Development on Applying Phase Diagram to Evaluation Method of Refractory Layer Erosion for Passive Debris Cooling System: Fundamental Study of UO_2-ZrO_2-Al_2O_2 Phase Diagram

摘要

In the event of a severe accident at a nuclear power plant, it is necessary to prevent the release of radioactive materials into the environment due to damage to the containment vessel. If debris falls down from the reactor vessel onto the pedestal floor, concrete forming the pedestal floor will be eroded, producing non-condensable gases resulting in pressurization of the containment vessel. Therefore, we have been developing a safety system to stabilize the core melt and avoid molten core concrete interaction by installing a refractory layer between the reactor vessel and the concrete. In order to estimate the effect of the refractory layer, it is necessary to consider the reaction between corium and the refractory layer. It is effective to apply a phase diagram to evaluation of the refractory layer erosion, including a eutectic reaction. In this study, we investigated the phase diagrams of corium and candidate refractory materials. Specifically, phase diagram analysis and heating tests of UO_2-ZrO_2-Al_2O_3 were carried out. The results of the phase diagram analyses were consistent with experimental data. The results of this study suggest that it should be possible to apply phase diagram analysis to the evaluation of refractory layer erosion.