Experimental investigation on reflooding of debris beds

•A downcomer can significantly improve the beds’ coolability.•The perforated downcomer was occupied by steam and thus without effect.•Comparable quenching times in DEBRIS and PRELUDE.•Good agreement of MEWA calculation with the experiment in case of open downcomer. In case of a severe accident, continuous unavailability of cooling water to the core may result in over heating of the fuel elements and the loss of core integrity. Under such conditions a structure of heated particles of different sizes and shapes (debris) may be formed by fragmentation of core material inside the reactor pressure vessel (RPV). To avoid any damage to the RPV the reflooding is of great importance in order to establish long-term coolability. In the framework of an GRS R&D project and the SARNET network, specific experimental investigations on the coolability of debris beds with different bed contents (e.g. mono-/polydispersed bed of stainless steel balls with 6/3/2mm in diameter, irregularly shaped particles from PREMIX experiments – KIT) and various initial bed temperatures at ambient pressure (1bar) were carried out at IKE using the DEBRIS test facility and the small DEBRIS test set-up. In both experimental configurations the particles are volumetrically heated by an electromagnetic induction coil to predefined temperatures and then flooded with subcooled water from top (top-flooding) or from bottom (bottom-flooding). Depending on the flooding situation the cooling down (quenching) behaviour of the beds varies significantly due to the change of co- and counter-current liquid–vapour flow and respective heat transfer between solid and generated two-phase flow. This paper presents the main experimental results of systematic quenching studies at IKE. Furthermore, some representative results of benchmark experiments performed by IKE and IRSN (PRELUDE test facility) in the frame of the SARNET joint work are demonstrated. Finally, exemplary comparisons between experimental data and numerical results of simulations with IKE’s code MEWA-2D are shown.