"root universe" needs to contain all the cells and other universes?

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1

Dear exports,

I have a question about the root universe feature of OpenMC.

I am trying to build a small reactor containing external structures, and using the lattice repeating structure for core fuel region. My question is: do I need to fill only this fuel region into the root universe, or I need to fill all cells of the whole model into the root universe?

And if for the first case, export to xml should be like this? I mean, fill all the cells to “geometry”?

geometry = openmc.Geometry([root_universe, reflector_cell, B4C_cell, ods_cell, …])
geometry.export_to_xml()

Thank you.

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2

Hi @chenchcc and welcome to the community. The root universe and anything that is contained within it is the only thing that OpenMC “sees”, so if you don’t have the external structures in your root universe, they will not show up in the simulation. Also, just a clarification on calling Geometry(...). You can either pass a universe:

geom = openmc.Geometry(root_universe)

or a list of cells:

geom = openmc.Geometry([cell1, cell2, ...])

but you can’t mix the two. Hope this helps!

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3

Thanks, @paulromano .Now I know how to build the model.