The PREMIX experiments have been performed to study the premixing of sizable amounts of very hot oxidic melts with water when being released as a jet in a reasonably characterized way and with full optical access. Alumina at 2600 K from a thermite reaction was used to simulate the corium melt. A technique has been developed to retain the molten iron in the source so that the contribution of iron to the melt is well below 10 %. PREMIX involves the full physics of the mixing process including jet break-up and melt drop fragmentation. But, of course, on the other hand, the initial and boundary conditions are more difficult to control and to vary compared to experiments with solid spheres such as QUEOS.

Experimental facility Figure &
A single sampler unit

Complex measurements were performed at the integral high temperature test facility CODEX (COre Degradation Experiment) between 1995-2002 with electrically heated UO2 fuel rod bundles. The main advantages of the CODEX facility are the use of real UO2 pellets, the sophisticated data acquisition technique including aerosol measurements and the large flexibility in the selection of test conditions. The most imporant limitations are the use of fresh – non-irradited - fuel pellets and the application of electrical heating burdened with positive temperature feed-back effect.

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.

The CHIP programme aims to reduce the level of uncertainty on radioactive iodine releases during a core meltdown accident in a nuclear reactor. The programme results will also be used to better define the means and measures to be implemented in order to limit such releases.

This programme sets out to reduce uncertainties when evaluating the environmental release of radioactive products such as iodine or ruthenium following a core meltdown accident in a pressurised water reactor (PWR). The experimental data gained from this programme are used to develop and validate numerical simulation tools needed to assess the consequences of such an accident and to evaluate the efficiency of the prevention means.

The PWR PACTEL test facility is designed and constructed in 2009 to be used in the safety studies related to thermal hydraulics of pressurized water reactors with EPR type vertical steam generators

The PHEBUS FP (Fission Products) international research programme was conducted between 1988 and 2010. Its purpose was to improve the understanding of the phenomena occurring during a core meltdown accident in a light water reactor and to validate the computational software used to represent these phenomena in reactor safety evaluations. The report of the last test was published in December 2010 and was the topic of a closing seminar organised in June 2012.

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).

This facility comprises a water supply pipe, a quartz test section (110, 180 or 290 mm diameter) in which the debris bed is placed, together with its instrumentation, and a steam relief pipe. It is used to conduct refl ooding tests by means of injecting water onto a bed of metal particles heated by induction. The instrumentation measures the different temperatures and pressures in the debris bed, the fl ow of injected water and the fl ow of generated steam.

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.