Experimental Study On The Effect Of Extreme Rainfall On Radon Control Of Red Soil Overburden On The Beach Surface Of Uranium Tailings Reservoir

At present,the main radon pollution control method for decommissioned uranium tailings in the world is the covering method,which has a relatively good effect.Red soil mulching is the main means of beach surface treatment of decommissioned uranium tailings reservoir,and its properties are easily affected by external forces,thus affecting the radon control performance.By adjusting the parameters of red soil covering materials(thickness,compactness,etc.),the change of radon exhalation rate on the beach surface of uranium tailings pond was observed,and the change law of radon exhalation rate was analyzed.The relationship between red soil overburden parameters and radon reduction coefficient is deduced,and the mathematical model of red soil overburden parameters and radon reduction coefficient is established.The simulation experiment of radon migration on the beach surface of uranium tailings was carried out by considering the different compactness of red soil overburden under the action of extreme rainfall.Based on the measured data,the variation characteristics of overburden compaction and moisture content are analyzed,and the influence of overburden compaction and moisture content on radon exhalation rate under extreme rainfall conditions is studied.In this experiment,the radon exhalation test device(artificial microclimate chamber)was designed for simulating the overburden layer of uranium tailings pond.The red soil and the tailings of a uranium tailings pond in South China were selected as samples to study the relationship between the thickness,compactness,moisture content of overburden layer and radon exhalation rate.The conclusions are as follows:(1)When the compactness is 0.56,the radon exhalation rate decreases gradually with the increase of overburden thickness from 0cm to 20cm;when the compactness of overburden with the same quality increases from 0.56 to 0.93,the radon exhalation rate first decreases slowly and then decreases greatly;with the increase of overburden compactness,the radon reduction coefficient first increases slowly and then increases greatly.(2)Under the action of extreme rainfall,the change of water content of overburden layer decreases slowly at first,then decreases rapidly,and finally tends to be stable.(3)With the decrease of water content,radon exhalation first increased,then decreased,and finally stabilized.From 24 h to 48 h after rainfall,the radon exhalation rate increases due to the rapid evaporation of water molecules in the red soil overburden and the decrease of radon solubility in water.During the 48h-96 h after rainfall,the pore water in the red soil overburden evaporates rapidly.The capillary water in the water makes the soil moisture continuously transmit to the water gas interface of the surface layer to maintain evaporation,which leads to the formation of dense plate on the surface of the red soil and the obstruction of the radon migration channel.At this time,the radon exhalation rate decreases.During the 96h-120 h after rainfall,the surface layer of red soil gradually forms a dense state,which slows down the evaporation rate of water,and the radon migration pathway does not change much,so the radon exhalation rate gradually tends to be stable.