Simulation of Molten Corium Concrete Interaction in a Stratified Configuration: The COMET-L2-L3 Benchmark

In the late phase of Molten Core Concrete Interaction (MCCI) the ablation rate becomes low and the gas flow rate issued from the concrete decomposition is reduced. Moreover the oxide phase becomes lighter than the metal phase due to the addition of the light oxide from the concrete. A large density difference and a low gas flow rate ensure that a stratified configuration will occur. The stratified configuration has then to be taken into account in the MCCI simulation tools. Only few experimental programs were conducted with stratified pools; among them the BETA tests were performed at FZK with a large test matrix. The COMET-L2 and L3 experiments were recently conducted at FZK in a stratified configuration. In the frame of SARNET WP11.2 a benchmark was organised in order to compare the MCCI code results regarding these experiments. COMET-L2 was used for a post-test simulation and after that COMET-L3 was used as a blind simulation. The participants and codes were AREVA with COSACO, CEA with TOLBIAC-ICB, EDF with TOLBIAC-ICB, FZK with WECHSL, GRS with MEDICIS and WEX, IRSN with MEDICIS, UPM with MELCOR and VTT with MELCOR. The results show a large discrepancy between the code results, due to the different models used in the stratified regime.