Drag coefficient estimation in FSI for PWR fuel assembly bowing

Assembly bowing in a PWR core can be a serious problem for managing the power during normal operation or for periodical maintenance. One of the causes of this phenomenon is the transverse flow in the core, generated by the non-uniformity of the axial flow. Modelling the mechanical behaviour of a PWR core is made difficult by the complex geometry and the numerous friction points that lead to non-linearities. A simple but efficient way to deal with these issues is the porous medium model proposed by Ricciardi et al. (2009). In this model, the equations used at the fluid–structure interface require empirical parameters such as the added mass, or axial and normal drag coefficients. Using a new experimental setup at CEA, Eudore, which hosts 3 half-scale fuel assemblies in a line, the forces acting on the assembly by a non-uniform flow profile were measured. An analytical model to retrieve the normal drag coefficient was then proposed. This coefficient is then used in FSCORE, a numerical software based on the porous medium approach. The experimental and numerical results are presented and show good agreement.