ISOTHERMAL STUDY OF THE FLOW AT THE JUNCTION BETWEEN AN AUXILIARY LINE AND PRIMARY CIRCUIT OF PRESSURIZED-WATER REACTORS

This paper deals with an experimental and numerical study of an isothe rmal flow at the junction of a high Reynolds number piping system and both very small and zero flow-rate pipe. The motivation is to understa nd and model the hydraulic behaviour of various auxiliary lines connec ted to the primary circuit of Pressurised Water Reactors. Experimental data have been obtained on a hydraulic mock-up using flow visualisati on method and particle image velocimetry (PIV). They shown an helicoid al flow extending along the auxiliary pipe. Numerical calculations per formed with the 3D ESTET code are presented and contrast the performan ce between a k-epsilon eddy viscosity model and a second moment closur e turbulence model. Coarse (100 000), medium (400 000) and fine (1 500 000) meshes were used to test the influence from mesh. The numerical results obtained with the second moment closure turbulence model and t he finest mesh confirm the swirl flow structure into the dead leg obse rved on the mock-up. On the other hand the k-epsilon eddy viscosity mo del is not able to predict the vortex penetration along the auxiliary pipe. These results illustrate the necessity to use second moment clos ure turbulence model to simulate flows in piping system dead legs.