MODELING THE ATMOSPHERIC DISPERSION OF RADON ORIGINATING FROM AREA SOURCES CONNECTED WITH URANIUM MILLING AND MINING FACILITIES

Under the government of the former German Democratic Republic a multit ude of area sources for radon exhalation have built up in context with uranium milling and mining activities in the Federal States of Thurin gia, Saxony, and Saxony-Anhalt. The European Commission and the Bundes amt fur Strahlenschutz funded a project to investigate source term alo ng with atmospheric transport and diffusion of radon emanating from ar ea sources in the vicinity of Lengenfeld (Saxony), where 'typical' com positions of a variety of area sources have been identified. The Lenge nfeld area is characterized by low-range orographic structures. Source strengths have been determined experimentally in this area within an onsite series of programs; long-term meteorological data for two sites were available for the modelling of atmospheric dispersion over a qua dratic area (5 km x 5 km) by means of the Gaussian model MILDOS-AREA, and the program system WITRAK/WIKLI. It has been proved that the compl ex modelling of flow and dispersion paths based on WITRAK/WIKLI yields results, which are more realistic than those obtained using the Gauss ian type model MILDOS-AREA. Additionally, nomograms have been prepared on the basis of a particle simulation model (LASAT), to enable a rapi d and easy estimation of radon concentrations in the immediate vicinit y of normalized area sources. These normalized calculations have been carried our for 6 different stability classes. For selected stability classes the effect of varying wind speeds on resulting radon concentra tions in the environment is shown.