Lesson learned from numerical activities in support to the development of SCWRs at the University of Pisa

Supercritical Water-Cooled Reactors are among the selected proposed designs for the upcoming GEN IV of nuclear power plants. They represent the natural evolution of presently available LWRs: borrowing the experiences and competences developed during several decades of operation of both PWRs and BWRs, it indeed aims at increasing the efficiency of the thermodynamic cycle while reducing the construction capital costs. During the last two decades the European Union and IAEA launched projects in support of the development of such a technology: the University of Pisa joined the common efforts providing numerical analyses addressing the thermal-hydraulics aspects of SCWRs. Among the most challenging issues related to the development of SCWRs, the prediction of heat transfer to supercritical fluids probably represents one of the toughest ones. In fact, the interesting phenomenon of heat transfer deterioration can hardly be predicted by both CFD approaches and heat transfer correlations. Since heat transfer deterioration is the consequence of the superposition of dramatic thermophysical properties changes, of buoyancy effects and flow acceleration, generally available approaches are found unable to provide suitable predictions of this complex phenomenon: the development of improved modelling techniques is thus required. The present paper reports on the recent numerical activities performed at the University of Pisa in support of the development of SCWRs, also providing information about the next steps in the research and on possible developments in modelling.