Insights from the FOREVER-Programme and the accompanying finite element calculations

To obtain an improved understanding and knowledge of the melt pool convection thermal loads, the vessel creep, and vessel failure modes occurring during the late phase of a core melt down accident the FOREVER-experiments have been performed at the Royal Institute of Technology, Stockholm. These experiments simulated the behaviour of the lower head of the RPV under the thermal loads of a convecting melt pool with decay heating, and under the pressure loads that the vessel experiences in a depressurised vessel scenario. A Finite Element model was developed simulating melt pool convection and calculating the temperature field within the melt pool and within the vessel wall. After performing successful pre- and post-test calculations, a discussion about the lessons learned from the experiments and the analyses led to the idea of providing a vessel support and an external water-flooding device.