Modelling external radiation doses in contaminated urban areas: implications for development of decontamination strategies

The Chernobyl accident in 1986 highlighted the need for contingency strategies for identification and mitigation of the potential long-term consequences of a radioactively contaminated (essentially with 137Cs) urban environment. To satisfy this need, the PC model URGENT has been developed. The model predicts, as a function of time, the dose rate in urban environments of various population densities. Input parameters for the model, together with associated uncertainties, were derived mostly from in situ measurements following the Chernobyl accident. The model shows that in the case of dry deposited fallout, indoor surfaces can make a significant contribution to the total radiation dose. This is addressed in terms of 'location factors' which describe potential fractional dose inside the buildings. In principle, URGENT can be used to describe any decontamination procedure and assess its effectiveness at any time after deposition. Worked examples of how the calculations can be exploited in the development of decontamination strategies are given. (author)