A FINITE ELEMENT MODEL FOR PRE- AND POSTTEST CALCULATIONS OF THE FOREVER-EXPERIMENTS

摘要

To get an improved understanding of the processes occurring during the late phase of a core melt down accident the FOREVER-experiments are currently underway. These experiments are simulating the behaviour of the RPV lower head under the thermal loads of a convicting melt pool with decay heating and simultaneous pressure loads. The geometrical scale of the experiments is 1:10 compared to a common Light Water Reactor. Due to the multi axial creep deformation of the vessel with a non-uniform temperature field these experiments are on the one hand an excellent source of data to validate creep models for different pressure vessel steels; and on the other hand the results of pre-test calculations can be used to optimize the experimental procedure. In this paper a Finite Element model is developed: - using the Computational Fluid Dynamics module the temperature field within the melt pool and within the vessel wall is evaluated. - transient structural mechanical calculations are then performed applying an advanced creep model which takes into account large temperature, stress and strain variations. Post test calculations of the FOREVER-C2 experiment were performed. If the temperature field in the vessel wall is fixed along creeping process, the calculated creep curves disagree with the measurement. Considering the variation of the temperature field, the calculated results show a good agreement with the measurements.