This internship offer aims to calculate, for an equal quantity of poison, the effect of a heterogeneous and random distribution of consumable poison using Monte Carlo modeling with the TRIPOLI-4 code. These calculations will be compared to certain models in the scientific literature. Finally, it will be a question of proposing a methodology allowing these effects to be propagated to the heart calculation and according to the wear of the poisons. This internship will allow the candidate to develop his physical sense of the behavior of consumable neutron poisons on small scales and self-protection phenomena. The overall vision of core neutron calculation will remain a goal: this subject consists of taking into account a third spatial scale where neutron calculation generally only has two (that of the assembly and that of the core).