Characteristics of self-leveling behavior of debris beds in a series of experiments
Cheng, S.; Yamano, Hidemasa ; Suzuki, Toru; Tobita, Yoshiharu; Nakamura, Yuya*; Zhang, B.*; Matsumoto, Tatsuya*; Morita, Koji*
During a hypothetical core-disruptive accident (CDA) in a sodium-cooled fast reactor (SFR), degraded core materials can form conically-shaped debris beds over the core-support structure and/or in the lower inlet plenum of the reactor vessel from rapid quenching and fragmentation of core material pool. However, coolant boiling may lead ultimately to leveling of the debris bed that is crucial to the relocation of molten core and heat-removal capability of debris bed. To clarify the mechanisms underlying this self-leveling behavior, a great amount of experiments were performed within a variety of conditions in recent years under the constructive collaboration between Japan Atomic Energy Agency (JAEA) and Kyushu University (Japan). The present contribution synthesizes and gives detailed comparative analyses of those experiments. Effects of various experimental parameters that may have potential influence on the leveling process such as boiling mode (bottom-heated, depressurization boiling and gas injection), particle size, particle density, particle shape (spherical and non-spherical), boiling intensity (or gas flow rate), water depth along with column geometry, were investigated, thus, giving a large palette of favorable data for better understanding of CDAs and improved verifications of computer models developed in advanced fast reactor safety analysis codes.