Natural convection heat transfer experiment in a hemispherical pool

Natural convection plays an important role in determining the thermal load from molten core accumulated in the reactor vessel lower head during a severe accident. Several numerical and experimental programs were conducted to study the heat transfer in the molten pool. Previous investigations were mostly related to the rectangular and semicircular pools. Except for COPO, UCLA, ACOPO, and BAU, previous investigations suffer from inadequate representation of high modified Rayleigh number (Ra′) in the hemispherical pool that may be formed in the reactor core and lower plenum. Thus, experimental work is conducted utilizing SIGMA SP (Simulant Internal Gravitated Material Apparatus Spherical Pool) producing high Ra′ turbulent natural convection in a hemispherical pool up to 5.3×10¹¹. The heating method has already been tested in SIGMA CP (Circular Pool). Six thin cable-type heaters, each with a diameter of 6 mm, are employed to simulate internal heating in the pool. They are uniformly distributed in the hemispherical pool to supply a maximum of 7.8 kW power to the pool. SIGMA SP has the inner and outer diameters of 500 mm and 520 mm, respectively. The upper flat plate and the curved wall of pool, with a 10 mm thick stainless steel plate, are cooled by a regulated water loop. A water-cooling system is used to maintain the temperature of water surrounding the test section nearly constant with time. This study focuses on quantifying the directional heat losses, angular heat flux distribution, and temperature distribution inside the molten pool.