Behavior of the melt pool in the lower plenum of the reactor pressure vessel. Review of experimental programs and background of the LIVE program

Retention of core melt in the lower plenum of the reactor pressure vessel (RPV) is one of the severe accident management strategies, which were investigated quite intensely in the last years. In several organizations over the world experiments were conducted to enhance this strategy which has already been approved to be a part of the severe accident management strategy for the Loviisa plant (Finland) and for the Westinghouse AP-600 design. The most important experiments to reach this goal were: - COPO experiments at Fortum Nuclear Services and CEA (France) - BALI experiments at CEA (France) - SIMECO experiments at KTH (Sweden) - ACOPO experiments at the University of California, Santa Barbara (USA) - RASPLAV experiments at the Kurchatov Institute (Russia) These investigations were performed not only to study the possibility of retaining the core melt inside the reactor pressure vessel (as an accident management measure) but also to understand the fundamental behavior of the molten pool inside the RPV (for homogeneous and stratified configuration of the molten pool). With the help of the results of these experiments we want to identify models and correlations, which can be used in severe accident computer codes. Forschungszentrum Karlsruhe is involved in this research with the experimental LIVE (Late In-Vessel Phase Experiments) program. The major objective of the current report is to summarize the findings obtained in earlier experimental programs on melt behavior in the RPV in order to provide a coherent picture of the state of knowledge and to identify the remaining uncertainties. Further on the report will show how these uncertainties shall be investigated in the LIVE experimental program. (orig.)