Research On The Mechanism Of Densoty Lock

Density lock is a passive device, functioning as a valve. It has no moving parts and does not need outside power and any operator during the process from closure to open. It only depends on the change of the characteristics of working medium in the reactor to achieve cut-off or connected of fluid channels. Therefore, a detailed knowledge related to the technology and design of density lock is of important significance to further improve the security of nuclear power plants.With the methods of experimental study and theoretical analysis, the research on the density lock technology and design method was carried out. According to the work environment of density lock, the work condition of density lock can be divided into 4 categories:the static condition without external disturbance; horizontal disturbance condition with horizontal flow above the density lock; vertical oscillation condition with the vertical oscillations of stratification; comprehensive condition with both horizontal disturbance and vertical oscillation. The experiment study was carried out in sequence and the effect of different parameters on the density lock was analyzed as well. The method of density lock design was proposed based on the research results and a prototype was also designed. The main work and results are given as follows:First, according to the function of density lock, working requirements of density lock were given. Based on these requirements, the research steps can be determined. Then, we built the experimental loop of density lock and took the research on the characteristics of density lock at the static condition. The results show that:a very clear stratification can be formed in the static condition and it also has a well stability and large temperature gradient; through the analysis of heat and mass transfer in density lock, it is proved that density lock can separated the fluid around it by stratification in static condition, and a condition which is required at the design of density lock was obtained as well.Second, reconstructed the experimental loop for horizontal disturbance condition and studied the effect of the flow rate, temperature difference and structure on the density lock. The results show that:fluid in density lock can be divided into three zones:mixing zone, stratification zone and constant temperature zone; the stratification zone can be divided into strong stratification and weak stratification and the interface is located between the mixing zone and the stratification zone; based on zone model, the temperature field of density lock is divided into five categories in which the second class is the best for normal work; when the horizontal flow rate is small, the temperature gradient of stratification in horizontal disturbance condition is large and closes to the static condition; with the horizontal flow rate becoming larger, the stratification will form later and with a low temperature gradient; when the horizontal flow rate exceeds a critical value, the stratification can not form or will disappear soon and density lock is out of work; with the increase of temperature difference, the temperature gradient increases and the stability of density lock is enhanced; the anti-disturbance ability of density lock can be enhanced by the structure of grid and the stratification also can form at a upper place; the heat transfer model of density lock in horizontal disturbance condition is established and validated by the experimental data.Third, the vertical oscillation experimental loop was rebuilt and the effect of amplitude, frequency, temperature difference and structure on the density lock was researched through the experiment. The results show that:because of the vertical oscillations, the mode of heat transfer in density lock has been changed from heat conduction to convection, enhancing the heat transfer from the density lock to outside, so it leads to that the temperature field of density lock moving to high temperature heat source when oscillation speed is large; temperature offset distance formula is given through theoretical analysis.Fourth, the effect of different factors on the density lock was carried out through experiment at comprehensive consideration; the conditions of density lock failure were discussed and three solutions were proposed which were verified by experiment. Through the analysis of the structural parameters of density lock, the design process of density lock was proposed; based on design process, the density lock prototype structure was given at last.