Importing MCNP Models

MCNP (Monte Carlo N‑Particle) is a general‑purpose radiation transport code that simulates how particles move through matter.

CUBIT can read an MCNP input file and convert its constructive solid geometry — cells, surfaces, and lattices — into an ACIS solid model geometry. This makes it possible to take an existing MCNP model and turn it into CAD geometry that can be cleaned up, meshed, and exported for radiation-transport workflows such as DAGMC. The conversion is based on the open-source mcnp2cad translator that has been converted to use native CUBIT functionality.

The command used to import an MCNP file is:

Import MCNP '<filename>' [verbose] [debug] [debug_output] [debug_input] [extra_effort] [skip_mats] [skip_merge] [skip_imps] [skip_nums] [skip_graveyard] [skip_imprint] [uwuw_names] [tol <value>]

A log of the conversion is always written to a file named mcnp_import.log in the current working directory.

Import Options

By default the importer tags the generated geometry with the information needed by downstream neutronics workflows and cleans up the result by imprinting and merging. The options below, most of which begin with skip_, turn individual steps off.

• By default, the MCNP material assignment for each cell is attached to the corresponding volume. Use skip_mats to import the geometry without tagging materials.
• By default, cell importances are tagged on the geometry. Use skip_imps to omit them.
• By default, the original MCNP cell ID is tagged on each volume. Use skip_nums to omit the cell IDs.
• By default, a surrounding "graveyard" volume (the bounding shell used to terminate particles in a transport calculation) is generated. Use skip_graveyard to suppress it.
• By default the converted geometry is imprinted. Use skip_imprint to skip imprinting.
• By default coincident geometry is merged after conversion. Use skip_merge to skip merging. Note that merging requires imprinting; if imprinting is skipped, merging is skipped as well.
• The uwuw_names option causes materials to be named using the UWUW (Unified Workflow for Universal Weight-windows) convention used by some DAGMC tools.
• The extra_effort option directs the translator to spend additional effort resolving infinite lattices.
• The tol option overrides the default conversion tolerance with the specified value. The expected range is greater than 0 and no larger than 0.1; values outside this range are accepted but produce a warning in the log.
• The verbose and debug options produce additional and diagnostic output during the conversion. The debug_input and debug_output options restrict debugging output to the input-deck parsing phase and the geometry-generation phase, respectively.