In the article basis of calculation of the evolution in time and space one of the most important factors in lesions of radiation accidents – radioactive dust is proposed. The composition of the dust mass and size parameters are analyzed. It is shown that decontamination of territories contaminated with radioactive dust, should be carried out in several stages. If the first phase refers to cleaning of the surface, form the larger dust particles, which quickly settled, then during in the second stage one should carry out cleaning of the air from very small particles, since these particles constitute the greatest danger to the respiratory tract. The basis of calculation of these secondary action terms is presented. The three steps of evolution of radioactive dust in the gravitational field are determined. The equations that give the description of the evolution of dust particles of arbitrary size are derived.
environmental impact, the accident, radiation dust, sedimentation