[en] The ASTRID project (Advanced Sodium Technological Reactor for Industrial Demonstration) is a Generation IV nuclear reactor concept under development in France. In this frame, studies are underway to optimize radial reflectors and protections. Considering radial protections made in natural boron carbide, this study is conducted to assess the neutronic performances of the MgO as the reference choice for reflector material, in comparison with other possible materials including a more conventional stainless steel. The analysis is based upon a simplified 1-D and 2-D deterministic modelling of the reactor, providing simplified interfaces between core, reflector and protections. Such models allow examining detailed reaction rate distributions; they also provide physical insights into local spectral effects occurring at the core-reflector and at the reflector-protection interfaces. The results show that the comparisons are clearly in favour of the MgO reflector, even though MgAl₂O₄ or Y₃Al₅O₁₂ are very close in terms of reactivity, and TiC or ZrC are slightly better in shielding