Facilities

In order to comply with experimental device design requirements, different devices were developped, tested and set up on CARAIDAS:

• experimental enclosure in which representative thermodynamic conditions could be achieved,
• the monosized drops generator, the drops diameter measurements and the drops collector,
• the cesium iodide aerosols generator, concentration and size distribution measurements.

Facility is not operating.

TUBA (thermo-phoresis and diffusiophoresis) programme included experiments represented conditions expected in the SG tubes. Laminar flow was used in TUBA tests (TUBA-T: thermophoresis and TUBA-D: diffusiophoresis & thermo-diffusiophoresis).

From the comparison of experimental results and SOPHAEROS calculations it was concluded that there was sufficient agreement for most of the cases studied.
Facility is dismanteled.

RECI is a 2½ year experimental programme that was brought to completion as of October 2004. 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 aerosol generator selected limits the RECI programme to the study of water soluble substances, namely cesium and cadmium iodides: silver iodide is insoluble in water, and indium monoiodide is hydrolysed. However, the experimental results can be interpolated with reasonable confidence, since CsI and CdI2 are the two end-terms in the stability range of the relevant iodides. The instability of metal iodides, in a wet and oxidizing atmosphere, already demonstrated in chemistry laboratories, has been confirmed in more relevant physico-chemical conditions. The high conversion yields obtained do not come as a surprise since the RECI experiments provide a close analogy to the processes known as spray drying and spray (reactive-, or oxidizing-) pyrolysis, widely used in the laboratory and in the manufacturing industry. Both processes capitalize upon the high surface/volume ratio of aerosol particles to master comparatively slow chemical reactions and to produce nano-particles, the precursor material being often a finely powdered metal halide.

The experimental test bench consists of 4 units.

• Aerosol generation: an ultrasonic aerosol generator atomises the aqueous solution of a water soluble iodide. Monodispersed droplets are then dried, yielding iodide particles, the size of which is determined by the concentration of the solution. The input power of the ultrasonic acoustic transducer sets the aerosol concentration.
• Recombiner surrogate: a clear fused quartz or alumina tubing, which can accommodate a catalyst foil, is heated in a vertical tube furnace.
• Aerosol characterization: particles concentration & size distribution measurements. • Gaseous iodine analysis: 3 independently calibrated methods are implemented in the flue gas.

Facility is dismanteled.

In case of prolonged loss of cooling accident, the fuel rods of the core of a pressurized water reactor (PWR) will be damaged, and will collapse to form what is called a "debris bed", i.e. an agglomeration of fragments of zircaloy cladding and UO2 pellets (or UO2 and PuO2 pellets in the case of MOX fuel rods) which, if not rapidly cooled, will melt and become increasingly difficult to cool. This problem was identified through analysis of the Three Mile Island accident (TMI-2) which occurred in the United States in 1979.



One of the recommended actions to mitigate such accident sequences consists of reinjecting cooling water into the core, an action so-called "reflooding". Although essential for cooling the fuel assemblies, this action may nevertheless compromise the integrity of the reactor containment building. Indeed, reflooding a melting core at very high temperature may cause an explosive thermal reaction, so-called "steam explosion", between the cooling water and the molten corium. Such an explosion can generate projectiles which could damage the containment building. Furthermore, the water vapor resulting from the vaporization of the injected water will oxidize the metallic compounds of the core (zircaloy cladding, steel structures) and generate hydrogen with the potential to undergo a combustion inside the containment, as it was observed during the Fukushima accident.



The "Debris bed reflooding" experimental research program was launched in order to better understand and model these phenomena, the final objective being to determine the conditions under which cooling water can be injected so as to cool the core in an efficient manner with an acceptable risk for the containment. This additional knowledge will be subsequently used to clarify the choice of emergency operating procedures for severe accident conditions and to support the assessment of the relevance of EDF's Severe Accident Operating Guidelines.

Facility is in operation.

The tests conducted in the PRELUDE facility help to validate key technical options for PEARL:

• Induction heating to obtain heating sequences between 100-300 W/kg with homogeneous distribution in the different particle beds (slightly oxidised steel balls with 1, 2, 4 and 8 mm diameters), as well as to reach a temperature of 1,000°C at the hottest spot in the debris bed.
• Material of the test section ensuring the thermomechanical resistance of the tube containing the particles bed,
• Instrumentation to record the fi rst thermohydraulic measurements at atmospheric pressure when refl ooding the particle bed (about 25 kg) heated to of 400, 700 and 1,000°C.

This modular facility will remain operational to support the larger-scale PEARL facility (debris bed of about 500 kg) for complementary separate effects tests.

Facility is not operating, now called PEARL.