Droplets Flow and Heat Transfer at Top Region of Core in Reflood Phase

摘要

The heat transfer at the top region of core is complicated due to the strong thermal non-equilibrium just after the start of reflood phase in a postulated PWR-LOCA experiment. The film taken with a high-speed cinecamera shows upward droplets flow and falling water film on the non-heated rod just after the start of reflood at elevation 3235 mm above the bottom of heated length of heater rods in Slab Core Reflood Test. The measured mean diameter of droplet is about 1 mm. This value of mean diameter is larger than the measured result for the annular dispersed flow in a pipe. On the other hand, the corresponding Weber number is smaller than the Weber number in the accelerating flow obtained in the previous studies. The calculated heat transfer coefficient of the droplets flow approximately agrees with the sum of Dittus-Boelter's convective heat transfer term and radiative heat transfer term evaluated with the network analysis by Sun et al. (Atomindex citation 15:059454)