Molten core relocation analysis of Cora-17 And Cora-18 for the SAMPSON/MCRA validation

Severe core damage accident analysis of Boiling Water Reactor (BWR) has gained more importance after the Fukushima-Daiichi nuclear accident in March 2011. The accident progression phenomena are governed by those mechanisms including chemical, metallurgical as well as thermal hydraulics interactions among the core materials. An exothermal reaction, i.e., high temperature Zirconium-steam interaction could lead to a temperature excursion affecting the melting progress by a positive feedback. Moreover the geometry of a BWR core complicates the modeling. The existence of channel boxes and control blades represents a significant challenge for heat transfer calculations, in particular with the thermal radiation that could not be neglected. In this paper the CORA-17 and CORA-18 experiments carried out at KfK have been selected as validation basis for the information on the damage progression of a BWR fuel element. Simulations of those experiments have been performed with the severe accident analysis code SYSTEM SAMPSON/MCRA where the models required for simulating those tests have been implemented. In the experiments the Zirconium oxidation assumes to be more important as the temperature gets higher than 1300 K, leading to a considerable heat release and hydrogen generation. Moreover a quenching phase followed the heaters shut down in the CORA-17 experiment, resulting in a much more hydrogen generation. Calculated temperature transient, rate of hydrogen generated and effects of oxidation for both CORA-17 and CORA-18 will be compared with the corresponding experimental results.