Effect of sea salt on the interaction between simulated corium and concrete

During the progression of the severe accident at the Fukushima Daiichi Nuclear Power Station, seawater flowed down to the lower plenum and was predicted to react with molten corium and concrete. For the removal and storage of fuel debris, knowing the effects of seawater components on the characteristics of reaction products in the fuel debris is crucial. To understand changes in the microstructure of fuel debris, a reaction test was conducted by introducing sea salt to simulated corium and concrete under a temperature gradient. Three distinctive microstructures were formed during the reaction test: (i) oxide precipitated in silicate glass, (ii) metallic precipitates, and (iii) unmelted but thermally degraded concrete. Among the components of sea salt, sulfur formed iron sulfide within the metallic precipitate. It was predicted to form through a reaction between stainless steel and SO_x gas, which was released by the thermal decomposition of sea salt. Analysis of vaporized species indicated that most of Cl, some Na and K in the sea salt might volatilize during heating rather than react with simulated corium and concrete. Calcium and a small amount of Mg, Na, and K in the sea salt might be trapped in the silicate glass.