Studyon Optimization Of Covering Soil Regarding Reducing Radon From Waste Dump And Tailings

In recent years,with the amount of ecommissioneduranium mined increasing,the amount of untreated radioactive waste rock and tailings produced in uranium exploration increased,and the radioactive products has brought serious damage in the local environment and residents’health.Therefore,it is urgent to solve theprocessing problems of waste rock pile and tailings pile.The most harmful substance in all the radioactive products is radon,that is why reducing the radon exhalation rateof waste rock pile and tailings is the key pointin retired management.At present,the soil cover is the most effective solution among the existing management methods in the world.However,by this means a lot of soil and large engineering volume is required,which will damage ecological environment.Thus it plays an important roles on the improvement of covering materials.The standard module（35 cm*35 cm*12 cm）with stable radon exhalation rate was used as the source term in this dissertation,and made a height-adjustableexperiment box with asquare cross section（30 cm*30cm）.The moisture content（18%）and compactness（1.67g/cm³）must be consistent during the experiment.The radon exhalation rate of this standard module and the surface of soil was measured by the activated carbon gamma energy spectrum.This paper found that there is no significant change in radon exhalation rate with temporal change when measured by electrostatic collection during 24h.In order to reduce the effect of water absorbed by activated carbon,the sampling device was modified（seamlessly connected to a 9 cm high and 9 cm diameter PVC pipe under a carbon box）and verified on the standard radon exhalation ratedevice.Red soil（filter with pore size of 5mm）near the laboratory is selected,low radon exhalation rate of soil is found in this paper,which was negligible compared to the radon exhalation rate of module.Coveringsoil with a height of 0.4m on the source1,the radon exhalation rate of soil’surface became stable on the second day when continuously measured 5 times（each time a day）.Bentonite and lime powder were selected as the additive materials for this experiment.Different proportions（0%,1%,2%,3%,4%）of Bentonite or lime powderto the soil was added,comparing the corresponding radon reduce effectto the soil in different thickness.The results showed that with the more increasing the proportion of bentonite or lime powder is,the better the effect of radon reduction is,and it was found out that using bentonite is better than lime powderto reduce radon.The fitting lines illustratedthat the relationship between logarithmic of radon reduction factor and the thickness of soil with different proportions of bentonite or lime powder,and the coefficient of radon diffusionis calculated.The relationship between the radon exhalation rate of before covering and the thicknessof covered soil was deduced when meeting the retired management limit of 0.74 Bq·m^-2·s^-1,which provides a conservative calculationfor retired governance.Based on analysis of the results,it came to conclusion that the required thickness is reduced with the ratio of bentonite or lime powder increasing when the radon exhalation rate decreases to 0.74 Bq·m^-2·s^-1.Take certain mine as an example,the economic comparison analysis shows that its cost is higher than using the original soilwhen adding a lower proportion of material（1%and2%）,while its cost is lower than using the original soilwhen adding a higher proportion of material（3%and 4%）.And the required cost is decreasedwith the increase of adding proportion.