In recent years, a number of events have occurred in which anthropogenic radionuclides have been detected by radiological filter stations in a number of European countries without any knowledge on the origin of those radionuclides. In such cases, there is a need to locate potential release sites by inverse dispersion modelling methodologies. However, if the release site is actually known, or a potential release site has been localized by inverse methods as described in the NKS-B project SLIM, there is a need to estimate the radionuclide release rates from this location as a function of time, i.e. the source term, in order to quantify the total release and the atmospheric dispersion of radionuclides.
The MUD and AVESOME NKS projects have demonstrated that inherent uncertainties play a significant role for the atmospheric dispersion model results. In SOCHAOTIC, methods will be developed and applied to quantify the uncertainties of the estimated release profiles.
Two kinds of radiological monitoring networks exist, viz. filter stations and gamma stations. Filter stations detect radionuclide-specific time-averaged concentrations with high accuracy and low thresholds, however with long averaging periods (e.g. between one and seven days). Gamma stations record time-averaged gamma dose rates, in general with lower accuracy, higher thresholds compared to filter stations and no radionuclide-specific information, however with much short averaging periods (down to 10 minutes).
For operational use, nuclear decision-support systems should be extended with modules handling such monitoring data automatically, e.g. by employing the European Radiological Data Exchange Platform (EURDEP), and conveying the data together with the geographical coordinates of the release point to the national meteorological centre accompanied by a request to estimate the temporal evolution of the release rates.
In the SLIM project, methodologies have been developed to localize an unknown source of radionuclides dispersed in the atmosphere and detected by a radiological monitoring network. In the SOCHAOTIC project, we will develop methodologies, suited for operational use, that focus on characterization of source terms whose locations are known, i.e. estimate the temporal release profiles of the radionuclides detected.