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Numerical simulation of hydrogen mitigation using passive catalytic recombiner
, Prabhudharwdkar D., Iyer K.N.
Published in
2007
Abstract
During severe accidents in nuclear power plants, such as loss of coolant accident (LOCA), large quantities of hydrogen may be released into the containment atmosphere due to the reaction between the clad, made of Zircalloy, and the coolant (i.e. water). This evolved hydrogen may form an ignitable mixture with the containment air depending on the local concentration of hydrogen and temperature. The ignition of this released hydrogen can lead to an uncontrolled combustion process (detonation), which may threaten the integrity of the containment building. To avoid such gas phase ignitions, a catalytic recombiner is used to mitigate this released hydrogen at temperatures much lower than those required for gas phase ignitions. The catalytic recombiners use platinum as the catalyst. The catalytic recombiner is much smaller in size compared to the containment compartments. In order to fully resolve the recombination processes during the containment simulations, it requires the geometric details of the recombiner to be modelled and a very fine mesh size inside the recombiner channels. This component when integrated with containment mixing calculations would result in a large number of mesh elements which may take large computational times. This paper describes a method to resolve this simulation difficulty. In this exercise, the catalytic recombiner alone was first modelled in detail using the best suited option to describe the reaction rate [1]. A detailed parametric study was conducted, from which correlations for the heat of reaction (hence the rate of reaction) and the heat transfer coefficient were obtained. These correlations were then used to model the recombiner channels as single computational cells providing necessary volumetric sources/sinks to the energy and species transport equations. This avoids full resolution of these channels, thereby allowing larger mesh size in the recombiners. The above mentioned method was successfully validated using a test problem and the results indicate satisfactory modelling of the component.
About the journal
JournalProceedings - 12th International Topical Meeting on Nuclear Reactor Thermal Hydraulics, NURETH-12
Open AccessNo