Abstract
During a severe accident in a nuclear reactor, the core can melt and the melt can be relocated into the lower head forming a melt pool. If the vessel fails, the molten corium can be relocated in the containment cavity forming a melt pool. Such a pool or bed, if not quenched in time, may interact with the concrete basement of the cavity causing its ablation resulting in generation of non-condensable gases and water vapor, which poses a threat of containment pressurization, explosion and ground contamination. In order to devise the strategy to retard the progression of severe accidents in stipulated time, understanding of the corium coolability is very much essential. Coolability of molten corium in such ex-vessel condition is limited depending on depth of water ingression. But the question arises about to what extent the water will ingress? Thermal and physical properties of corium change drastically with increase in concrete percentage which strongly affects the coolability. The phenomenon of corium coolability is not fully understood owing to its complexity involving multi phase multi component heat and mass transfer. In order to better understand the phenomenon, experiments at present are the only answer; since modeling the complex phenomenon is still difficult. In order to gain some insights into melt coolability, the authors have carried out an experiment on quenching behavior of top flooded molten pool. A simulant material (sodium borosilicate glass) of about 25 liters at temperature 1200 oC was poured into the test section and was flooded from top with water. The transient temperature of the molten pool was measured. The experiment highlighted that, under adiabatic conditions, water ingression occurred only upto 10 mm depth, below which a stable solid crust was formed which limited the heat transfer. Also, no gap between crust and vessel was formed.
Published Version
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