Investigation Of Environment Radioactivity At A Decommissioned Uranium Mine In Southern China

Uranium is an essential and important resource for the development of nuclear energy.The sustainable development of nuclear energy cannot be separated from the safe decommissioning of uranium mines and the effective management of environmental radiation.In order to eliminate the hidden danger of environmental radiation safety of decommissioned uranium mines,it is necessary to conduct an all-round multi-parameter coupled investigation to fully understand the current situation of environmental radiation of decommissioned uranium mines in my country,comprehensively evaluate the reliability of the decommissioning treatment plans adopted and take remedial measures.Provide reference for the design of subsequent uranium mine decommissioning treatment plans.In this paper,a decommissioned uranium mine in south China was investigated for 2years（monitoring sampling frequency was at least once a month）,and a comprehensive environmental radioactivity survey（including soil,surface water and air）was carried out to comprehensively evaluate the effect of decommissioning treatment,and corresponding rectification measures were taken for the source items that did not meet the management limits.The key study contents and results of this paper are described briefly below:（1）In order to improve the status quo that the management limits of decommissioned uranium mines are not comprehensive,extensive research has been conducted on the relevant industry standards and specifications of uranium mining,metallurgy and associated radioactive mines at home and abroad,and the management limits applicable to radiation environmental assessment of decommissioned uranium mines have been summarized and analyzed.In order to objectively and accurately evaluate the environmental radiation level of decommissioned uranium mines in my country.（2）The activity concentration of natural radionuclides and radon exhalation rate in soil were measured.The radon exhalation rate in soil of all monitoring sites met the decommissioning management limit requirements below 740 m Bq·m^-2·s^-1,but was still higher than that in residential areas and reference areas.At the same time,the activity concentration of ²³⁸U,²²⁶Ra and ²³²Th in the 15-30cm soil of the four monitoring points exceeded the management limit due to the insufficient ground leveling of the secondary tailings pond.Therefore,it is necessary to increase the soil cover thickness of the secondary tailings pond.（3）The measurement of radionuclide concentration in surface water shows that All test results are below the corresponding management limits,indicating that the surface water decommissioning treatment effect is good.（4）According to the difference in the range ofαparticles with different energies in the same medium,the influence of ²²⁰Rn daughters is eliminated by covering polycarbonate filters of different thicknesses.Based on the CR-39 track sheet,a set of ²²²Rn daughters is designed to measure accurately device.（5）Analysis based on dose calculation model found that:The highest annual effective doses due toγexternal irradiation were 1.16m Sv and 1.32m Sv for residents around the mining area and permanent staff of decommissioned uranium mines,and 2.75m Sv and3.22m Sv for ²²²Rn and its daughter.Compared with the highest effective dose 1.31m Sv and2.66m Sv caused byγray and ²²²Rn and their offspring,the former has no significant difference,indicating that the uranium mine decommissioning treatment project has a good shielding effect onγexternal irradiation（6）Combined with the monitoring values and dose estimation results of various aspects,comprehensively evaluate the effectiveness of the decommissioning plan of uranium mines.The results show that:the workplaces with higher soil radon precipitation rates have higher radon concentration levels in the air,indicating that soil radon concentration levels are also higher.The precipitation rate is a potential cause of the high radon concentration in the air.In order to reduce the annual effective dose of ²²²Rn and its progeny caused by ²²²Rn and its progeny for resident workers in decommissioned uranium mines,and to reduce radon precipitation,constructing the approximate model of soil cover thickness,which provides the basis for estimating the actual soil cover thickness of each site,and can realize the optimization of radiation protection in the practical decommissioning treatment project of uranium mines.