LIVE EXPERIMENTS ON THE IN-VESSEL MELT POOL BEHAVIOUR WITH EXTERNAL COOLING CONDITIONS AND THE SIMULATION RESULTS WITH A COUPLED MELCOR-PECM APPROACH

摘要

The LIVE program investigates late in-vessel melt pool behaviour in case of a severe accident under large scale 3D conditions and different relocation modes. The melt retention by flooding the reactor vessel externally is regarded as an effective severe accident management strategy. One question is how the melt pool heat transfer to the vessel walls depends on different external cooling conditions. In this paper, the melt's thermal behaviour, such as melt temperature, heat flux and crust profiles, of two LIVE tests with different external coolant temperatures are compared: one with nucleate boiling condition, the other with sub-cooling condition. Other test conditions, such as simulant material, heating power and the upper boundary condition were similar in the two experiments. The experimental results are simulated with coupled MELCOR and PECM codes. The program DINAMO, which was developed at KIT, was used to realize this coupling exchange. Using DINAMO it is possible to add new or enhanced models to the nuclear safety code MELCOR without the necessity of changing the MELCOR source code. Thus, it is possible to combine the advantages of the CFD-based Phase-Change Effective Convectivity Model (PECM) and MELCOR as an integral code. Implementing the advantages of the PECM code to MELCOR, such as the temperature distribution in the molten pool, heat flux distribution on the curved vessel wall and treatment of non-eutectic solidification, the prediction accuracy of MELCOR can be considerably improved concerning the analysis of core melt behaviour in the lower plenum during a core melt accident.