Cellborn filter

User Support
1

Hi everyone!

I have a question regarding the cellborn filter: In the docs it says: This filter allows the tally to be scored to only when particles were originally born in a specified cell.
Is born meant only as a result of fission or also other reactions?

Also, is there a way to automatically convert the geometry form MCNP to OpenMC?

Thank you for the help,
Juan

2

Hi Juan,

In a k-eigenvalue calculation, the cellborn filter will give you scores for particles that were born from fission in a given cell, since “source” in a k-eigenvalue calculation is the fission source. Neutrons produced from, say, (n,2n) and (n,3n) are immediately transported rather than being stored and used for a subsequent generation. In a fixed source calculation, on the other hand, neutrons are sampled from an external source defined by the user, so in this case the cellborn filter will apply to where external source neutrons are born.

I do have some scripts that automatically convert MCNP -> OpenMC but they are a bit out of date and haven’t been checked. If you think this would be a useful capability, I could consider polishing up what I have and adding it to our Python API.

Best regards,
Paul

3

Hello, I have a few quick clarifying questions about the CellBornFilter for fixed source calculations.

First, the documentation says, “Bins tally events based on which Cell the neutron was born in.” Could this be used with photons also by incorporating a photon ParticleFilter?

Specifically, I’m interested in quantifying which cells are generating photons in a coupled neutron-photon simulation with a fixed neutron source. Can the CellBornFilter be used in coupled neutron-photon calculations to calculate photon flux generated from a given cell? For instance, if I want to see the photon flux in cell 1 from photons originating from neutron interactions in cell 2, could I use a CellFilter for cell 1, a CellBornFilter for cell 2, and a photon ParticleFilter?

Thanks!

4

@kevinm387 Yes, as far as I can tell, this should work for photons that are born from neutron interactions. Looks like we need to update the documentation (thanks for pointing that out).

5

Ok thanks @paulromano! I tried it on a few models and it seems to have worked.