A Model for Nuclear Explosion Cloud Movement and Fallout Estimation

Abstract

This study attempts to simulate nuclear cloud movement and radioactive fallout produced by nuclear explosion tests in the atmosphere.

The dynamic cloud rise method is used in this model for which nuclear debris deposition before cloud stabilization is considered. The cloud height is a function of nuclear weapon yield and the time after explosion. As nuclear debris particles are rising with the cloud, they also fall because of gravity. The nuclear cloud is considered as a cylinder that may be divided vertically into discs. The particle size is also divided into classes. The discs move and drop individually with the cloud and wind. The radioactivity per unit area at any point of ground surface is the sum of each disc activity resulting from landing around a given point.

The particle size and activity distribution is supposed to be log-normal. In the early stage of the burst, the width of the clouds depends upon the weapon yield. After about one hour of burst, it is controlled by large-scale atmospheric turbulence. The horizontal relative diffusion parameter is from Gifford’s (1982) results of Lagrangian-dynamical theory. The radioactivity decay follows the law of t ^−1.25

The calculated results are compared with the DELFIC model for 4 cases. The model demonstrates an increased precision of 50% and is simpler and clearer.