An Experimental investigation on self-leveling behavior of debris beds using gas-injection

Cheng, S.; Yamano, Hidemasa   ; Suzuki, Toru; Tobita, Yoshiharu; Gondai, Yoji*; Nakamura, Yuya*; Zhang, B.*; Matsumoto, Tatsuya*; Morita, Koji*

Although in the past, several experiments have been conducted to investigate the self-leveling behavior of debris beds, most of these were under comparatively lower gas velocities, the findings of which might be not directly applicable to actual reactor accident conditions. Current experiments were conducted using gas-injection in a large-scale cylindrical tank, in which nitrogen gas, water and different kinds of solid particles, simulate the fission gas, coolant and fuel debris, respectively. During experiments, to accomplish the bubble-based leveling as expected in reactor conditions, two experimental approaches, termed respectively as the gas pre-charge method and the pressure-adjustment method, have been attempted. Through elaborate comparisons and evaluations, it is found that compared to the gas pre-charge way the pressure-adjustment method can alleviate the liquid disturbance from bottom inlet pipelines more effectively. Further, based on experimental data using pressure-adjustment method, influence of particle size, particle density and gas flow rate on the leveling has been confirmed under current higher gas velocities. In addition, the liquid convection in the water pool, which is not evident within lower gas velocities, is observed to play an important role within current conditions, especially for experimental runs using larger-size but lower-density particles at rather higher gas flow rates.