To simulate a fuel and coolant interaction phenomenon during a postulated severe accident in a nuclear reactor, a series of experiments were performed using a partially oxidized corium, which is a mixture of UO2, ZrO2, Zr, and stainless steel. The composition of the melt was chosen such that a separation of the oxidic liquid from the metallic liquid occurred due to the existence of a miscibility gap. A melting and solidifying experiment and two fuel and coolant interaction experiments to explore the possibility of an energetic steam explosion were performed in the TROI facility.
The placement of a metal-rich layer consisting of U, Fe, and ZrO2 beneath the oxidic corium layer due to the existence of a miscibility gap was observed in the melting and solidifying experiment. An energetic steam explosion with a propagation of the dynamic pressure wave was observed in one test out of the two tests. The physical and chemical analyses were performed for the corium particles collected after the experiments. It is shown that U, Zr, and Fe formed a heterogeneous mixture and the morphology was in irregular shape with many pores at nonuniform sizes. In the case of nonenergetic interaction, where the melt temperature was lower than the energetic case, the mean particle size was bigger than that of the energetic case, and the melt-water interaction resulted in a substantial amount of hydrogen gas generation, while the amount of hydrogen gas generation was negligible in the case with an energetic steam explosion.