Reaction behavior of molten 316L stainless steel with B4C at 1450℃ during a core melt accident of BWR

• B 4 C reacts with molten stainless steel at 1450 °C and dissolves. • H 2 O in the atmosphere is not related to a dissolution rate of B 4 C. • Borides of Fe and Cr precipitate at the interface of B 4 C and stainless steel. • Precipitated C at the interface reduces the dissolution rate of B 4 C. In the severe accident at the Fukushima Daiichi Nuclear Power Station, molten core material migrated downward and generated fuel debris at the bottom of the containment vessel and other locations. The composition of the generated melt changes as it moves because it reacts with structural materials. The composition of fuel debris is determined by the initial melt composition and reactions during migration. In this study, the reaction rate between molten 316 L stainless steel and B 4 C at 1450 °C was experimentally investigated, assuming that control rods would melt and stainless steel-based melts would stagnate in the lower plenum in boiling water reactors. The effect of H 2 O gas on the reaction between the molten metal and B 4 C was investigated, and an estimation of the rate-limiting process of the reaction and the rate of B₄C was carried out. The rate-limiting process of the reaction changed from the dissolution reaction of B 4 C to the diffusion of alloying elements and the precipitation of carbon as the reaction proceeded. Including these rate-limiting processes, an overall dissolution rate of B₄C melting in the B₄C/molten stainless steel reaction at 1450 °C was obtained.