| Ionizing radiation has been widely used in industry,agriculture,medical and health services,scientific research and other fields.It brings human great social and economic benefits,but corresponding radiation hazards or even catastrophic consequences as well due to operational errors,inadequate protection or other factors.Frequent occurrence of worldwide terrorist events and the enhancement of terrorists' professional ability make risk of nuclear and radiological terrorism events increase significantly.Under such background,this paper carried out detailed research on the risk identification,risk classification and risk control measures for ionizing radiation.In addition,this paper also conducted an initial evaluation of radiation accident risks and consequences.Then We seted up Shanghai municipal radiation risk assessment index matrix table,meanwhile,the radiation risk index was determined as well as the risk levels.Finally,we listed priority controlled risk categories and risk-causing factors to effectively prevent nuclear and radiation emergencies from occurring?The radiation risk in Shanghai mainly comes from various types of nuclear technology application units,whose density is the highest all around the country.According to the statistics,there are more than 1,100 nuclear technology application units in Shanghai 19 districts,involving non destructive testing,hospital,material modification and materials processing,radiation sterilization etc.This paper analyzed the distribution data and found the distribution is quite uneven in Shanghai.The number of units in suburban districts is much higher than that of central areas.The fields in which the nuclear technology is applied are focused on hospital and research,while in suburbs mainly on industrial uses.Moreover,radioactive sources are mainly ?,?,? sources,the places where unsealed sources,are mainly Class B and Class C,only one Class A all around the city,to the Radiation-Emitting Apparatus,? ones are the majority.While ? sources are mainly used for non-destructive testing.In non-destructive testing industry,the number of X-Ray testing apparatus is almost equal to that of radioactive sources which was applied.192Ir accounted for approximately 60%of the total radioactive sources in non-destructive testing,33%for 75Se.60Co was utilized in the state-owned large enterprises,only 7%of the total.Not only X-ray detection but also radioactive sources most used in suburban district.In this paper,the concentration of radionuclide in air,water and soil were tested,air absorbed dose rate was also monitored.The results showed that the radioactivity in above-mentioned environmental media were consisteout from 1983 to 1990.Thus illustrated the natural radiation level in Shanghai was in a relatively nt with the result of national survey of natural radioactivity levels which was carried stable state.External exposure index,internal exposure index and radium equivalent activity were calculated to assess the level of natural radiation.The results suggested the natural radiation level of Shanghai is within the safety limits.Compared the concentration of radionuclide in the soil of Shanghai to that of other countries and areas,the concentration in Shanghai was at the normal level and the annual effective dose value was also calculated.The result,0.44mSv-0.47mSv was around the world average annual effective dose from external exposure limit(0.46mSv).The value of personal risk caused by natural radiation was computed on the basis of the population in 2009.The value of personal risk is 1.5×1O-6 yr-1 which is much lower than those caused by other factors,for example the risk value caused by nuclear-energy is 6×10-4yr-1.This paper analyzed the likelihood of risk qualitatively or quantitatively and established the matrix of risk considering the potential loss of life,environmental pollution,social,economic and political influence,according to the previous occurrence of nuclear and radiological emergencies and the actual regulation of radiation safety,this paper estimated the types of emergencies which may happen in Shanghai through the identification of various risk factors of radiation and the possibility of occurrence.Secondly,this paper calculated the risk index and the risk level based on uniform standards of risk ranking.The results showed that the risk level caused by NDT devices,radioactive sources or devices with sources lost/stolen and irradiation installation,NDT devices failure was higher than other incidents.As to nuclear and radiological terrorism events,they were less likely to occur except threat/hoax.However,generally speaking terrorism events had much heavier influence than other radiological incidents.According to the application situations of shanghai nuclear and radiation devices,radiation risks status and natural condition,social and economical states,radiation risk evaluation and decision model was was established preliminarily.This paper not only put forward a radiation accident coping strategy based on "Prevention first,scientific regulatory"but also developed the radiation accident emergency evaluation and decision process system.Four scenarios of terrorism including spreading radioactive materials,dirty bomb attack and explosion or arson on the radiation facilities were assumed.We developed an emergency evaluation system which can predict the effects of nuclear and radiological terrorism events.Gaussian diffusion model was employed to predict the spread and deposition of radioactive materials,and both the external and internal doses were estimated for the representative person by using the corresponding dose conversion factor.Through integration of the computing system and Mapinfo GIS,the predicted results were visually displayed on the electronic maps of Shanghai.According to the predicted results,the corresponding proposed disposal was given.And this system also can provide the function of queries,map display and management for nuclear technology units.In order to verify the reliability of the evaluation system,this paper applied the similar software Hotspot to predict the same scenarios and the results of the two software system were consistent very well.The deviation between this system and Hotspot was less than 0.2km for predicted isoplethic curves of dose rate downwind.In the end,this paper put forward the corresponding radiation risk control measures according to the characteristic of radiation risk in Shanghai from improving law and regulation,strengthening the safety and security of radioactive sources,enriching emergency plans,enhancing monitoring and early warning,increasing personnel training and emergency response drills. |
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