Investigations on the Debris Bed Formation Behavior of the Heated Solid Particles

Abstract During the later stages of the postulated Core Disruptive Accidents (CDAs) of a sodium-cooled fast reactor, the porous debris bed is expected to form in the lower plenum region. The geometries of the debris beds are significant for the coolability and the risk of neutronic subcriticality. In this paper, the sedimentation and formation behavior at different factors of the debris bed is experimentally investigated; the mound dimple diameter and mound dimple depth are chosen as the critical quantitative parameters, which can express the flatness of the debris bed intuitively. The results show that the particles formed a concave debris bed at normal temperature. The general tendency of developing a relatively large dimple area is observed with larger nozzle size, lower particle diameter, lower particle density, and higher water level. The prediction model of the mound dimple volume of the debris bed is established, and the error is less than 30%. When the particles are in the film boiling regime, the vapor film reduces the friction between the particle and fluid, thereby increasing the impact momentum and driving the debris bed in a flat direction.