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International audience; Radon-222 is a progeny of U-238, naturally present in the Earth’s crust. After diffusing out of the soil, it reaches the atmosphere. As a noble gas, it does not interact with other gas or aerosol particles. Transported by the atmosphere, it can be breathed. Its disintegration inside the lung can damage the cells, increasing the risk of cancer. Radon-222 is therefore a major public health issue in some regions. Significant Radon-222 air concentration at one location is the combination of a potentially high local source – within few kilometers – and a long-distance origin – dozens or hundreds of kilometers. A local source can be estimated by modelling or measuring the ground exhalation rate. A distant origin is far more problematic to determine since it involves all the atmospheric processes and many potential exhalation sites. Therefore, the simulation of Radon-222 air concentrations must be made at regional or continental scale. We built a Radon-222 atmospheric transport modelling calculation chain, from input data to model-to-measurement comparisons. The main issues about the input data were to get reliable the radon exhalation rate and meteorological data. The quality of the modelling was then evaluated by a model-to-measurements comparison. Hundreds of gamma dose rate monitoring stations are available in France, recording data each five minutes all year round. They record dose rate peaks due to the Radon-222 progenies concentrated in rainfall events. Preliminary results are presented.

International audience; Radon-222 is a progeny of Uranium-238, naturally present in the Earth’s crust. After its migration through the soil, it reaches the atmosphere. As a noble gas, it does not interact with other gas or aerosol particles whereas its progenies do. These progenies can concentrate in rain drops and lead to gamma dose rate peaks occurring during rainfall events. This may trigger alarms of emergency monitoring networks. These peaks can be used as a suitable radiological case study for model validation and improvement. Hundreds of gamma dose rate monitoring stations are available in France, recording data each five minutes all year round. Atmospheric dispersion models used for emergency purposes are usually meant to simulate the atmospheric transport of radioisotopes released from a damaged nuclear facility. The quality of this response is a critical issue and has to be constantly improved. However, long-range measurement campaigns for model validation are scarce, especially for radioactive pollutants. We built a Radon-222 atmospheric transport modelling calculation chain, from input data to model-to-measurement comparisons on a national scale. Preliminary results of these comparisons are presented. The final objective is to discriminate, on a gamma dose rate monitoring network, false alarms due to natural radioactivity from real nuclear incidents in a forecast mode.

International audience; Deposition is a key process in atmospheric transport modelling of radionuclides consecutive to an accidental release. Following the emission and the atmospheric transport, it is the final step to obtain a map of deposit, on which relies a long-term crisis management. The Fukushima Daiichi Nuclear Power Plant accident of 11th March 2011 led to a significant release of radionuclides in the environment. Most releases were dispersed over the Pacific Ocean whereas about 20% were deposited on the Japan main island causing areas of significant deposit. Numerous radiological measurements taken in the Japanese environment enabled the scientists to substantially reconstruct the main sequences of release to identify the probable trajectories of the radioactive plumes, and to link them with precipitation data to explain the areas of deposition. Fortunately, easurements are all available together at certain location and can be compared to each other: 137Cs hourly air concentrations retrieved from filter tapes of air quality monitoring sites, hourly gamma dose rate and meteorological data from the AMEDAS monitoring network which provides rain-gauges, rain radars and visibility detection. This multiple point of view permitted to establish some lessons about the wet deposition process in case of a nuclear release. The measurements were supplemented by modelling techniques. The most significant progress come from the quantification of the atmospheric releases, the improvement of meteorological data to better take into account the influence of the complex orography on the plumes trajectories and the modelling of deposition processes. The analysis shows some necessary improvements to be done for wet deposition modelling. Several factors are of importance: scavenging of plumes in altitude, impact of light rains in particular before rainfalls. These features are now taken into account in the IRSN operational atmospheric transport model.