Thank you, Julien, that’s good work to localize the problem, and sorry I didn’t have any suggestions in this case since I also thought that the photons and neutrons would exponentially increase in a supercritical medium bombarded by neutrons.
Also, a long time ago ( 2016 Question on openmc fixed source calculation - #2 by paulromano ), Paul said that in fixed source calculation, the cases were treated as subcritical multiplication problems which as you also mentioned, in supercritical problems will overflow the secondary particle bank.
thanks for your great explanation. I hope the developer can respond to this discussion to give some clarity.
Also, great work on ONIX, I am modifying some lines of your code locally to make it compatible with the newer version of openmc.
Thanks Julien,
Wahid