Numerical Simulation Of Dispersion Of Street-scale Radionuclides Within Complex Blocks Under Dirty Bomb Attacks

With the increasing popularity of nuclear energy and nuclear science and technology,nuclear and radiological terrorism presents more significant threats to societal security.There is no doubt that people and environment suffer enormous harm from the consequences under nuclear and radiological attacks.The “dirty bomb” terrorist attack is one of the typical nuclear and radiological attacks with relatively lower technical threshold,cost and difficulty in implementation.However,this kind of terrorism has the highest threat level to societal and national security.Thus,research on numerical simulation of radionuclides dispersion under dirty bomb attacks,is considerably meaningful for risk controlling and emergency management.Previous studies often focus on large or meso scale in ideal scenarios,while those in small scale within complicated scenarios are relatively fewer.In this study,a real block is selected as the simulation study area.Based on the Euler model,numerical simulation of radionuclides dispersion in complex street geometry is conducted.Moreover,laws of radionuclides dispersion with different wind fields and releasing locations are concluded.Furthermore,high-risk regions and the regions where safe or suitable for evacuation are indicated.Results of this research are expected to provide basic support for the establishment of scenario database for nuclear and radiological emergency platform.The results are as follows,(1)Analysis of radionuclides dispersion results with different wind fields and releasing locations: results show that higher wind speed witnesses more significant influence of street complexity on indoor or outdoor radionuclides dispersion;compared to outdoor dispersion,the indoor dispersion has lower velocity,being less sensitive to wind fields,being more likely to produce secondary radiation sources and proved difficult near walls and corners;when wind speed is lower than 2m/s,impact of wind direction on radionuclides dispersion is limited,and it is easy to form a large high-contaminated area near the source,presenting a Gaussian distribution;in vertical direction,when wind speed is around 2m/s,the radionuclides dispersion is close to the ground,while when the wind speed is 10m/s,the dispersion reaches the highest height.For the entire block with the same wind field,by summing the radiological risk values of all exits,it is found out that the risk indoor is higher than that outdoor.(2)Analysis of high-risk regions and the regions where safe or suitable for evacuation: according to the real block studied in this research,when dirty bomb attacking happens,it is suggested to avoid staying at the downwind areas near the buildings,as well as where with densely or open circular buildings,and it is also advised that exits near these areas should be forbidden during the evacuating period.