Quenching Experiments: Coolability of Debris Bed

Abstract

In the case of a severe accident, continuous unavailability of cooling water to the core will result in overheating and subsequent meltdown of the fuel elements that would eventually result in the loss of fuel integrity. Under such conditions a porous structure, which is made of heat-generating particles of different sizes and shapes, may be formed. The presence of decay heat in such a debris bed poses a critical threat to the reactor pressure vessel (RPV). To avoid any damage to the RPV, the removal of decay heat from the debris bed is of great importance. The debris bed needs to be quenched by water either flooding from the top or flooding from the bottom until continuous cooling is established. To investigate the quenching behavior of the debris bed by means of experiments, the nonnuclear test facility “DEBRIS” has been established at Institut für Kernenergetik und Energiesysteme (IKE). Experimental investigations of quenching behavior for a preheated debris bed, at various initial bed temperatures, are carried out at IKE. In the new quenching tests, the cooling-down behavior of a superheated polydispersed particle bed from stainless steel spheres at different thermohydraulic conditions has been investigated. Numerical investigation with IKE’s MEWA-2D code has also been carried out for the quenching experiments in order to promote better understanding of the experimental results as well as to verify the code’s applicability to the quenching process.