Update: I know that absorption is not an issue now, for this is the fuel cell absorption tally:
Therefore I investigate a bit more into this. I tally the nu-fission rate of the fuel cell. This is the result:
Nu-fission is the total production of neutron per fission reaction. Here are the scores for different nuclide in the fuel:
It differs on U232, and that difference is enough to drown the keff.
Quod erad demonstratum 
Thank you for the help these past days, @wahidluthfi
Best regards,
Chris