Impact of oxidized HANATM and Zircaloy-4 cladding materials under high temperature on the coolability of light water reactors

In this study, oxidized HANATM and Zircaloy-4 exposed to steam at a temperature of 1200 °C for a duration of 136–1536 s were characterized, and their coolability under nuclear accident conditions was discussed. Under the given environmental oxidization conditions, the differences in the surface conditions and effective thermal properties of oxidized HANATM and Zircaloy-4 resulted in different degrees of coolability. For different oxidation resistances of these cladding materials, the reduction in their thermal conductivity by oxidation showed a difference, resulting in different heat transport phenomena that determine the Leidenfrost temperature, TL. However, TL did not increase further after the oxide layer reached an equivalent cladding reacted (ECR) of at least 24%, which is the penetration depth of the oxide layer. A 1-D transient heat transfer analysis based on the droplet behavior showed that TL did not increase even after reaching the penetration depth of the oxide layer. The analysis results also indicated that the delay in the heat transfer in the oxide layer did not affect TL after reaching the penetration depth of the oxide layer.