Study of Phénix control rod withdrawal tests with a multi-physics coupling approach

Before the definitive shutdown of the reactor Phénix, a series of end of life tests were performed, by CEA (Commissariat à l’Energie Atomique et aux Energies Alternatives), EDF (Électricité de France) and AREVA, in order to enlarge the experimental database and to improve the research field on sodium cooled fast reactors. Due to this important opportunity, the IAEA (International Atomic Energy Agency) decided to establish a Coordinate Research Project among different countries to allow computational codes validation and results comparison. In this context, a benchmark was established on the “Control Rod Withdrawal Test Performed during the Phénix End-of-Life Experiments”, with the objective of the investigation on the flux and power local deformations in the core as a result of different control rod insertion and extraction configurations. In this study, the simulation of the test has been performed following IAEA benchmark and using a multi-physics approach that allows to account for the reactivity feedbacks from the thermal-hydraulics calculations on the neutronic model. The objective is to explore the contribution of such a multi-physics model on the results. A neutronic Monte Carlo code (Serpent 2) was coupled with a simplified thermal-hydraulic model (built in Python). At first, a convergence study on the Monte Carlo results was performed. Subsequently, both neutronic and thermal-hydraulic results in the test configurations were compared to the experimental ones. Finally, a convergence study was made on the coupling process and a comparison between coupled and uncoupled results was presented.