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In order to mitigate the impact of a possible hydrogen combustion and to avoid containment failure, passive auto-catalytic recombiners (PAR) are used for hydrogen removal in an increasing number of European nuclear power plants. Hydrogen and oxygen react exothermally even below conventional flammability limits on the catalytic surfaces inside a PAR generating steam and heat. Modelling of the operational behaviour of PAR is one part of development issues in order to achieve reliable predictions of local atmosphere conditions. International research activities, e.g. in the European FP-6/FP-7 Network of Excellence SARNET (Severe Accident Research NETwork), investigate these aspects. At Forschungszentrum Ju¨lich, two strategies are pursued. First, the detailed evaluation of the reaction kinetics and heat and mass transport phenomena on a single catalyst element is performed by a direct implementation of the transport and kinetic approaches in ANSYS CFX-11. Second, in order to model the interaction of PAR with the containment, REKO-DIREKT, a detailed user model of the relevant processes inside a PAR based on Fortran 90 will be implemented in CFX. At present, validation against the available experimental database is performed. The validity of the numerical models strongly depends on the experimental data available. For this purpose, detailed experiments are performed at Ju¨lich. In the small-scale test facility REKO-3, representing a recombiner section, detailed investigations of the reaction kinetics under well-defined and steady-state conditions have been performed. In co-operation with RWTH Aachen University, a new test vessel REKO-4 is currently under preparation for testing PAR behaviour under natural convection conditions. It will provide various possibilities for instrumentation to measure temperatures and gas compositions and in particular it will be equipped with particle image velocimetry (PIV) for measuring the flow field around the PAR. |
