Measurement of ablation and estimation of the interfacial heat flux profiles during molten corium concrete interactions

Catastrophic fire incidents in nuclear reactors can cause rapid ablation of the concrete during molten corium concrete interactions (MCCI). In this work, experimental and numerical analysis are carried out to evaluate the interfacial heat flux profiles between the concrete and molten metal. The granite based concrete which contained Ordinary Portland Cement (OPC) is used and it's interaction with the molten mixture of MnO and TiO₂ are studied. The transient temperature distribution inside the concrete and ablation depths are measured after pouring the molten metal into the concrete cavity. It is observed that the maximum ablation occurred at the bottom of the cavity due to initial severe interaction of molten metal with the concrete. The ablation depths at the base and the side walls are 28 mm and 15 mm, respectively. Comparison with 1D heat transfer and semi-infinite model confirmed that heat transfer in concrete can be analysed using semi-infinite medium approach up to Fourier number of 0.45. An inverse heat transfer problem is solved using sequential function specification method and estimated the interfacial heat flux profiles from measured transient subsurface temperature distribution. Subsurface temperatures are measured using sheathed K-type thermocouples. Consistent with the experimental observations, higher heat fluxes are observed for thermocouples located at the bottom and lower heat flux are observed for thermocouples placed at the side walls and corners. The heat flux profiles rise from the beginning, reach to a peak value and then, gradually decreased with time. Heat flux values are observed to be in the range of 1—19 kW/m². The experimental observations of this study are compared with the literature and the possible values of ablation depths for the case of the actual nuclear reactor are estimated.