Design Of Experimental Device And Numerical Simulation Of Hydrogen Combustion With Obstacles For PWR

A great amount of hydrogen may be generated during severe accidents of a nuclear reactor.The hydrogen may be ignited and even explosion occurs under certain conditions,which will seriously threaten the integrity of reactor containment.After Three Mile Island nuclear accident in the United States,Japan's Fukushima nuclear accident proved once again the hydrogen explosion causes serious consequences.In order to achieve the objectives proposed by the administrative authority in charge of nuclear power,i.e.,striving to actually eliminate the possibility of release of radioactive material at the design phase,it is necessary to further conduct three dimensional analysis of hydrogen safety in a nuclear reactor,and to develop a hydrogen combustion model in the space with obstacles,applicable to the three dimensional analysis.Therefore,an experimental device of hydrogen combustion with obstacles was designed and the corresponding numerical simulations were carried out in this thesis,aiming at further understanding the behavior of hydrogen combustion in a space with obstacles,and providing data for the model development.The design of the experimental device is the basis of the numerical simulation and future experiments.A preliminary design was carried out firstly,consisting of safety container,experimental pipe,gas supply system,heating and thermal preservation system,ignitor,high-speed camera,data acquisition system,and other auxiliary equipments.The safety container and experimental pipe are the vessels used for hydrogen combustion,and the gas premixing container is applied to prepare the initial mixing gases.In detail,the safety container is a horizontal closed structure,serving as the secondary safety shield and also being used to perform experiments with low hydrogen concentrations.And the experimental pipe is a semi-confined pipe with obstacles inside,and used to investigate the influence of obstacle on the characteristics of hydrogen combustion.There are many sensors fixed in both the safety container and the experimental pipe for measuring pressure,temperature and flame propagation velocity.The numerical simulations were carried out based on the preliminary design.The results showed that in the semi-confined pipe the obstacles can promote the flame propagation and raise the gas combustion pressure.Both the gas pressure and the flame velocity increase with the increase of the number of obstacles or blocking rate,and reach their maxima when the obstacle spacing is three times of pipe diameter.With the same blocking rate,the annular obstacle is more helpful to promote flame propagation and increase combustion pressure than the semicircular obstacles.In a closed space,steam was found to inhibit the reaction rate of combustion and decrease the flame velocity,combustion pressure and temperature.And this inhibition effect is greater with higher concentrations of steam.The combustion reaction is strongest and the combustion pressure and the temperature are highest when the equivalent ratio of hydrogen is close to 1.The gas combustion pressure and the flame propagation velocity increase with increase in the initial pressure of the premixed gases and decrease with increase in the initial temperature.The ignition location has influence on the rise speed of pressure and temperature while it has little influence on the maximum pressure and temperature.The maximum rise speed of pressure and temperature appears when the combustion is ignited at the center position.