Numerical analysis of hydrodynamic fine fragmentation of corium melt drop during fuel-coolant interaction

Hydrodynamic fine fragmentation of melt drops is important in increasing melt-coolant contact area, and thus directly affects heat transfer, oxidation and solidification. The interfacial instabilities incurred by relative flow and density gradient are the dominant factors for melt drops deformation and fragmentation. In this study, we modelled melt drop breakup behavior using a meshless Lagrangian MPS method, and validated the numerical model with the experimental results. Then, the melt fragments amount, size distribution and normalized perimeter were analyzed under different Weber numbers. The results indicate that the melt drop breakup process could be divided into two phases: initial deformation and fragmentation phase governed by flow inertial force and the subsequent fragments coalescence phase under the impact of fluid surface tension. Fragments amount increased in fragmentation phase but decreased in coalescence phase. The amount of fragments with smaller size (d/d₀ < 0.04) was significantly larger at high Weber number cases, but the amount of large-scale fragments (d/d₀ > 0.05) was equivalent among different weber number cases. The maximum fragments perimeter reached 20 times of the initial melt drop perimeter for case of We = 2618, which was about 3.3 times of that at We = 291.