V. CHAUDRON(1), A. LAURENT(3) , F. ARNOULD(1), C. LATGE(2)
(1)- Technicatome, Service d'Etudes Physiques et S{reti, Direction de l'Inginierie, BP34000, 13791 Aix-en-Provence Cedex 3, France (2)- Commissariat ` l'Energie Atomique, Centre d'Etudes de Cadarache, DRN/DER/STML, 13108 St Paul-lez-Durance Cedex, France (3)- Institut National Polytechnique de Lorraine, Laboratoire des Sciences du Ginie Chimique, 1 Rue Grandville, BP 451, 54001 Nancy Cedex, France
Significant quantities of hydrogen may be generated inside the fusion reactor during a loss of coolant accident (LOCA) by chemical reaction between steam released into the torus and plasma facing components at high temperature. As the confinement of radioactive materials is the key issue in a experimental reactor such as ITER (International Thermonuclear Experimental Reactor), hydrogen hazard is of particular concern because it represents, in case of contact with oxygen, a risk of explosion with subsequent damages and release of radioactive products.
On the basis of functional specifications issued from accidental sequences analysis, it appears that the implementation of an anaerobic hydrogen absorption system inside the torus and its expansion volume is the most advisable mitigation means because it allows the hydrogen removal at its source of production and before it come into contact with oxygen. After a preliminary selection from literature review, an experimental investigation of hydrogen getters in batch mode conversion at laboratory scale is presented in this paper. The aim of this preliminary evaluation of several getters is:(i) to prepare the different chemical formulations and to optimize the preparation procedure using characterization techniques, (ii) to evaluate the influence of some parameters such as temperature, pressure and humidity in order to provide unavailable data at this present time and required to optimize the tests at pilot scale, (iii) to select the most efficient getters that will be tested in the MIRHABEL (MItigation of the Risk linked to Hydrogen by ABsorption and Elimination) pilot installation in order to validate and qualify their efficiencies in representative conditions of accidental sequences in a fusion reactor.
Several formulations of potential hydrogen getters have been prepared, characterized and studied comparatively in order to evaluate their efficiency in terms of capacity and kinetics. These different formulations correspond to the combination of metal oxides (MnO2, CuO,Co3O4) with precious-metal catalysts (Pd, Ag, Pt) prepared by various methods. Experiments have been carried out in PRECARITY (PREparation-ChARacterisation and activITY of hydrogen absorbers) loop which comprises notably a static reactor (60 cm3) equiped with heating devices, a feed-gas line, a pressure transducer device and a vacuum line. Removal tests were conducted by introducing a gas mixture of 50% hydrogen in nitrogen to a pressure of 2 bar into the reactor, which contains 1 g of a given formulation. The total hydrogen uptake (measured by variation of pressure) was followed as a function of time until no further pressure variation was observed. From all the tested absorbers at this time, the best - Manganese oxide catalyzed by silver compounds - appears efficient for hydrogen elimination at room temperature.
The hydrogen capacity of these materials was found higher than 0.1 m3 STP/kg MnO2 and the kinetic of hydrogen absorption was about 0.2 m3 STP/kg/s. Consequently, these materials have to be considered as reliable candidates for the removal of hydrogen from a closed system at room temperature and will be qualified at pilot scale in representative conditions of accidental sequences in a fusion reactor in the MIRHABEL pilot installation.
*This work has been performed with the support of the European Technology Program for Fusion