| High concentrations of radon and its daughters mainly exist in caves and underground chambers.Due to the pressure and concentration gradient,the gas radon produced by the decay of radium in the rock and soil can easily pass through the cracks and pores of the foundation and the interface,diffuse and seep into the chamber space,causing it to accumulate in a limited space and seriously endanger the staff in the chamber.health.In this paper,the chamber containing cracks is taken as the research object,and the law of radon migration under different pressure difference,permeability and humidity conditions is studied through the method of combining numerical simulation and experimental measurement.(1)Based on the fractal theory of porous media,the seepage model of fractal cracks is used to characterize the seepage characteristics of wall cracks.Using Fluent software,the radon migration of the fracture model under pressure difference was simulated,and compared with the experiment.The difference between the simulated and experimental results is within the reliable range,which proves the feasibility of the fracture model.(2)The radon migration in a chamber with cracks under a pressure difference of 5Pa?30Pa is simulated and compared with the measured data.The results show that with the increase of the pressure difference,the mass flow rate of radon out of the crack and the average concentration of radon in the body both decrease,while the mass flow rate out of the exhaust port increases.When the pressure difference is 20 Pa,the radon discharge effect is the best,which is most conducive to the control of radon in the chamber.(3)The effects of fracture porosity(2.5%-20%)and partial pressure of water vapor(30%-60%)on radon migration are simulated.The increase in the porosity of the cracks in building materials leads to an increase in the permeability of the cracks,making it easier for radon to pass through the cracks.With the increase of fracture porosity,the average radon concentration in the chamber increases by 9.5 times.The regularity of the influence of humidity on the concentration of radon is not obvious.(4)Independently designed a radon concentration measuring device in a sealed cabin,and made a wall crack sample based on fractal theory.Changing the ratio of uranium ore sand in the radon source sample has realized a low radon source environment(standard sand: uranium ore =5:1)and a high radon source environment(standard sand: uranium ore =2:1).Under these two constant temperature environmental conditions,The influence of the pressure difference between the inside and outside of the cabin(5?30Pa)and the radon collection time(0?200min)on the dynamic changes of the radon concentration in a sealed cabin with cracks was studied.The results show that under the same radon collection time,with the increase of the pressure difference,the radon extraction rate and the radon concentration in the sealed chamber both decrease.Under the same pressure difference,with the increase of radon collection time,the radon extraction rate gradually decreases and approaches zero.(5)According to the analysis results,the pressure difference is negatively correlated with the mass flow of radon at the fracture(r=-0.983)and the average radon concentration(r=-0.985);it is positively correlated with the mass flow at the exhaust port(r= 0.967).The porosity is positively correlated with the mass flow of radon at the fracture(r=0.919),the mass flow at the exhaust outlet(r=0.918),and the average radon concentration(r=0.997).Humidity has no correlation with the mass flow of radon at the crack(p=0.305);it is negatively correlated with the mass flow at the exhaust outlet(r=-0.853,p=0.015);it is related to the average radon concentration in the chamber(r=0.781,p=0.011)is positively correlated. |
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