A PC software package for dose assessments in the near-field of the Belgian nuclear power plants, Doel and Tihange, has been developed. The model aims to enable a quick assessment to be made of the off-site radiological situation by the licensee and preparation of a report to the authorities with respect to off-site consequences and indications for countermeasures. Such a model has to operate with the available on-plant information on source terms and metrological data. This paper discusses the problems of conversion of on-plant observations to model input, dispersion and exposure modelling and reporting of the output. The same system is suitable for recording the early environmental monitoring data, and converting these to dose estimates. The system tries to deliver, periodically, a review of the situation due to past releases, and to predict the evolution over some hours, in order to evaluate the potential opportunity for preventive actions. Operational requirements, limits and possible outcomes of the system are discussed.