Novel simulation technique of radioactive aerosol substances propagation into the motionless atmosphere suddenly disseminated by wind to surrounding environment

Abstract

Accidental discharges of radioactive aerosol into the motionless (calm) atmosphere are examined with aim to quantify ensuing radiological impact on population. This paper offers an advanced methodology that facilitates and accelerates the demanding modelling process in the calm region. The modelling simulates continuous, quite volatile, radioactive releases under strong variations of the atmospheric conditions by a chain of discrete Gaussian pulses. An original idea of insertion of the nested inner cycle enables to comprise the atmosphere state changes during individual pulse propagation. The radioactivity concentration in air at the calm end period becomes a quite non-Gaussian sum of the Gaussian puffs. The novel processing provides a simple and sufficiently precise estimate of its statistical properties. The processing approximates the sum by a single “super-puff” distribution of the Gaussian type. It remarkably facilitates analysis of the ensuing convective transport of the radioactivity package. Instead of many calculating runs of the convective transport for each individual puff, only one run realises. The approximation is based on Bayes’ paradigm (AB). The numerical experiments confirm the acceptability of the AB procedure under the inspected circumstances. The proposed way converts the laborious modelling of radiological fields into a feasible one. It supports practicability of the sampling based methods of uncertainty and sensitivity analyses, as well as the data assimilation methods, especially their inverse modelling techniques based on simulation of multiplex radiological trajectories.