source + volume together (setting up sources and estimating material volumes): Read docs/sources.md + docs/volume-tracks.md

Cluster K — CMFD Acceleration

CMFD / CMFDRun / CMFDMesh / cmfd acceleration / coarse mesh / k_cmfd / cmfd fission source / CMFD feedback / cmfd_on / cmfd_balance / StatePoint cmfd readback / h5py cmfd group: Read docs/cmfd.md

Cluster L — DAGMC / CAD Geometry

DAGMC / DAGMCUniverse / DAGMCCell / CAD geometry / h5m / DAGMC file / UWUW / material override / sync_dagmc_universes / dagmc_universe_cell_ids / imprint mesh / graveyard: Read docs/dagmc.md

Cluster M — Random Ray / MG Data Authoring

Random ray / random-ray / multigroup solver / energy_mode multi-group / MGXSLibrary / XSdata / MG data file / mgxs.h5 / convert_to_random_ray / convert_to_multigroup / distance_active / distance_inactive / ray_source / MG cross section authoring / XSdata.set_scatter_matrix / scatter matrix shape: Read docs/random-ray.md

Cluster N — Model Mutation & Kinetics

In-place model mutation / rotate_cells / translate_cells / update_densities / update_cell_temperatures / update_material_volumes / differentiate_mats / differentiate_depletable_mats / in-place mutation / parametric sweep / material perturbation / diff_volume_method / InvalidIDError: Read docs/model.md

IFP kinetics / IFP / kinetics parameters / generation time / beta effective / beta_eff / delayed neutron fraction / add_kinetics_parameters_tallies / get_kinetics_parameters / KineticsParameters / ifp-time-numerator / ifp-beta-numerator / ifp-denominator / kinetics parameters readback: Read docs/model.md + docs/statepoint.md

Mutation + kinetics together (setup through readback): Read docs/model.md + docs/statepoint.md

Full Simulation Co-loads

Full simulation (geometry + materials + settings + tallies + results): Read docs/geometry-csg.md + docs/materials.md + docs/settings.md + docs/tallies.md + docs/statepoint.md

Full simulation with lattice geometry (geometry + lattice + materials + settings + tallies + results): Read docs/geometry-csg.md + docs/geometry-lattices.md + docs/materials.md + docs/settings.md + docs/tallies.md + docs/statepoint.md