How to assign compound materials to the region

Dear Fluka experts,

I’m kind of confused about how to assign the compound material to the region. The region I have drawn is shown below, all of materials have been assigned into the region, except the “mixele” material that assigns into “fuel” region (blue color) is still confused.
I think it is because of complicating in creating my geometry that forces me to assign only the density of fuel per rod (around 3.5 g/cm3) in to “fuel” region, more than that will cause a stack overflow. I’m not sure that if I assign the density per rod to “mixele” card, is it make sense?
Because the “fuel” region is not separated into fuel-1,fuel-2,…, fuel-n rod, in this case, it will make sense to assign density per rod.

Sorry about my explanation, if it doesn’t clear please let me know.

Best regards,

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Dear @phaiph ,

I am not sure I understand your issue. I checked your flair file, and the “mixele” material is correctly assigned to the region “fuel”. So, what exactly is your question? Do you need to assign a different density to every rod? If so, you’ll need to redefine your geometry. Every rod will need to be a different region and not a zone of the same region as it is now. Also, you’ll need to add material and compound cards for each different mixele density. For each material card, density is fixed. If you need the same material, i.e. the same chemical composition, but different densities, then you need to multiple material cards.