Experimental Investigation of Melt Coolability and Ablation Behavior of Oxidic Sacrificial Material at Prototypic Conditions in Scaled Down Core Catcher

Abstract

To minimize the potential risk of design extension conditions (DEC) with core meltdown, some advanced reactors employ ex-vessel core catchers which stabilize and cool the corium for prolonged period by strategically flooding it. This paper describes the coolability of the melt pool and ablation process in a scaled down ex-vessel core catcher employing sacrificial material which reduces the specific volumetric heat, temperature, and density of the melt pool. To understand these phenomena, a simulated experiment was carried out. The experiment was performed by melting about 500 kg of corium simulant using thermite reaction at about 2500 °C. The bricks of oxidic sacrificial material were arranged in the core catcher vessel which was surrounded by a tank filled with water up to a certain level. After the time required for melt inversion, water was introduced to flood the test section from the top. The melt pool temperatures were monitored at various locations using “K” and “C” type thermocouples to obtain ablation depth at different elevations with time. The results show that the coolability of the molten pool in the presence of water for the present geometry is achievable with outside vessel temperatures not exceeding 100 °C. A ceramic stable crust was observed at the top surface of the melt pool, which prevented water ingression into the molten corium. The ablation rate was found to be maximum at the lower corners of the brick arrangement with the maximum value being 0.75 mm/s. An average rate of about 0.18 mm/s was obtained in the brick matrix.