Adding support for DAGMC export to other neutronics codes

[shimwell]

OpenMC is the default code for the DAGMC export function but it can be useful to support other codes.

DAGMC geometry tags are slightly different

in openmc we can use material strings, these strings come from the shape name

mat:steel

in MCNP we add the density of the material and use a material integer

mat:1/rho:0.023

in Shift we use an integer

mat:0

To add this support we can add another argument to shape.export_dagmc_h5m and reactor.export_dagmc_h5m.

I'm going to get this started by adding some unit tests

[shimwell]

I've added some tests to this branch
https://github.com/fusion-energy/paramak/tree/adding_tests_for_dagmc_export_to_other_codes

[shimwell]

Another complication is that we currently export graveyard free geometries and openmc can support this by filling a CSG universe with a DAGMC geometry. However I don't think Shift or MCNP allow graveyard free geometries.

There is a method of creating a graveyard in the paramak which can be called by the export_dgamc_h5m method which could help here

[jbae11]

[i] is integer, [f] is float
MCNP:

• all volumes must belong to a group
• normal materials: mat:[i]/rho:[f]
• vacuums:mat:Vacuum
• graveyard: mat:Graveyard

Shift

• normal matierals: mat:[i]
• graveyard: mat:graveyard (note the lowercase g..)

So given this maybe two changes can make this easiest:

1. Have flags for other formats:
   • convert material names to list of numbers: (e.g. new_mat_list = list(range(len(set(mat_list)))))
   • names are replaces by numbers, and suffixes if required
2. Have Paramak do graveyards
   • the above format will dictate the graveyard:
     • none for openmc, mat:Graveyard for MCNP, mat:graveyard for Shift.

[shimwell]

thanks for this info, I think this PR covers the various tag options that are needed apart from the graveyard. I shall merge it in and then get started on the graveyard

[shimwell]

the default graveyard size is 20000cm which requires a lot of triangles to mesh using the current meshing algorithm.

uses currently have to use the reactor.graveyard_size to reduce the size of the graveyard so that it can be meshed in a reasonable time. Option to fix this are reduce the default mesh size or use a different meshing algorithm as mentioned here fusion-energy/brep_to_h5m#5