Experimental study on self-leveling behavior of solid debris beds

Abstract

In Sodium Cooled Fast Reactors (SFRs), as a hypothetical Disruptive Core Accident (DCA) occurs, the molten fuel flows downward and contacts with sodium liquid. Due to violent interaction with subcooled sodium, the molten disintegrates into small particles, then disperses in the coolant, and eventually accommodates in the core debris catchers (such debris trays) in the lower plenum of the reactor vessel. The debris mound formed in conical shape will flatten itself, which is caused by sodium vapor released from the debris bed due to the decay heat generated by fuel debris. This phenomenon is called self-leveling behavior. This mechanism is an inherent safety in SFRs, which ensures the integrity of reactor vessel from the molten fuel. Thus, the risk of releasing radioactive material can be prevented.
In order to understand the characteristics of self-leveling behavior, series of experiments of homogeneous (simulated) particle beds have been carried out by decompressed and bottom heated methods in the previous studies. In this study, a further investigation on self-leveling behavior of mixed solid debris beds is focused on by using gas injection method. Furthermore, an empirical model is proposed to predict the transient change of the debris bed height with time.