Experimental investigation of melt infiltration and solidification in a pre-heated particle bed

Abstract

Fluid infiltration, solidification, and remelting in a particle bed are complex phenomena that can occur in the lower head of a reactor pressure vessel (an in-vessel phenomenon) or in the reactor cavity below the vessel (an ex-vessel phenomenon) during a severe accident in a nuclear power plant. When the non-homogeneous corium, consisting of metal and oxide components, reheats, the lower-melting metals will melt first and move downward to the bottom of the reactor pressure vessel. This will change the global debris bed configuration and its physical and chemical properties, and thereby actively influence the accident progression, specifically the mode and timing of possible vessel failure and the melt characteristics upon release. Similar ex-vessel debris can form on the cavity floor below the vessel, which can threaten containment integrity if stable cooling is not established. In this paper, we present an experimental program employing recently constructed MRSPOD (multicomponent remelting, relocation, and solidification in porous debris) facility that mainly investigates melt infiltration, solidification, remelting, and relocation in a particulate debris bed. The facility uses a 12 × 130 cm2 (OD × Length) quartz tube in a cylindrical furnace and allows a debris bed to be configured, heated, and/or pressurized prior to fluid infiltration through the bed. The MRSPOD experiments were instrumented with thermocouples (TCs), fiber Bragg grating (FBG) sensors, laser sensor, video, and infrared cameras, which are essential in describing the overall melt infiltration and solidification behavior. Here, a eutectic Sn–Bi melt with superheat temperature between 50 and 70 °C is poured into a preheated particle bed consisting of 1.5-mm spherical particles made of either copper (Cu), Sn-coated Cu, stainless steel (SS), Sn-coated SS, and/or glass beads to study the effect of thermal properties and wettability on the melt infiltration. Moreover, melt infiltration into a single-layer, multi-layer, and two-columnar particle beds is performed. Measurements from TCs, FBGs, and observations from video cameras have revealed a non-linear kinetics of melt infiltration. Moreover, the extracted ingots after the experiments have shown the complex infiltration process under similar test conditions.