Heat transfer characteristics of single-layer and two-layer corium pool in elliptical lower head

In this study, we investigated the characteristics of natural convection heat transfer of single-layer and two-layer corium pool in the elliptical lower head by the numerical method. Numerical simulations were performed using FLUENT software with the WMLES (Wall-Modeled Large Eddy Simulation) turbulence model, solid-liquid phase change model and the VOF (Volume of Fluid) model. The heat transfer characteristics such as pool temperature field, flow velocity field and heat flux distribution were obtained. For the single-layer corium pool, different degrees of melting occurred on the wall surface from about 1712 mm arc length inside the inner wall to the liquid level. The transient velocity field of single-layer corium pool showed that the natural convection first occurs near the wall surface and then gradually forms in the center of the corium pool as the temperature rises. When the quasi-steady state is reached, the upper part of the pool forms strong turbulence, while the lower part has lower velocity and forms transverse flow. For the two-layer corium pool, the lower head wall is more severely melted than the single-layer configuration. Whereas, the crust at the wall near the stratified interface is only slightly melted due to the lower flow rate and weaker heat transfer capacity. The research revealed the flow and heat transfer mechanisms of corium pool, and provided reference for the technology design, system optimization and safety evaluation of the IVR (In-Vessel Retention) – ERVC (External Reactor Vessel Cooling) severe accident mitigation strategy for the large-scale advanced pressurized water reactor. •Heat transfer characteristics of corium pool in elliptical lower head were simulated by CFD method.•Melting of vessel wall and solidification of corium were simulated coupling heat transfer.•Results revealed the flow and heat transfer mechanisms of corium pool.