Study On The Formation Process Of Radioactive Cloud From Earth Penetrating Nuclear Explosion Based On Fluid Dynamics

The radioactive cloud generated by the nuclear explosion in the borehole contains a large number of radioactive particles.With the movement of the cloud and atmospheric diffusion,a large area of radioactive deposition can be formed,which can cause radioactive damage to personnel.Studying the formation process of radioactive clouds in underground nuclear explosions is of great significance for predicting radioactive deposition in underground nuclear explosions,which helps to more accurately estimate the degree of harm and avoid unnecessary harm to personnel.This paper studied the formation law of shallow underground explosion clouds by conducting the shallow buried depth and small-scale quantitative explosion scale test.Based on the open-source fluid mechanics database Open FOAM,the rising movement model of chemical explosion and atmospheric nuclear explosion clouds was established.The test data were compared and analyzed.On this basis,the formation process of radioactive clouds from an underground nuclear explosion was studied.The main research contents and conclusions are as follows:（1）We conducted shallow underground explosion scaling tests with different yields（1 kg to 100 kg）and burial depths(5.24 m/kt^1/3 to 71.70 m/kt^1/3).After obtaining the spatial distribution pattern and top height data of clouds,we analyzed the data to get the relationship between the rise height of shallow underground explosion clouds and the yield and proportional burial depths.（2）Based on Open FOAM,the Cb PFoam solver coupled with a scalar field was developed under uniform atmospheric conditions.The pollutant concentration was used to trace the cloud.After comparison and analysis with the surface chemical explosion cloud test data under multiple working conditions,it was found that the error of cloud top height was within 10%,which proved the feasibility of using an unsteady compressible solver to simulate explosion cloud based on Open FOAM;after comparing and analyzing the cloud top height data of different yields（10 kg to 100 kg）shallow underground chemical explosion tests with a buried depth of 16.29 m/kt^1/3,it can be concluded that the internal energy conversion rate is about 20%under this buried depth ratio.（3）Under standard atmosphere conditions,the two-phase flow solver,buoyant Parcel Foam,which can couple the Lagrange library and calculate the upward motion of nuclear explosion cloud and the movement of radioactive particles,has been developed.We used this model to simulate the movement process of clouds in two air explosion nuclear tests.It was found that the error of stable cloud top height was less than5%,and the distribution patterns of particles with different particle sizes in the stable cloud were obtained.（4）We studied the influence of the subatmospheric pressure zone on the rising speed of clouds after nuclear explosions.The simulation of a near-Earth nuclear explosion test found that the cloud center’s rising speed reached around 150 m/s immediately after the explosion and decayed to 70 m/s after 10 seconds,far exceeding the rising speed of the cloud driven by buoyancy force under similar yield conditions.It proves that a subatmospheric pressure zone can significantly improve the initial rising speed of the cloud.（5）The proportion of energy conversion from shallow underground nuclear explosions to internal energy was studied.Comparing the stable cloud top height with the empirical formula of the KDFOC3 model,it was found that when the proportional burial depth is less than 5 m/kt^1/3,the energy conversion rate of the fireball rising out of the ground is about 30%.As the proportional burial depth increases,the energy conversion rate decreases.When the proportional burial depth is 8.92 m/kt^1/3,the energy conversion rate is about 25%.（6）We studied the radioactive distribution of underground nuclear explosion cloud.Simulations were conducted on the upward motion of clouds generated by the explosion of B61-12 at the ultimate penetration depth under four yield conditions.The simulation results of nuclear explosion clouds with the most apparent penetration effect at a burial depth of 8.92 m/kt^1/3 were analyzed based on the particle size versus radioactivity distribution model.The radioactive distribution at different heights in stable clouds was obtained.The radioactivity was mainly concentrated in the lower layer of the cloud,accounting for more than 50%of the total radioactivity.