TACTUS: A code for simulation of the flow of caesium-137 in urban surroundings

When discussing the impact of radioactive pollution event on a larger populated areas, and subsequent countermeasures to be taken, it is essential to evaluate the consequences with respect to time. In an accident phase it is of greatest importance to gain sufficiently detailed knowledge on how the deposited activity will migrate on various types of surfaces so that predictions can be made as to which reclamation techniques would be the most effective at a given time, and whether or not evacuation programmes should be carried out. The need to model the behaviour of radionuclides deposited in an urban environment was emphasized during the Chernobyl cleanup phase. While most previous computer models, like almost all the literature on the subject written before 1986, dealt with activity flow in rural surroundings, the aim of this model, TACTUS (transfer to activity in urban surroundings), is to use experimental data to reflect the system of retention and migration processes which might typically be found in an urban environment. In its present form, the model is restricted to cover the migration of a single radionuclide - 137Cs. The urban area under examination can be either user defined or defined by one of four standard environments. (author). 13 refs, 2 figs, 2 tabs