OpenMC Energy Group

I am a relatively new user to OpenMC who just started for a few months now. I have performed eigenvalue, depletion and power distribution calculations. I am using ENDF/B-VIII.0 cross section library.
I cannot figure out how many energy groups am I using in the simulation codes? I have come across that my simulations are for multigroup energies but how can I figure out how many groups am I using?

Hi @Taiba,

Welcome to the forum and thank you for your query!

The ENDF/B-VIII.0 datasets you’ve mentioned are what we consider to be continuous energy cross-sections. The data is technically discrete pointwise information in the energy domain, but the energy grid varies to capture all relevant features of the continuous energy information defined by various models, probability tables, correlations etc.

OpenMC can use multigroup cross-sections, however. It can also generate multigroup cross sections from continuous energy simulations if needed. This is typically done to speed up simulation times or provide cross section data for codes using other solution methods like diffusion.

The other place energy groups are relevant is when looking at tallied information that results from an OpenMC simulation such as plotting a flux spectrum. An example of such an exercise along with a lot of other useful examples can be found here: openmc-notebooks/flux-spectrum.ipynb at main · openmc-dev/openmc-notebooks · GitHub

I hope this touches on your question somewhat.