Math hydrogen catalytic recombiner: engineering model for dynamic full-scale calculations

Abstract

To protect a hermetic enclosure and the equipment and systems of a reactor installation housed in it from damage caused by the ignition (explosion) of hydrogen, most nuclear power plants with pressurized water reactors are provided with a hydrogen concentration monitoring system and an emergency hydrogen removal system. These systems prevent the formation of explosive mixtures in the accident localization zone by maintaining the concentration volume of hydrogen in the mixture below the safety limits, which ensures the preservation of the density and strength of the hermetic enclosure and the operability of other localizing safety systems. A key component of an emergency hydrogen removal system is a passive autocatalytic hydrogen recombiner that operates on the principle of the catalytic recombination of hydrogen and oxygen.

There is an urgent need for a full-scale dynamic calculation of the development of emergency conditions in a nuclear power plant containment accompanied by a large release of hydrogen. In efforts to achieve this, we constructed, and justified, a simple engineering thermohydraulic model of hydrogen removal in the operation of a passive autocatalytic recombiner based on the available experimental data.

This paper presents the application results of the model as a part of contour industry codes RELAP, TRACE and CORSAR, intended, among other things, for carrying out multifactor and full-scale calculations of the dynamics of emergency processes with the release of hydrogen into nuclear power plant premises. This model allows us to substantiate the dynamics of local concentrations of gas components of a mixture in a confined space; the temperature of the mixture, the catalyst and the walls of the box; and the pressure when hydrogen or steam is supplied to the box.

We have analysed various rates of hydrogen supply to a closed box to numerically substantiate the time at which the concentration reaches the maximum level. Furthermore, we have calculated the performance for several entrance concentrations of hydrogen, and obtained a satisfactory agreement between the dynamics of the concentrations, the temperatures of the catalyst and gas, and the productivity of the passive autocatalytic hydrogen recombiner. These calculations are based on the results of comparisons between calculated and available experimental data