Conjugate heat transfer study of a wire spacer SFR fuel assembly with the thermal code SYRTHES and the CFD code Code-Saturne - 14082

In France, fast reactors with liquid metal coolant (one of the proposals for the Generation IV reactors) have recently received a renewed interest. In order to evaluate nuclear plant design and safety, three-dimensional numerical studies are in progress at EDF. The present paper focuses on a HPC calculation of a conjugate heat transfer simulation in fuel assembly as those found in liquid metal coolant fast reactors. The wire spacers, helically wound along each pin axis, generate a strong secondary flow pattern in opposition to smooth pins. Assemblies with a range of pins going from 7 to 271 have been simulated, 271 pins corresponding to the biggest industrial case. Both the fluid and the solid parts are detailed, leading to very large meshes. The fluid is handled by the CFD code Code-Saturne using 98 million cells, while the solid domain is handled thanks to the thermal code SYRTHES on meshes up to 240 million cells. Both codes are fully parallel and run on cluster with hundreds of processors. Simulations of nominal as well as degraded situations have been done. Fluid calculations are able to find the head losses given by correlations. The main interest of these studies is to have access to the thermal distribution within the cladding, the fuel or the sodium. Calculations show that the periphery of the assembly behaves quite differently from the center. Among other interesting results, one shows that even if the wire has a positive effect on mixing, this mixing behaves very differently in the center of the assembly and in regions close to the hexagonal can. Calculations with different inlet velocity profiles have also been performed and show the influence on the temperature evolution inside the pins and the sodium flow. (authors)