Impact of heat conduction in the basemat on the end of Molten Corium Concrete Interaction (MCCI)

In case of severe accident in a nuclear pressurised water reactor with vessel rupture, the corium will interact with the basemat concrete. Various codes such as ASTEC, CORCON, CORQUENCH or TOLBIAC-ICB are used to simulate the Molten Corium Concrete Interaction (MCCI). In certain MCCI configurations, the heat conduction within the concrete is responsible for stopping concrete ablation. However, some codes, such ASTEC or CORCON, did not account for this phenomenon, and others consider it optionally in a simplified manner. To address this issue, this paper introduces a new criterion for stopping the MCCI calculation in codes lacking heat conduction modeling. This criterion is determined from ten one-dimensional heat conduction computations. It aims to incorporate the termination of concrete erosion as well as the reduction in the volume of ablated concrete caused by thermal conduction during the transient phase. In certain specific configurations, the application of this criterion can result in a reduction of concrete ablation by a few tens of centimeters out of an overall ablation about one meter.