The role of CFD combustion modeling in hydrogen safety management - III: Validation based on homogeneous hydrogen-air-diluent experiments

Large quantities of hydrogen can be generated and released into the containment during a severe accident in a PWR. The generated hydrogen, when mixed with air, can lead to hydrogen combustion. The dynamic pressure loads resulting from hydrogen combustion can be detrimental to the structural integrity of the reactor safety systems and the reactor containment. Therefore, accurate prediction of these pressure loads is an important safety issue. In our previous article, a CFD based method to determine these pressure loads was presented. This CFD method is based on the application of a turbulent flame speed closure combustion model. The method was validated against three uniform hydrogen-air deflagration experiments with different blockage ratio performed in the ENACCEF facility. It was concluded that the maximum pressures were predicted within 13% accuracy, while the rate of pressure rise dp/dt was predicted within about 30%. The eigen frequencies of the residual pressure wave phenomena were predicted within a few %. In the present article, we perform additional validation of the CFD based method against three uniform hydrogen-air-CO2-He deflagration experiments with three different concentrations of the CO2-He diluent. The trends of decrease in the flame velocity, the intermediate peak pressure, the rate of pressure rise dp/dt, and the maximum value of the mean pressure with an increase in the CO2-He dilution are captured well in the simulations. From the presented validation analyses, it can be concluded that the maximum value of the mean pressures and the intermediate peak pressures were predicted respectively within 12 and 29% accuracy, while the rate of pressure rise dp/dt was typically underpredicted within 15-90%. The eigen frequencies of the residual pressure wave phenomena were predicted within 6%. It was overall concluded that the current model predicts the considered ENACCEF experiments well. (C) 2014 Elsevier B.V. All rights reserved.