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

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 B4C at 1450 degrees 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 H2O gas on the reaction between the molten metal and B4C 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 B4C 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 degrees C was obtained.