Atmospheric Dispersion Transport Of Radionuclides And Public Emergency Response Study Under Severe Accidents

Nuclear power is a stable and efficient clean energy,and it is expected to replace traditional fossil energy on a large scale as base-load energy to solve the problems of energy shortage and environmental pollution.Nuclear safety has always been the lifeline of nuclear power development.When a severe accident occurs,a large amount of radioactive material is released into the environment,which will cause severe harm to the public and the environment.In response to severe accidents in nuclear power plants,in order to reduce the consequences of nuclear accidents and ensure public safety,it is necessary to analyze the dispersion and migration process of radionuclides in the atmospheric environment,and then analyze the radioactive effects caused by the accident to determine the corresponding emergency response protection actions.n the current emergency response studies of severe accidents,the prediction of meteorological wind field around the accident and the simulation of atmospheric dispersion of radionuclides are mostly coupled in an off-line way,which is time-consuming and costly and cannot be simulated in real time at the early stage of severe accidents,which is not conducive to the emergency response of nuclear accidents.In addition,the prediction results of atmospheric dispersion simulations are affected by uncertainties such as wind fields,source terms,decay and depositions,which are not fully considered by most current models.This paper improves the atmospheric dispersion model WRF-Chem,and studies the atmospheric environment dispersion and migration model suitable for radionuclides.Based on the improved model,the real-time assessment method of environmental radiation dose under severe accident,public emergency response action and off-site emergency evacuation path optimization method were studied.Firstly,the fully coupled atmospheric dispersion model WRF-Chem was improved to study the atmospheric environmental dispersion transport model applicable to radionuclides.Options related to the dispersion and migration process of radionuclides are defined in the WRF-Chem model,and the definition package of air concentration,source term,dry deposition and wet deposition variable parameters related to radionuclides is expanded.On this basis,the decay process of radionuclides I-131 and Cs-137,the dry and wet deposition process of radionuclide gases and aerosols were added,and a high-resolution inventory of atmospheric radioactive emission sources was established.The model was validated using environmental monitoring data such as meteorological field data,radionuclide air concentrations,ground deposition and radiation dose rates from the Fukushima accident,and compared with other studies.The results show that the model can effectively analyze the dispersion trajectory of the radioactive plume,the variation of the air concentration of radionuclides and the distribution of ground radioactive deposits,and is suitable for the study of the atmospheric dispersion and migration process of radionuclides.Secondly,based on the atmospheric dispersion and migration model of radionuclides,the global dispersion process of radionuclides leaked from the severe accident of Fukushima Daiichi Nuclear Power Station was studied.The global-scale dispersion simulation performance of the model was evaluated using data from global monitoring stations,and the impact of the Fukushima accident on my country was analyzed based on monitoring data from my country’s environmental protection department.The results show that the global dispersion model can predict the arrival time and peak appearance time of the radioactive plume well,and local meteorological changes will affect the dispersion trajectory of the radioactive plume;The correlation between the simulated and observed concentrations of most monitoring stations is statistically significant,and the simulation effect of close-range stations is better than that of distant stations;Uncertainty in global-scale dispersion simulations increases further with time and transmission distance.The radionuclides released by the Fukushima accident completed the dispersion process around the earth from March 12 to the end of March.From the mainland of Japan,it has reached North America,Europe and East Asia successively.The airborne radioactivity concentration in these areas is more than 10~4times diluted compared with that near the Fukushima nuclear power plant.The Fukushima accident has no significant impact on the radioactivity level of the atmospheric environment in my country.The airborne radioactivity concentration in China is about 10~2m Bq/m~3.There are three possible routes for the transmission of radionuclides to my country.Thirdly,for the public emergency response in severe accident situations,a method is proposed to determine the public emergency response actions based on the early radiation consequences of severe accidents.The radiation consequences are assessed in real time based on the radionuclide atmospheric transport model with the effective dose conversion factor,and the public emergency response actions are determined in combination with the operational intervention level.The radiation consequences to surrounding countries and regions caused by a hypothetical accident of the AP1000 reactor of Haiyang Nuclear Power Plant were analyzed.Different levels of operational intervention can be determined according to the deposited radiation dose rate and inhaled radiation dose rate at 1m above the ground,so that the public in the emergency area can quickly and directly determine what kind of protection and response actions the public should take.Finally,in response to a severe accident public off-site emergency evacuation,a multi-objective optimization method for off-site emergency evacuation paths under severe accidents is proposed.The real-time evaluation method of environmental radiation dose is used combined with the improved chaotic ant colony optimization algorithm and road resistance model to optimize the evacuation path under different main targets.The method considers the optimal path scheme between the two potentially conflicting goals of evacuation time and radiation dose in nuclear accident emergency decision-making,the optimization goal is to minimize the potential risk to the public,and to minimize the evacuation Total travel time during the period.When a hypothetical accident occurs in the HPR1000 reactor of Fuqing Nuclear Power Station,two kinds of off-site emergency evacuation paths,onshore and offshore,are optimized and analyzed.The optimal paths under different optimization main objectives are recommended,and the combination of multiple evacuation paths can effectively relieve the pressure in the emergency evacuation process.