Numerical study of convective heat transfer between core and steam generator in severe accident with loss of heat removal to secondary side of VVER reactors

The article discusses the possibility of overheating and failure of heat exchanging tubes in VVER steam generators in the course of severe accidents. The importance of this phenomenon is due to the risk of bypassing the containment by radioactive substances. Natural convection of superheated steam in the hot leg of the main circulation loop is considered as the major mechanism for heat transfer from the core to steam generators. To model convective flows and steam temperature distribution in a system, three-dimensional CFD codes are used. The simulation results demonstrate that the intensity of convective heat transfer from reactor to hot collector of steam generator is insufficient for significant heating and catastrophic degradation of strength of the heat exchange tubes material.