Health Risk Assessment Ofairborne Radon In Uranium Mine Based On Monte Carlo Simulation

Uranium mining and milling activities produce a large quantity of radioactive waste,especially the radioactive contamination caused by airborne radon,which is a serious danger to public health.However,the current evaluation on radiation protection in our country is still very weak,and many issues need further study.The main problem is that traditional assessment method based on a single factor index cannot provide a quantitative probability of health hazard which impact the scientific value of the result.Health risk assessment describes the harm from contaminants to human health quantitatively with unified hazard indicators.From the1990 s,our country gradually carried out health risk assessments about chemical plants,smelters,garbage dumps,nuclear power plants and other contaminated sites,which promote scientific decision-making of the related industries on environmental protection effectively.Through introducing health risk assessment into radiation protection work of uranium ore,the impact of human health from uranium mining radionuclide is evaluated quantitatively,which is of scientific and practical significance.Researches on this area are rarely reported currently.Based on the four steps of health risk assessment: hazard identification,exposure assessment,dose-response assessment and risk assessment,this paper analyzes the status of the distribution of the radionuclides in a decommissioning uranium mine,identifying the radon which is discharged from underground mine ventilation shaft and precipitated naturally from the waste rock field,ore stacking and crushing field,heap leaching field as gaseous pollution source,and monitoring the emission of each gas source.Then on the basis of the monitoring data on radon concentration,theoretical research of the health risk assessment based on uncertainty is carried out,and health risk assessment system of airborne radon in uranium ore is built.Based on Monte Carlo,the exposure and carcinogenic risk caused by the intake of radon and its daughter are analysed through the Crystal Ball software.The carcinogenic risk of airborne radon and its progeny fromuranium mining and milling system is evaluated quantitatively.Probability distribution of carcinogenic risk and scope is obtained.The result shows that: annual effective dose of public caused by airborne radon and its progeny in the 80 km scope from the evaluation center is below dose constraint value specified in GB18871-2002.From the perspective of dose constraint,radiation protection in 0 ~ 1km range and more distant ranges from the assessment center is up to the relevant requirements.But health risk characterization shows that the health risk level in 0-1km range from assessment center is 10-6,which is higher than acceptable recommended by US Environmental Protection Agency(USEPA).The largest health risk value exceeds the limit of 3.275 times.Appropriate optimization and radiation protection control should be carried out.From the perspective of risk control,the carcinogenic risk in the range of 0 ~ 1km from the assessment center is greater,and health risk value is exceeded.The other more distant range of cancer risk can be negligible.The study shows that: Because the effective radiation dose constraint value of public cannot provide quantitative probability distribution of cancer risk which may occur by the radiation exposure distribution information,thereby the scientificity of evaluation result is affected.Based on the uncertainty theory,the dose constraint(individual dose limit)and risk constraint(irradiation individual risk limit)are kept as low as reasonably in uranium mining and milling practice by considering economic and social factors.Our country standard sets that public annual effective radiation value of dose constraint is 1mSv corresponding to the cancer risk of 5E-5,which is 50 times the USEPA recommended value.If dose constraint value is about 0.25mSv/a,it corresponds to cancer risk of1.25E-5,which is 12.5 times USEPA recommended value.Compared with other countries who are well developed in uranium production,our country work is still a wide gap in radiation protection of uranium mining and metallurgy.Therefore,in order to protect the staff of uranium mining and metallurgy and the safety of public in uranium area,it urgently needs to further strengthen the study on the health risk assessment of uranium mining and metallurgy system,make the quantitative analysis more actual for uranium radiation protection optimization,determine the doseconstraint value and risk constraint value in line with national conditions and evaluate the impact of radionuclide from uranium ore zone to human health quantitatively.The work is of great scientific and practical significance.