A comparative study on local fuel-coolant interactions in a liquid pool with different interaction modes

From the past analyses of Core Disruptive Accidents (CDA) for sodium-cooled fast reactors, it has been recognized that with the assumption of very pessimistic conditions, a large-scale molten-fuel pool, which contains sufficient amount of fuel to achieve the prompt criticality by fuel compaction, might be formed. Due to the potential entrapment of liquid sodium into the fuel pool, local Fuel-Coolant Interaction (FCI) in the pool is considered to be one of the various initial factors resulting in such compactive fluid motions. To ascertain the mechanisms underlying this interaction more reliably, in our earlier publication a number of simulated experiments was carried out by releasing a given amount of liquid water into a molten pool (comprised of a low-melting-point alloy) using the PMCI (Pressurization characteristics in Melt-Coolant Interaction) facility recently developed at the Sun Yat-sen University. In this work, motivated to acquire more enhanced understanding, the effect of interaction mode on local FCIs is further investigated by adding new experimental data within the Melt-Injection (MI) mode. From detailed analyses, it is found that except the existence of a similar impact of melt temperature, much difference in the influence of other experimental parameters such as the liquid volume delivered, water subcooling along with the pool depth is observed. In addition, the performed analyses in this work also confirm that compared to previous Coolant-Injection (CI) mode, the mechanical energy conversion efficiency is much lower within the MI-mode condition. This work provides a large palette of beneficial experimental data and evidence for the better understanding of CDAs and improved verifications of fast reactor safety accident analysis codes in China.