Numerical Simulation Investigation On Hydrogen Distribution And Stratification Characteristics

Hydrogen safety issue once again became a focus of nuclear industry because of Fukushima accident.It indicates that during severe accident accumulation and stratification of hydrogen will bring big challenge to integrity of containment once the concentration of hydrogen exceeded the limits.Therefore,it is necessary to further investigate on characteristics of hydrogen distribution to figure out the position where hydrogen accumulates and take measures to minimize its possibility to explosion.The NNSA has announced specific requirement for nuclear power plant to do hydrogen CFD analysis to verify its safety condition.Therefore,this article uses CFX code to investigate on the characteristics of hydrogen distribution and stratification.In advance,use THAI HM2 to verify CFD models,including mesh sensitivity analysis and turbulence model availability analysis.By comparing the experimental and simulating data,it turns out that the deviation between results using k-ε model and experiment is smallest and it is advisable to choose k-ε model when doing analysis of hydrogendistribution.Concerning the containment experimental facility,this article employs the method of “base condition + single factor comparison” to investigate on impacts of different factors on the hydrogen distribution and stratification inside containment,including buoyancy jet with different momentum and flux,different injecting location,different injecting direction,mixture of hydrogen and steam and cooling by wall heat transfer with wall condensation,injecting inside steam generator compartment.Besides,this paper investigates on interaction between buoyant steam jet and stratification and stratification breakup by the steam jet.The results show that these factors have a certain effect on the diffusion of hydrogen,especially in the case of wall heat transfer and vapor condensation,the diffusion of helium will be accelerated due to natural convection,which makes it difficult to formulate a stable helium stratification.This indicates that the wall cooling and condensation of the steam has played a positive role in reducing the accumulation of hydrogen.When the steam buoyant jet interacts with the helium layer,if the interface Fr is much smaller than 1,then the jet can not enter the interior of the layer.When the interface Fr is close to 1,the buoyancy jet interacts with the layer.When the interface Fr is larger than 1,the stratification is destroyed gradually as the interaction continues.All of these investigation will support the succeeding work of experiment investigation.