Chemical Reactions Between Light Water Reactor Core Melt and Concrete

The chemical reactions taking place during the core melt/concrete interaction phase of a light water reactor core meltdown accident have been compiled in view of their major effects on the course of the accident. There are two main processes of chemical interactions between core melt and concrete, which have a strong influence on the composition and properties of the melt:

1. successive oxidation of the metallic fraction of the melt by water vapor and carbon dioxide released from the concrete structures
2. intermixture of the oxide fraction of the melt with molten concrete.

The oxidation behavior of the main constituents and fission products was qualitatively investigated by crucible experiments. Its influence extends to the heat balance and the partition of the heat sources as well as to the miscibility behavior of the melt. The solidification temperatures of the metallic and oxide fractions of the melt depend on their compositions. They were obtained for different types of core melt and concrete, basaltic, and limestone, as a function of the degree of oxidation and of the amount of concrete dissolved in the oxide melt.