Plasma transferred arc rotary furnace for "Corium" melting

In the event of a highly unlikely core melt-down accident in Pressurised Water Nuclear Reactors (PWRs), scenarios in which the reactor pressure vessel fails and the core melt mixture (called cerium and mainly composed of UO2, ZrO2, Zr, Fe and fission products) relocates into the reactor cavity, cannot be excluded. In this context, large R&D efforts within the European Union are currently directed towards ex-vessel cerium behaviour with particular emphasis on long-term cerium retention and coolability in order to keep it in the containment. In France, the Nuclear Reactor Division (CEA/DRN), with the support of its industrial partners : EDF and FRAMATOME, has undertaken an experimental programme, named VULCANO (for "Versatile UO2 Lab for Cerium Analyses and Observation". The objective of this programme is to study cerium behaviour under representative conditions with the view to qualifying the future EPR (European Pressurised Reactor) core catcher concept based on spreading the cerium on a large surface and subsequently cooling by flooding with water. The main aim of this programme is to improve understanding of the phenomena which play a key role in the physico-chemical and thermal-hydraulic behaviour of cerium, especially spreading and interaction with structure materials in particular sacrificial concrete and refractory protective layer. The VULCANO facility mainly consists of a furnace and a test section whose geometry depends on the specific objectives of each experiment. The furnace has been designed to accommodate about one hundred kilograms of cerium up to 3000 K composed of representative materials : depleted UO2, ZrO2, Zr and Fe. The technique chosen to melt the cerium constitutive materials is to heat, in a rotary plasma are furnace, the load composed of a mixture of powders up to 3000 K. Thanks to the rotation of the furnace, powders are centrifugated allowing the formation on the furnace axis of a 300 kW plasma are at very high temperature (10000 to 20000K depending on gases) which first heats and melts load surface layer by thermal radiation; then, deeper layers by conduction. The furnace is cooled by water circulation in a double jacket. Seven thermocouples embedded in powder load measure temperature evolution inside the furnace during all the melting process; the signals are transmitted through an infrared telemetry device which rotates with the furnace. A bichromatic pyrometer measuring melt surface temperature at the furnace outlet gives hot temperature. These measurements enable us to control the process and to decide on the time at which the molten product can be poured into the test section.