EXPERIMENTAL SIMULATION OF CERIUM DISPERSION PHENOMENA IN DIRECT CONTAINMENT HEATING

In a direct containment heating (DCH) accident scenario, the degree of cerium dispersion is one of the most significant factors responsible for the reactor containment heating and pressurization. To study the m echanisms of the cerium dispersion phenomenon, a DCH separate effect t est facility of 1:10 linear scale for Zion PWR geometry is constructed . Experiments are carried out with air-water and air-woods metal simul ating steam and molten core materials. The physical process of cerium dispersion is studied in derail through various instruments, as well a s with flow visualization at several locations. The accident transient begins with the liquid jet discharge at the bottom of the reactor pre ssure vessel. Once the jet impinges on the cavity bottom floor, it imm ediately spreads out and moves rapidly to the cavity exit as a film fl ow. Part of the discharged liquid flows out of the cavity before gas b lowdown, and the rest is subjected to the entrainment process due to t he high speed gas stream. The liquid film and droplet flows from the r eactor cavity will then experience subcompartment trapping and re-entr ainment. Consequently, the dispersed liquid droplets that follow the g as stream are transported into the containment atmosphere, resulting i n containment heating and pressurization in the prototypic condition. Comprehensive measurements are obtained in this study, including the l iquid jet velocity, liquid film thickness and velocity transients in t he test cavity, gas velocity and velocity profile in the cavity, dropl et size distribution and entrainment rate, and the fraction of dispers ed liquid in the containment building. These data are of great importa nce for better understanding of the cerium dispersion mechanisms.