The coupled DYN3D/ATHLET code system was recently adapted for Sodium cooled Fast Reactors (SFRs) applications. The main objective of this study is to validate further the DYN3D/ATHLET code system by performing a coupled 3D neutron kinetics/thermal-hydraulics analysis of six transient start-up tests conducted at the French Superphenix (SPX) reactor. The tests were a part of the startup test program aiming at evaluation of the core reactivity feedback characteristics. Peculiarity of these transients is the necessity of accounting for the thermal expansions of the primary system structural elements influencing the position of control rods in the core.
The paper includes a brief summary on the benchmark specification, description of the neutronics and thermal-hydraulics models, and comparison of the simulation results to the available experimental data. For all six transients, a good agreement between simulations and experiments was observed confirming a reasonable performance of DYN3D/ATHLET.