This internship project aims to quantify the possible bias introduced by the neutron calculation scheme based on APOLLO3® when calculating these degraded situations. It is proposed to address this question by establishing comparisons with reference results obtained by the Monte-Carlo TRIPOLI-4® code, for different distributions of materials representative of these situations. The first part of the work will consist of taking charge of the SEASON/SIMMER-V platform to carry out simulation and post-processing of serious accidents. The objective is to become familiar with the current calculation system and to generate degraded reactor situations in 3D to define the APOLLO3<->TRIPOLI-4 comparison points. The second part of the work will consist of interfacing the SEASON/SIMMER-V output (hdf5 format) with the inputs of the APOLLO3® and TRIPOLI-4® codes which have different meshing and material distribution conventions. The third part will consist of carrying out the comparison itself, carrying out the analysis and synthesis of the results, and defining avenues for future improvement.