CFD studies of hydrogen mitigation by recombiner using correlations of reaction rates obtained from detailed mechanism

Abstract

In this study, an accurate and efficient method is proposed to simulate hydrogen mitigation using catalytic recombiner in a nuclear reactor containment. Using a point model and a detailed set of reaction kinetics equations, the variation of hydrogen reaction rates with surface temperature for various hydrogen and water vapor concentration are found. The entire reactant domain is divided into two zones, Zone 1 and Zone 2. In Zone 1, when the mixture is heated, there is a sudden onset of surface reactions at a threshold temperature (catalytic auto ignition temperature) beyond which the reaction rate falls. In Zone 2, the reaction rate gradually builds up beyond a threshold temperature, reaching maxima (maximum reaction temperature) and then falls. Correlations for catalytic ignition/maximum reaction rate temperature and reaction rates have been developed for both the zones. Using the developed correlations, a recombiner CFD model is evolved to simulate the REKO-3 experiments performed in REKO test facility to validate the recombiner model. The present investigation reveal the importance of radiation heat transfer in correctly predicting the catalyst plate temperature. From numerical computations, the best suited radiation model is identified. A parametric study is then carried out to predict the highest catalyst plate temperature under diverse operating conditions. From the obtained results, an engineering correlation is developed which successfully predicts the highest plate temperature for the entire range of REKO-3 data.