Deposition of radionuclides in precipitation

The Chernobyl accident demonstrated that localised wet deposition of radioactive aerosols can have major implications for the consequences of a nuclear accident. Traditionally very simple concepts have been used in assessment of this deposition, based on wash-out ratios or very simplified wash-out/rain-out models. These do not allow for the full influence of the dynamical nature of storm systems, and the range of microphysical and chemical processes involved. This paper will illustrate the variability likely to occur, and particular situations which may lead to enhanced hot-spot areas in addition to the variations in the intensity of precipitation. The uncertainties will be illustrated by results from more sophisticated models of storm systems, and the transport of radioactive aerosols through them. Some of the practical implications for real-time consequence assessment and emergency procedures will then be discussed