On-going atmospheric dispersion activities in the field of environmental radiation protection in Europe: data assimilation, ensemble forecasting, and experimental evaluation studies

Off-site emergency management and decision support activities in Europe are pt. concerned with reduction of uncertainties associated with model-based dose and consequence assessment. One such activity is data assimilation of near-range atmospheric dispersion predictions in the light of on-line monitoring data available in the early release phase. Kalman filter theory is used to assimilate radiological monitoring data in real-time to better the plume predictions 'on-the fly', and to reduce the uncertainty on the plume geometry and the source terms. Another activity concerns the development of an ensemble-based decision support system for real-time exchange and evaluation of long-range dispersion forecasts of nuclear releases. This project addresses the problem of achieving a common coherent strategy across Europe's many national emergency centers when long-range dispersion forecasts differs from one another during atmospheric releases of radioactive material. Experimental evaluation activities are also performed with tracer plumes released jointly together with routine releases of 41Ar from air-cooled research reactors. Visible tracer (smoke) injected into the emission stack enables Lidar scanning of the exact plume geometry. Simultaneous measurements reveal the corresponding radiation field from the 41Ar decay, the meteorology, and the source terms. These experimental evaluation data sets now provide valuable resources for atmospheric dispersion and dose rate model evaluation