Research on Heat Transfer Calculation of Ellipsoidal Melt Pool

Abstract The in-vessel melt retention (IVR) technology, as one of the typical technologies to cope with severe accidents in third-generation nuclear power, has been widely used in pressurized water reactor (PWR) nuclear power plants. Based on the computational study of melt pool heat transfer in VVER-1000 under severe accidents, a steady-state heat transfer model of melt retention inside the elliptical lower head pressure vessel was established, and the wall heat flux at each place of the ellipsoidal lower head wall, the thickness of the oxide crust formed by the liquid-phase oxidic layer being cooled and solidified, the residual wall thickness of the pressure vessel, and the failure of the pressure vessel were computed and analyzed. The calculation results show that: the heat flux at the bottom of ellipsoidal pressure vessel lower head is the smallest, the heat flow distribution on the wall surface from the ellipsoidal part to the cylindrical part is discontinuous, and obvious heat focusing effect is observed in the metal layer; the thickness of oxidic crust decreases with the increase of axial height of ellipsoidal melt pool, and the higher the volumetric heat release rate of oxidic pool is, the smaller the thickness of oxidic crust is; the wall of the pressure vessel starts to melt at a certain place of the lower head, and the thickness of wall thins with the increase of heat flux. The wall thickness decreases with the increase of heat flux, and the ablation of the pressure vessel wall increases to the maximum value due to the drastic increase of heat flux in the metal layer area, and the thinner the metal layer is, the smaller the wall thickness of the pressure vessel in contact with the metal layer is, and the greater the probability of failure of the pressure vessel is; therefore, the wall surface of the pressure vessel in contact with the metal layer is the most dangerous position in the case of a serious accident.