Study of experimental configurations of the VENUS research reactor for the improvement of nuclear data

According to the International Criticality Safety Benchmark Evaluation Project (ICSBEP) 3000 experiments were made for safety/criticity in thermal domain, 700 in fast domain and almost zero in between. The epithermal domain was left behind since the beginning of the nuclear industry because of the need to study thermal neutron for nuclear reactors and fast neutrons for nuclear weapons or fast reactors. However for several years now, a lot of research was carried out to fill this gap, indeed the epithermal domain remains important, when slowing down neutrons pass through this range of energies. This internship follows this trend and aims at modelling the core of a fast reactor (VENUS) on TRIPOLI-4 and then modifying a little part of it to build nuclear configurations that enable the study of epithermal domain. The report is organized in two main parts, first the modelization and validation of the geometry with Serpent then TRIPOLI-4, it was first a work of comparison between a previous work already validated and the present work on Serpent, this was the base that we used to build then verify the model on TRIPOLI-4. Then the building of new nuclear configurations associated with the study of materials substitution that lead to the conception of a configuration with FLiBe and polyethylene moderators that achieved to thermalize enough the flux to prove the possibility of making experiments that can lead to new data for the epithermal domain.