Experimental simulation and theoretical analysis of molten-corium/structure interaction

In analysis of core degradation in boiling water reactors, two processes are of particular importance: the heatup and melting of the lower core plate in contact with molten fuel and the interaction between molten debris and the lower head and its various penetrations. Accurate modeling of the simultaneous melting/freezing phenomena occurring between molten corium (UO2 mixed with liquefied Zircaloy and steel) and solid structures is very important in predicting the overall consequences of hypothetical reactor accidents. To provide data for the assessment of models developed for the APRIL code, an experimental program based on simulant materials was undertaken at Rensselaer Polytechnic Institute. To identify appropriate simulant materials, extensive comparative and scaling analyses were performed. As a result, two main simulant materials were selected: tetracosane paraffin (the solid) and Wood's metal (the melt). The X-radiography technique that was used in the experiments allowed for visualization of the corium attack and the resultant wall ablation. The results of these measurements were used as the basis for the development of analytical models and for the verification of the various modeling assumptions made