Transient refractory material dissolution by a volumetrically-heated melt

• We describe a test investigating ceramic dissolution by a molten non-eutectic melt.
• The evolution of the interface temperature between melt and refractory is measured.
• A theoretical model describing dissolution kinetics is proposed.
• When dissolution stops, interface temperature is the liquidus temperature of the melt.

The present work addresses the question of corium–ceramic interaction in a core catcher during a core-melt accident in a nuclear power plant. It provides an original insight into transient aspects concerning dissolution of refractory material by a volumetrically heated pool. An experiment with simulant material (LIVECERAM) is presented.Test results clearly show that dissolution of solid refractory material can occur in a non-eutectic melt at a temperature which is lower than the melting temperature of the refractory material. During the dissolution transient, the interface temperature rises above the liquidus temperature, corresponding to the instantaneous average composition of the melt pool.With constant power dissipation in the melt and external cooling of the core-catcher, a final steady-state situation is reached. Dissolution stops when the heat flux (delivered by the melt to the refractory) can be removed by conduction through the residual thickness of the ceramic, with Tinterface = Tliquidus (calculated for the average composition of the final liquid pool). The final steady state corresponds to a uniform pool composition and uniform interface temperature distribution. Convection in the pool is governed by natural thermal convection and the heat flux distribution is therefore similar to what would be obtained for a single component pool.An interpretation of the experiment with two model-based approaches (0D and 1D) is presented. The mass transfer kinetics between the interface and the bulk is controlled by a diffusion sublayer within the boundary layer. During the dissolution transient, the liquid composition at the interface is concentrated in the refractory species. During the transient, the interface temperature is equal to the liquidus temperature corresponding to the local and instantaneous composition of the liquid at the interface.Regarding the design of a protective layer made of refractory materials, we can answer the question of how much ceramic can be dissolved and its impact on melt temperature evolution during the dissolution process. It also impacts on subsequent corium solidification since the additional mass of dissolved ceramic leads to increased volume of the molten material, significantly increasing the time required for complete solidification. For the long term, ceramic material does not offer better confinement than a crust made of solidified corium.This work served as support to a generalisation of the model of transient evolution of interface temperature in various severe accident situations (Seiler and Combeau, 2014).