Overview of the research on corium

Several French companies and public laboratories have cooperated to develop computer programs for the simulation of corium propagation and experimental facilities to test these simulations. The cutting of corium is a preliminary step before the recovery of the Fukushima corium, two 10 kg bulks of corium substitute made of hafnium have been used to test the laser cutting technique on the Plinius experiment platform at CEA Cadarache. The Viti experiment has given results to characterize and simulate the solidifying of materials like boron, carbon, iron and oxygen. Thermodynamic calculations have been performed to study the distribution of boron in the oxide phases and metallic phases of the corium. The Plinius experiment platform is also used to understand the interaction between corium and concrete and the formation of by-products. Two strategies for the management of core meltdown are considered for light water reactors: the in-vessel retention where the corium stays confined in the reactor vessel and the ex-vessel retention (EVR) where the corium is expected to spread on the concrete base slab. EDF considers an EVR strategy with corium spreading in the reactor pit. CEA proposes 2 devices for mitigating core meltdown consequences: an internal corium collector able to extract its residual heat and corium discharge channels to evacuate corium while reducing criticality hazards. (A.C.)