During a severe accident, one of the strategies for mitigating the risk of perforating the reactor basemat is to stabilise the molten corium by reflooding it with water.
The French National Research Agency (ANR) has a project called RSNR/MIT3BAR in which the IRSENE Nuclear Technology Department (DTN) teams are participating; this project is examining the mechanisms of corium cooling under such conditions.
The purpose is to study the impact of a metal phase in the corium on the coolability of corium under water. Reflood tests were performed with water in the MERELAVA experimental device belonging to the PLINIUS platform.
The MERELAVA device was commissioned in 2019 for corium reflood experiments, including gravity water injection from the top of the device.
This device is designed to melt metal-oxide corium mixtures (up to 80 kg) by provoking a thermite reaction, i.e. a highly exothermic, self-sustained reaction involving an oxidation-reduction mechanism.
The corium is contained in a zirconium crucible instrumented with thermocouples to measure the temperature.
The first tests were performed on different corium compositions, i.e.UO2/ZrO2, siliceous concrete, and steel.
For the first time on 22 March 2023, an experiment involving the interaction between corium and concrete under water with a prototypical mixture (UO2+ZrO2+metal) was performed with induction heating to simulate the reactor decay heat (watch video).
The corium was melted by a thermite reaction, i.e. a highly exothermic, self-sustained reaction involving oxidation-reduction. The molten corium contained in a zirconium crucible was instrumented with thermocouples to measure the temperature. Once the corium was molten and the concrete ablated, an induction heating system around the device was used to simulate the decay heat during the reflood cooling sequences.