Characteristic Analysis Of Tornados And Study On The Anti-tornado Wind Speed Design Of Nuclear Power Plant Under Probabilistic Model Of Annual Frequency In Jiangsu Province

Tornado is a kind of small-scale weather system which is very destructive.The United States is the country with the most tornado disasters.Although the frequency of tornadoes in China is less than that in the United States,the damage caused cannot be ignored.Jiangsu Province is a high-risk area of tornado disaster in China.Its weather and terrain conditions are conducive to the formation and development of tornadoes.Historically,there have been many major disasters such as " Yancheng Tornadoes in June 23" in this area.Tornado loads are generally not considered in the building codes of various countries,but for important lifeline projects,such as nuclear power plants,anti-tornado design is required.Once a nuclear power plant accident occurs,it will often cause huge loss of life and property,so it is very important for the design and research of anti-tornado nuclear power plants.This article took 65 years of tornado statistics in Jiangsu Province from 1950 to 2000 and 2004 to 2017 as the research object,the detailed analysis of the tornadoes in Jiangsu Province was carried out in the following three aspects,with a view to provide a reference for the anti-tornado design of the nuclear power plants in Jiangsu Province.Firstly,collecting frequency information and using the EF scale method to judgment the intensity grade of 528 tornadoes that occurred in 65 years,and the error description of the judgment result was given.The characteristics of the tornado in Jiangsu Province were studied from four aspects: spatial distribution,time distribution,grade distribution and associated disasters.The study results completed the analysis of the characteristics of the tornado in Jiangsu Province.Secondly,Using the unit grid to divide Jiangsu Province into 16 parts,and the spatial correlation and discrete analysis of the annual frequency of tornadoes in each unit were carried out.With the help of hierarchical Bayesian theory,we used the randomized Negative Binomial distribution,Poisson distribution,and Polya distribution to establish a suitable hierarchical Bayesian model which is based on the premise of annual frequency spatial correlation.Then we used MCMC method to obtain the estimated value of posterior distribution parameter,which lays the foundation for the calculation of anti-tornado design wind speed in nuclear power plants.By comparing the simulated value with the actual value,it was found that the Bayesian spatial probability model of tornado annual frequency which is based on the consideration of the spatial correlation of tornado annual frequency is reasonable.Finally,based on the analysis of the annual frequency of tornadoes and combined with the statistical results of the tornado disaster length and width in the disaster investigation and the judgment of the tornado wind speed in EF Scale,the sampling method of tornado wind speed and disaster area was optimized to establish the probability model of tornado equivalent wind speed annual surpass.Then we calculated the tornado-resistant design wind speed of nuclear power plants in Jiangsu Province.We Compared the impact of different sampling methods for tornado design wind speed.The annual frequency of tornado in each unit adopts from the moving average method and the hierarchical Bayesian model to compare and analyze the influence of annual frequency for the tornado design wind speed.Based on the results,the recommended wind speed of the anti-tornado design in each unit was finally given.