Atmospheric dispersal of radioactive pollutants over long distances and the calculation of collective dose

The important factors influencing dispersal of atmospheric releases of radioactive nuclides over various distance ranges, are considered. Appropriate modelling techniques after the first few hours of travel are discussed and it is shown that spatial and temporal changes in the boundary layer are important in assessing contributions to collective dose beyond 30 or 40 km. A model is described which has been designed to study the effects of routine releases from European nuclear installations, this model considers releases of a few hours duration at a time from any selected site and uses pressure fields at 6 hour intervals and quasi-geostrophic forecasting methods to track the meandering paths taken by a series of discrete puffs of radioactive material up to one or two thousand kilometres across a prescribed map area. The development and dispersion of each puff in different synoptic weather situations is simulated using local meteorological data at the time of passage to estimate population dose. The use of the model is illustrated for representative nuclides