Experimental study on local fuel–coolant interaction in molten pool with different melts

•New experiments conducted by delivering water into molten LBE pool.•Similar trend in transient behavior and parametric effect confirmed for two melts.•Despite lower thermal diffusivity, water cooling on surrounding LBE is limited.•Pressurization in LBE experiments is larger due to enhanced melt density.•Compared to static pressure, melt depth is affected more by melt penetration. In a Core Disruptive Accident (CDA) of Sodium-cooled Fast Reactor (SFR), by supposing rather pessimistic condition, a large molten fuel pool would be possibly formed that contains enough fuel with the potential to exceed prompt criticality due to fuel compactive motion. Local fuel-coolant interaction (FCI) in the molten pool is identified as one of the typical inducing factors that may result in such compactive motion. To understand the characteristics of this interaction, owing to the PMCI (Pressurization characteristics in Melt-Coolant Interaction) facility recently established at the Sun Yat-sen University, in our earlier publications two series of simulated experiments, i.e. Coolant-Injection (CI) experiments and Melt-Injection (MI) experiments, have been conducted, in which water and low-melting-point Bi-Sn-In alloy (60% Bi, 20% In and 20% Sn) were used respectively as the simulant materials for sodium and molten fuel. In this study, aimed at checking the generality of the experimental findings as well as achieving further enhanced understanding on this interaction, a large number of experiments are newly performed through delivering water into a simulated molten fuel pool comprised of Lead-Bismuth Eutectic (LBE) alloy (another low-melting-point alloy). Through detailed comparisons (with the CI-mode experiments using Bi-Sn-In alloy), it is found that a similar trend in the transient pressure and temperate history as well as the overall effect of experimental parameters (such as water quantity, melt and water temperature, water-lump shape and melt depth) on the pressurization characteristics can be reproduced for the new LBE experiments. Despite a much lower thermal diffusivity, for the LBE experiments it is confirmed that the most likely reason resulting in the limited pressurization as water volume increases should be also primarily owing to the isolation effect of vapor bubbles generated at the melt-water interface. Possibly due to the enhanced melt density which facilitates the penetration of melt through vapor bubbles, under the same parametric condition the pressurizati