CEA is largely involved in the study of GEN-IV Sodium Fast Reactors (SFR). Some innovative reactivity control systems are proposed such as utilization of different absorbers or moderators materials, modification of absorber pin geometry, and application of burnable neutron poison. These designs possess potentials to improve its safety margin, economical performance or core characteristics while its complete analysis requires notably more accurate calculation of efficiency and evolution of isotopes’ concentrations under irradiation.

At the same time, the new determinist transport code APOLLO3® is under development at CEA and it will replace ERANOS code for fast reactors analysis. The scheme in APOLLO3® is constituted with two steps: sub-assembly calculation and core calculation with Multi-Parametric Output Library as connectors which enable the interpolation of cross-sections according to specific parameter. In this paper, each step and different cross-section scheme are detailed and validated by continuous energy Monte Carlo calculations. These results are also compared with determinist code system ERANOS.

Our works show high adaptability of TDT solver in APOLLO3® to complexes geometries and evolution of isotopes. With the ability of MINARET to treat unstructured mesh, the heterogeneous geometry, keeping absorber pins at core level calculation, improves significantly the calculation of control rods’ efficiency. APOLLO3® compute more accurately core’s reactivity variation with burn-up tabulated cross section scheme. Although variation of spatial self-shielding effect is very significant in absorber depletion, tabulated cross-sections scheme is able to bring this variation from sub-assembly calculation to core calculation. Hence, even homogeneous control rod description at core level shows accurate computation of reactivity variation.

Consequently, with development and validations, APOLLO3® shows improvement on SFR control rods neutronic simulation and analysis. With these new schemes presented in this paper, innovative reactivity control systems designs will be completely characterized and investigated in the near future.