A research program on reflood of an overheated core and corresponding topics is running at KIT, including large scale bundle tests at IAM-WPT , various kinds of separate-effects tests at IAM-AWP , model development and code application.

Short fuel rod experiments were carried out in the framework of the EU 5FWP COLOSS Project. The simultaneous dissolution of UO2 pellets and ZrO2 by molten Zr was investigated with PWR and VVER samples.

(LWR OFF-NORMAL BEHAVIOUR INVESTIGATION) A Reactor Thermal-Hydraulic Safety Research Programme carried out by the Commission of the European Communities at the Ispra Site of the Joint Research Centre.

Facility consists of the hemispherical test vessel, a volumetric heating system in the test vessel to simulate the decay heat, a heating furnace to generate and pour the simulated corium melt, and a multitude of instrumentation to characterize the status of the melt. The test vessel is a 1:5 scaled RPV of a typical PWR with no penetrations of the lower head, and is equipped with different measurement techniques like heat flux sensors and thermocouples. The hemispherical bottom is closed by an upper lid and different openings in this upper lid allow the pour of melt to the central region or close to the perimeter of the lower head. Test vessel can be cooled by water or air at the outer surface, as it is surrounded by a second cooling vessel.

The MISTRA facility is a steel cylindrical vessel with a top flat cap and a curved bottom. The internal volume is 99.5m3, the internal diameter - 4.25m, the height - 7.4m. The vessel is thermally insulated, but the wall temperature is not controlled. Three cylindrical condensers are inserted inside the vessel, close to the wall and one above the other (so that they span over most of the vessel height). The facility is designed in such a way that almost all steam condensation is supposed to occur on the interior side of the condensers. The facility was additionally equipped with sprays located below the vessel ceiling. The instrumentation includes devices for measuring pressure, temperature, gas concentration and velocity (laser Doppler anemometry).

The OECD-IAEA Paks Fuel Project aimed to support the understanding of fuel behaviour in accident conditions on the basis of analyses of the Paks-2 event. Numerical simulation of the most relevant aspects of the event and comparison of the calculation results with the available information was carried out between 2006 and 2007.

The aim of the RECI (RECombiner & Iodine) program was to quantify the iodide → iodine conversion in realistic conditions of recombiner operation, albeit under the following constraints: the experiments were to be performed with non-radioactive substances, and without hydrogen. The comprehensive tests grid allowed to investigate into the decomposition of cesium and cadmium iodides under thermal-hydraulics conditions that mimics the recombiner operation, despite the technical limitations of the RECI test bench.

The VULCANO facility is mainly composed of a furnace and a test section, which is thoroughly instrumented. In the experiments with prototypic material the furnace has the following characteristics:

• Capability to melt oxidic mixtures of various compositions (UO2, ZrO2, SiO2, FeOx) with the possible addition of metals.
• Liquidus temperature of the load between 1700 and 2900 °C.
• Capacity to melt & pour 100 kg. •Continuous low pouring rates (0.1–1 l/s).

FARO (Furnace And Release Oven) experimental facility began the experiments of the LWR-MFCI phenomena in 1990 in collaboration with several reactor safety research organizations from European Union member countries and with the participation of the United States Nuclear Regulatory Commission.

The ARISG-I was developed to estimate the aerosol deposition in the near-field of tube breach under dry conditions. It was based on ‘filter concept’, which means that aerosol flowing through a bundle of obstacles is submitted to forces that tend to clean up the gas by removing particles onto obstacle surfaces. Under SGTR conditions, the major deposition mechanisms in the break stage are turbulent deposition and inertial impaction.

In case of a steam explosion, e.g. as a consequence of a severe reactor accident, part of the thermal energy of the melt is transferred into mechanical energy. At Forschungszentrum Karlsruhe, the ECO experiments are being directed to measure the conversion factor under well-defined conditions. The programme was launched in 2000. Alumina from a thermite reaction is used as a simulating material instead of corium. Dimensions of the test facility as well as major test conditions, e.g. temperature and release mode of the melt, water inventory and test procedure, are based on the former PREMIX experiments (from 1994 to 1999).

The QUEOS facility serves to study premixing phenomena with solid spheres, i.e. without the danger of a steam explosion and the complication of melt fragmentation. Emphasis was put on high sphere temperatures (up to 2600 K) and the use of large numbers of comparatively small spheres so that intensive multiphase interactions with strong coupling of the phases (collective motion of the spheres) are observed. In order to simulate melt jets as closely as possible, the spheres are released as a cylindrical jet into a three-dimensional test vessel.