Superimposition of regions causing low k-effective

Hello everyone!

Recently I was making a model of the ALFRED reactor core and I had a big problem related to the low k-effective of the whole core.
Being a new user without a big experience in a Monte Carlo codes, I was not able to define the cause of the problem. I changed the geometry several times, a lot of tallies were created for a check.
After spending a lot of time on the revision of the code with @lorenzoloi, we found out that the reason of the very low k-effective is a badly defined cell region of the lead, that was added as a coolant in the core. Before, I was checking the correctness of my geometry by checking tallies and plotting, where the superimposition of the core lattice with a lead coolant was not shown.

I would like to ask you if there is a possibility to fix this issue for future users, probably, by giving error when something similar happens. Because in my case code seemed to work perfectly with the only problem of low k-effective and quite thermal spectrum of neutrons in the fuel.

Thank you very much for your work!
I really appreciate what you are doing!