TIM model application to corium concrete interaction: Ablation regimes and instabilities

This paper deals with the extension of the Transient Interface Model (TIM), initially developed for in-vessel and ceramic dissolution situations, to molten core concrete interaction (MCCI) conditions. The application of the TIM model to MCCI leads to evidence of two interaction regimes, depending on the nature of the concrete. For siliceous concrete, there is no crust nor mushy zone at the ablated corium/concrete interface and the interface temperature is close to the liquidus temperature of concrete (Low Interface Temperature-LIT regime). For limestone common sand concrete, a mushy zone or crust can form at the interface between the corium and the concrete and the interface temperature (between mushy zone and melt) is close to the pool liquidus temperature (High Interface Temperature-HIT regime). No intermediate regime exists, but rather regime transitions (HIT to LIT, or LIT to HIT), which may occur on a limited number to all interfaces during MCCI. The work described herein demonstrates that these regime transitions are abrupt and happen within a short time period. These regime transitions are shown to cause ablation instabilities. Many combinations of regime transitions on various interfaces at various pool temperatures (in comparison to pool liquidus) are possible. Only a limited number of these transitions have been calculated; the results indicate that different trends in temperature evolutions observed during MCCI tests can be reproduced. New calculations of the CCl2, CCl3 and M3B tests are presented.