Atomic Density Input in OpenMC Materials

User Support
1

Hi all,

I want to ask regarding atomic density input in openmc materials. As what i have read in several example, we do not need to tell openmc the atomic density of the nuclides/isotopes we want to use as materials but only the density of whole materials. So where do openmc know it?

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Thanks,

Kristina

2

Hi Kristina,

If I need to enter atomic density in materials.xml, I would enter like this:

where n-U235 is the atomic density of U235 and n-U238 is the atomic density of U238 in atom/b-cm.

-Vedha

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3

OpenMC will renormalize whatever atom or weight fractions are specified by the total density that is given for the material. If you want to specify nuclide atom fractions exactly, then you can give them in atom/b-cm and list the density as units=“sum”, as Vedha suggests.

Best,
Paul

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4

Hi Vedha and Paul, thanks for your explanation!