The TOSQAN facility was initially designed within the framework of studies carried out by the IRSN on severe accidents in nuclear power plants. Indeed, explosive combustion of hydrogen generated by core melting could damage the containment integrity or the engineered safety equipments of the plant. Running the TOSQAN facility during the 8-year duration of the programme has demonstrated the efficiency of the instrumentation adapted for characterizing multiphase flow in demanding experimental conditions. Then, the TOSQAN facility is presently implemented in new research projects.
This FP7 European project is studying in particular the phenomenon of de-stratification of hydrogen induced by spraying at various experimental scales. These studies complete the results of the TOSQAN programme carried out between 2000 and 2008.
The main objective of this programme, which began in 2009, is to establish the correlations describing the scavenging of particule matter by different types of characteristic rain, from well controlled and finely instrumented analytical experiments. The TOSQAN facility makes it possible to study the washout of aerosols by droplets, by simulating certain conditions representative of atmospheric washout (millimetric droplets, terminal fall velocity, rain intensity, etc.). Within the scope of this programme, a thesis directed by LAMP (Physical Meteorology Laboratory) in Clermont Ferrand was initiated in 2009.
Within the ITER International Project on fusion research, a study is being carried out on the dust distribution in the Tokamak vacuum vessel and its interting in case of air ingress employed as a means of mitigation countermeasure of explosion risk due to the presence of hydrogen, carbon monoxide and particular matter. TOSQAN makes it possible to simulate certain accidental scenarios (loss of vacuum through air or water ingress) that could arise in the Tokamak ITER with a view to acquiring experimental data that will be used to validate CFD codes.
The ALIDS project, leaded by IRSN within the EUFAR network of the European Seventh Framework Program (FP7), concerns the development of an airborne optical instrumentation devoted to the in-flight measurement of rain droplets size distribution from an aircraft (www.eufar.net). The ALIDS probe is based on out of focus imaging optical diagnosis previously developed in the TOSQAN facility to characterise the particle size of sprayed droplets.
The TOSQAN programme: studying hydrogen risks issues during a severe accident in a nuclear power plant
The TOSQAN programme is part of the research conducted at IRSN on severe accidents that can affect nuclear reactors. The mechanical effects resulting from combustion of hydrogen emitted during deterioration of a reactor core can damage containment in the reactor or lead to failure of its safety systems. The TOSQAN programme, conducted between 2000 and 2010, allowed the principal phenomena affecting hydrogen distribution in the containment vessel of a reactor, which can lead to generation of flammable mixtures, to be studied. The experimental data acquired have contributed to validating the various physical models embedded in the nuclear safety computational codes used or developed at IRSN (TONUS, ASTEC), and so to verifying the ability of the computational software to simulate hydrogen distribution.
The TOSQAN experimental facility allows thermohydraulic conditions representative of the ones occurring in a containment vessel during a severe accident. The physical phenomena that have received particular attention are condensation of water steam on the walls and exchanges between the sump and the atmosphere. The effect of spraying has also been studied, because it can contribute to hydrogen risk mitigation by mixing the hydrogen and other gases present in the containment vessel. Spraying also aims to capture the fission products. The TOSQAN spraying programme has in particular studied the phenomena of evaporation/condensation of water droplets sprayed by nozzles and aerosols wash-out sprays.
In ten years of operation, over 300 analytical experiments were conducted. Physical models dealing with wall condensation, wash-out of aerosols by a spray droplets, and gas-sump exchanges have been successfully validated.
Several of these TOSQAN experiments have moreover served as references in international benchmarks such as ISP-47,in the frame of the OECD, or the European SARNET and SARNET-2 networks of excellence dealing with severous accidents, steered by IRSN.
The TOSQAN programme has led to about thirty publications in international journals and approximately 70 publications for international conferences.