A 3D model to solve U-tube steam generator secondary side thermal-hydraulics with coupled primary-to-secondary side heat transfer

Abstract

The U-tubes of steam generators (SG) are concerned by vibration issues. The vibration behavior is driven by the local secondary flow (velocity, void fraction, two-phase pattern). Fluid-elastic instability (FEI) can be considered as the most severe vibration phenomenon, since it features high vibration amplitudes and tube-to-tube contacts, which can rapidly cause tube rupture. In order to predict if the fluid forces exerted along the tube bundle can trigger a FEI, numerical tools able to calculate the secondary side of a SG are needed. In the frame of its mission of assessing methods adopted by utilities for demonstrating the safe operation of nuclear facilities, the French Institut de Radioprotection et de Sûreté Nucléaire (IRSN) has developed such a numerical model. The model is based on a 3D homogeneous drift-flux formulation of the SG steam-water mixture, together with a porous media approach to account for the tube bundle. The model is implemented in the ANSYS Fluent CFD code. The SG primary side is solved using a dedicated meshing. The secondary side and the primary side meshes communicate through heat transfer, which is fundamental to obtain consistent numerical results. The details of the numerical approach are described in the first part of this paper. Then, numerical versus experimental results comparisons in terms of heat transfer are provided for a SG test facility: numerical and experimental results are in good agreement. The model was then applied to a real SG: numerical results are in good agreement with nominal operating parameters.